bind9/doc/arm/Bv9ARM-book.xml

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<!-- Converted by db4-upgrade version 1.0 -->
<book xmlns:db="http://docbook.org/ns/docbook" version="5.0">
  <info>
    <title>BIND 9 Administrator Reference Manual</title>
    <!-- insert copyright start -->
    <copyright>
      <year>2000</year>
      <year>2001</year>
      <year>2002</year>
      <year>2003</year>
      <year>2004</year>
      <year>2005</year>
      <year>2006</year>
      <year>2007</year>
      <year>2008</year>
      <year>2009</year>
      <year>2010</year>
      <year>2011</year>
      <year>2012</year>
      <year>2013</year>
      <year>2014</year>
      <year>2015</year>
      <year>2016</year>
      <year>2017</year>
      <year>2018</year>
      <year>2019</year>
      <year>2020</year>
      <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
    </copyright>
    <!-- insert copyright end -->
    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="releaseinfo.xml"/>
  </info>

  <chapter xml:id="Bv9ARM.ch01"><info><title>Introduction</title></info>

    <para>
      The Internet Domain Name System (<acronym>DNS</acronym>)
      consists of the syntax
      to specify the names of entities in the Internet in a hierarchical
      manner, the rules used for delegating authority over names, and the
      system implementation that actually maps names to Internet
      addresses.  <acronym>DNS</acronym> data is maintained in a
      group of distributed
      hierarchical databases.
    </para>

    <section xml:id="doc_scope"><info><title>Scope of Document</title></info>

      <para>
	The Berkeley Internet Name Domain
	(<acronym>BIND</acronym>) implements a
	domain name server for a number of operating systems. This
	document provides basic information about the installation and
	care of the Internet Systems Consortium (<acronym>ISC</acronym>)
	<acronym>BIND</acronym> version 9 software package for
	system administrators.
      </para>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="pkgversion.xml"/>
    </section>

    <section xml:id="organization"><info><title>Organization of This Document</title></info>

      <para>
	In this document, <emphasis>Chapter 1</emphasis> introduces
	the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Chapter 2</emphasis>
	describes resource requirements for running <acronym>BIND</acronym> in various
	environments. Information in <emphasis>Chapter 3</emphasis> is
	<emphasis>task-oriented</emphasis> in its presentation and is
	organized functionally, to aid in the process of installing the
	<acronym>BIND</acronym> 9 software. The task-oriented
	section is followed by
	<emphasis>Chapter 4</emphasis>, which contains more advanced
	concepts that the system administrator may need for implementing
	certain options. <emphasis>Chapter 5</emphasis>
	describes the <acronym>BIND</acronym> 9 lightweight
	resolver.  The contents of <emphasis>Chapter 6</emphasis> are
	organized as in a reference manual to aid in the ongoing
	maintenance of the software. <emphasis>Chapter 7</emphasis> addresses
	security considerations, and
	<emphasis>Chapter 8</emphasis> contains troubleshooting help. The
	main body of the document is followed by several
	<emphasis>appendices</emphasis> which contain useful reference
	information, such as a <emphasis>bibliography</emphasis> and
	historic information related to <acronym>BIND</acronym>
	and the Domain Name
	System.
      </para>
    </section>
    <section xml:id="conventions"><info><title>Conventions Used in This Document</title></info>

      <para>
	In this document, we use the following general typographic
	conventions:
      </para>

      <informaltable>
	<tgroup cols="2">
	  <colspec colname="1" colnum="1" colwidth="3.000in"/>
	  <colspec colname="2" colnum="2" colwidth="2.625in"/>
	  <tbody>
	    <row>
	      <entry colname="1">
		<para>
		  <emphasis>To describe:</emphasis>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  <emphasis>We use the style:</emphasis>
		</para>
	      </entry>
	    </row>
	    <row>
	      <entry colname="1">
		<para>
		  a pathname, filename, URL, hostname,
		  mailing list name, or new term or concept
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  <filename>Fixed width</filename>
		</para>
	      </entry>
	    </row>
	    <row>
	      <entry colname="1">
		<para>
		  literal user
		  input
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  <userinput>Fixed Width Bold</userinput>
		</para>
	      </entry>
	    </row>
	    <row>
	      <entry colname="1">
		<para>
		  program output
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  <computeroutput>Fixed Width</computeroutput>
		</para>
	      </entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>

      <para>
	The following conventions are used in descriptions of the
	<acronym>BIND</acronym> configuration file:<informaltable colsep="0" frame="all" rowsep="0">
		  <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
		      <colspec colname="1" colnum="1" colsep="0" colwidth="3.000in"/>
	    <colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
	    <tbody>
	      <row rowsep="0">
		<entry colname="1" colsep="1" rowsep="1">
		  <para>
		    <emphasis>To describe:</emphasis>
		  </para>
		</entry>
		<entry colname="2" rowsep="1">
		  <para>
		    <emphasis>We use the style:</emphasis>
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1" colsep="1" rowsep="1">
		  <para>
		    keywords
		  </para>
		</entry>
		<entry colname="2" rowsep="1">
		  <para>
		    <literal>Fixed Width</literal>
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1" colsep="1" rowsep="1">
		  <para>
		    variables
		  </para>
		</entry>
		<entry colname="2" rowsep="1">
		  <para>
		    <varname>Fixed Width</varname>
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1" colsep="1">
		  <para>
		    Optional input
		  </para>
		</entry>
		<entry colname="2">
		  <para>
		    <optional>Text is enclosed in square brackets</optional>
		  </para>
		</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>
      </para>
    </section>
    <section xml:id="dns_overview"><info><title>The Domain Name System (<acronym>DNS</acronym>)</title></info>

      <para>
	This document explains the installation
	and upkeep of the <acronym>BIND</acronym> (Berkeley Internet
	Name Domain) software package. We
	begin by reviewing the fundamentals of the Domain Name System
	(<acronym>DNS</acronym>) as they relate to <acronym>BIND</acronym>.
      </para>

      <section xml:id="dns_fundamentals"><info><title>DNS Fundamentals</title></info>

	<para>
	  The Domain Name System (DNS) is a hierarchical, distributed
	  database.  It stores information for mapping Internet host names to
	  IP
	  addresses and vice versa, mail routing information, and other data
	  used by Internet applications.
	</para>

	<para>
	  Clients look up information in the DNS by calling a
	  <emphasis>resolver</emphasis> library, which sends queries to one or
	  more <emphasis>name servers</emphasis> and interprets the responses.
	  The <acronym>BIND</acronym> 9 software distribution
	  contains a name server, <command>named</command>, and a
	  resolver library, <command>liblwres</command>.
	</para>

	</section>
	<section xml:id="domain_names"><info><title>Domains and Domain Names</title></info>

	<para>
	  The data stored in the DNS is identified by <emphasis>domain names</emphasis> that are organized as a tree according to
	  organizational or administrative boundaries. Each node of the tree,
	  called a <emphasis>domain</emphasis>, is given a label. The domain
	  name of the
	  node is the concatenation of all the labels on the path from the
	  node to the <emphasis>root</emphasis> node.  This is represented
	  in written form as a string of labels listed from right to left and
	  separated by dots. A label need only be unique within its parent
	  domain.
	</para>

	<para>
	  For example, a domain name for a host at the
	  company <emphasis>Example, Inc.</emphasis> could be
	  <literal>ourhost.example.com</literal>,
	  where <literal>com</literal> is the
	  top level domain to which
	  <literal>ourhost.example.com</literal> belongs,
	  <literal>example</literal> is
	  a subdomain of <literal>com</literal>, and
	  <literal>ourhost</literal> is the
	  name of the host.
	</para>

	<para>
	  For administrative purposes, the name space is partitioned into
	  areas called <emphasis>zones</emphasis>, each starting at a node and
	  extending down to the "leaf" nodes or to nodes where other zones
	  start.
	  The data for each zone is stored in a <emphasis>name server</emphasis>, which answers queries about the zone using the
	  <emphasis>DNS protocol</emphasis>.
	</para>

	<para>
	  The data associated with each domain name is stored in the
	  form of <emphasis>resource records</emphasis> (<acronym>RR</acronym>s).
	  Some of the supported resource record types are described in
	  <xref linkend="types_of_resource_records_and_when_to_use_them"/>.
	</para>

	<para>
	  For more detailed information about the design of the DNS and
	  the DNS protocol, please refer to the standards documents listed in
	  <xref linkend="rfcs"/>.
	</para>
      </section>

      <section xml:id="zones"><info><title>Zones</title></info>

	<para>
	  To properly operate a name server, it is important to understand
	  the difference between a <emphasis>zone</emphasis>
	  and a <emphasis>domain</emphasis>.
	</para>

	<para>
	  As stated previously, a zone is a point of delegation in
	  the <acronym>DNS</acronym> tree. A zone consists of
	  those contiguous parts of the domain
	  tree for which a name server has complete information and over which
	  it has authority. It contains all domain names from a certain point
	  downward in the domain tree except those which are delegated to
	  other zones. A delegation point is marked by one or more
	  <emphasis>NS records</emphasis> in the
	  parent zone, which should be matched by equivalent NS records at
	  the root of the delegated zone.
	</para>

	<para>
	  For instance, consider the <literal>example.com</literal>
	  domain which includes names
	  such as <literal>host.aaa.example.com</literal> and
	  <literal>host.bbb.example.com</literal> even though
	  the <literal>example.com</literal> zone includes
	  only delegations for the <literal>aaa.example.com</literal> and
	  <literal>bbb.example.com</literal> zones.  A zone can
	  map
	  exactly to a single domain, but could also include only part of a
	  domain, the rest of which could be delegated to other
	  name servers. Every name in the <acronym>DNS</acronym>
	  tree is a
	  <emphasis>domain</emphasis>, even if it is
	  <emphasis>terminal</emphasis>, that is, has no
	  <emphasis>subdomains</emphasis>.  Every subdomain is a domain and
	  every domain except the root is also a subdomain. The terminology is
	  not intuitive and we suggest reading RFCs 1033, 1034, and 1035
	  to
	  gain a complete understanding of this difficult and subtle
	  topic.
	</para>

	<para>
	  Though <acronym>BIND</acronym> is called a "domain name
	  server",
	  it deals primarily in terms of zones. The "primary" and "secondary"
	  declarations in the <filename>named.conf</filename> file
	  specify
	  zones, not domains. When BIND asks some other site if it is willing to
	  be a secondary server for a <emphasis>domain</emphasis>, it is
	  actually asking for secondary service for some collection of <emphasis>zones</emphasis>.
	</para>
      </section>

      <section xml:id="auth_servers"><info><title>Authoritative Name Servers</title></info>

	<para>
	  Each zone is served by at least
	  one <emphasis>authoritative name server</emphasis>,
	  which contains the complete data for the zone.
	  To make the DNS tolerant of server and network failures,
	  most zones have two or more authoritative servers, on
	  different networks.
	</para>

	<para>
	  Responses from authoritative servers have the "authoritative
	  answer" (AA) bit set in the response packets.  This makes them
	  easy to identify when debugging DNS configurations using tools like
	  <command>dig</command> (<xref linkend="diagnostic_tools"/>).
	</para>

	<section xml:id="primary_master"><info><title>The Primary Server</title></info>

	  <para>
	    The authoritative server where the main copy of the zone
	    data is maintained is called the
	    <emphasis>primary</emphasis> (or
	    <command>master</command>) server, or simply the
	    <emphasis>primary</emphasis>.  Typically it loads the zone
	    contents from some local file edited by humans or perhaps
	    generated mechanically from some other local file which is
	    edited by humans.  This file is called the
	    <emphasis>zone file</emphasis> or
	    <emphasis>master file</emphasis>.
	  </para>

	  <para>
	    In some cases, however, the zone file may not be edited
	    by humans at all, but may instead be the result of
	    <emphasis>dynamic update</emphasis> operations.
	  </para>
	</section>

	<section xml:id="slave_server"><info><title>Secondary Servers</title></info>

	  <para>
	    The other authoritative servers, called the
	    <emphasis>secondary</emphasis>
	    (or <command>slave</command>) servers, load the zone
	    contents from another server using a replication
	    process known as a <emphasis>zone transfer</emphasis>.
	    Typically the data is transferred directly from the primary
	    master, but it is also possible to transfer it from another
	    secondary.  In other words, a secondary server may itself act as a
	    primary to a subordinate secondary server.
	  </para>
	  <para>
	    Periodically, the secondary server must send a refresh query to
	    determine whether the zone contents have been updated. This
	    is done by sending a query for the zone's Start of Authority (SOA) record and
	    checking whether the SERIAL field has been updated; if so,
	    a new transfer request is initiated. The timing of these
	    refresh queries is controlled by the SOA REFRESH and RETRY
	    fields, but can be overridden with the
	    <command>max-refresh-time</command>,
	    <command>min-refresh-time</command>,
	    <command>max-retry-time</command>, and
	    <command>min-retry-time</command> options.
	  </para>
	  <para>
	    If the zone data cannot be updated within the time specified
	    by the SOA EXPIRE option (up to a hard-coded maximum of
	    24 weeks), the secondary zone expires and no longer
	    responds to queries.
	  </para>
	</section>

	<section xml:id="stealth_server"><info><title>Stealth Servers</title></info>

	  <para>
	    Usually, all of the zone's authoritative servers are listed in
	    NS records in the parent zone.  These NS records constitute
	    a <emphasis>delegation</emphasis> of the zone from the parent.
	    The authoritative servers are also listed in the zone file itself,
	    at the <emphasis>top level</emphasis> or <emphasis>apex</emphasis>
	    of the zone.  Servers that are not in the parent's NS delegation can be listed in the zone's top-level NS
	    records, but servers that are not present at
	    the zone's top level cannot be listed in the parent's delegation.
	  </para>

	  <para>
	    A <emphasis>stealth server</emphasis> is a server that is
	    authoritative for a zone but is not listed in that zone's NS
	    records.  Stealth servers can be used for keeping a local copy of
	    a
	    zone, to speed up access to the zone's records, or to make sure that
	    the
	    zone is available even if all the "official" servers for the zone
	    are
	    inaccessible.
	  </para>

	  <para>
	    A configuration where the primary server itself is a
	    stealth server is often referred to as a "hidden primary"
	    configuration.  One use for this configuration is when the primary
	    is behind a firewall and is therefore unable to communicate directly
	    with the outside world.
	  </para>

	</section>

      </section>
      <section xml:id="cache_servers"><info><title>Caching Name Servers</title></info>

	<!--
	  - Terminology here is inconsistent.  Probably ought to
	  - convert to using "recursive name server" everywhere
	  - with just a note about "caching" terminology.
	  -->

	<para>
	  The resolver libraries provided by most operating systems are
	  <emphasis>stub resolvers</emphasis>, meaning that they are not
	  capable of
	  performing the full DNS resolution process by themselves by talking
	  directly to the authoritative servers.  Instead, they rely on a
	  local
	  name server to perform the resolution on their behalf.  Such a
	  server
	  is called a <emphasis>recursive</emphasis> name server; it performs
	  <emphasis>recursive lookups</emphasis> for local clients.
	</para>

	<para>
	  To improve performance, recursive servers cache the results of
	  the lookups they perform.  Since the processes of recursion and
	  caching are intimately connected, the terms
	  <emphasis>recursive server</emphasis> and
	  <emphasis>caching server</emphasis> are often used synonymously.
	</para>

	<para>
	  The length of time for which a record may be retained in
	  the cache of a caching name server is controlled by the
	  Time-To-Live (TTL) field associated with each resource record.
	</para>

	<section xml:id="forwarder"><info><title>Forwarding</title></info>

	  <para>
	    Even a caching name server does not necessarily perform
	    the complete recursive lookup itself.  Instead, it can
	    <emphasis>forward</emphasis> some or all of the queries
	    that it cannot satisfy from its cache to another caching name
	    server,
	    commonly referred to as a <emphasis>forwarder</emphasis>.
	  </para>

	  <para>
	    Forwarders are typically used when an administrator does not
	    wish for all the servers at a given site to interact
	    directly with the rest of the Internet. For example, a
	    common scenario is when multiple internal DNS servers are
	    behind an Internet firewall. Servers behind the firewall
	    forward their requests to the server with external access,
	    which queries Internet DNS servers on the internal servers'
	    behalf.
	  </para>

	  <para>
	    Another scenario (largely now superseded by Response Policy
	    Zones) is to send queries first to a custom server for RBL
	    processing before forwarding them to the wider Internet.
	  </para>

	  <para>
	    There may be one or more forwarders in a given setup. The
	    order in which the forwarders are listed in
	    <filename>named.conf</filename> does not determine the
	    sequence in which they are queried; rather,
	    <command>named</command> uses the response times from
	    previous queries to select the server that is likely to
	    respond the most quickly. A server that has not yet been
	    queried is given an initial small random response time to
	    ensure that it is tried at least once. Dynamic adjustment of
	    the recorded response times ensures that all forwarders are
	    queried, even those with slower response times.  This
	    permits changes in behavior based on server responsiveness.
	  </para>
	</section>

      </section>

      <section xml:id="multi_role"><info><title>Name Servers in Multiple Roles</title></info>

	<para>
	  The <acronym>BIND</acronym> name server can
	  simultaneously act as
	  a primary for some zones, a secondary for other zones, and a caching
	  (recursive) server for a set of local clients.
	</para>

	<para>
	  However, since the functions of authoritative name service
	  and caching/recursive name service are logically separate, it is
	  often advantageous to run them on separate server machines.

	  A server that only provides authoritative name service
	  (an <emphasis>authoritative-only</emphasis> server) can run with
	  recursion disabled, improving reliability and security.

	  A server that is not authoritative for any zones and only provides
	  recursive service to local
	  clients (a <emphasis>caching-only</emphasis> server)
	  does not need to be reachable from the Internet at large and can
	  be placed inside a firewall.
	</para>

      </section>
    </section>

  </chapter>

  <chapter xml:id="Bv9ARM.ch02"><info><title><acronym>BIND</acronym> Resource Requirements</title></info>

    <section xml:id="hw_req"><info><title>Hardware requirements</title></info>
      <para>
	<acronym>DNS</acronym> hardware requirements have
	traditionally been quite modest.
	For many installations, servers that have been retired from
	active duty have performed admirably as <acronym>DNS</acronym> servers.
      </para>
      <para>
	However, the DNSSEC features of <acronym>BIND</acronym> 9
	may be quite
	CPU-intensive, so organizations that make heavy use of these
	features may wish to consider larger systems for these applications.
	<acronym>BIND</acronym> 9 is fully multithreaded, allowing
	full utilization of
	multiprocessor systems for installations that need it.
      </para>
    </section>
    <section xml:id="cpu_req"><info><title>CPU Requirements</title></info>
      <para>
	CPU requirements for <acronym>BIND</acronym> 9 range from
	i386-class machines,
	for serving static zones without caching, to enterprise-class
	machines to process many dynamic updates and DNSSEC-signed zones,
	serving many thousands of queries per second.
      </para>
    </section>
    <section xml:id="mem_req"><info><title>Memory Requirements</title></info>
      <para>
	Server memory must be sufficient to hold both the
	cache and the zones loaded from disk.  The <command>max-cache-size</command>
	option can limit the amount of memory used by the cache,
	at the expense of reducing cache hit rates and causing more <acronym>DNS</acronym>
	traffic.
	If additional section caching
	(<xref linkend="acache"/>) is enabled,
	the <command>max-acache-size</command> option can be used to
	limit the amount
	of memory used by the mechanism.
	It is still good practice to have enough memory to load
	all zone and cache data into memory; unfortunately, the best
	way
	to determine this for a given installation is to watch the name server
	in operation. After a few weeks, the server process should reach
	a relatively stable size where entries are expiring from the cache as
	fast as they are being inserted.
      </para>
      <!--
	- Add something here about leaving overhead for attacks?
	- How much overhead?  Percentage?
	-->
    </section>

    <section xml:id="intensive_env"><info><title>Name Server-Intensive Environment Issues</title></info>

      <para>
	For name server-intensive environments, there are two
	configurations that may be used. The first is one where clients and
	any second-level internal name servers query a main name server, which
	has enough memory to build a large cache; this approach minimizes
	the bandwidth used by external name lookups. The second alternative
	is to set up second-level internal name servers to make queries
	independently.
	In this configuration, none of the individual machines need to
	have as much memory or CPU power as in the first alternative, but
	this has the disadvantage of making many more external queries,
	as none of the name servers share their cached data.
      </para>
    </section>

    <section xml:id="supported_os"><info><title>Supported Operating Systems</title></info>

      <para>
	ISC <acronym>BIND</acronym> 9 compiles and runs on many
	Unix-like operating systems and on
	Microsoft Windows Server 2012 R2, 2016 and Windows 10.
	For an up-to-date
	list of supported systems, see the PLATFORMS.md file in the top-level
	directory
	of the BIND 9 source distribution.
      </para>
    </section>
  </chapter>

  <chapter xml:id="Bv9ARM.ch03"><info><title>Name Server Configuration</title></info>

    <para>
      In this chapter we provide some suggested configurations, along
      with guidelines for their use.  We suggest reasonable values for
      certain option settings.
    </para>

    <section xml:id="sample_configuration"><info><title>Sample Configurations</title></info>

      <section xml:id="cache_only_sample"><info><title>A Caching-only Name Server</title></info>

	<para>
	  The following sample configuration is appropriate for a caching-only
	  name server for use by clients internal to a corporation.  All
	  queries
	  from outside clients are refused using the <command>allow-query</command>
	  option.  The same effect can be achieved using
	  suitable
	  firewall rules.
	</para>

<programlisting>
// Two corporate subnets we wish to allow queries from.
acl corpnets { 192.168.4.0/24; 192.168.7.0/24; };
options {
     // Working directory
     directory "/etc/namedb";

     allow-query { corpnets; };
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
     type master;
     file "localhost.rev";
     notify no;
};
</programlisting>

      </section>

      <section xml:id="auth_only_sample"><info><title>An Authoritative-only Name Server</title></info>

	<para>
	  This sample configuration is for an authoritative-only server
	  that is the primary server for "<filename>example.com</filename>"
	  and a secondary server for the subdomain "<filename>eng.example.com</filename>".
	</para>

<programlisting>
options {
     // Working directory
     directory "/etc/namedb";
     // Do not allow access to cache
     allow-query-cache { none; };
     // This is the default
     allow-query { any; };
     // Do not provide recursive service
     recursion no;
};

// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
     type master;
     file "localhost.rev";
     notify no;
};
// We are the primary server for example.com
zone "example.com" {
     type master;
     file "example.com.db";
     // IP addresses of secondary servers allowed to
     // transfer example.com
     allow-transfer {
	  192.168.4.14;
	  192.168.5.53;
     };
};
// We are a secondary server for eng.example.com
zone "eng.example.com" {
     type slave;
     file "eng.example.com.bk";
     // IP address of eng.example.com primary server
     masters { 192.168.4.12; };
};
</programlisting>

      </section>
    </section>

    <section xml:id="load_balancing"><info><title>Load Balancing</title></info>

      <!--
	- Add explanation of why load balancing is fragile at best
	- and completely pointless in the general case.
	-->

      <para>
	A primitive form of load balancing can be achieved in
	the <acronym>DNS</acronym> by using multiple records
	(such as multiple A records) for one name.
      </para>

      <para>
	For example, assuming three HTTP servers with network addresses
	of 10.0.0.1, 10.0.0.2, and 10.0.0.3, a set of records such as the
	following means that clients will connect to each machine one-third
	of the time:
      </para>

      <informaltable colsep="0" rowsep="0">
	<tgroup cols="5" colsep="0" rowsep="0" tgroupstyle="2Level-table">
	  <colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
	  <colspec colname="2" colnum="2" colsep="0" colwidth="0.500in"/>
	  <colspec colname="3" colnum="3" colsep="0" colwidth="0.750in"/>
	  <colspec colname="4" colnum="4" colsep="0" colwidth="0.750in"/>
	  <colspec colname="5" colnum="5" colsep="0" colwidth="2.028in"/>
	  <tbody>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  Name
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  TTL
		</para>
	      </entry>
	      <entry colname="3">
		<para>
		  CLASS
		</para>
	      </entry>
	      <entry colname="4">
		<para>
		  TYPE
		</para>
	      </entry>
	      <entry colname="5">
		<para>
		  Resource Record (RR) Data
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <literal>www</literal>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  <literal>600</literal>
		</para>
	      </entry>
	      <entry colname="3">
		<para>
		  <literal>IN</literal>
		</para>
	      </entry>
	      <entry colname="4">
		<para>
		  <literal>A</literal>
		</para>
	      </entry>
	      <entry colname="5">
		<para>
		  <literal>10.0.0.1</literal>
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para/>
	      </entry>
	      <entry colname="2">
		<para>
		  <literal>600</literal>
		</para>
	      </entry>
	      <entry colname="3">
		<para>
		  <literal>IN</literal>
		</para>
	      </entry>
	      <entry colname="4">
		<para>
		  <literal>A</literal>
		</para>
	      </entry>
	      <entry colname="5">
		<para>
		  <literal>10.0.0.2</literal>
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para/>
	      </entry>
	      <entry colname="2">
		<para>
		  <literal>600</literal>
		</para>
	      </entry>
	      <entry colname="3">
		<para>
		  <literal>IN</literal>
		</para>
	      </entry>
	      <entry colname="4">
		<para>
		  <literal>A</literal>
		</para>
	      </entry>
	      <entry colname="5">
		<para>
		  <literal>10.0.0.3</literal>
		</para>
	      </entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>
      <para>
	When a resolver queries for these records, <acronym>BIND</acronym> rotates
	them and responds to the query with the records in a different
	order.  In the example above, clients randomly receive
	records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
	use the first record returned and discard the rest.
      </para>
      <para>
	For more detail on ordering responses, check the
	<command>rrset-order</command> sub-statement in the
	<command>options</command> statement, see
	<xref endterm="rrset_ordering_title" linkend="rrset_ordering"/>.
      </para>

    </section>

    <section xml:id="ns_operations"><info><title>Name Server Operations</title></info>

      <section xml:id="tools"><info><title>Tools for Use With the Name Server Daemon</title></info>
	<para>
	  This section describes several indispensable diagnostic,
	  administrative, and monitoring tools available to the system
	  administrator for controlling and debugging the name server
	  daemon.
	</para>
	<section xml:id="diagnostic_tools"><info><title>Diagnostic Tools</title></info>
	  <para>
	    The <command>dig</command>, <command>host</command>, and
	    <command>nslookup</command> programs are all command-line tools
	    for manually querying name servers.  They differ in style and
	    output format.
	  </para>

	  <variablelist>
	    <varlistentry>
	      <term xml:id="dig"><command>dig</command></term>
	      <listitem>
		<para>
		  <command>dig</command>
		  is the most versatile and complete of these lookup tools.
		  It has two modes: simple interactive
		  mode for a single query, and batch mode, which executes a
		  query for
		  each in a list of several query lines. All query options are
		  accessible
		  from the command line.
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>dig</command>
		  <arg choice="opt" rep="norepeat">@<replaceable>server</replaceable></arg>
		  <arg choice="plain" rep="norepeat"><replaceable>domain</replaceable></arg>
		  <arg choice="opt" rep="norepeat"><replaceable>query-type</replaceable></arg>
		  <arg choice="opt" rep="norepeat"><replaceable>query-class</replaceable></arg>
		  <arg choice="opt" rep="norepeat">+<replaceable>query-option</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-<replaceable>dig-option</replaceable></arg>
		  <arg choice="opt" rep="norepeat">%<replaceable>comment</replaceable></arg>
		</cmdsynopsis>
		<para>
		  The usual simple use of <command>dig</command> takes the form
		</para>
		<simpara>
		  <command>dig @server domain query-type query-class</command>
		</simpara>
		<para>
		  For more information and a list of available commands and
		  options, see the <command>dig</command> man
		  page.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>host</command></term>
	      <listitem>
		<para>
		  The <command>host</command> utility emphasizes
		  simplicity
		  and ease of use.  By default, it converts
		  between host names and Internet addresses, but its
		  functionality
		  can be extended with the use of options.
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>host</command>
		  <arg choice="opt" rep="norepeat">-aCdlnrsTwv</arg>
		  <arg choice="opt" rep="norepeat">-c <replaceable>class</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-N <replaceable>ndots</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-t <replaceable>type</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-W <replaceable>timeout</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-R <replaceable>retries</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-m <replaceable>flag</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-4</arg>
		  <arg choice="opt" rep="norepeat">-6</arg>
		  <arg choice="plain" rep="norepeat"><replaceable>hostname</replaceable></arg>
		  <arg choice="opt" rep="norepeat"><replaceable>server</replaceable></arg>
		</cmdsynopsis>
		<para>
		  For more information and a list of available commands and
		  options, see the <command>host</command> man
		  page.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>nslookup</command></term>
	      <listitem>
		<para><command>nslookup</command>
		  has two modes: interactive and
		  non-interactive. Interactive mode allows the user to
		  query name servers for information about various
		  hosts and domains, or to print a list of hosts in a
		  domain. Non-interactive mode is used to print just
		  the name and requested information for a host or
		  domain.
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>nslookup</command>
		  <arg rep="repeat" choice="opt">-option</arg>
		  <group choice="opt" rep="norepeat">
		    <arg choice="opt" rep="norepeat"><replaceable>host-to-find</replaceable></arg>
		    <arg choice="opt" rep="norepeat">- <arg choice="opt" rep="norepeat">server</arg></arg>
		  </group>
		</cmdsynopsis>
		<para>
		  Interactive mode is entered when no arguments are given (the
		  default name server is used) or when the first argument
		  is a
		  hyphen ("-") and the second argument is the host name or
		  Internet address
		  of a name server.
		</para>
		<para>
		  Non-interactive mode is used when the name or Internet
		  address
		  of the host to be looked up is given as the first argument.
		  The
		  optional second argument specifies the host name or address
		  of a name server.
		</para>
		<para>
		  Due to its arcane user interface and frequently inconsistent
		  behavior, we do not recommend the use of <command>nslookup</command>.
		  Use <command>dig</command> instead.
		</para>
	      </listitem>

	    </varlistentry>
	  </variablelist>
	</section>

	<section xml:id="admin_tools"><info><title>Administrative Tools</title></info>
	  <para>
	    Administrative tools play an integral part in the management
	    of a server.
	  </para>
	  <variablelist>
	    <varlistentry xml:id="named-checkconf" xreflabel="Named Configuration Checking application">

	      <term><command>named-checkconf</command></term>
	      <listitem>
		<para>
		  The <command>named-checkconf</command> program
		  checks the syntax of a <filename>named.conf</filename> file.
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>named-checkconf</command>
		  <arg choice="opt" rep="norepeat">-jvz</arg>
		  <arg choice="opt" rep="norepeat">-t <replaceable>directory</replaceable></arg>
		  <arg choice="opt" rep="norepeat"><replaceable>filename</replaceable></arg>
		</cmdsynopsis>
	      </listitem>
	    </varlistentry>
	    <varlistentry xml:id="named-checkzone" xreflabel="Zone Checking application">

	      <term><command>named-checkzone</command></term>
	      <listitem>
		<para>
		  The <command>named-checkzone</command> program
		  checks a zone file for
		  syntax and consistency.
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>named-checkzone</command>
		  <arg choice="opt" rep="norepeat">-djqvD</arg>
		  <arg choice="opt" rep="norepeat">-c <replaceable>class</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-o <replaceable>output</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-t <replaceable>directory</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-w <replaceable>directory</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-k <replaceable>(ignore|warn|fail)</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-n <replaceable>(ignore|warn|fail)</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-W <replaceable>(ignore|warn)</replaceable></arg>
		  <arg choice="plain" rep="norepeat"><replaceable>zone</replaceable></arg>
		  <arg choice="opt" rep="norepeat"><replaceable>filename</replaceable></arg>
		</cmdsynopsis>
	      </listitem>
	    </varlistentry>
	    <varlistentry xml:id="named-compilezone" xreflabel="Zone Compilation application">
	      <term><command>named-compilezone</command></term>
	      <listitem>
		<para>
		  This tool is similar to <command>named-checkzone,</command> but
		  it always dumps the zone content to a specified file
		  (typically in a different format).
		</para>
	      </listitem>
	    </varlistentry>
	    <varlistentry xml:id="rndc" xreflabel="Remote Name Daemon Control application">

	      <term><command>rndc</command></term>
	      <listitem>
		<para>
		  The remote name daemon control
		  (<command>rndc</command>) program allows the
		  system
		  administrator to control the operation of a name server.
		  If <command>rndc</command> is run without any
		  options,
		  it displays a usage message as follows:
		</para>
		<cmdsynopsis label="Usage" sepchar=" ">
		  <command>rndc</command>
		  <arg choice="opt" rep="norepeat">-c <replaceable>config</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-s <replaceable>server</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-p <replaceable>port</replaceable></arg>
		  <arg choice="opt" rep="norepeat">-y <replaceable>key</replaceable></arg>
		  <arg choice="plain" rep="norepeat"><replaceable>command</replaceable></arg>
		  <arg rep="repeat" choice="opt"><replaceable>command</replaceable></arg>
		</cmdsynopsis>

		<para>See <xref linkend="man.rndc"/> for details of
		  the available <command>rndc</command> commands.
		</para>

		<para>
		  <command>rndc</command> requires a configuration file,
		  since all
		  communication with the server is authenticated with
		  digital signatures that rely on a shared secret, and
		  there is no way to provide that secret other than with a
		  configuration file.  The default location for the
		  <command>rndc</command> configuration file is
		  <filename>/etc/rndc.conf</filename>, but an
		  alternate
		  location can be specified with the <option>-c</option>
		  option.  If the configuration file is not found,
		  <command>rndc</command> also looks in
		  <filename>/etc/rndc.key</filename> (or whatever
		  <varname>sysconfdir</varname> was defined when
		  the <acronym>BIND</acronym> build was
		  configured).
		  The <filename>rndc.key</filename> file is
		  generated by
		  running <command>rndc-confgen -a</command> as
		  described in
		  <xref linkend="controls_statement_definition_and_usage"/>.
		</para>

		<para>
		  The format of the configuration file is similar to
		  that of <filename>named.conf</filename>, but is
		  limited to
		  only four statements: the <command>options</command>,
		  <command>key</command>, <command>server</command>, and
		  <command>include</command>
		  statements.  These statements are what associate the
		  secret keys to the servers with which they are meant to
		  be shared.  The order of statements is not
		  significant.
		</para>

		<para>
		  The <command>options</command> statement has
		  three clauses:
		  <command>default-server</command>, <command>default-key</command>,
		  and <command>default-port</command>.
		  <command>default-server</command> takes a
		  host name or address argument and represents the server
		  that
		  is contacted if no <option>-s</option>
		  option is provided on the command line.
		  <command>default-key</command> takes
		  the name of a key as its argument, as defined by a <command>key</command> statement.
		  <command>default-port</command> specifies the
		  port to which
		  <command>rndc</command> should connect if no
		  port is given on the command line or in a
		  <command>server</command> statement.
		</para>

		<para>
		  The <command>key</command> statement defines a
		  key to be used
		  by <command>rndc</command> when authenticating
		  with
		  <command>named</command>.  Its syntax is
		  identical to the
		  <command>key</command> statement in <filename>named.conf</filename>.
		  The keyword <userinput>key</userinput> is
		  followed by a key name, which must be a valid
		  domain name, though it need not actually be hierarchical;
		  thus,
		  a string like "<userinput>rndc_key</userinput>" is a valid
		  name.
		  The <command>key</command> statement has two
		  clauses:
		  <command>algorithm</command> and <command>secret</command>.
		  While the configuration parser accepts any string as the
		  argument
		  to <command>algorithm</command>, currently only the strings
		  "<userinput>hmac-md5</userinput>",
		  "<userinput>hmac-sha1</userinput>",
		  "<userinput>hmac-sha224</userinput>",
		  "<userinput>hmac-sha256</userinput>",
		  "<userinput>hmac-sha384</userinput>",
		  and "<userinput>hmac-sha512</userinput>"
		  have any meaning.  The secret is a Base64-encoded string
		  as specified in RFC 3548.
		</para>

		<para>
		  The <command>server</command> statement
		  associates a key
		  defined using the <command>key</command>
		  statement with a server.
		  The keyword <userinput>server</userinput> is followed by a
		  host name or address.  The <command>server</command> statement
		  has two clauses: <command>key</command> and <command>port</command>.
		  The <command>key</command> clause specifies the
		  name of the key
		  to be used when communicating with this server, and the
		  <command>port</command> clause can be used to
		  specify the port <command>rndc</command> should
		  connect
		  to on the server.
		</para>

		<para>
		  A sample minimal configuration file is as follows:
		</para>

<programlisting>
key rndc_key {
     algorithm "hmac-sha256";
     secret
       "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
     default-server 127.0.0.1;
     default-key    rndc_key;
};
</programlisting>

		<para>
		  This file, if installed as <filename>/etc/rndc.conf</filename>,
		  allows the command:
		</para>

		<para>
		  <prompt>$ </prompt><userinput>rndc reload</userinput>
		</para>

		<para>
		  to connect to 127.0.0.1 port 953 and causes the name server
		  to reload, if a name server on the local machine is
		  running with
		  following controls statements:
		</para>

<programlisting>
controls {
	inet 127.0.0.1
	    allow { localhost; } keys { rndc_key; };
};
</programlisting>

		<para>
		  and it has an identical key statement for
		  <literal>rndc_key</literal>.
		</para>

		<para>
		  Running the <command>rndc-confgen</command>
		  program
		  conveniently creates an <filename>rndc.conf</filename>
		  file, and also displays the
		  corresponding <command>controls</command>
		  statement needed to
		  add to <filename>named.conf</filename>.
		  Alternatively,
		  it is possible to run <command>rndc-confgen -a</command>
		  to set up
		  an <filename>rndc.key</filename> file and not
		  modify
		  <filename>named.conf</filename> at all.
		</para>

	      </listitem>
	    </varlistentry>
	  </variablelist>

	</section>
      </section>

      <section xml:id="signals"><info><title>Signals</title></info>
	<para>
	  Certain Unix signals cause the name server to take specific
	  actions, as described in the following table.  These signals can
	  be sent using the <command>kill</command> command.
	</para>
	<informaltable frame="all">
	  <tgroup cols="2">
	    <colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
	    <colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
	    <tbody>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>SIGHUP</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Causes the server to read <filename>named.conf</filename> and
		    reload the database.
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>SIGTERM</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Causes the server to clean up and exit.
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>SIGINT</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Causes the server to clean up and exit.
		  </para>
		</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>
      </section>
    </section>
  </chapter>

  <chapter xml:id="Bv9ARM.ch04"><info><title>Advanced DNS Features</title></info>

    <section xml:id="notify"><info><title>Notify</title></info>
      <para>
	<acronym>DNS</acronym> NOTIFY is a mechanism that allows primary
	servers to notify their secondary servers of changes to a zone's data. In
	response to a <command>NOTIFY</command> from a primary server, the
	secondary checks to see that its version of the zone is the
	current version and, if not, initiates a zone transfer.
      </para>

      <para>
	For more information about <acronym>DNS</acronym>
	<command>NOTIFY</command>, see the description of the
	<command>notify</command> option in <xref linkend="boolean_options"/> and
	the description of the zone option <command>also-notify</command> in
	<xref linkend="zone_transfers"/>.  The <command>NOTIFY</command>
	protocol is specified in RFC 1996.
      </para>

      <note><simpara>
	As a secondary zone can also be a primary to other secondaries, <command>named</command>,
	by default, sends <command>NOTIFY</command> messages for every zone
	it loads.  Specifying <command>notify primary-only;</command>
	causes <command>named</command> to only send <command>NOTIFY</command> for primary
	zones that it loads.
      </simpara></note>

    </section>

    <section xml:id="dynamic_update"><info><title>Dynamic Update</title></info>

      <para>
	Dynamic Update is a method for adding, replacing, or deleting
	records in a primary server by sending it a special form of DNS
	messages.  The format and meaning of these messages is specified
	in RFC 2136.
      </para>

      <para>
	Dynamic update is enabled by including an
	<command>allow-update</command> or an <command>update-policy</command>
	clause in the <command>zone</command> statement.
      </para>

      <para>
	If the zone's <command>update-policy</command> is set to
	<userinput>local</userinput>, updates to the zone
	are permitted for the key <varname>local-ddns</varname>,
	which is generated by <command>named</command> at startup.
	See <xref linkend="dynamic_update_policies"/> for more details.
      </para>

      <para>
	Dynamic updates using Kerberos-signed requests can be made
	using the TKEY/GSS protocol, either by setting the
	<command>tkey-gssapi-keytab</command> option, or
	by setting both the <command>tkey-gssapi-credential</command>
	and <command>tkey-domain</command> options. Once enabled,
	Kerberos-signed requests are matched against the update
	policies for the zone, using the Kerberos principal as the
	signer for the request.
      </para>

      <para>
	Updating of secure zones (zones using DNSSEC) follows RFC
	3007: RRSIG, NSEC, and NSEC3 records affected by updates are
	automatically regenerated by the server using an online
	zone key.  Update authorization is based on transaction
	signatures and an explicit server policy.
      </para>

      <section xml:id="journal"><info><title>The Journal File</title></info>

	<para>
	  All changes made to a zone using dynamic update are stored
	  in the zone's journal file.  This file is automatically created
	  by the server when the first dynamic update takes place.
	  The name of the journal file is formed by appending the extension
	  <filename>.jnl</filename> to the name of the
	  corresponding zone
	  file, unless specifically overridden.  The journal file is in a
	  binary format and should not be edited manually.
	</para>

	<para>
	  The server also occasionally writes ("dumps")
	  the complete contents of the updated zone to its zone file.
	  This is not done immediately after
	  each dynamic update, because that would be too slow when a large
	  zone is updated frequently.  Instead, the dump is delayed by
	  up to 15 minutes, allowing additional updates to take place.
	  During the dump process, transient files are created
	  with the extensions <filename>.jnw</filename> and
	  <filename>.jbk</filename>; under ordinary circumstances, these
	  are removed when the dump is complete, and can be safely
	  ignored.
	</para>

	<para>
	  When a server is restarted after a shutdown or crash, it replays
	  the journal file to incorporate into the zone any updates that
	  took
	  place after the last zone dump.
	</para>

	<para>
	  Changes that result from incoming incremental zone transfers are
	  also
	  journaled in a similar way.
	</para>

	<para>
	  The zone files of dynamic zones cannot normally be edited by
	  hand because they are not guaranteed to contain the most recent
	  dynamic changes; those are only in the journal file.
	  The only way to ensure that the zone file of a dynamic zone
	  is up-to-date is to run <command>rndc stop</command>.
	</para>

	<para>
	  To make changes to a dynamic zone
	  manually, follow these steps:
	  first, disable dynamic updates to the zone using
	  <command>rndc freeze <replaceable>zone</replaceable></command>.
	  This updates the zone file with the changes
	  stored in its <filename>.jnl</filename> file.
	  Then, edit the zone file.  Finally, run
	  <command>rndc thaw <replaceable>zone</replaceable></command>
	  to reload the changed zone and re-enable dynamic updates.
	</para>

	<para>
	  <command>rndc sync <replaceable>zone</replaceable></command>
	  updates the zone file with changes from the journal file
	  without stopping dynamic updates; this may be useful for viewing
	  the current zone state.  To remove the <filename>.jnl</filename>
	  file after updating the zone file, use
	  <command>rndc sync -clean</command>.
	</para>

      </section>

    </section>

    <section xml:id="incremental_zone_transfers"><info><title>Incremental Zone Transfers (IXFR)</title></info>

      <para>
	The incremental zone transfer (IXFR) protocol is a way for
	secondary servers to transfer only changed data, instead of having to
	transfer an entire zone. The IXFR protocol is specified in RFC
	1995. See <xref linkend="proposed_standards"/>.
      </para>

      <para>
	When acting as a primary server, <acronym>BIND</acronym> 9
	supports IXFR for those zones
	where the necessary change history information is available. These
	include primary zones maintained by dynamic update and secondary zones
	whose data was obtained by IXFR.  For manually maintained primary
	zones, and for secondary zones obtained by performing a full zone
	transfer (AXFR), IXFR is supported only if the option
	<command>ixfr-from-differences</command> is set
	to <userinput>yes</userinput>.
      </para>

      <para>
	When acting as a secondary server, <acronym>BIND</acronym> 9
	attempts to use IXFR unless
	it is explicitly disabled. For more information about disabling
	IXFR, see the description of the <command>request-ixfr</command> clause
	of the <command>server</command> statement.
      </para>
    </section>

    <section xml:id="split_dns"><info><title>Split DNS</title></info>

      <para>
	Setting up different views of the DNS space to
	internal and external resolvers is usually referred to as a
	<emphasis>split DNS</emphasis> setup. There are several
	reasons an organization might want to set up its DNS this way.
      </para>
      <para>
	One common reason to use split DNS is
	to hide "internal" DNS information from "external" clients on the
	Internet. There is some debate as to whether this is actually
	useful.
	Internal DNS information leaks out in many ways (via email headers,
	for example) and most savvy "attackers" can find the information
	they need using other means.
	However, since listing addresses of internal servers that
	external clients cannot possibly reach can result in
	connection delays and other annoyances, an organization may
	choose to use split DNS to present a consistent view of itself
	to the outside world.
      </para>
      <para>
	Another common reason for setting up a split DNS system is
	to allow internal networks that are behind filters or in RFC 1918
	space (reserved IP space, as documented in RFC 1918) to resolve DNS
	on the Internet. Split DNS can also be used to allow mail from outside
	back into the internal network.
      </para>
      <section xml:id="split_dns_sample"><info><title>Example Split DNS Setup</title></info>
	<para>
	  Let's say a company named <emphasis>Example, Inc.</emphasis>
	  (<literal>example.com</literal>)
	  has several corporate sites that have an internal network with
	  reserved
	  Internet Protocol (IP) space and an external demilitarized zone (DMZ),
	  or "outside" section of a network, that is available to the public.
	</para>
	<para>
	  <emphasis>Example, Inc.</emphasis> wants its internal clients
	  to be able to resolve external hostnames and to exchange mail with
	  people on the outside. The company also wants its internal resolvers
	  to have access to certain internal-only zones that are not available
	  at all outside of the internal network.
	</para>
	<para>
	  In order to accomplish this, the company sets up two sets
	  of name servers. One set is on the inside network (in the
	  reserved
	  IP space) and the other set is on bastion hosts, which are
	  "proxy"
	  hosts in the DMZ that can talk to both sides of its network.
	</para>
	<para>
	  The internal servers are configured to forward all queries,
	  except queries for <filename>site1.internal</filename>, <filename>site2.internal</filename>, <filename>site1.example.com</filename>,
	  and <filename>site2.example.com</filename>, to the servers
	  in the
	  DMZ. These internal servers will have complete sets of information
	  for <filename>site1.example.com</filename>, <filename>site2.example.com</filename>, <filename>site1.internal</filename>,
	  and <filename>site2.internal</filename>.
	</para>
	<para>
	  To protect the <filename>site1.internal</filename> and <filename>site2.internal</filename> domains,
	  the internal name servers must be configured to disallow all queries
	  to these domains from any external hosts, including the bastion
	  hosts.
	</para>
	<para>
	  The external servers, which are on the bastion hosts, are
	  configured to serve the "public" version of the <filename>site1.example.com</filename> and <filename>site2.example.com</filename> zones.
	  This could include things such as the host records for public servers
	  (<filename>www.example.com</filename> and <filename>ftp.example.com</filename>)
	  and mail exchange (MX) records (<filename>a.mx.example.com</filename> and <filename>b.mx.example.com</filename>).
	</para>
	<para>
	  In addition, the public <filename>site1.example.com</filename> and <filename>site2.example.com</filename> zones
	  should have special MX records that contain wildcard ("*") records
	  pointing to the bastion hosts. This is needed because external mail
	  servers do not have any other way of looking up how to deliver mail
	  to those internal hosts. With the wildcard records, the mail is
	  delivered to the bastion host, which can then forward it on to
	  internal hosts.
	</para>
	<para>
	  Here's an example of a wildcard MX record:
	</para>
	<programlisting>*   IN MX 10 external1.example.com.</programlisting>
	<para>
	  Now that they accept mail on behalf of anything in the internal
	  network, the bastion hosts need to know how to deliver mail
	  to internal hosts. The resolvers
	  on
	  the bastion hosts need to be configured to point to the internal
	  name servers for DNS resolution.
	</para>
	<para>
	  Queries for internal hostnames are answered by the internal
	  servers, and queries for external hostnames are forwarded back
	  out to the DNS servers on the bastion hosts.
	</para>
	<para>
	  For all of this to work properly, internal clients
	  need to be configured to query <emphasis>only</emphasis> the internal
	  name servers for DNS queries. This could also be enforced via
	  selective
	  filtering on the network.
	</para>
	<para>
	  If everything has been set properly, <emphasis>Example, Inc.</emphasis>'s
	  internal clients are now able to:
	</para>
	<itemizedlist>
	  <listitem>
	    <simpara>
	      Look up any hostnames in the <literal>site1.example.com</literal>
	      and
	      <literal>site2.example.com</literal> zones.
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Look up any hostnames in the <literal>site1.internal</literal> and
	      <literal>site2.internal</literal> domains.
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>Look up any hostnames on the Internet.</simpara>
	  </listitem>
	  <listitem>
	    <simpara>Exchange mail with both internal and external users.</simpara>
	  </listitem>
	</itemizedlist>
	<para>
	  Hosts on the Internet are able to:
	</para>
	<itemizedlist>
	  <listitem>
	    <simpara>
	      Look up any hostnames in the <literal>site1.example.com</literal>
	      and
	      <literal>site2.example.com</literal> zones.
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Exchange mail with anyone in the <literal>site1.example.com</literal> and
	      <literal>site2.example.com</literal> zones.
	    </simpara>
	  </listitem>
	</itemizedlist>

	<para>
	  Here is an example configuration for the setup just
	  described above. Note that this is only configuration information;
	  for information on how to configure the zone files, see <xref linkend="sample_configuration"/>.
	</para>

	<para>
	  Internal DNS server config:
	</para>

<programlisting>

acl internals { 172.16.72.0/24; 192.168.1.0/24; };

acl externals { <varname>bastion-ips-go-here</varname>; };

options {
    ...
    ...
    forward only;
    // forward to external servers
    forwarders {
	<varname>bastion-ips-go-here</varname>;
    };
    // sample allow-transfer (no one)
    allow-transfer { none; };
    // restrict query access
    allow-query { internals; externals; };
    // restrict recursion
    allow-recursion { internals; };
    ...
    ...
};

// sample primary zone
zone "site1.example.com" {
  type master;
  file "m/site1.example.com";
  // do normal iterative resolution (do not forward)
  forwarders { };
  allow-query { internals; externals; };
  allow-transfer { internals; };
};

// sample secondary zone
zone "site2.example.com" {
  type slave;
  file "s/site2.example.com";
  masters { 172.16.72.3; };
  forwarders { };
  allow-query { internals; externals; };
  allow-transfer { internals; };
};

zone "site1.internal" {
  type master;
  file "m/site1.internal";
  forwarders { };
  allow-query { internals; };
  allow-transfer { internals; }
};

zone "site2.internal" {
  type slave;
  file "s/site2.internal";
  masters { 172.16.72.3; };
  forwarders { };
  allow-query { internals };
  allow-transfer { internals; }
};
</programlisting>

	<para>
	  External (bastion host) DNS server config:
	</para>

<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };

acl externals { bastion-ips-go-here; };

options {
  ...
  ...
  // sample allow-transfer (no one)
  allow-transfer { none; };
  // default query access
  allow-query { any; };
  // restrict cache access
  allow-query-cache { internals; externals; };
  // restrict recursion
  allow-recursion { internals; externals; };
  ...
  ...
};

// sample secondary zone
zone "site1.example.com" {
  type master;
  file "m/site1.foo.com";
  allow-transfer { internals; externals; };
};

zone "site2.example.com" {
  type slave;
  file "s/site2.foo.com";
  masters { another_bastion_host_maybe; };
  allow-transfer { internals; externals; }
};
</programlisting>

	<para>
	  In the <filename>resolv.conf</filename> (or equivalent) on
	  the bastion host(s):
	</para>

<programlisting>
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</programlisting>

      </section>
    </section>
    <section xml:id="tsig"><info><title>TSIG</title></info>

      <para>
	TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS
	messages, originally specified in RFC 2845. It allows DNS messages
	to be cryptographically signed using a shared secret.  TSIG can
	be used in any DNS transaction, as a way to restrict access to
	certain server functions (e.g., recursive queries) to authorized
	clients when IP-based access control is insufficient or needs to
	be overridden, or as a way to ensure message authenticity when it
	is critical to the integrity of the server, such as with dynamic
	UPDATE messages or zone transfers from a primary to a secondary server.
      </para>
      <para>
	This section is a guide to setting up TSIG in <acronym>BIND</acronym>.
	It describes the configuration syntax and the process of creating
	TSIG keys.
      </para>
      <para>
	<command>named</command> supports TSIG for server-to-server
	communication, and some of the tools included with
	<acronym>BIND</acronym> support it for sending messages to
	<command>named</command>:
	<itemizedlist>
	  <listitem>
	    <xref linkend="man.nsupdate"/> supports TSIG via the
	    <option>-k</option>, <option>-l</option>, and
	    <option>-y</option> command-line options, or via
	    the <command>key</command> command when running
	    interactively.
	  </listitem>
	  <listitem>
	    <xref linkend="man.dig"/> supports TSIG via the
	    <option>-k</option> and <option>-y</option>
		command-line options.
	  </listitem>
	</itemizedlist>
      </para>

      <section><info><title>Generating a Shared Key</title></info>
	<para>
	  TSIG keys can be generated using the <command>tsig-keygen</command>
	  command; the output of the command is a <command>key</command> directive
	  suitable for inclusion in <filename>named.conf</filename>.  The
	  key name, algorithm, and size can be specified by command-line parameters;
	  the defaults are "tsig-key", HMAC-SHA256, and 256 bits, respectively.
	</para>
	<para>
	  Any string which is a valid DNS name can be used as a key name.
	  For example, a key to be shared between servers called
	  <emphasis>host1</emphasis> and <emphasis>host2</emphasis> could
	  be called "host1-host2.", and this key can be generated using:
	</para>
<programlisting>
  $ tsig-keygen host1-host2. > host1-host2.key
</programlisting>
	<para>
	  This key may then be copied to both hosts.  The key name and secret
	  must be identical on both hosts.
	  (Note: copying a shared secret from one server to another is beyond
	  the scope of the DNS. A secure transport mechanism should be used:
	  secure FTP, SSL, ssh, telephone, encrypted email, etc.)
	</para>
	<para>
	  <command>tsig-keygen</command> can also be run as
	  <command>ddns-confgen</command>, in which case its output includes
	  additional configuration text for setting up dynamic DNS in
	  <command>named</command>.  See <xref linkend="man.ddns-confgen"/>
	  for details.
	</para>
      </section>

      <section><info><title>Loading a New Key</title></info>
	<para>
	  For a key shared between servers called
	  <emphasis>host1</emphasis> and <emphasis>host2</emphasis>,
	  the following could be added to each server's
	  <filename>named.conf</filename> file:
	</para>
<programlisting>
key "host1-host2." {
	algorithm hmac-sha256;
	secret "DAopyf1mhCbFVZw7pgmNPBoLUq8wEUT7UuPoLENP2HY=";
};
</programlisting>
	<para>
	  (This is the same key generated above using
	  <command>tsig-keygen</command>.)
	</para>
	<para>
	  Since this text contains a secret, it
	  is recommended that either <filename>named.conf</filename> not be
	  world-readable, or that the <command>key</command> directive
	  be stored in a file which is not world-readable and which is
	  included in <filename>named.conf</filename> via the
	  <command>include</command> directive.
	</para>
	<para>
	  Once a key has been added to <filename>named.conf</filename> and the
	  server has been restarted or reconfigured, the server can recognize
	  the key.  If the server receives a message signed by the
	  key, it is able to verify the signature.  If the signature
	  is valid, the response is signed using the same key.
	</para>
	<para>
	  TSIG keys that are known to a server can be listed using the
	  command <command>rndc tsig-list</command>.
	</para>
      </section>

      <section><info><title>Instructing the Server to Use a Key</title></info>
	<para>
	  A server sending a request to another server must be told whether
	  to use a key, and if so, which key to use.
	</para>
	<para>
	  For example, a key may be specified for each server in the
	  <command>masters</command> statement in the definition of a
	  secondary zone; in this case, all SOA QUERY messages, NOTIFY
	  messages, and zone transfer requests (AXFR or IXFR) are
	  signed using the specified key.  Keys may also be specified
	  in the <command>also-notify</command> statement of a primary
	  or secondary zone, causing NOTIFY messages to be signed using
	  the specified key.
	</para>
	<para>
	  Keys can also be specified in a <command>server</command>
	  directive. Adding the following on <emphasis>host1</emphasis>,
	  if the IP address of <emphasis>host2</emphasis> is 10.1.2.3, would
	  cause <emphasis>all</emphasis> requests from <emphasis>host1</emphasis>
	  to <emphasis>host2</emphasis>, including normal DNS queries, to be
	  signed using the <command>host1-host2.</command> key:
	</para>
<programlisting>
server 10.1.2.3 {
	keys { host1-host2. ;};
};
</programlisting>
	<para>
	  Multiple keys may be present in the <command>keys</command>
	  statement, but only the first one is used.  As this directive does
	  not contain secrets, it can be used in a world-readable file.
	</para>
	<para>
	  Requests sent by <emphasis>host2</emphasis> to <emphasis>host1</emphasis>
	  would <emphasis>not</emphasis> be signed, unless a similar
	  <command>server</command> directive were in <emphasis>host2</emphasis>'s
	  configuration file.
	</para>
	<para>
	  Whenever any server sends a TSIG-signed DNS request, it expects
	  the response to be signed with the same key. If a response is not
	  signed, or if the signature is not valid, the response is
	  rejected.
	</para>
      </section>

      <section><info><title>TSIG-Based Access Control</title></info>
	<para>
	  TSIG keys may be specified in ACL definitions and ACL directives
	  such as <command>allow-query</command>, <command>allow-transfer</command>,
	  and <command>allow-update</command>.
	  The above key would be denoted in an ACL element as
	  <command>key host1-host2.</command>
	</para>
	<para>
	  Here is an example of an <command>allow-update</command> directive using
	  a TSIG key:
	</para>
<programlisting>
allow-update { !{ !localnets; any; }; key host1-host2. ;};
</programlisting>
	<para>
	  This allows dynamic updates to succeed only if the UPDATE
	  request comes from an address in <command>localnets</command>,
	  <emphasis>and</emphasis> if it is signed using the
	  <command>host1-host2.</command> key.
	</para>
	<para>
	  See <xref linkend="dynamic_update_policies"/> for a discussion of
	  the more flexible <command>update-policy</command> statement.
	</para>
      </section>

      <section><info><title>Errors</title></info>
	<para>
	  Processing of TSIG-signed messages can result in several errors:
	  <itemizedlist>
	    <listitem>
	      If a TSIG-aware server receives a message signed by an
	      unknown key, the response will be unsigned, with the TSIG
	      extended error code set to BADKEY.
	    </listitem>
	    <listitem>
	      If a TSIG-aware server receives a message from a known key
	      but with an invalid signature, the response will be unsigned,
	      with the TSIG extended error code set to BADSIG.
	    </listitem>
	    <listitem>
	      If a TSIG-aware server receives a message with a time
	      outside of the allowed range, the response will be signed but
	      the TSIG extended error code set to BADTIME, and the time values
	      will be adjusted so that the response can be successfully
	      verified.
	    </listitem>
	  </itemizedlist>
	  In all of the above cases, the server returns a response code
	  of NOTAUTH (not authenticated).
	</para>
      </section>
    </section>

    <section xml:id="tkey"><info><title>TKEY</title></info>

      <para>
	TKEY (Transaction KEY) is a mechanism for automatically negotiating
	a shared secret between two hosts, originally specified in RFC 2930.
      </para>
      <para>
	There are several TKEY "modes" that specify how a key is to be
	generated or assigned.  <acronym>BIND</acronym> 9 implements only
	one of these modes: Diffie-Hellman key exchange.  Both hosts are
	required to have a KEY record with algorithm DH (though this
	record is not required to be present in a zone).
      </para>
      <para>
	The TKEY process is initiated by a client or server by sending
	a query of type TKEY to a TKEY-aware server.  The query must include
	an appropriate KEY record in the additional section, and
	must be signed using either TSIG or SIG(0) with a previously
	established key.  The server's response, if successful,
	contains a TKEY record in its answer section.  After this transaction,
	both participants have enough information to calculate a
	shared secret using Diffie-Hellman key exchange.  The shared secret
	can then be used by to sign subsequent transactions between the
	two servers.
      </para>
      <para>
	TSIG keys known by the server, including TKEY-negotiated keys, can
	be listed using <command>rndc tsig-list</command>.
      </para>
      <para>
	TKEY-negotiated keys can be deleted from a server using
	<command>rndc tsig-delete</command>.  This can also be done via
	the TKEY protocol itself, by sending an authenticated TKEY query
	specifying the "key deletion" mode.
      </para>

    </section>
    <section xml:id="sig0"><info><title>SIG(0)</title></info>

      <para>
	<acronym>BIND</acronym> partially supports DNSSEC SIG(0)
	transaction signatures as specified in RFC 2535 and RFC 2931.
	SIG(0) uses public/private keys to authenticate messages.  Access control
	is performed in the same manner as with TSIG keys; privileges can be
	granted or denied in ACL directives based on the key name.
      </para>
      <para>
	When a SIG(0) signed message is received, it is only
	verified if the key is known and trusted by the server. The
	server does not attempt to recursively fetch or validate the
	key.
      </para>
      <para>
	SIG(0) signing of multiple-message TCP streams is not supported.
      </para>
      <para>
	The only tool shipped with <acronym>BIND</acronym> 9 that
	generates SIG(0) signed messages is <command>nsupdate</command>.
      </para>
    </section>

    <section xml:id="DNSSEC"><info><title>DNSSEC</title></info>
      <para>
	Cryptographic authentication of DNS information is possible
	through the DNS Security (<emphasis>DNSSEC-bis</emphasis>) extensions,
	defined in RFC 4033, RFC 4034, and RFC 4035.
	This section describes the creation and use of DNSSEC signed zones.
      </para>

      <para>
	In order to set up a DNSSEC secure zone, there are a series
	of steps which must be followed.  <acronym>BIND</acronym>
	9 ships
	with several tools
	that are used in this process, which are explained in more detail
	below.  In all cases, the <option>-h</option> option prints a
	full list of parameters.  Note that the DNSSEC tools require the
	keyset files to be in the working directory or the
	directory specified by the <option>-d</option> option.
      </para>

      <para>
	There must also be communication with the administrators of
	the parent and/or child zone to transmit keys.  A zone's security
	status must be indicated by the parent zone for a DNSSEC-capable
	resolver to trust its data.  This is done through the presence
	or absence of a <literal>DS</literal> record at the
	delegation
	point.
      </para>

      <para>
	For other servers to trust data in this zone, they must
	be statically configured with either this zone's zone key or the
	zone key of another zone above this one in the DNS tree.
      </para>

      <section xml:id="dnssec_keys"><info><title>Generating Keys</title></info>

	<para>
	  The <command>dnssec-keygen</command> program is used to
	  generate keys.
	</para>

	<para>
	  A secure zone must contain one or more zone keys.  The
	  zone keys will sign all other records in the zone, as well as
	  the zone keys of any secure delegated zones.  Zone keys must
	  have the same name as the zone, have a name type of
	  <command>ZONE</command>, and be usable for
	  authentication.
	  It is recommended that zone keys use a cryptographic algorithm
	  designated as "mandatory to implement" by the IETF; currently
	  the only one is RSASHA1.
	</para>

	<para>
	  The following command generates a 768-bit RSASHA1 key for
	  the <filename>child.example</filename> zone:
	</para>

	<para>
	  <userinput>dnssec-keygen -a RSASHA1 -b 768 -n ZONE child.example.</userinput>
	</para>

	<para>
	  Two output files are produced:
	  <filename>Kchild.example.+005+12345.key</filename> and
	  <filename>Kchild.example.+005+12345.private</filename>
	  (where
	  12345 is an example of a key tag).  The key filenames contain
	  the key name (<filename>child.example.</filename>), the
	  algorithm (3
	  is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in
	  this case).
	  The private key (in the <filename>.private</filename>
	  file) is
	  used to generate signatures, and the public key (in the
	  <filename>.key</filename> file) is used for signature
	  verification.
	</para>

	<para>
	  To generate another key with the same properties but with
	  a different key tag, repeat the above command.
	</para>

	<para>
	  The <command>dnssec-keyfromlabel</command> program is used
	  to get a key pair from a crypto hardware device and build the key
	  files. Its usage is similar to <command>dnssec-keygen</command>.
	</para>

	<para>
	  The public keys should be inserted into the zone file by
	  including the <filename>.key</filename> files using
	  <command>$INCLUDE</command> statements.
	</para>

      </section>
      <section xml:id="dnssec_signing"><info><title>Signing the Zone</title></info>

	<para>
	  The <command>dnssec-signzone</command> program is used
	  to sign a zone.
	</para>

	<para>
	  Any <filename>keyset</filename> files corresponding to
	  secure sub-zones should be present.  The zone signer
	  generates <literal>NSEC</literal>, <literal>NSEC3</literal>,
	  and <literal>RRSIG</literal> records for the zone, as
	  well as <literal>DS</literal> for the child zones if
	  <literal>-g</literal> is specified.  If <literal>-g</literal>
	  is not specified, then DS RRsets for the secure child
	  zones need to be added manually.
	</para>

	<para>
	  By default, all zone keys which have an available private key are
	  used to generate signatures. The following command signs the zone, assuming it is in a
	  file called <filename>zone.child.example</filename>:
	</para>

	<para>
	  <userinput>dnssec-signzone -o child.example zone.child.example</userinput>
	</para>

	<para>
	  One output file is produced:
	  <filename>zone.child.example.signed</filename>.  This
	  file
	  should be referenced by <filename>named.conf</filename>
	  as the
	  input file for the zone.
	</para>

	<para><command>dnssec-signzone</command>
	  also produces keyset and dsset files.
	  These are used to provide the parent zone
	  administrators with the <literal>DNSKEYs</literal> (or their
	  corresponding <literal>DS</literal> records) that are the
	  secure entry point to the zone.
	</para>

      </section>

      <section xml:id="dnssec_config"><info><title>Configuring Servers for DNSSEC</title></info>

	<para>
	  To enable <command>named</command> to respond appropriately
	  to DNS requests from DNSSEC-aware clients,
	  <command>dnssec-enable</command> must be set to yes.
	  (This is the default setting.)
	</para>

	<para>
	  To enable <command>named</command> to validate answers from
	  other servers, the <command>dnssec-enable</command> option
	  must be set to <userinput>yes</userinput>, and the
	  <command>dnssec-validation</command> option must be set to
	  <userinput>yes</userinput> or <userinput>auto</userinput>.
	</para>

	<para>
	  If <command>dnssec-validation</command> is set to
	  <userinput>auto</userinput>, then a default
	  trust anchor for the DNS root zone is used.
	  If it is set to <userinput>yes</userinput>, however,
	  then at least one trust anchor must be configured
	  with a <command>trusted-keys</command> or
	  <command>managed-keys</command> statement in
	  <filename>named.conf</filename>, or DNSSEC validation
	  will not occur.  The default setting is
	  <userinput>yes</userinput>.
	</para>

	<para>
	  <command>trusted-keys</command> are copies of DNSKEY RRs
	  for zones that are used to form the first link in the
	  cryptographic chain of trust.  All keys listed in
	  <command>trusted-keys</command> (and corresponding zones)
	  are deemed to exist and only the listed keys are used
	  to validate the DNSKEY RRset that they are from.
	</para>

	<para>
	  <command>managed-keys</command> are trusted keys which are
	  automatically kept up-to-date via RFC 5011 trust anchor
	  maintenance.
	</para>

	<para>
	  <command>trusted-keys</command> and
	  <command>managed-keys</command> are described in more detail
	  later in this document.
	</para>

	<para>
	  <acronym>BIND</acronym>
	  9 does not verify signatures on load, so zone keys for
	  authoritative zones do not need to be specified in the
	  configuration file.
	</para>

	<para>
	  After DNSSEC is established, a typical DNSSEC configuration
	  looks something like the following.  It has one or
	  more public keys for the root, which allows answers from
	  outside the organization to be validated.  It also
	  has several keys for parts of the namespace that the organization
	  controls.  These are here to ensure that <command>named</command>
	  is immune to compromised security in the DNSSEC components
	  of parent zones.
	</para>

<programlisting>
managed-keys {
	/* Root Key */
	"." initial-key 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
				 JxrGkxJWoZu6I7PzJu/E9gx4UC1zGAHlXKdE4zYIpRh
				 aBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3zy2Xy
				 4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYg
				 hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
				 5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M/lUUVRbke
				 g1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq
				 66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
				 97S+LKUTpQcq27R7AT3/V5hRQxScINqwcz4jYqZD2fQ
				 dgxbcDTClU0CRBdiieyLMNzXG3";
};

trusted-keys {
	/* Key for our organization's forward zone */
	example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
			      5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
			      GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
			      4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
			      kBOUKUf/mC7HvfwYH/Be22GnClrinKJp1O
			      g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
			      TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
			      FxmAVZP20igTixin/1LcrgX/KMEGd/biuv
			      F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
			      /oyWR8BW/hWdzOvnSCThlHf3xiYleDbt/o
			      1OTQ09A0=";

	/* Key for our reverse zone. */
	2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc
				       xOdNax071L18QqZnQQQAVVr+i
				       LhGTnNGp3HoWQLUIzKrJVZ3zg
				       gy3WwNT6kZo6c0tszYqbtvchm
				       gQC8CzKojM/W16i6MG/eafGU3
				       siaOdS0yOI6BgPsw+YZdzlYMa
				       IJGf4M4dyoKIhzdZyQ2bYQrjy
				       Q4LB0lC7aOnsMyYKHHYeRvPxj
				       IQXmdqgOJGq+vsevG06zW+1xg
				       YJh9rCIfnm1GX/KMgxLPG2vXT
				       D/RnLX+D3T3UL7HJYHJhAZD5L
				       59VvjSPsZJHeDCUyWYrvPZesZ
				       DIRvhDD52SKvbheeTJUm6Ehkz
				       ytNN2SN96QRk8j/iI8ib";
};

options {
	...
	dnssec-enable yes;
	dnssec-validation yes;
};
</programlisting>

	<note><simpara>
	  None of the keys listed in this example are valid.  In particular,
	  the root key is not valid.
	</simpara></note>

	<para>
	  When DNSSEC validation is enabled and properly configured,
	  the resolver rejects any answers from signed, secure zones
	  which fail to validate, and returns SERVFAIL to the client.
	</para>

	<para>
	  Responses may fail to validate for any of several reasons,
	  including missing, expired, or invalid signatures, a key which
	  does not match the DS RRset in the parent zone, or an insecure
	  response from a zone which, according to its parent, should have
	  been secure.
	</para>

	<note>
	  <para>
	    When the validator receives a response from an unsigned zone
	    that has a signed parent, it must confirm with the parent
	    that the zone was intentionally left unsigned.  It does
	    this by verifying, via signed and validated NSEC/NSEC3 records,
	    that the parent zone contains no DS records for the child.
	  </para>
	  <para>
	    If the validator <emphasis>can</emphasis> prove that the zone
	    is insecure, then the response is accepted.  However, if it
	    cannot, the validator must assume an insecure response to be a
	    forgery; it rejects the response and logs an error.
	  </para>
	  <para>
	    The logged error reads "insecurity proof failed" and
	    "got insecure response; parent indicates it should be secure".
	  </para>
	</note>
      </section>
    </section>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dnssec.xml"/>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="managed-keys.xml"/>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="pkcs11.xml"/>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dlz.xml"/>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dyndb.xml"/>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="catz.xml"/>

    <section xml:id="ipv6"><info><title>IPv6 Support in <acronym>BIND</acronym> 9</title></info>
      <para>
	<acronym>BIND</acronym> 9 fully supports all currently
	defined forms of IPv6 name-to-address and address-to-name
	lookups.  It also uses IPv6 addresses to make queries when
	running on an IPv6-capable system.
      </para>

      <para>
	For forward lookups, <acronym>BIND</acronym> 9 supports
	only AAAA records.  RFC 3363 deprecated the use of A6 records,
	and client-side support for A6 records was accordingly removed
	from <acronym>BIND</acronym> 9.
	However, authoritative <acronym>BIND</acronym> 9 name servers still
	load zone files containing A6 records correctly, answer queries
	for A6 records, and accept zone transfer for a zone containing A6
	records.
      </para>

      <para>
	For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports
	the traditional "nibble" format used in the
	<emphasis>ip6.arpa</emphasis> domain, as well as the older, deprecated
	<emphasis>ip6.int</emphasis> domain.
	Older versions of <acronym>BIND</acronym> 9
	supported the "binary label" (also known as "bitstring") format,
	but support of binary labels has been completely removed per
	RFC 3363.
	Many applications in <acronym>BIND</acronym> 9 do not understand
	the binary label format at all anymore, and return an
	error if one is given.
	In particular, an authoritative <acronym>BIND</acronym> 9
	name server will not load a zone file containing binary labels.
      </para>

      <para>
	For an overview of the format and structure of IPv6 addresses,
	see <xref linkend="ipv6addresses"/>.
      </para>

      <section><info><title>Address Lookups Using AAAA Records</title></info>

	<para>
	  The IPv6 AAAA record is a parallel to the IPv4 A record,
	  and, unlike the deprecated A6 record, specifies the entire
	  IPv6 address in a single record.  For example:
	</para>

<programlisting>
$ORIGIN example.com.
host            3600    IN      AAAA    2001:db8::1
</programlisting>

	<para>
	  Use of IPv4-in-IPv6 mapped addresses is not recommended.
	  If a host has an IPv4 address, use an A record, not
	  a AAAA, with <literal>::ffff:192.168.42.1</literal> as
	  the address.
	</para>
      </section>
      <section><info><title>Address-to-Name Lookups Using Nibble Format</title></info>

	<para>
	  When looking up an address in nibble format, the address
	  components are simply reversed, just as in IPv4, and
	  <literal>ip6.arpa.</literal> is appended to the
	  resulting name.
	  For example, the following would provide reverse name lookup for
	  a host with address
	  <literal>2001:db8::1</literal>:
	</para>

<programlisting>
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0  14400   IN    PTR    (
				    host.example.com. )
</programlisting>

      </section>
    </section>
  </chapter>

  <chapter xml:id="Bv9ARM.ch05"><info><title>The <acronym>BIND</acronym> 9 Lightweight Resolver</title></info>

    <section xml:id="lightweight_resolver"><info><title>The Lightweight Resolver Library</title></info>

      <para>
	Traditionally, applications have been linked with a stub resolver
	library that sends recursive DNS queries to a local caching name
	server.
      </para>
      <para>
	At first, IPv6 introduced new complexity into the resolution process,
	such as following A6 chains and DNAME records, and simultaneous
	lookup of IPv4 and IPv6 addresses.  Though most of the complexity was
	then removed, these are hard or impossible
	to implement in a traditional stub resolver.
      </para>
      <para>
	<acronym>BIND</acronym> 9 therefore can also provide resolution
	services to local clients
	using a combination of a lightweight resolver library and a resolver
	daemon process running on the local host.  These communicate using
	a simple UDP-based protocol, the "lightweight resolver protocol,"
	that is distinct from and simpler than the full DNS protocol.
      </para>
    </section>
    <section xml:id="lwresd"><info><title>Running a Resolver Daemon</title></info>

      <para>
	To use the lightweight resolver interface, the system must
	run the resolver daemon <command>lwresd</command> or a
	local
	name server configured with a <command>lwres</command>
	statement.
      </para>

      <para>
	By default, applications using the lightweight resolver library
	make
	UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
	The
	address can be overridden by <command>lwserver</command>
	lines in
	<filename>/etc/resolv.conf</filename>.
      </para>

      <para>
	The <command>lwresd</command> daemon is essentially a
	caching-only name server that responds to requests using the
	lightweight
	resolver protocol rather than the DNS protocol.  Because it needs
	to run on each host, it is designed to require no or minimal
	configuration.
	Unless otherwise instructed, it uses the name servers listed on
	<command>nameserver</command> lines in <filename>/etc/resolv.conf</filename>
	as forwarders, but is also capable of doing the resolution
	autonomously if
	none are specified.
      </para>
      <para>
	The <command>lwresd</command> daemon may also be
	configured with a
	<filename>named.conf</filename>-style configuration file,
	in
	<filename>/etc/lwresd.conf</filename> by default.  A name
	server may also
	be configured to act as a lightweight resolver daemon using the
	<command>lwres</command> statement in <filename>named.conf</filename>.
      </para>
      <para>
	The number of client queries that the <command>lwresd</command>
	daemon serves can be set using the
	<option>lwres-tasks</option> and <option>lwres-clients</option>
	statements in the configuration.
      </para>
    </section>
  </chapter>

  <chapter xml:id="Bv9ARM.ch06"><info><title><acronym>BIND</acronym> 9 Configuration Reference</title></info>

    <section xml:id="configuration_file_elements"><info><title>Configuration File Elements</title></info>

      <para>
	Following is a list of elements used throughout the <acronym>BIND</acronym> configuration
	file documentation:
      </para>
      <informaltable colsep="0" rowsep="0">
	<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
	  <colspec colname="1" colnum="1" colsep="0" colwidth="1.855in"/>
	  <colspec colname="2" colnum="2" colsep="0" colwidth="3.770in"/>
	  <tbody>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>acl_name</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  The name of an <varname>address_match_list</varname> as
		  defined by the <command>acl</command> statement.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>address_match_list</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A list of one or more
		  <varname>ip_addr</varname>,
		  <varname>ip_prefix</varname>, <varname>key_id</varname>,
		  or <varname>acl_name</varname> elements; see
		  <xref linkend="address_match_lists"/>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>masters_list</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A named list of one or more <varname>ip_addr</varname>
		  with optional <varname>key_id</varname> and/or
		  <varname>ip_port</varname>.
		  A <varname>masters_list</varname> may include other
		  <varname>masters_list</varname>s.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>domain_name</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A quoted string which is used as
		  a DNS name; for example, <literal>my.test.domain</literal>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>namelist</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A list of one or more <varname>domain_name</varname>
		  elements.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>dotted_decimal</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  One to four integers valued 0 through
		  255 separated by dots ("."), such as <command>123.45.67</command> or <command>89.123.45.67</command>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip4_addr</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  An IPv4 address with exactly four elements
		  in <varname>dotted_decimal</varname> notation.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip6_addr</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  An IPv6 address, such as <command>2001:db8::1234</command>.
		  IPv6-scoped addresses that have ambiguity on their
		  scope zones must be disambiguated by an appropriate
		  zone ID with the percent character ("%") as a
		  delimiter.  It is strongly recommended to use
		  string zone names rather than numeric identifiers,
		  to be robust against system configuration
		  changes.  However, since there is no standard
		  mapping for such names and identifier values,
		  only interface names as link identifiers
		  are supported, assuming one-to-one mapping between
		  interfaces and links.  For example, a link-local
		  address <command>fe80::1</command> on the link
		  attached to the interface <command>ne0</command>
		  can be specified as <command>fe80::1%ne0</command>.
		  Note that on most systems link-local addresses
		  always have ambiguity and need to be
		  disambiguated.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip_addr</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  An <varname>ip4_addr</varname> or <varname>ip6_addr</varname>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip_dscp</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A <varname>number</varname> between 0 and 63, used
		  to select a differentiated services code point (DSCP)
		  value for use with outgoing traffic on operating systems
		  that support DSCP.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip_port</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  An IP port <varname>number</varname>.
		  The <varname>number</varname> is limited to 0
		  through 65535, with values
		  below 1024 typically restricted to use by processes running
		  as root.
		  In some cases, an asterisk ("*") character can be used as a
		  placeholder to
		  select a random high-numbered port.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>ip_prefix</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  An IP network specified as an <varname>ip_addr</varname>,
		  followed by a slash ("/") and then the number of bits in the
		  netmask.
		  Trailing zeros in an <varname>ip_addr</varname>
		  may be omitted.
		  For example, <command>127/8</command> is the
		  network <command>127.0.0.0</command> with
		  netmask <command>255.0.0.0</command> and <command>1.2.3.0/28</command> is
		  network <command>1.2.3.0</command> with netmask <command>255.255.255.240</command>.
		</para>
		<para>
		  When specifying a prefix involving a IPv6-scoped address,
		  the scope may be omitted.  In that case, the prefix
		  matches packets from any scope.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>key_id</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A <varname>domain_name</varname> representing
		  the name of a shared key, to be used for transaction
		  security.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>key_list</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A list of one or more
		  <varname>key_id</varname>s,
		  separated by semicolons and ending with a semicolon.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>number</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A non-negative 32-bit integer
		  (i.e., a number between 0 and 4294967295, inclusive).
		  Its acceptable value might be further
		  limited by the context in which it is used.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>fixedpoint</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A non-negative real number that can be specified to
		  the nearest one-hundredth.  Up to five digits can be
		  specified before a decimal point, and up to two
		  digits after, so the maximum value is 99999.99.
		  Acceptable values might be further limited by the
		  contexts in which they are used.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>path_name</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A quoted string which is used as
		  a pathname, such as <filename>zones/master/my.test.domain</filename>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>port_list</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A list of an <varname>ip_port</varname> or a port
		  range.
		  A port range is specified in the form of
		  <userinput>range</userinput> followed by
		  two <varname>ip_port</varname>s,
		  <varname>port_low</varname> and
		  <varname>port_high</varname>, which represents
		  port numbers from <varname>port_low</varname> through
		  <varname>port_high</varname>, inclusive.
		  <varname>port_low</varname> must not be larger than
		  <varname>port_high</varname>.
		  For example,
		  <userinput>range 1024 65535</userinput> represents
		  ports from 1024 through 65535.
		  In either case an asterisk ("*") character is not
		  allowed as a valid <varname>ip_port</varname>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>size_spec</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A 64-bit unsigned integer, or the keywords
		  <userinput>unlimited</userinput> or
		  <userinput>default</userinput>.
		</para>
		<para>
		  Integers may take values
		  0 &lt;= value &lt;= 18446744073709551615, though
		  certain parameters
		  (such as <command>max-journal-size</command>) may
		  use a more limited range within these extremes.
		  In most cases, setting a value to 0 does not
		  literally mean zero; it means "undefined" or
		  "as big as possible," depending on the context.
		  See the explanations of particular parameters
		  that use <varname>size_spec</varname>
		  for details on how they interpret its use.
		</para>
		<para>
		  Numeric values can optionally be followed by a
		  scaling factor:
		  <userinput>K</userinput> or <userinput>k</userinput>
		  for kilobytes,
		  <userinput>M</userinput> or <userinput>m</userinput>
		  for megabytes, and
		  <userinput>G</userinput> or <userinput>g</userinput>
		  for gigabytes, which scale by 1024, 1024*1024, and
		  1024*1024*1024 respectively.
		</para>
		<para>
		  <varname>unlimited</varname> generally means
		  "as big as possible," and is usually the best
		  way to safely set a very large number.
		</para>
		<para>
		  <varname>default</varname>
		  uses the limit that was in force when the server was started.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>size_or_percent</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  A <varname>size_spec</varname> or integer value
		  followed by "%" to represent percent.
		</para>
		<para>
		  The behavior is exactly the same as
		  <varname>size_spec</varname>, but
		  <varname>size_or_percent</varname> also allows
		  specifying a positive integer value followed by the
		  "%"" sign to represent percent.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>yes_or_no</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  Either <userinput>yes</userinput> or <userinput>no</userinput>.
		  The words <userinput>true</userinput> and <userinput>false</userinput> are
		  also accepted, as are the numbers <userinput>1</userinput>
		  and <userinput>0</userinput>.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para>
		  <varname>dialup_option</varname>
		</para>
	      </entry>
	      <entry colname="2">
		<para>
		  One of <userinput>yes</userinput>,
		  <userinput>no</userinput>, <userinput>notify</userinput>,
		  <userinput>notify-passive</userinput>, <userinput>refresh</userinput>, or
		  <userinput>passive</userinput>.
		  When used in a zone, <userinput>notify-passive</userinput>,
		  <userinput>refresh</userinput>, and <userinput>passive</userinput>
		  are restricted to secondary and stub zones.
		</para>
	      </entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>
      <section xml:id="address_match_lists"><info><title>Address Match Lists</title></info>

	<section><info><title>Syntax</title></info>

<programlisting><replaceable>address_match_list</replaceable> = <replaceable>address_match_list_element</replaceable> <command>;</command> ...

<replaceable>address_match_list_element</replaceable> = [ <command>!</command> ] ( <replaceable>ip_address</replaceable> | <replaceable>ip_prefix</replaceable> |
     <command>key</command> <replaceable>key_id</replaceable> | <replaceable>acl_name</replaceable> | <command>{</command> <replaceable>address_match_list</replaceable> <command>}</command> )
</programlisting>

	</section>
	<section><info><title>Definition and Usage</title></info>

	  <para>
	    Address match lists are primarily used to determine access
	    control for various server operations. They are also used in
	    the <command>listen-on</command> and <command>sortlist</command>
	    statements. The elements which constitute an address match
	    list can be any of the following:
	  </para>
	  <itemizedlist>
	    <listitem>
	      <simpara>an IP address (IPv4 or IPv6)</simpara>
	    </listitem>
	    <listitem>
	      <simpara>an IP prefix (in "/" notation)</simpara>
	    </listitem>
	    <listitem>
	      <simpara>
		a key ID, as defined by the <command>key</command>
		statement
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>the name of an address match list defined with
		the <command>acl</command> statement
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>a nested address match list enclosed in braces</simpara>
	    </listitem>
	  </itemizedlist>

	  <para>
	    Elements can be negated with a leading exclamation mark ("!"),
	    and the match list names "any", "none", "localhost", and
	    "localnets" are predefined. More information on those names
	    can be found in the description of the <command>acl</command>
	    statement.
	  </para>

	  <para>
	    The addition of the key clause made the name of this syntactic
	    element something of a misnomer, since security keys can be used
	    to validate access without regard to a host or network address.
	    Nonetheless, the term "address match list" is still used
	    throughout the documentation.
	  </para>

	  <para>
	    When a given IP address or prefix is compared to an address
	    match list, the comparison takes place in approximately O(1)
	    time.  However, key comparisons require that the list of keys
	    be traversed until a matching key is found, and therefore may
	    be somewhat slower.
	  </para>

	  <para>
	    The interpretation of a match depends on whether the list is being
	    used for access control, defining <command>listen-on</command> ports, or in a
	    <command>sortlist</command>, and whether the element was negated.
	  </para>

	  <para>
	    When used as an access control list, a non-negated match
	    allows access and a negated match denies access. If
	    there is no match, access is denied. The clauses
	    <command>allow-notify</command>,
	    <command>allow-recursion</command>,
	    <command>allow-recursion-on</command>,
	    <command>allow-query</command>,
	    <command>allow-query-on</command>,
	    <command>allow-query-cache</command>,
	    <command>allow-query-cache-on</command>,
	    <command>allow-transfer</command>,
	    <command>allow-update</command>,
	    <command>allow-update-forwarding</command>,
	    <command>blackhole</command>, and
	    <command>keep-response-order</command> all use address match
	    lists.  Similarly, the <command>listen-on</command> option causes the
	    server to refuse queries on any of the machine's
	    addresses which do not match the list.
	  </para>

	  <para>
	    Order of insertion is significant.  If more than one element
	    in an ACL is found to match a given IP address or prefix,
	    preference is given to the one that came
	    <emphasis>first</emphasis> in the ACL definition.
	    Because of this first-match behavior, an element that
	    defines a subset of another element in the list should
	    come before the broader element, regardless of whether
	    either is negated. For example, in
	    <command>1.2.3/24; ! 1.2.3.13;</command>
	    the 1.2.3.13 element is completely useless because the
	    algorithm matches any lookup for 1.2.3.13 to the 1.2.3/24
	    element.  Using <command>! 1.2.3.13; 1.2.3/24</command> fixes
	    that problem by blocking 1.2.3.13 via the negation, but
	    all other 1.2.3.* hosts pass through.
	  </para>
	</section>
      </section>

      <section xml:id="comment_syntax"><info><title>Comment Syntax</title></info>

	<para>
	  The <acronym>BIND</acronym> 9 comment syntax allows
	  comments to appear
	  anywhere that whitespace may appear in a <acronym>BIND</acronym> configuration
	  file. To appeal to programmers of all kinds, they can be written
	  in the C, C++, or shell/perl style.
	</para>

	<section><info><title>Syntax</title></info>

	  <para>
	    <programlisting>/* This is a <acronym>BIND</acronym> comment as in C */</programlisting>
	    <programlisting>// This is a <acronym>BIND</acronym> comment as in C++</programlisting>
	    <programlisting># This is a <acronym>BIND</acronym> comment as in common Unix shells
# and perl</programlisting>
	  </para>
	</section>
	<section><info><title>Definition and Usage</title></info>

	  <para>
	    Comments may appear anywhere that whitespace may appear in
	    a <acronym>BIND</acronym> configuration file.
	  </para>
	  <para>
	    C-style comments start with the two characters /* (slash,
	    star) and end with */ (star, slash). Because they are completely
	    delimited with these characters, they can be used to comment only
	    a portion of a line or to span multiple lines.
	  </para>
	  <para>
	    C-style comments cannot be nested. For example, the following
	    is not valid because the entire comment ends with the first */:
	  </para>
	  <para>

<programlisting>/* This is the start of a comment.
   This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
   This is no longer in any comment. */
</programlisting>

	  </para>

	  <para>
	    C++-style comments start with the two characters // (slash,
	    slash) and continue to the end of the physical line. They cannot
	    be continued across multiple physical lines; to have one logical
	    comment span multiple lines, each line must use the // pair.
	    For example:
	  </para>
	  <para>

<programlisting>// This is the start of a comment.  The next line
// is a new comment, even though it is logically
// part of the previous comment.
</programlisting>

	  </para>
	  <para>
	    Shell-style (or perl-style) comments start
	    with the character <literal>#</literal> (number sign)
	    and continue to the end of the
	    physical line, as in C++ comments.
	    For example:
	  </para>

	  <para>

<programlisting># This is the start of a comment.  The next line
# is a new comment, even though it is logically
# part of the previous comment.
</programlisting>

	  </para>

	  <warning>
	    <para>
	      The semicolon (";") character
	      cannot start a comment, unlike in a zone file. The
	      semicolon indicates the end of a configuration
	      statement.
	    </para>
	  </warning>
	</section>
      </section>
    </section>

    <section xml:id="Configuration_File_Grammar"><info><title>Configuration File Grammar</title></info>

      <para>
	A <acronym>BIND</acronym> 9 configuration consists of
	statements and comments.
	Statements end with a semicolon; statements and comments are the
	only elements that can appear without enclosing braces. Many
	statements contain a block of sub-statements, which are also
	terminated with a semicolon.
      </para>

      <para>
	The following statements are supported:
      </para>

      <informaltable colsep="0" rowsep="0">
	<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
	  <colspec colname="1" colnum="1" colsep="0" colwidth="1.336in"/>
	  <colspec colname="2" colnum="2" colsep="0" colwidth="3.778in"/>
	  <tbody>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>acl</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Defines a named IP address
		  matching list, for access control and other uses.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>controls</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Declares control channels to be used
		  by the <command>rndc</command> utility.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>include</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Includes a file.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>key</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Specifies key information for use in
		  authentication and authorization using TSIG.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>logging</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Specifies what information the server logs and where
		  the log messages are sent.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>lwres</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Configures <command>named</command> to
		  also act as a lightweight resolver daemon (<command>lwresd</command>).
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>masters</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Defines a named list of primary servers for
		  inclusion in stub and secondary zones'
		  <command>masters</command> or
		  <command>also-notify</command> lists.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>options</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Controls global server configuration
		  options and sets defaults for other statements.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>server</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Sets certain configuration options on
		  a per-server basis.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>statistics-channels</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Declares communication channels to get access to
		  <command>named</command> statistics.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>trusted-keys</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Defines trusted DNSSEC keys.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>managed-keys</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Lists DNSSEC keys to be kept up-to-date
		  using RFC 5011 trust anchor maintenance.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>view</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Defines a view.
		</para>
	      </entry>
	    </row>
	    <row rowsep="0">
	      <entry colname="1">
		<para><command>zone</command></para>
	      </entry>
	      <entry colname="2">
		<para>
		  Defines a zone.
		</para>
	      </entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>

      <para>
	The <command>logging</command> and
	<command>options</command> statements may only occur once
	per
	configuration.
      </para>

      <section xml:id="acl_grammar"><info><title><command>acl</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="acl.grammar.xml"/>
      </section>
      <section xml:id="acl"><info><title><command>acl</command> Statement Definition and
	  Usage</title></info>

	<para>
	  The <command>acl</command> statement assigns a symbolic
	  name to an address match list. It gets its name from one of the primary
	  uses of address match lists: Access Control Lists (ACLs).
	</para>

	<para>
	  The following ACLs are built-in:
	</para>

	<informaltable colsep="0" rowsep="0">
	  <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
	    <colspec colname="1" colnum="1" colsep="0" colwidth="1.130in"/>
	    <colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
	    <tbody>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>any</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Matches all hosts.
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>none</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Matches no hosts.
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>localhost</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Matches the IPv4 and IPv6 addresses of all network
		    interfaces on the system.  When addresses are
		    added or removed, the <command>localhost</command>
		    ACL element is updated to reflect the changes.
		  </para>
		</entry>
	      </row>
	      <row rowsep="0">
		<entry colname="1">
		  <para><command>localnets</command></para>
		</entry>
		<entry colname="2">
		  <para>
		    Matches any host on an IPv4 or IPv6 network
		    for which the system has an interface.
		    When addresses are added or removed,
		    the <command>localnets</command>
		    ACL element is updated to reflect the changes.
		    Some systems do not provide a way to determine the prefix
		    lengths of
		    local IPv6 addresses;
		    in such cases, <command>localnets</command>
		    only matches the local
		    IPv6 addresses, just like <command>localhost</command>.
		  </para>
		</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</informaltable>
      </section>
      <section xml:id="controls_grammar"><info><title><command>controls</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="controls.grammar.xml"/>
      </section>

      <section xml:id="controls_statement_definition_and_usage"><info><title><command>controls</command> Statement Definition and
	  Usage</title></info>

	<para>
	  The <command>controls</command> statement declares control
	  channels to be used by system administrators to manage the
	  operation of the name server. These control channels are
	  used by the <command>rndc</command> utility to send
	  commands to and retrieve non-DNS results from a name server.
	</para>

	<para>
	  An <command>inet</command> control channel is a TCP socket
	  listening at the specified <command>ip_port</command> on the
	  specified <command>ip_addr</command>, which can be an IPv4 or IPv6
	  address.  An <command>ip_addr</command> of <literal>*</literal> (asterisk) is
	  interpreted as the IPv4 wildcard address; connections are
	  accepted on any of the system's IPv4 addresses.
	  To listen on the IPv6 wildcard address,
	  use an <command>ip_addr</command> of <literal>::</literal>.
	  If <command>rndc</command> is only used on the local host,
	  using the loopback address (<literal>127.0.0.1</literal>
	  or <literal>::1</literal>) is recommended for maximum security.
	</para>

	<para>
	  If no port is specified, port 953 is used. The asterisk
	  "<literal>*</literal>" cannot be used for <command>ip_port</command>.
	</para>

	<para>
	  The ability to issue commands over the control channel is
	  restricted by the <command>allow</command> and
	  <command>keys</command> clauses.
	  Connections to the control channel are permitted based on the
	  <command>address_match_list</command>.  This is for simple
	  IP address-based filtering only; any <command>key_id</command>
	  elements of the <command>address_match_list</command>
	  are ignored.
	</para>

	<para>
	  A <command>unix</command> control channel is a Unix domain
	  socket listening at the specified path in the file system.
	  Access to the socket is specified by the <command>perm</command>,
	  <command>owner</command>, and <command>group</command> clauses.
	  Note on some platforms (SunOS and Solaris), the permissions
	  (<command>perm</command>) are applied to the parent directory
	  as the permissions on the socket itself are ignored.
	</para>

	<para>
	  The primary authorization mechanism of the command
	  channel is the <command>key_list</command>, which
	  contains a list of <command>key_id</command>s.
	  Each <command>key_id</command> in the <command>key_list</command>
	  is authorized to execute commands over the control channel.
	  See <xref linkend="rndc"/> in <xref linkend="admin_tools"/>)
	  for information about configuring keys in <command>rndc</command>.
	</para>

	<para>
	  If the <command>read-only</command> clause is enabled, the
	  control channel is limited to the following set of read-only
	  commands: <command>nta -dump</command>,
	  <command>null</command>, <command>status</command>,
	  <command>showzone</command>, <command>testgen</command>, and
	  <command>zonestatus</command>. By default,
	  <command>read-only</command> is not enabled and the control
	  channel allows read-write access.
	</para>

	<para>
	  If no <command>controls</command> statement is present,
	  <command>named</command> sets up a default
	  control channel listening on the loopback address 127.0.0.1
	  and its IPv6 counterpart ::1.
	  In this case, and also when the <command>controls</command> statement
	  is present but does not have a <command>keys</command> clause,
	  <command>named</command> attempts to load the command channel key
	  from the file <filename>rndc.key</filename> in
	  <filename>/etc</filename> (or whatever <varname>sysconfdir</varname>
	  was specified when <acronym>BIND</acronym> was built).
	  To create an <filename>rndc.key</filename> file, run
	  <userinput>rndc-confgen -a</userinput>.
	</para>

	<para>
	  The key name and the size of the secret cannot be easily changed; if it
	  is desirable to change those things, make a
	  <filename>rndc.conf</filename> with a custom key.  The <filename>rndc.key</filename> file
	  also has its
	  permissions set such that only the owner of the file (the user that
	  <command>named</command> is running as) can access it.
	  For greater flexibility in allowing other users to access
	  <command>rndc</command> commands, create
	  a
	  <filename>rndc.conf</filename> file and make it group-readable by a group
	  that contains the users who should have access.
	</para>

	<para>
	  To disable the command channel, use an empty
	  <command>controls</command> statement:
	  <command>controls { };</command>.
	</para>

      </section>
      <section xml:id="include_grammar"><info><title><command>include</command> Statement Grammar</title></info>

	<programlisting><command>include</command> <replaceable>filename</replaceable><command>;</command></programlisting>
      </section>
      <section xml:id="include_statement"><info><title><command>include</command> Statement Definition and Usage</title></info>

	<para>
	  The <command>include</command> statement inserts the
	  specified file at the point where the <command>include</command>
	  statement is encountered. The <command>include</command>
		statement facilitates the administration of configuration
	  files
	  by permitting the reading or writing of some things but not
	  others. For example, the statement could include private keys
	  that are readable only by the name server.
	</para>

      </section>
      <section xml:id="key_grammar"><info><title><command>key</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="key.grammar.xml"/>
      </section>

      <section xml:id="key_statement"><info><title><command>key</command> Statement Definition and Usage</title></info>

	<para>
	  The <command>key</command> statement defines a shared
	  secret key for use with TSIG (see <xref linkend="tsig"/>)
	  or the command channel
	  (see <xref linkend="controls_statement_definition_and_usage"/>).
	</para>

	<para>
	  The <command>key</command> statement can occur at the
	  top level
	  of the configuration file or inside a <command>view</command>
	  statement.  Keys defined in top-level <command>key</command>
	  statements can be used in all views.  Keys intended for use in
	  a <command>controls</command> statement
	  (see <xref linkend="controls_statement_definition_and_usage"/>)
	  must be defined at the top level.
	</para>

	<para>
	  The <replaceable>key_id</replaceable>, also known as the
	  key name, is a domain name that uniquely identifies the key. It can
	  be used in a <command>server</command>
	  statement to cause requests sent to that
	  server to be signed with this key, or in address match lists to
	  verify that incoming requests have been signed with a key
	  matching this name, algorithm, and secret.
	</para>

	<para>
	  The <replaceable>algorithm_id</replaceable> is a string
	  that specifies a security/authentication algorithm.  The
	  <command>named</command> server supports <literal>hmac-md5</literal>,
	  <literal>hmac-sha1</literal>, <literal>hmac-sha224</literal>,
	  <literal>hmac-sha256</literal>, <literal>hmac-sha384</literal>,
	  and <literal>hmac-sha512</literal> TSIG authentication.
	  Truncated hashes are supported by appending the minimum
	  number of required bits preceded by a dash, e.g.,
	  <literal>hmac-sha1-80</literal>.  The
	  <replaceable>secret_string</replaceable> is the secret
	  to be used by the algorithm, and is treated as a Base64-encoded string.
	</para>

      </section>
      <section xml:id="logging_grammar"><info><title><command>logging</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="logging.grammar.xml"/>
      </section>

      <section xml:id="logging_statement"><info><title><command>logging</command> Statement Definition and Usage</title></info>

	<para>
	  The <command>logging</command> statement configures a
	  wide
	  variety of logging options for the name server. Its <command>channel</command> phrase
	  associates output methods, format options, and severity levels with
	  a name that can then be used with the <command>category</command> phrase
	  to select how various classes of messages are logged.
	</para>
	<para>
	  Only one <command>logging</command> statement is used to
	  define
	  as many channels and categories as desired. If there is no <command>logging</command> statement,
	  the logging configuration is:
	</para>

<programlisting>logging {
     category default { default_syslog; default_debug; };
     category unmatched { null; };
};
</programlisting>

	<para>
	  If <command>named</command> is started with the
	  <option>-L</option> option, it logs to the specified file
	  at startup, instead of using syslog. In this case the logging
	  configuration is:
	</para>

<programlisting>logging {
     category default { default_logfile; default_debug; };
     category unmatched { null; };
};
</programlisting>

	<para>
	  The logging configuration
	  is only established when
	  the entire configuration file has been parsed. When the server starts up, all logging messages
	  regarding syntax errors in the configuration file go to the default
	  channels, or to standard error if the <option>-g</option> option
	  was specified.
	</para>

	<section xml:id="channel"><info><title>The <command>channel</command> Phrase</title></info>

	  <para>
	    All log output goes to one or more <emphasis>channels</emphasis>;
	    there is no limit to the number of channels that can be created.
	  </para>

	  <para>
	    Every channel definition must include a destination clause that
	    says whether messages selected for the channel go to a file, go to a
	    particular syslog facility, go to the standard error stream, or are
	    discarded. The definition can optionally also limit the message severity level
	    that is accepted by the channel (the default is
	    <command>info</command>), and whether to include a
	    <command>named</command>-generated time stamp, the
	    category name,
	    and/or the severity level (the default is not to include any).
	  </para>

	  <para>
	    The <command>null</command> destination clause
	    causes all messages sent to the channel to be discarded;
	    in that case, other options for the channel are meaningless.
	  </para>

	  <para>
	    The <command>file</command> destination clause directs
	    the channel
	    to a disk file.  It can include limitations
	    both on how large the file is allowed to become, and on how many
	    versions
	    of the file are saved each time the file is opened.
	  </para>

	  <para>
	    If the <command>versions</command> log file
	    option is used, then
	    <command>named</command> retains that many backup
	    versions of the file by
	    renaming them when opening.  For example, to keep
	    three old versions
	    of the file <filename>lamers.log</filename>, just
	    before it is opened
	    <filename>lamers.log.1</filename> is renamed to
	    <filename>lamers.log.2</filename>, <filename>lamers.log.0</filename> is renamed
	    to <filename>lamers.log.1</filename>, and <filename>lamers.log</filename> is
	    renamed to <filename>lamers.log.0</filename>.
	    The <command>versions unlimited</command> option can be set to
	    not limit
	    the number of versions.
	    If a <command>size</command> option is associated with
	    the log file,
	    then renaming is only done when the file being opened exceeds the
	    indicated size.  No backup versions are kept by default; any
	    existing
	    log file is simply appended.
	  </para>

	  <para>
	    The <command>size</command> option for files is used
	    to limit log
	    growth. If the file ever exceeds the size, then <command>named</command>
	    stops writing to the file unless it also has a <command>versions</command> option
	    associated with it.  If backup versions are kept, the files are
	    rolled as
	    described above and a new one begun.  If there is no
	    <command>versions</command> option, no more data is
	    written to the log
	    until some out-of-band mechanism removes or truncates the log to
	    less than the
	    maximum size.  The default behavior is not to limit the size of
	    the
	    file.
	  </para>

	  <para>
	    Here is an example using the <command>size</command> and
	    <command>versions</command> options:
	  </para>

<programlisting>channel an_example_channel {
    file "example.log" versions 3 size 20m;
    print-time yes;
    print-category yes;
};
</programlisting>

	  <para>
	    The <command>syslog</command> destination clause
	    directs the
	    channel to the system log.  Its argument is a
	    syslog facility as described in the <command>syslog</command> man
	    page. Known facilities are <command>kern</command>, <command>user</command>,
	    <command>mail</command>, <command>daemon</command>, <command>auth</command>,
	    <command>syslog</command>, <command>lpr</command>, <command>news</command>,
	    <command>uucp</command>, <command>cron</command>, <command>authpriv</command>,
	    <command>ftp</command>, <command>local0</command>, <command>local1</command>,
	    <command>local2</command>, <command>local3</command>, <command>local4</command>,
	    <command>local5</command>, <command>local6</command>, and
	    <command>local7</command>; however, not all facilities
	    are supported on
	    all operating systems.
	    How <command>syslog</command> handles messages
	    sent to
	    this facility is described in the <command>syslog.conf</command> man
	    page. On a system which uses a very old version of <command>syslog</command>, which
	    only uses two arguments to the <command>openlog()</command> function,
	    then this clause is silently ignored.
	  </para>
	  <para>
	    On Windows machines, syslog messages are directed to the EventViewer.
	  </para>
	  <para>
	    The <command>severity</command> clause works like <command>syslog</command>'s
	    "priorities," except that they can also be used when writing
	    straight to a file rather than using <command>syslog</command>.
	    Messages which are not at least of the severity level given are
	    not selected for the channel; messages of higher severity
	    levels
	    are accepted.
	  </para>
	  <para>
	    When using <command>syslog</command>, the <command>syslog.conf</command> priorities
	    also determine what eventually passes through. For example,
	    defining a channel facility and severity as <command>daemon</command> and <command>debug</command>, but
	    only logging <command>daemon.warning</command> via <command>syslog.conf</command>,
	    causes messages of severity <command>info</command> and
	    <command>notice</command> to
	    be dropped. If the situation were reversed, with <command>named</command> writing
	    messages of only <command>warning</command> or higher,
	    then <command>syslogd</command> would
	    print all messages it received from the channel.
	  </para>

	  <para>
	    The <command>stderr</command> destination clause
	    directs the
	    channel to the server's standard error stream.  This is intended
	    for
	    use when the server is running as a foreground process, as
	    when debugging a configuration, for example.
	  </para>

	  <para>
	    The server can supply extensive debugging information when
	    it is in debugging mode. If the server's global debug level is
	    greater
	    than zero, debugging mode is active. The global debug
	    level is set either by starting the <command>named</command> server
	    with the <option>-d</option> flag followed by a positive integer,
	    or by running <command>rndc trace</command>.
	    The global debug level
	    can be set to zero, and debugging mode turned off, by running <command>rndc
		notrace</command>. All debugging messages in the server have a debug
	    level; higher debug levels give more detailed output. Channels
	    that specify a specific debug severity, for example:
	  </para>

<programlisting>channel specific_debug_level {
    file "foo";
    severity debug 3;
};
</programlisting>

	  <para>
	    get debugging output of level 3 or less any time the
	    server is in debugging mode, regardless of the global debugging
	    level. Channels with <command>dynamic</command>
	    severity use the
	    server's global debug level to determine what messages to print.
	  </para>
	  <para>
	    If <command>print-time</command> is set to
	    <userinput>yes</userinput>, then the date and time are logged.
	    <command>print-time</command> may be specified for a
	    <command>syslog</command> channel, but is usually
	    unnecessary since <command>syslog</command> also logs
	    the date and time. If <command>print-category</command> is
	    set to <userinput>yes</userinput>, then the
	    category of the message is logged as well. Finally, if
	    <command>print-severity</command> is set, then the severity
	    level of the message is logged.
	    The <command>print-</command> options may
	    be used in any combination, and are always printed in the
	    following
	    order: time, category, severity. Here is an example where all
	    three <command>print-</command> options
	    are on:
	  </para>

	  <para>
	    <computeroutput>28-Feb-2000 15:05:32.863 general: notice: running</computeroutput>
	  </para>

	  <para>
	    If <command>buffered</command> has been turned on, the output
	    to files is not flushed after each log entry.  By default
	    all log messages are flushed.
	  </para>

	  <para>
	    There are four predefined channels that are used for
	    <command>named</command>'s default logging, as follows.
	    If <command>named</command> is started with the
	    <option>-L</option>, then a
	    fifth channel, <command>default_logfile</command>, is added.
	    How they are
	    used is described in <xref linkend="the_category_phrase"/>.
	  </para>

<programlisting>channel default_syslog {
    // send to syslog's daemon facility
    syslog daemon;
    // only send priority info and higher
    severity info;
};

channel default_debug {
    // write to named.run in the working directory
    // Note: stderr is used instead of "named.run" if
    // the server is started with the '-g' option.
    file "named.run";
    // log at the server's current debug level
    severity dynamic;
};

channel default_stderr {
    // writes to stderr
    stderr;
    // only send priority info and higher
    severity info;
};

channel null {
   // toss anything sent to this channel
   null;
};

channel default_logfile {
    // this channel is only present if named is
    // started with the -L option, whose argument
    // provides the file name
    file "...";
    // log at the server's current debug level
    severity dynamic;
};
</programlisting>

	  <para>
	    The <command>default_debug</command> channel has the
	    special
	    property that it only produces output when the server's debug
	    level is
	    non-zero.  It normally writes to a file called <filename>named.run</filename>
	    in the server's working directory.
	  </para>

	  <para>
	    For security reasons, when the <option>-u</option>
	    command-line option is used, the <filename>named.run</filename> file
	    is created only after <command>named</command> has
	    changed to the
	    new UID, and any debug output generated while <command>named</command> is
	    starting - and still running as root - is discarded.
	    To capture this output, run the server with the <option>-L</option>
	    option to specify a default logfile, or the <option>-g</option>
	    option to log to standard error which can be redirected to a file.
	  </para>

	  <para>
	    Once a channel is defined, it cannot be redefined.
	    The built-in channels cannot be altered directly, but
	    the default logging can be modified by pointing categories at defined channels.
	  </para>
	</section>

	<section xml:id="the_category_phrase"><info><title>The <command>category</command> Phrase</title></info>

	  <para>
	    There are many categories, so desired logs
	    can be sent anywhere while unwanted logs are ignored. If
	    a list of channels is not specified for a category, log
	    messages
	    in that category are sent to the <command>default</command> category
	    instead. If no default category is specified, the following
	    "default default" is used:
	  </para>

<programlisting>category default { default_syslog; default_debug; };
</programlisting>

	  <para>
	    If <command>named</command> is started with the
	    <option>-L</option> option, the default category is:
	  </para>

<programlisting>category default { default_logfile; default_debug; };
</programlisting>

	  <para>
	    As an example, let's say a user wants to log security events to
	    a file, but also wants to keep the default logging behavior. They would
	    specify the following:
	  </para>

<programlisting>channel my_security_channel {
    file "my_security_file";
    severity info;
};
category security {
    my_security_channel;
    default_syslog;
    default_debug;
};</programlisting>

	  <para>
	    To discard all messages in a category, specify the <command>null</command> channel:
	  </para>

<programlisting>category xfer-out { null; };
category notify { null; };
</programlisting>

	  <para>
	    The following are the available categories and brief descriptions
	    of the types of log information they contain. More
	    categories may be added in future <acronym>BIND</acronym> releases.
	  </para>
	  <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="logging-categories.xml"/>
	</section>
	<section xml:id="query_errors"><info><title>The <command>query-errors</command> Category</title></info>
	  <para>
	    The <command>query-errors</command> category is
	    used to indicate why and how specific queries resulted in
	    responses which indicate an error.  Normally, these messages
	    will be logged at <command>debug</command> logging levels;
	    note, however, that if query logging is active, some are
	    logged at <command>info</command>. The logging levels are
	    described below:
	  </para>

	  <para>
	    At <command>debug</command> level 1 or higher - or at
	    <command>info</command>, when query logging is active - each
	    response with response code SERVFAIL is logged as follows:
	  </para>
	  <para>
	    <computeroutput>client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</computeroutput>
	  </para>
	  <para>
	    This means an error resulting in SERVFAIL was detected at line
	    3880 of source file <filename>query.c</filename>.  Log messages
	    of this level are particularly helpful in identifying the cause of
	    SERVFAIL for an authoritative server.
	  </para>
	  <para>
	    At <command>debug</command> level 2 or higher, detailed
	    context information about recursive resolutions that resulted in
	    SERVFAIL is logged.  The log message looks like this:
	  </para>
	  <para>
<!-- NOTE: newlines and some spaces added so this would fit on page -->
	    <programlisting>
fetch completed at resolver.c:2970 for www.example.com/A
in 10.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,quota:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
	    </programlisting>
	  </para>
	  <para>
	    The first part before the colon shows that a recursive
	    resolution for AAAA records of www.example.com completed
	    in 10.000183 seconds, and the final result that led to the
	    SERVFAIL was determined at line 2970 of source file
	    <filename>resolver.c</filename>.
	  </para>
	  <para>
	    The next part shows the detected final result and the
	    latest result of DNSSEC validation.  The latter is always
	    "success" when no validation attempt was made.  In this example,
	    this query probably resulted in SERVFAIL because all name
	    servers are down or unreachable, leading to a timeout in 10
	    seconds.  DNSSEC validation was probably not attempted.
	  </para>
	  <para>
	    The last part, enclosed in square brackets, shows statistics
	    collected for this particular resolution attempt.
	    The <varname>domain</varname> field shows the deepest zone that
	    the resolver reached; it is the zone where the error was
	    finally detected.  The meaning of the other fields is
	    summarized in the following table.
	  </para>

	  <informaltable colsep="0" rowsep="0">
	    <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
	      <colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
	      <colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
	      <tbody>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>referral</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of referrals the resolver received
		      throughout the resolution process.
		      In the above example there are two, which are most
		      likely com and example.com.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>restart</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of cycles that the resolver tried
		      remote servers at the <varname>domain</varname>
		      zone.
		      In each cycle, the resolver sends one query
		      (possibly resending it, depending on the response)
		      to each known name server of
		      the <varname>domain</varname> zone.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>qrysent</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of queries the resolver sent at the
		      <varname>domain</varname> zone.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>timeout</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of timeouts since the resolver
		      received the last response.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>lame</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of lame servers the resolver detected
		      at the <varname>domain</varname> zone.
		      A server is detected to be lame either by an
		      invalid response or as a result of lookup in
		      BIND 9's address database (ADB), where lame
		      servers are cached.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>quota</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of times the resolver was unable
		      to send a query because it had exceeded the
		      permissible fetch quota for a server.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>neterr</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of erroneous results that the
		      resolver encountered in sending queries
		      at the <varname>domain</varname> zone.
		      One common case is when the remote server is
		      unreachable and the resolver receives an "ICMP
		      unreachable" error message.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>badresp</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The number of unexpected responses (other than
		      <varname>lame</varname>) to queries sent by the
		      resolver at the <varname>domain</varname> zone.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>adberr</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      Failures in finding remote server addresses
		      of the <varname>domain</varname> zone in the ADB.
		      One common case of this is that the remote
		      server's name does not have any address records.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>findfail</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      Failures to resolve remote server addresses.
		      This is a total number of failures throughout
		      the resolution process.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><varname>valfail</varname></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      Failures of DNSSEC validation.
		      Validation failures are counted throughout
		      the resolution process (not limited to
		      the <varname>domain</varname> zone), but should
		      only happen in <varname>domain</varname>.
		    </para>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	  <para>
	    At <command>debug</command> level 3 or higher, the same
	    messages as those at <command>debug</command> level 1 are
	    logged for errors other than SERVFAIL. Note that negative
	    responses such as NXDOMAIN are not errors, and are not logged
	    at this debug level.
	  </para>
	  <para>
	    At <command>debug</command> level 4 or higher, the
	    detailed context information logged at <command>debug</command>
	    level 2 is logged for errors other than SERVFAIL and
	    for negative responses such as NXDOMAIN.
	  </para>
	</section>
      </section>

      <section xml:id="lwres_grammar"><info><title><command>lwres</command> Statement Grammar</title></info>

	<para>
	   This is the grammar of the <command>lwres</command>
	  statement in the <filename>named.conf</filename> file:
	</para>

<programlisting><command>lwres {</command>
  [ <command>listen-on {</command>
    ( <replaceable>ip_addr</replaceable> [ <command>port</command> <replaceable>ip_port</replaceable> ] [ <command>dscp</command> <replaceable>ip_dscp</replaceable> ] <command>;</command> )
      ...
    <command>};</command> ]
  [ <command>view</command> <replaceable>view_name</replaceable><command>;</command> ]
  [ <command>search {</command> <replaceable>domain_name</replaceable> <command>;</command> ... <command>};</command> ]
  [ <command>ndots</command> <replaceable>number</replaceable><command>;</command> ]
  [ <command>lwres-tasks</command> <replaceable>number</replaceable><command>;</command> ]
  [ <command>lwres-clients</command> <replaceable>number</replaceable><command>;</command> ]
<command>};</command>
</programlisting>

      </section>
      <section xml:id="lwres_statement"><info><title><command>lwres</command> Statement Definition and Usage</title></info>

	<para>
	  The <command>lwres</command> statement configures the
	  name
	  server to also act as a lightweight resolver server. (See
	  <xref linkend="lwresd"/>.)  There may be multiple
	  <command>lwres</command> statements configuring
	  lightweight resolver servers with different properties.
	</para>

	<para>
	  The <command>listen-on</command> statement specifies a
	  list of
	  IPv4 addresses (and ports) that this instance of a lightweight
	  resolver daemon
	  should accept requests on.  If no port is specified, port 921 is
	  used.
	  If this statement is omitted, requests are accepted on
	  127.0.0.1,
	  port 921.
	</para>

	<para>
	  The <command>view</command> statement binds this
	  instance of a
	  lightweight resolver daemon to a view in the DNS namespace, so that
	  the
	  response is constructed in the same manner as a normal DNS
	  query
	  matching this view.  If this statement is omitted, the default view
	  is
	  used; if there is no default view, an error is triggered.
	</para>

	<para>
	  The <command>search</command> statement is equivalent to
	  the
	  <command>search</command> statement in
	  <filename>/etc/resolv.conf</filename>.  It provides a
	  list of domains
	  which are appended to relative names in queries.
	</para>

	<para>
	  The <command>ndots</command> statement is equivalent to
	  the
	  <command>ndots</command> statement in
	  <filename>/etc/resolv.conf</filename>.  It indicates the
	  minimum
	  number of dots in a relative domain name that should result in an
	  exact-match lookup before search path elements are appended.
	</para>
	<para>
	  The <option>lwres-tasks</option> statement specifies the number
	  of worker threads the lightweight resolver dedicates to serving
	  clients.  By default, the number is the same as the number of CPUs on
	  the system; this can be overridden using the <option>-n</option>
	  command-line option when starting the server.
	</para>
	<para>
	  The <option>lwres-clients</option> statement specifies
	  the number of client objects per thread the lightweight
	  resolver should create to serve client queries.
	  By default, if the lightweight resolver runs as a part
	  of <command>named</command>, 256 client objects are
	  created for each task; if it runs as <command>lwresd</command>,
	  1024 client objects are created for each thread. The maximum
	  value is 32768; higher values are silently ignored and
	  the maximum is used instead.
	  Note that setting too high a value may overconsume
	  system resources.
	</para>
	<para>
	  The maximum number of client queries that the lightweight
	  resolver can handle at any one time equals
	  <option>lwres-tasks</option> times <option>lwres-clients</option>.
	</para>
      </section>
      <section xml:id="masters_grammar"><info><title><command>masters</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="masters.grammar.xml"/>
      </section>

      <section xml:id="masters_statement"><info><title><command>masters</command> Statement Definition and
	  Usage</title></info>

	<para><command>masters</command>
	  lists allow for a common set of primaries to be easily used by
	  multiple stub and secondary zones in their <command>masters</command>
	  or <command>also-notify</command> lists.
	</para>
      </section>

      <section xml:id="options_grammar"><info><title><command>options</command> Statement Grammar</title></info>

	<para>
	  This is the grammar of the <command>options</command>
	  statement in the <filename>named.conf</filename> file:
	</para>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="options.grammar.xml"/>
      </section>

      <section xml:id="options"><info><title><command>options</command> Statement Definition and
	  Usage</title></info>

	<para>
	  The <command>options</command> statement sets up global
	  options
	  to be used by <acronym>BIND</acronym>. This statement
	  may appear only
	  once in a configuration file. If there is no <command>options</command>
	  statement, an options block with each option set to its default is
	  used.
	</para>

	<variablelist>

	    <varlistentry>
	      <term><command>attach-cache</command></term>
	      <listitem>
		<para>
		  This option allows multiple views to share a single cache
		  database.
		  Each view has its own cache database by default, but
		  if multiple views have the same operational policy
		  for name resolution and caching, those views can
		  share a single cache to save memory, and possibly
		  improve resolution efficiency, by using this option.
		</para>

		<para>
		  The <command>attach-cache</command> option
		  may also be specified in <command>view</command>
		  statements, in which case it overrides the
		  global <command>attach-cache</command> option.
		</para>

		<para>
		  The <replaceable>cache_name</replaceable> specifies
		  the cache to be shared.
		  When the <command>named</command> server configures
		  views which are supposed to share a cache, it
		  creates a cache with the specified name for the
		  first view of these sharing views.
		  The rest of the views simply refer to the
		  already-created cache.
		</para>

		<para>
		  One common configuration to share a cache is to
		  allow all views to share a single cache.
		  This can be done by specifying
		  <command>attach-cache</command> as a global
		  option with an arbitrary name.
		</para>

		<para>
		  Another possible operation is to allow a subset of
		  all views to share a cache while the others
		  retain their own caches.
		  For example, if there are three views A, B, and C,
		  and only A and B should share a cache, specify the
		  <command>attach-cache</command> option as a view of A (or
		  B)'s option, referring to the other view name:
		</para>

<programlisting>
  view "A" {
    // this view has its own cache
    ...
  };
  view "B" {
    // this view refers to A's cache
    attach-cache "A";
  };
  view "C" {
    // this view has its own cache
    ...
  };
</programlisting>

		<para>
		  Views that share a cache must have the same policy
		  on configurable parameters that may affect caching.
		  The current implementation requires the following
		  configurable options be consistent among these
		  views:
		  <command>check-names</command>,
		  <command>cleaning-interval</command>,
		  <command>dnssec-accept-expired</command>,
		  <command>dnssec-validation</command>,
		  <command>max-cache-ttl</command>,
		  <command>max-ncache-ttl</command>,
		  <command>max-cache-size</command>, and
		  <command>zero-no-soa-ttl</command>.
		</para>

		<para>
		  Note that there may be other parameters that may
		  cause confusion if they are inconsistent for
		  different views that share a single cache.
		  For example, if these views define different sets of
		  forwarders that can return different answers for the
		  same question, sharing the answer does not make
		  sense or could even be harmful.
		  It is administrator's responsibility to ensure that
		  configuration differences in different views do
		  not cause disruption with a shared cache.
		</para>
	      </listitem>

	    </varlistentry>

	  <varlistentry>
	    <term><command>directory</command></term>
	    <listitem>
	      <para>
		This sets the working directory of the server.
		Any non-absolute pathnames in the configuration file are
		taken as relative to this directory. The default
		location for most server output files
		(e.g., <filename>named.run</filename>) is this directory.
		If a directory is not specified, the working directory
		defaults to "<filename>.</filename>", the directory from
		which the server was started. The directory specified
		should be an absolute path. It is
		<emphasis>strongly recommended</emphasis>
		that the directory be writable by the effective user
		ID of the <command>named</command> process.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnstap</command></term>
	    <listitem>
	      <para>
		<command>dnstap</command> is a fast, flexible method
		for capturing and logging DNS traffic. Developed by
		Robert Edmonds at Farsight Security, Inc., and supported
		by multiple DNS implementations, <command>dnstap</command>
		uses
		<command>libfstrm</command> (a lightweight high-speed
		framing library, see
		<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://github.com/farsightsec/fstrm">https://github.com/farsightsec/fstrm</link>) to send
		event payloads which are encoded using Protocol Buffers
		(<command>libprotobuf-c</command>, a mechanism for
		serializing structured data developed
		by Google, Inc.; see
		<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://developers.google.com/protocol-buffers/">https://developers.google.com/protocol-buffers</link>).
	      </para>
	      <para>
		To enable <command>dnstap</command> at compile time,
		the <command>fstrm</command> and <command>protobuf-c</command>
		libraries must be available, and <acronym>BIND</acronym> must be configured with
		<option>--enable-dnstap</option>.
	      </para>
	      <para>
		The <command>dnstap</command> option is a bracketed list
		of message types to be logged. These may be set differently
		for each view. Supported types are <literal>client</literal>,
		<literal>auth</literal>, <literal>resolver</literal>, and
		<literal>forwarder</literal>.  Specifying type
		<literal>all</literal> causes all <command>dnstap</command>
		messages to be logged, regardless of type.
	      </para>
	      <para>
		Each type may take an additional argument to indicate whether
		to log <literal>query</literal> messages or
		<literal>response</literal> messages; if not specified,
		both queries and responses are logged.
	      </para>
	      <para>
		Example: To log all authoritative queries and responses,
		recursive client responses, and upstream queries sent by
		the resolver, use:
<programlisting>dnstap {
  auth;
  client response;
  resolver query;
};
</programlisting>
	      </para>
	      <para>
		Logged <command>dnstap</command> messages can be parsed
		using the <command>dnstap-read</command> utility (see
		<xref linkend="man.dnstap-read"/> for details).
	      </para>
	      <para>
		For more information on <command>dnstap</command>, see
		<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://dnstap.info">http://dnstap.info</link>.
	      </para>
	      <para>
		The fstrm library has a number of tunables that are exposed
		in <filename>named.conf</filename>, and can be modified
		if necessary to improve performance or prevent loss of data.
		These are:
	      </para>
	      <itemizedlist>
		<listitem>
		  <simpara>
		    <command>fstrm-set-buffer-hint</command>: The
		    threshold number of bytes to accumulate in the output
		    buffer before forcing a buffer flush. The minimum is
		    1024, the maximum is 65536, and the default is 8192.
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-flush-timeout</command>: The number
		    of seconds to allow unflushed data to remain in the
		    output buffer. The minimum is 1 second, the maximum is
		    600 seconds (10 minutes), and the default is 1 second.
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-output-notify-threshold</command>:
		    The number of outstanding queue entries to allow on
		    an input queue before waking the I/O thread.
		    The minimum is 1 and the default is 32.
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-output-queue-model</command>:
		    The queuing semantics to use for queue
		    objects. The default is <literal>mpsc</literal>
		    (multiple producer, single consumer); the other
		    option is <literal>spsc</literal> (single producer,
		    single consumer).
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-input-queue-size</command>: The
		    number of queue entries to allocate for each
		    input queue. This value must be a power of 2.
		    The minimum is 2, the maximum is 16384, and
		    the default is 512.
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-output-queue-size</command>:
		    The number of queue entries to allocate for each
		    output queue. The minimum is 2, the maximum is
		    system-dependent and based on <option>IOV_MAX</option>,
		    and the default is 64.
		  </simpara>
		</listitem>
		<listitem>
		  <simpara>
		    <command>fstrm-set-reopen-interval</command>:
		    The number of seconds to wait between attempts to
		    reopen a closed output stream. The minimum is 1 second,
		    the maximum is 600 seconds (10 minutes), and the default
		    is 5 seconds.
		  </simpara>
		</listitem>
	      </itemizedlist>
	      <para>
		Note that all of the above minimum, maximum, and default
		values are set by the <command>libfstrm</command> library,
		and may be subject to change in future versions of the
		library. See the <command>libfstrm</command> documentation
		for more information.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnstap-output</command></term>
	    <listitem>
	      <para>
		This configures the path to which the <command>dnstap</command>
		frame stream is sent if <command>dnstap</command>
		is enabled at compile time and active.
	      </para>
	      <para>
		The first argument is either <literal>file</literal> or
		<literal>unix</literal>, indicating whether the destination
		is a file or a Unix domain socket.  The second argument
		is the path of the file or socket.  (Note: when using a
		socket, <command>dnstap</command> messages are
		only sent if another process such as
		<command>fstrm_capture</command>
		(provided with <command>libfstrm</command>) is listening on
		the socket.)
	      </para>
	      <para>
		<command>dnstap-output</command> can only be set globally
		in <command>options</command>. Currently, it can only be
		set once while <command>named</command> is running;
		once set, it cannot be changed by
		<command>rndc reload</command> or
		<command>rndc reconfig</command>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnstap-identity</command></term>
	    <listitem>
	      <para>
		This specifies an <command>identity</command> string to send in
		<command>dnstap</command> messages. If set to
		<literal>hostname</literal>, which is the default, the
		server's hostname is sent. If set to
		<literal>none</literal>, no identity string is sent.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnstap-version</command></term>
	    <listitem>
	      <para>
		This specifies a <command>version</command> string to send in
		<command>dnstap</command> messages. The default is the
		version number of the <acronym>BIND</acronym> release. If set to
		<literal>none</literal>, no version string is sent.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>geoip-directory</command></term>
	    <listitem>
	      <para>
		When <command>named</command> is compiled using the
		MaxMind GeoIP2 geolocation API, or the legacy GeoIP API,
		this specifies the directory containing GeoIP
		database files.  By default, the option is set based on
		the prefix used to build the <command>libmaxminddb</command>
		module; for example, if the library is installed in
		<filename>/usr/local/lib</filename>, then the default
		<command>geoip-directory</command> is
		<filename>/usr/local/share/GeoIP</filename>. On Windows,
		the default is the <command>named</command> working
		directory.  See <xref linkend="acl"/> for details about
		<command>geoip</command> ACLs.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>key-directory</command></term>
	    <listitem>
	      <para>
		This is the
		directory where the public and private DNSSEC key files
		should be found when performing a dynamic update of secure zones, if different than the current working
		directory.  (Note that this option has no effect on the
		paths for files containing non-DNSSEC keys such as
		<filename>bind.keys</filename>,
		<filename>rndc.key</filename>, or
		<filename>session.key</filename>.)
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>lmdb-mapsize</command></term>
	    <listitem>
	      <para>
		When <command>named</command> is built with liblmdb,
		this option sets a maximum size for the memory map of
		the new-zone database (NZD) in LMDB database format.
		This database is used to store configuration information
		for zones added using <command>rndc addzone</command>.
		Note that this is not the NZD database file size, but
		the largest size that the database may grow to.
	      </para>
	      <para>
		Because the database file is memory mapped, its size is
		limited by the address space of the <command>named</command> process.  The
		default of 32 megabytes was chosen to be usable with
		32-bit <command>named</command> builds.  The largest
		permitted value is 1 terabyte. Given typical zone
		configurations without elaborate ACLs, a 32 MB NZD file
		ought to be able to hold configurations of about 100,000
		zones.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>managed-keys-directory</command></term>
	    <listitem>
	      <para>
		This specifies the directory in which to store the files that
		track managed DNSSEC keys.  By default, this is the working
		directory.  The directory <emphasis>must</emphasis>
		be writable by the effective user ID of the
		<command>named</command> process.
	      </para>
	      <para>
		If <command>named</command> is not configured to use views,
		managed keys for the server are tracked in a single
		file called <filename>managed-keys.bind</filename>.
		Otherwise, managed keys are tracked in separate files,
		one file per view; each file name is the view name
		(or, if it contains characters that are incompatible with
		use as a file name, the SHA256 hash of the view name),
		followed by the extension
		<filename>.mkeys</filename>.
	      </para>
	      <para>
		(Note: in earlier releases, file names for views
		always used the SHA256 hash of the view name. To ensure
		compatibility after upgrading, if a file using the old
		name format is found to exist, it is used instead
		of the new format.)
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>named-xfer</command></term>
	    <listitem>
	      <para>
		<emphasis>This option is obsolete.</emphasis>
		In <acronym>BIND</acronym> 9, no separate
		<command>named-xfer</command> program is needed;
		its functionality is built into the name server.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>tkey-gssapi-keytab</command></term>
	    <listitem>
	      <para>
		This is the KRB5 keytab file to use for GSS-TSIG updates. If
		this option is set and tkey-gssapi-credential is not
		set, updates are allowed with any key
		matching a principal in the specified keytab.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>tkey-gssapi-credential</command></term>
	    <listitem>
	      <para>
		This is the security credential with which the server should
		authenticate keys requested by the GSS-TSIG protocol.
		Currently only Kerberos 5 authentication is available;
		the credential is a Kerberos principal which the
		server can acquire through the default system key
		file, normally <filename>/etc/krb5.keytab</filename>.
		The location of the keytab file can be overridden using the
		<command>tkey-gssapi-keytab</command> option. Normally this principal is
		of the form "<userinput>DNS/</userinput><varname>server.domain</varname>".
		To use GSS-TSIG, <command>tkey-domain</command> must
		also be set if a specific keytab is not set with
		<command>tkey-gssapi-keytab</command>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>tkey-domain</command></term>
	    <listitem>
	      <para>
		This domain is appended to the names of all shared keys
		generated with <command>TKEY</command>.  When a
		client requests a <command>TKEY</command> exchange,
		it may or may not specify the desired name for the
		key. If present, the name of the shared key is
		<varname>client-specified part</varname> +
		<varname>tkey-domain</varname>.  Otherwise, the
		name of the shared key is <varname>random hex
		digits</varname> + <varname>tkey-domain</varname>.
		In most cases, the <command>domainname</command>
		should be the server's domain name, or an otherwise
		nonexistent subdomain like
		"_tkey.<varname>domainname</varname>".  If
		using GSS-TSIG, this variable must be defined, unless
		a specific keytab is specified using <command>tkey-gssapi-keytab</command>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>tkey-dhkey</command></term>
	    <listitem>
	      <para>
		This is the Diffie-Hellman key used by the server
		to generate shared keys with clients using the Diffie-Hellman
		mode
		of <command>TKEY</command>. The server must be
		able to load the
		public and private keys from files in the working directory.
		In
		most cases, the <varname>key_name</varname> should be the server's host name.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>cache-file</command></term>
	    <listitem>
	      <para>
		This is for testing only.  Do not use.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dump-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file the server dumps
		the database to, when instructed to do so with
		<command>rndc dumpdb</command>.
		If not specified, the default is <filename>named_dump.db</filename>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>memstatistics-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file the server writes memory
		usage statistics to on exit. If not specified,
		the default is <filename>named.memstats</filename>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>lock-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of a file on which <command>named</command>
		attempts to acquire a file lock when starting for
		the first time; if unsuccessful, the server
		terminates, under the assumption that another
		server is already running.  If not specified, the default is
		<filename>none</filename>.
	      </para>
	      <para>
		Specifying <command>lock-file none</command> disables the
		use of a lock file.  <command>lock-file</command> is
		ignored if <command>named</command> was run using the <option>-X</option>
		option, which overrides it.  Changes to
		<command>lock-file</command> are ignored if
		<command>named</command> is being reloaded or
		reconfigured; it is only effective when the server is
		first started.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>pid-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file the server writes its process ID
		in. If not specified, the default is
		<filename>/var/run/named/named.pid</filename>.
		The PID file is used by programs that send signals to
		the running
		name server. Specifying <command>pid-file none</command> disables the
		use of a PID file; no file is written and any
		existing one is removed.  Note that <command>none</command>
		is a keyword, not a filename, and therefore is not enclosed
		in
		double quotes.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>recursing-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file where the server dumps
		the queries that are currently recursing, when instructed
		to do so with <command>rndc recursing</command>.
		If not specified, the default is <filename>named.recursing</filename>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>statistics-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file the server appends statistics
		to, when instructed to do so using <command>rndc stats</command>.
		If not specified, the default is <filename>named.stats</filename> in the
		server's current directory.  The format of the file is
		described
		in <xref linkend="statsfile"/>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>bindkeys-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of a file to override the built-in trusted
		keys provided by <command>named</command>.
		See the discussion of <command>dnssec-validation</command>
		for details.  If not specified, the default is
		<filename>/etc/bind.keys</filename>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>secroots-file</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file the server dumps
		security roots to, when instructed to do so with
		<command>rndc secroots</command>.
		If not specified, the default is
		<filename>named.secroots</filename>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>session-keyfile</command></term>
	    <listitem>
	      <para>
		This is the pathname of the file into which to write a TSIG
		session key generated by <command>named</command> for use by
		<command>nsupdate -l</command>.  If not specified, the
		default is <filename>/var/run/named/session.key</filename>.
		(See <xref linkend="dynamic_update_policies"/>, and in
		particular the discussion of the
		<command>update-policy</command> statement's
		<userinput>local</userinput> option for more
		information about this feature.)
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>session-keyname</command></term>
	    <listitem>
	      <para>
		This is the key name to use for the TSIG session key.
		If not specified, the default is <varname>local-ddns</varname>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>session-keyalg</command></term>
	    <listitem>
	      <para>
		This is the algorithm to use for the TSIG session key.
		Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
		hmac-sha384, hmac-sha512, and hmac-md5.  If not
		specified, the default is hmac-sha256.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>port</command></term>
	    <listitem>
	      <para>
		This is the UDP/TCP port number the server uses to
		receive and send DNS protocol traffic.
		The default is 53.  This option is mainly intended for server
		testing;
		a server using a port other than 53 is not able to
		communicate with
		the global DNS.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dscp</command></term>
	    <listitem>
	      <para>
		This is the global Differentiated Services Code Point (DSCP)
		value to classify outgoing DNS traffic, on operating
		systems that support DSCP. Valid values are 0 through 63.
		It is not configured by default.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>random-device</command></term>
	    <listitem>
	      <para>
		This specifies a source of entropy to be used by the server.  Entropy is
		primarily needed
		for DNSSEC operations, such as TKEY transactions and dynamic
		update of signed
		zones.  This option specifies the device (or file) from which
		to read
		entropy.  If it is a file, operations requiring entropy will
		fail when the
		file has been exhausted.  If <command>random-device</command> is not specified, the default value
		is
		<filename>/dev/random</filename>
		(or equivalent) when present, and none otherwise.  The
		<command>random-device</command> option takes
		effect during
		the initial configuration load at server startup time and
		is ignored on subsequent reloads.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>preferred-glue</command></term>
	    <listitem>
	      <para>
		If specified, the listed type (A or AAAA) is emitted
		before other glue
		in the additional section of a query response.
		The default is to prefer A records when responding
		to queries that arrived via IPv4 and AAAA when
		responding to queries that arrived via IPv6.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry xml:id="root_delegation_only">
	    <term><command>root-delegation-only</command></term>
	    <listitem>
	      <para>
		This turns on enforcement of delegation-only in TLDs
		(top-level domains) and root zones with an optional
		exclude list.
	      </para>
	      <para>
		DS queries are expected to be made to and be answered by
		delegation-only zones.  Such queries and responses are
		treated as an exception to delegation-only processing
		and are not converted to NXDOMAIN responses, provided
		a CNAME is not discovered at the query name.
	      </para>
	      <para>
		If a delegation-only zone server also serves a child
		zone, it is not always possible to determine whether
		an answer comes from the delegation-only zone or the
		child zone.  SOA NS and DNSKEY records are apex-only
		records and a matching response that contains
		these records or DS is treated as coming from a
		child zone.  RRSIG records are also examined to see
		if they are signed by a child zone, and the
		authority section is examined to see if there
		is evidence that the answer is from the child zone.
		Answers that are determined to be from a child zone
		are not converted to NXDOMAIN responses.  Despite
		all these checks, there is still a possibility of
		false negatives when a child zone is being served.
	      </para>
	      <para>
		Similarly, false positives can arise from empty nodes
		(no records at the name) in the delegation-only zone
		when the query type is not <varname>ANY</varname>.
	      </para>
	      <para>
		Note that some TLDs are not delegation-only; e.g., "DE", "LV",
		"US", and "MUSEUM".  This list is not exhaustive.
	      </para>

<programlisting>
options {
	root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</programlisting>

	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>disable-algorithms</command></term>
	    <listitem>
	      <para>
		This disables the specified DNSSEC algorithms at and below the
		specified name.
		Multiple <command>disable-algorithms</command>
		statements are allowed.
		Only the best-match <command>disable-algorithms</command>
		clause is used to determine the algorithms.
	      </para>
	      <para>
		If all supported algorithms are disabled, the zones covered
		by the <command>disable-algorithms</command> setting are treated
		as insecure.
	      </para>
	      <para>
		Configured trust anchors in <command>trusted-keys</command>
		or <command>managed-keys</command> that match a disabled
		algorithm are ignored and treated as if they were not
		configured.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>disable-ds-digests</command></term>
	    <listitem>
	      <para>
		This disables the specified DS digest types at and below the
		specified name.
		Multiple <command>disable-ds-digests</command>
		statements are allowed.
		Only the best-match <command>disable-ds-digests</command>
		clause is used to determine the digest types.
	      </para>
	      <para>
		If all supported digest types are disabled, the zones covered
		by <command>disable-ds-digests</command> are treated
		as insecure.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnssec-lookaside</command></term>
	    <listitem>
	      <para>
		When set, <command>dnssec-lookaside</command> provides the
		validator with an alternate method to validate DNSKEY
		records at the top of a zone.  When a DNSKEY is at or
		below a domain specified by the deepest
		<command>dnssec-lookaside</command>, and the normal DNSSEC
		validation has left the key untrusted, the trust-anchor
		is appended to the key name and a DLV record is
		looked up to see if it can validate the key.  If the DLV
		record validates a DNSKEY (similarly to the way a DS
		record does), the DNSKEY RRset is deemed to be trusted.
	      </para>
	      <para>
		If <command>dnssec-lookaside</command> is set to
		<userinput>no</userinput>, then <command>dnssec-lookaside</command>
		is not used.
	      </para>
	      <para>
		Note: the ISC-provided DLV service at
		<literal>dlv.isc.org</literal> has been shut down.
		The <command>dnssec-lookaside auto;</command>
		configuration option, which set <command>named</command>
		to use ISC DLV with minimal configuration, has
		accordingly been removed.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnssec-must-be-secure</command></term>
	    <listitem>
	      <para>
		This specifies hierarchies which must be or may not be secure
		(signed and validated).  If <userinput>yes</userinput>,
		then <command>named</command> only accepts answers if
		they are secure.  If <userinput>no</userinput>, then normal
		DNSSEC validation applies, allowing insecure answers to
		be accepted.  The specified domain must be under a
		<command>trusted-keys</command> or
		<command>managed-keys</command> statement, or
		<command>dnssec-validation auto</command> must be active.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dns64</command></term>
	    <listitem>
	      <para>
		This directive instructs <command>named</command> to
		return mapped IPv4 addresses to AAAA queries when
		there are no AAAA records.  It is intended to be
		used in conjunction with a NAT64.  Each
		<command>dns64</command> defines one DNS64 prefix.
		Multiple DNS64 prefixes can be defined.
	      </para>
	      <para>
		Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
		64, and 96, per RFC 6052.  Bits 64..71 inclusive must
		be zero, with the most significant bit of the prefix in
		position 0.
	      </para>
	      <para>
		In addition, a reverse IP6.ARPA zone is created for
		the prefix to provide a mapping from the IP6.ARPA names
		to the corresponding IN-ADDR.ARPA names using synthesized
		CNAMEs.  <command>dns64-server</command> and
		<command>dns64-contact</command> can be used to specify
		the name of the server and contact for the zones. These
		can be set at the view/options level but not
		on a per-prefix basis.
	      </para>
	      <para>
		Each <command>dns64</command> supports an optional
		<command>clients</command> ACL that determines which
		clients are affected by this directive.  If not defined,
		it defaults to <userinput>any;</userinput>.
	      </para>
	      <para>
		Each <command>dns64</command> supports an optional
		<command>mapped</command> ACL that selects which
		IPv4 addresses are to be mapped in the corresponding
		A RRset.  If not defined, it defaults to
		<userinput>any;</userinput>.
	      </para>
	      <para>
		Normally, DNS64 does not apply to a domain name that
		owns one or more AAAA records; these records are
		simply returned.  The optional
		<command>exclude</command> ACL allows specification
		of a list of IPv6 addresses that are ignored
		if they appear in a domain name's AAAA records;
		DNS64 is applied to any A records the domain
		name owns.  If not defined, <command>exclude</command>
		defaults to ::ffff:0.0.0.0/96.
	      </para>
	      <para>
		A optional <command>suffix</command> can also
		be defined to set the bits trailing the mapped
		IPv4 address bits.  By default these bits are
		set to <userinput>::</userinput>.  The bits
		matching the prefix and mapped IPv4 address
		must be zero.
	      </para>
	      <para>
		If <command>recursive-only</command> is set to
		<command>yes</command>, the DNS64 synthesis
		only happens for recursive queries.  The default
		is <command>no</command>.
	      </para>
	      <para>
		If <command>break-dnssec</command> is set to
		<command>yes</command>, the DNS64 synthesis
		happens even if the result, if validated, would
		cause a DNSSEC validation failure.  If this option
		is set to <command>no</command> (the default), the DO
		is set on the incoming query, and there are RRSIGs on
		the applicable records, then synthesis does not happen.
	      </para>
<programlisting>
	acl rfc1918 { 10/8; 192.168/16; 172.16/12; };

	dns64 64:FF9B::/96 {
		clients { any; };
		mapped { !rfc1918; any; };
		exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
		suffix ::;
	};
</programlisting>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnssec-loadkeys-interval</command></term>
	    <listitem>
		<para>
		  When a zone is configured with <command>auto-dnssec
		  maintain;</command>, its key repository must be checked
		  periodically to see if any new keys have been added
		  or any existing keys' timing metadata has been updated
		  (see <xref linkend="man.dnssec-keygen"/> and
		  <xref linkend="man.dnssec-settime"/>).  The
		  <command>dnssec-loadkeys-interval</command> option
		  sets the frequency of automatic repository checks, in
		  minutes.  The default is <literal>60</literal> (1 hour),
		  the minimum is <literal>1</literal> (1 minute), and the
		  maximum is <literal>1440</literal> (24 hours); any higher
		  value is silently reduced.
		</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>dnssec-update-mode</command></term>
	    <listitem>
		<para>
		  If this option is set to its default value of
		  <literal>maintain</literal> in a zone of type
		  <literal>master</literal> which is DNSSEC-signed
		  and configured to allow dynamic updates (see
		  <xref linkend="dynamic_update_policies"/>), and
		  if <command>named</command> has access to the
		  private signing key(s) for the zone, then
		  <command>named</command> automatically signs all new
		  or changed records and maintains signatures for the zone
		  by regenerating RRSIG records whenever they approach
		  their expiration date.
		</para>
		<para>
		  If the option is changed to <literal>no-resign</literal>,
		  then <command>named</command> signs all new or
		  changed records, but scheduled maintenance of
		  signatures is disabled.
		</para>
		<para>
		  With either of these settings, <command>named</command>
		  rejects updates to a DNSSEC-signed zone when the
		  signing keys are inactive or unavailable to
		  <command>named</command>.  (A planned third option,
		  <literal>external</literal>, will disable all automatic
		  signing and allow DNSSEC data to be submitted into a zone
		  via dynamic update; this is not yet implemented.)
		</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>nta-lifetime</command></term>
	    <listitem>
		<para>
		  This specifies the default lifetime, in seconds,
		  for negative trust anchors added
		  via <command>rndc nta</command>.
		</para>
		<para>
		  A negative trust anchor selectively disables
		  DNSSEC validation for zones that are known to be
		  failing because of misconfiguration, rather than
		  an attack.  When data to be validated is
		  at or below an active NTA (and above any other
		  configured trust anchors), <command>named</command>
		  aborts the DNSSEC validation process and treats the data as
		  insecure rather than bogus.  This continues until the
		  NTA's lifetime is elapsed. NTAs persist
		  across <command>named</command> restarts.
		</para>
		<para>
		  For convenience, TTL-style time-unit suffixes can be
		  used to specify the NTA lifetime in seconds, minutes,
		  or hours.  <option>nta-lifetime</option> defaults to
		  one hour; it cannot exceed one week.
		</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>nta-recheck</command></term>
	    <listitem>
		<para>
		  This specifies how often to check whether negative
		  trust anchors added via <command>rndc nta</command>
		  are still necessary.
		</para>
		<para>
		  A negative trust anchor is normally used when a
		  domain has stopped validating due to operator error;
		  it temporarily disables DNSSEC validation for that
		  domain. In the interest of ensuring that DNSSEC
		  validation is turned back on as soon as possible,
		  <command>named</command> periodically sends a
		  query to the domain, ignoring negative trust anchors,
		  to find out whether it can now be validated.  If so,
		  the negative trust anchor is allowed to expire early.
		</para>
		<para>
		  Validity checks can be disabled for an individual
		  NTA by using <command>rndc nta -f</command>, or
		  for all NTAs by setting <option>nta-recheck</option>
		  to zero.
		</para>
		<para>
		  For convenience, TTL-style time-unit suffixes can be
		  used to specify the NTA recheck interval in seconds,
		  minutes, or hours.  The default is five minutes.  It
		  cannot be longer than <option>nta-lifetime</option>,
		  which cannot be longer than a week.
		</para>
	    </listitem>
	  </varlistentry>


	  <varlistentry>
	    <term><command>max-zone-ttl</command></term>
	    <listitem>
	      <para>
		This specifies a maximum permissible TTL value in seconds.
		For convenience, TTL-style time-unit suffixes may be
		used to specify the maximum value.
		When loading a zone file using a
		<option>masterfile-format</option> of
		<constant>text</constant> or <constant>raw</constant>,
		any record encountered with a TTL higher than
		<option>max-zone-ttl</option> causes the zone to
		be rejected.
	      </para>
	      <para>
		This is useful in DNSSEC-signed zones because when
		rolling to a new DNSKEY, the old key needs to remain
		available until RRSIG records have expired from
		caches.  The <option>max-zone-ttl</option> option guarantees
		that the largest TTL in the zone is no higher
		than the set value.
	      </para>
	      <para>
		(Note: because <constant>map</constant>-format files
		load directly into memory, this option cannot be
		used with them.)
	      </para>
	      <para>
		The default value is <constant>unlimited</constant>.
		A <option>max-zone-ttl</option> of zero is treated as
		<constant>unlimited</constant>.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>serial-update-method</command></term>
	    <listitem>
	      <para>
		Zones configured for dynamic DNS may use this
		option to set the update method to be used for
		the zone serial number in the SOA record.
	      </para>
	      <para>
		With the default setting of
		<command>serial-update-method increment;</command>, the
		SOA serial number is incremented by one each time
		the zone is updated.
	      </para>
	      <para>
		When set to
		<command>serial-update-method unixtime;</command>, the
		SOA serial number is set to the number of seconds
		since the Unix epoch, unless the serial number is
		already greater than or equal to that value, in which
		case it is simply incremented by one.
	      </para>
	      <para>
		When set to
		<command>serial-update-method date;</command>, the
		new SOA serial number is the current date
		in the form "YYYYMMDD", followed by two zeroes,
		unless the existing serial number is already greater
		than or equal to that value, in which case it is
		incremented by one.
	      </para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term><command>zone-statistics</command></term>
	    <listitem>
	      <para>
		If <userinput>full</userinput>, the server collects
		statistical data on all zones, unless specifically
		turned off on a per-zone basis by specifying
		<command>zone-statistics terse</command> or
		<command>zone-statistics none</command>
		in the <command>zone</command> statement.
		The default is <userinput>terse</userinput>, providing
		minimal statistics on zones (including name and
		current serial number, but not query type
		counters).
	      </para>
	      <para>
		These statistics may be accessed via the
		<command>statistics-channel</command> or
		using <command>rndc stats</command>, which
		dumps them to the file listed
		in the <command>statistics-file</command>.  See
		also <xref linkend="statsfile"/>.
	      </para>
	      <para>
		For backward compatibility with earlier versions
		of BIND 9, the <command>zone-statistics</command>
		option can also accept <userinput>yes</userinput>
		or <userinput>no</userinput>; <userinput>yes</userinput>
		has the same meaning as <userinput>full</userinput>.
		As of <acronym>BIND</acronym> 9.10,
		<userinput>no</userinput> has the same meaning
		as <userinput>none</userinput>; previously, it
		was the same as <userinput>terse</userinput>.
	      </para>
	    </listitem>
	  </varlistentry>
	</variablelist>

	<section xml:id="boolean_options"><info><title>Boolean Options</title></info>

	  <variablelist>

	    <varlistentry>
	      <term><command>automatic-interface-scan</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput> and supported by the operating
		  system, this automatically rescans network interfaces when the
		  interface addresses are added or removed.  The default is
		  <userinput>yes</userinput>.  This configuration option does
		  not affect the time-based <command>interface-interval</command>
		  option; it is recommended to set the time-based
		  <command>interface-interval</command> to 0 when the operator
		  confirms that automatic interface scanning is supported by the
		  operating system.
		</para>
		<para>
		  The <command>automatic-interface-scan</command> implementation
		  uses routing sockets for the network interface discovery;
		  therefore, the operating system must support the routing
		  sockets for this feature to work.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-new-zones</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then zones can be
		  added at runtime via <command>rndc addzone</command>.
		  The default is <userinput>no</userinput>.
		</para>
		<para>
		  Newly added zones' configuration parameters
		  are stored so that they can persist after the
		  server is restarted.  The configuration information
		  is saved in a file called
		  <filename><replaceable>viewname</replaceable>.nzf</filename>
		  (or, if <command>named</command> is compiled with
		  liblmdb, in an LMDB database file called
		  <filename><replaceable>viewname</replaceable>.nzd</filename>).
		  <replaceable>viewname</replaceable> is the name of the
		  view, unless the view name contains characters that are
		  incompatible with use as a file name, in which case a
		  cryptographic hash of the view name is used instead.
		</para>
		<para>
		  Configurations for zones added at runtime are
		  stored either in a new-zone file (NZF) or a new-zone
		  database (NZD), depending on whether
		  <command>named</command> was linked with
		  liblmdb at compile time.
		  See <xref linkend="man.rndc"/> for further details
		  about <command>rndc addzone</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>auth-nxdomain</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then the <command>AA</command> bit
		  is always set on NXDOMAIN responses, even if the server is
		  not actually
		  authoritative. The default is <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>deallocate-on-exit</command></term>
	      <listitem>
		<para>
		  This option was used in <acronym>BIND</acronym>
		  8 to enable checking
		  for memory leaks on exit. <acronym>BIND</acronym> 9 ignores the option and always performs
		  the checks.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>memstatistics</command></term>
	      <listitem>
		<para>
		  This writes memory statistics to the file specified by
		  <command>memstatistics-file</command> at exit.
		  The default is <userinput>no</userinput> unless
		  <userinput>-m record</userinput> is specified on the command line, in
		  which case it is <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dialup</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then the
		  server treats all zones as if they are doing zone transfers
		  across
		  a dial-on-demand dialup link, which can be brought up by
		  traffic
		  originating from this server. Although this setting has different effects
		  according
		  to zone type, it concentrates the zone maintenance so that
		  everything
		  happens quickly, once every <command>heartbeat-interval</command>,
		  ideally during a single call. It also suppresses some
		  normal
		  zone maintenance traffic. The default is <userinput>no</userinput>.
		</para>
		<para>
		  If specified in the <command>view</command> and
		  <command>zone</command> statements, the <command>dialup</command> option
		  overrides the global <command>dialup</command> option.
		</para>
		<para>
		  If the zone is a primary zone, the server sends out a
		  NOTIFY
		  request to all the secondaries (default). This should trigger the
		  zone serial
		  number check in the secondary (providing it supports NOTIFY),
		  allowing the secondary
		  to verify the zone while the connection is active.
		  The set of servers to which NOTIFY is sent can be controlled
		  by
		  <command>notify</command> and <command>also-notify</command>.
		</para>
		<para>
		  If the
		  zone is a secondary or stub zone, the server suppresses
		  the regular
		  "zone up to date" (refresh) queries and only performs them
		  when the
		  <command>heartbeat-interval</command> expires, in
		  addition to sending
		  NOTIFY requests.
		</para>
		<para>
		  Finer control can be achieved by using
		  <userinput>notify</userinput>, which only sends NOTIFY
		  messages;
		  <userinput>notify-passive</userinput>, which sends NOTIFY
		  messages and
		  suppresses the normal refresh queries; <userinput>refresh</userinput>,
		  which suppresses normal refresh processing and sends refresh
		  queries
		  when the <command>heartbeat-interval</command>
		  expires; and
		  <userinput>passive</userinput>, which disables normal
		  refresh
		  processing.
		</para>

		<informaltable colsep="0" rowsep="0">
		  <tgroup cols="4" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		    <colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
		    <colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
		    <colspec colname="3" colnum="3" colsep="0" colwidth="1.150in"/>
		    <colspec colname="4" colnum="4" colsep="0" colwidth="1.150in"/>
		    <tbody>
		      <row rowsep="0">
			<entry colname="1">
			  <para>
			    dialup mode
			  </para>
			</entry>
			<entry colname="2">
			  <para>
			    normal refresh
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    heart-beat refresh
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    heart-beat notify
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>no</command> (default)</para>
			</entry>
			<entry colname="2">
			  <para>
			    yes
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    no
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>yes</command></para>
			</entry>
			<entry colname="2">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    yes
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    yes
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>notify</command></para>
			</entry>
			<entry colname="2">
			  <para>
			    yes
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    yes
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>refresh</command></para>
			</entry>
			<entry colname="2">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    yes
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    no
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>passive</command></para>
			</entry>
			<entry colname="2">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    no
			  </para>
			</entry>
		      </row>
		      <row rowsep="0">
			<entry colname="1">
			  <para><command>notify-passive</command></para>
			</entry>
			<entry colname="2">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="3">
			  <para>
			    no
			  </para>
			</entry>
			<entry colname="4">
			  <para>
			    yes
			  </para>
			</entry>
		      </row>
		    </tbody>
		  </tgroup>
		</informaltable>

		<para>
		  Note that normal NOTIFY processing is not affected by
		  <command>dialup</command>.
		</para>

	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>fake-iquery</command></term>
	      <listitem>
		<para>
		  In <acronym>BIND</acronym> 8, this option
		  enabled simulating the obsolete DNS query type
		  IQUERY. <acronym>BIND</acronym> 9 never does
		  IQUERY simulation.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>fetch-glue</command></term>
	      <listitem>
		<para>
		  This option is obsolete.
		  In BIND 8, <userinput>fetch-glue yes</userinput>
		  caused the server to attempt to fetch glue resource records
		  it
		  did not have when constructing the additional
		  data section of a response.  This is now considered a bad
		  idea
		  and BIND 9 never does it.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>flush-zones-on-shutdown</command></term>
	      <listitem>
		<para>
		  When the nameserver exits upon receiving SIGTERM,
		  flush or do not flush any pending zone writes.  The default
		  is
		  <command>flush-zones-on-shutdown</command> <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>geoip-use-ecs</command></term>
	      <listitem>
		<para>
		  When BIND is compiled with GeoIP support and configured
		  with "geoip" ACL elements, this option indicates whether
		  the EDNS Client Subnet option, if present in a request,
		  should be used for matching against the GeoIP database.
		  The default is
		  <command>geoip-use-ecs</command> <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>has-old-clients</command></term>
	      <listitem>
		<para>
		  This option was incorrectly implemented
		  in <acronym>BIND</acronym> 8, and is ignored by <acronym>BIND</acronym> 9.
		  To achieve the intended effect
		  of
		  <command>has-old-clients</command> <userinput>yes</userinput>, specify
		  the two separate options <command>auth-nxdomain</command> <userinput>yes</userinput>
		  and <command>rfc2308-type1</command> <userinput>no</userinput> instead.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>host-statistics</command></term>
	      <listitem>
		<para>
		  In BIND 8, this enabled keeping of
		  statistics for every host that the name server interacts
		  with.
		  It is not implemented in BIND 9.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>root-key-sentinel</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, respond to root key sentinel probes as described in
		  draft-ietf-dnsop-kskroll-sentinel-08. The default is
		  <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>maintain-ixfr-base</command></term>
	      <listitem>
		<para>
		  <emphasis>This option is obsolete</emphasis>.
		  It was used in <acronym>BIND</acronym> 8 to
		  determine whether a transaction log was
		  kept for Incremental Zone Transfer. <acronym>BIND</acronym> 9 maintains a transaction
		  log whenever possible.  To disable outgoing
		  incremental zone
		  transfers, use <command>provide-ixfr</command> <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>message-compression</command></term> <listitem>
		<para>
		  If <userinput>yes</userinput>, DNS name compression is
		  used in responses to regular queries (not including
		  AXFR or IXFR, which always use compression).  Setting
		  this option to <userinput>no</userinput> reduces CPU
		  usage on servers and may improve throughput.  However,
		  it increases response size, which may cause more queries
		  to be processed using TCP; a server with compression
		  disabled is out of compliance with RFC 1123 Section
		  6.1.3.2. The default is <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>minimal-responses</command></term>
	      <listitem>
		<para>
		  If set to <userinput>yes</userinput>, then when generating
		  responses the server only adds records to the authority
		  and additional data sections when they are required (e.g.
		  delegations, negative responses).  This may improve the
		  performance of the server.
		</para>
		<para>
		  When set to <userinput>no-auth</userinput>, the
		  server omits records from the authority section
		  unless they are required, but it may still add
		  records to the additional section.  When set to
		  <userinput>no-auth-recursive</userinput>, this
		  is only done if the query is recursive.  These
		  settings are useful when answering stub clients,
		  which usually ignore the authority section.
		  <userinput>no-auth-recursive</userinput> is
		  designed for mixed-mode servers that handle
		  both authoritative and recursive queries.
		</para>
		<para>
		  The default is <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>minimal-any</command></term>
	      <listitem>
		<para>
		  If set to <userinput>yes</userinput>, the server replies with only one
		  of the RRsets for the query name, and its covering
		  RRSIGs if any, when
		  generating a positive response to a query of type
		  ANY over UDP, instead of replying with all known
		  RRsets for the name.  Similarly, a query for type
		  RRSIG is answered with the RRSIG records covering
		  only one type. This can reduce the impact of some kinds
		  of attack traffic, without harming legitimate
		  clients.  (Note, however, that the RRset returned is the
		  first one found in the database; it is not necessarily
		  the smallest available RRset.)
		  Additionally, <option>minimal-responses</option> is
		  turned on for these queries, so no unnecessary records
		  are added to the authority or additional sections.
		  The default is <userinput>no</userinput>.
		</para>
	    </listitem>
	  </varlistentry>

	    <varlistentry>
	      <term><command>multiple-cnames</command></term>
	      <listitem>
		<para>
		  This option was used in <acronym>BIND</acronym> 8 to allow
		  a domain name to have multiple CNAME records, in violation of
		  the DNS standards.  <acronym>BIND</acronym> 9.2 onwards
		  always strictly enforces the CNAME rules both in primary
		  files and dynamic updates.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput> (the default),
		  DNS NOTIFY messages are sent when a zone the server is
		  authoritative for
		  changes; see <xref linkend="notify"/>.  The messages are
		  sent to the
		  servers listed in the zone's NS records (except the primary
		  server identified
		  in the SOA MNAME field), and to any servers listed in the
		  <command>also-notify</command> option.
		</para>
		<para>
		  If <userinput>master-only</userinput>, notifies are only
		  sent
		  for primary zones.
		  If <userinput>explicit</userinput>, notifies are sent only
		  to
		  servers explicitly listed using <command>also-notify</command>.
		  If <userinput>no</userinput>, no notifies are sent.
		</para>
		<para>
		  The <command>notify</command> option may also be
		  specified in the <command>zone</command>
		  statement,
		  in which case it overrides the <command>options notify</command> statement.
		  It would only be necessary to turn off this option if it
		  caused secondary zones
		  to crash.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify-to-soa</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, do not check the name servers
		  in the NS RRset against the SOA MNAME.  Normally a NOTIFY
		  message is not sent to the SOA MNAME (SOA ORIGIN), as it is
		  supposed to contain the name of the ultimate primary server.
		  Sometimes, however, a secondary server is listed as the SOA MNAME in
		  hidden primary configurations; in that case,
		  the ultimate primary should be set to still send NOTIFY messages to
		  all the name servers listed in the NS RRset.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>recursion</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, and a
		  DNS query requests recursion, then the server attempts
		  to do
		  all the work required to answer the query. If recursion is
		  off
		  and the server does not already know the answer, it
		  returns a
		  referral response. The default is
		  <userinput>yes</userinput>.
		  Note that setting <command>recursion no</command> does not prevent
		  clients from getting data from the server's cache; it only
		  prevents new data from being cached as an effect of client
		  queries.
		  Caching may still occur as an effect the server's internal
		  operation, such as NOTIFY address lookups.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>request-nsid</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then an empty EDNS(0)
		  NSID (Name Server Identifier) option is sent with all
		  queries to authoritative name servers during iterative
		  resolution. If the authoritative server returns an NSID
		  option in its response, then its contents are logged in
		  the <command>resolver</command> category at level
		  <command>info</command>.
		  The default is <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>request-sit</command></term>
	      <listitem>
		<para>
		  This experimental option is obsolete.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>require-server-cookie</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, require a valid server cookie before sending a full
		  response to a UDP request from a cookie-aware client.
		  BADCOOKIE is sent if there is a bad or nonexistent
		  server cookie.
		  The default is <userinput>no</userinput>.
		</para>
		<para>
		  Users wishing to test that DNS COOKIE clients correctly handle BADCOOKIE, or who are
		  getting a lot of forged DNS requests with DNS COOKIES
		  present, should set this to <userinput>yes</userinput>.
		  Setting this to <userinput>yes</userinput>
		  results in a reduced amplification effect in a reflection
		  attack, as the BADCOOKIE response is smaller than
		  a full response, while also requiring a legitimate client
		  to follow up with a second query with the new, valid, cookie.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>answer-cookie</command></term>
	      <listitem>
		<para>
		  When set to the default value of <userinput>yes</userinput>,
		  COOKIE EDNS options are sent when applicable in
		  replies to client queries. If set to
		  <userinput>no</userinput>, COOKIE EDNS options are not
		  sent in replies.  This can only be set at the global
		  options level, not per-view.
		</para>
		<para>
		  <command>answer-cookie no</command> is only intended as a
		  temporary measure, for use when <command>named</command>
		  shares an IP address with other servers that do not yet
		  support DNS COOKIE.  A mismatch between servers on the
		  same address is not expected to cause operational
		  problems, but the option to disable COOKIE responses so
		  that all servers have the same behavior is provided out
		  of an abundance of caution. DNS COOKIE is an important
		  security mechanism, and should not be disabled unless
		  absolutely necessary.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>send-cookie</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then a COOKIE EDNS
		  option is sent along with the query.  If the
		  resolver has previously communicated with the server, the
		  COOKIE returned in the previous transaction is sent.
		  This is used by the server to determine whether
		  the resolver has talked to it before. A resolver
		  sending the correct COOKIE is assumed not to be an
		  off-path attacker sending a spoofed-source query;
		  the query is therefore unlikely to be part of a
		  reflection/amplification attack, so resolvers
		  sending a correct COOKIE option are not subject to
		  response rate limiting (RRL).  Resolvers which
		  do not send a correct COOKIE option may be limited
		  to receiving smaller responses via the
		  <command>nocookie-udp-size</command> option.
		  The default is <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>nocookie-udp-size</command></term>
	      <listitem>
		<para>
		  This sets the maximum size of UDP responses that are
		  sent to queries without a valid server COOKIE. A value
		  below 128 is silently raised to 128. The default
		  value is 1232, but the <command>max-udp-size</command>
		  option may further limit the response size.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>sit-secret</command></term>
	      <listitem>
		<para>
		  This experimental option is obsolete.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>cookie-algorithm</command></term>
	      <listitem>
		<para>
		  This sets the algorithm to be used when generating the
		  server cookie; the options are "aes", "sha1", or "sha256".
		  The default is "aes" if supported by the cryptographic
		  library; otherwise, "sha256".
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>cookie-secret</command></term>
	      <listitem>
		<para>
		  If set, this is a shared secret used for generating
		  and verifying EDNS COOKIE options
		  within an anycast cluster.  If not set, the system
		  generates a random secret at startup.  The
		  shared secret is encoded as a hex string and needs
		  to be 128 bits for AES128, 160 bits for SHA1, and
		  256 bits for SHA256.
		</para>
		<para>
		  If there are multiple secrets specified, the first
		  one listed in <filename>named.conf</filename> is
		  used to generate new server cookies.  The others
		  are only used to verify returned cookies.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>rfc2308-type1</command></term>
	      <listitem>
		<para>
		  Setting this to <userinput>yes</userinput>
		  causes the server to send NS records along with the SOA
		  record for negative
		  answers. The default is <userinput>no</userinput>.
		</para>
		<note>
		  <simpara>
		    This is not yet implemented in <acronym>BIND</acronym>
		    9.
		  </simpara>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>trust-anchor-telemetry</command></term>
	      <listitem>
		<para>
		  This causes <command>named</command> to send specially formed
		  queries once per day to domains for which trust anchors
		  have been configured via <command>trusted-keys</command>,
		  <command>managed-keys</command>, or
		  <command>dnssec-validation auto</command>.
		</para>
		<para>
		  The query name used for these queries has the
		  form "_ta-xxxx(-xxxx)(...)".&lt;domain&gt;, where
		  each "xxxx" is a group of four hexadecimal digits
		  representing the key ID of a trusted DNSSEC key.
		  The key IDs for each domain are sorted smallest
		  to largest prior to encoding. The query type is NULL.
		</para>
		<para>
		  By monitoring these queries, zone operators are
		  able to see which resolvers have been updated to
		  trust a new key; this may help them decide when it
		  is safe to remove an old one.
		</para>
		<para>
		  The default is <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>use-id-pool</command></term>
	      <listitem>
		<para>
		  <emphasis>This option is obsolete</emphasis>.
		  <acronym>BIND</acronym> 9 always allocates query
		  IDs from a pool.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>use-ixfr</command></term>
	      <listitem>
		<para>
		  <emphasis>This option is obsolete</emphasis>.
		  To disable IXFR to a particular server or
		  servers, see
		  the information on the <command>provide-ixfr</command> option
		  in <xref linkend="server_statement_definition_and_usage"/>.
		  See also
		  <xref linkend="incremental_zone_transfers"/>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>provide-ixfr</command></term>
	      <listitem>
		<para>
		  See the description of
		  <command>provide-ixfr</command> in
		  <xref linkend="server_statement_definition_and_usage"/>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>request-ixfr</command></term>
	      <listitem>
		<para>
		  See the description of
		  <command>request-ixfr</command> in
		  <xref linkend="server_statement_definition_and_usage"/>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>request-expire</command></term>
	      <listitem>
		<para>
		  See the description of
		  <command>request-expire</command> in
		  <xref linkend="server_statement_definition_and_usage"/>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>treat-cr-as-space</command></term>
	      <listitem>
		<para>
		  This option was used in <acronym>BIND</acronym>
		  8 to make
		  the server treat carriage return ("<command>\r</command>") characters the same way
		  as a space or tab character,
		  to facilitate loading of zone files on a Unix system that
		  were generated
		  on an NT or DOS machine. In <acronym>BIND</acronym> 9, both UNIX "<command>\n</command>"
		  and NT/DOS "<command>\r\n</command>" newlines
		  are always accepted,
		  and the option is ignored.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>additional-from-auth</command></term>
	      <term><command>additional-from-cache</command></term>
	      <listitem>

		<para>
		  These options control the behavior of an authoritative
		  server when
		  answering queries which have additional data, or when
		  following CNAME
		  and DNAME chains.
		</para>

		<para>
		  When both of these options are set to <userinput>yes</userinput>
		  (the default) and a
		  query is being answered from authoritative data (a zone
		  configured into the server), the additional data section of
		  the
		  reply is filled in using data from other authoritative
		  zones
		  and from the cache.  In some situations this is undesirable,
		  such
		  as when there is concern over the correctness of the cache,
		  or
		  in servers where secondary zones may be added and modified by
		  untrusted third parties.  Also, avoiding
		  the search for this additional data speeds up server
		  operations
		  at the possible expense of additional queries to resolve
		  what would
		  otherwise be provided in the additional section.
		</para>

		<para>
		  For example, if a query asks for an MX record for host <literal>foo.example.com</literal>,
		  and the record found is "<literal>MX 10 mail.example.net</literal>", normally the address
		  records (A and AAAA) for <literal>mail.example.net</literal> are provided as well,
		  if known, even though they are not in the example.com zone.
		  Setting these options to <command>no</command>
		  disables this behavior and makes
		  the server only search for additional data in the zone it
		  answers from.
		</para>

		<para>
		  These options are intended for use in authoritative-only
		  servers, or in authoritative-only views.  Attempts to set
		  them to <command>no</command> without also
		  specifying
		  <command>recursion no</command> will cause the
		  server to
		  ignore the options and log a warning message.
		</para>

		<para>
		  Specifying <command>additional-from-cache no</command> actually
		  disables the use of the cache not only for additional data
		  lookups
		  but also when looking up the answer.  This is usually the
		  desired
		  behavior in an authoritative-only server where the
		  correctness of
		  the cached data is an issue.
		</para>

		<para>
		  When a name server is non-recursively queried for a name
		  that is not
		  below the apex of any served zone, it normally answers with
		  an
		  "upwards referral" to the root servers or the servers of
		  some other
		  known parent of the query name.  Since the data in an
		  upwards referral
		  comes from the cache, the server is not able to provide
		  upwards
		  referrals when <command>additional-from-cache no</command>
		  has been specified.  Instead, it responds to such
		  queries
		  with REFUSED.  This should not cause any problems since
		  upwards referrals are not required for the resolution
		  process.
		</para>

	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>match-mapped-addresses</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, then an
		  IPv4-mapped IPv6 address matches any address-match
		  list entries that match the corresponding IPv4 address.
		</para>
		<para>
		  This option was introduced to work around a kernel quirk
		  in some operating systems that causes IPv4 TCP
		  connections, such as zone transfers, to be accepted on an
		  IPv6 socket using mapped addresses.  This caused address-match
		  lists designed for IPv4 to fail to match.  However,
		  <command>named</command> now solves this problem
		  internally.  The use of this option is discouraged.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>filter-aaaa-on-v4</command></term>
	      <listitem>
		<para>
		  This option is only available when
		  <acronym>BIND</acronym> 9 is compiled with the
		  <userinput>--enable-filter-aaaa</userinput> option on the
		  "configure" command line.  It is intended to help the
		  transition from IPv4 to IPv6 by not giving IPv6 addresses
		  to DNS clients unless they have connections to the IPv6
		  Internet.  This is not recommended unless absolutely
		  necessary.  The default is <userinput>no</userinput>.
		  The <command>filter-aaaa-on-v4</command> option
		  may also be specified in <command>view</command> statements
		  to override the global <command>filter-aaaa-on-v4</command>
		  option.
		</para>
		<para>
		  If <userinput>yes</userinput>,
		  the DNS client is at an IPv4 address, in <command>filter-aaaa</command>,
		  and if the response does not include DNSSEC signatures,
		  then all AAAA records are deleted from the response.
		  This filtering applies to all responses and not only
		  authoritative responses.
		</para>
		<para>
		  If <userinput>break-dnssec</userinput>,
		  then AAAA records are deleted even when DNSSEC is enabled.
		  As suggested by the name, this causes the response to not verify,
		  because the DNSSEC protocol is designed to detect deletions.
		</para>
		<para>
		  This mechanism can erroneously cause other servers to
		  not give AAAA records to their clients.
		  A recursing server with both IPv6 and IPv4 network connections,
		  that queries an authoritative server using this mechanism
		  via IPv4, is denied AAAA records even if its client is
		  using IPv6.
		</para>
		<para>
		  This mechanism is applied to authoritative as well as
		  non-authoritative records.
		  A client using IPv4 that is not allowed recursion can
		  erroneously be given AAAA records because the server is not
		  allowed to check for A records.
		</para>
		<para>
		  Some AAAA records are given to IPv4 clients in glue records.
		  IPv4 clients that are servers can then erroneously
		  answer requests for AAAA records received via IPv4.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>filter-aaaa-on-v6</command></term>
	      <listitem>
		<para>
		  This is identical to <command>filter-aaaa-on-v4</command>,
		  except it filters AAAA responses to queries from IPv6
		  clients instead of IPv4 clients.  To filter all
		  responses, set both options to <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>ixfr-from-differences</command></term>
	      <listitem>
		<para>
		  When <userinput>yes</userinput> and the server loads a new
		  version of a primary zone from its zone file or receives a
		  new version of a secondary file via zone transfer, it
		  compares the new version to the previous one and calculates
		  a set of differences.  The differences are then logged in
		  the zone's journal file so that the changes can be
		  transmitted to downstream secondaries as an incremental zone
		  transfer.
		</para>
		<para>
		  By allowing incremental zone transfers to be used for
		  non-dynamic zones, this option saves bandwidth at the
		  expense of increased CPU and memory consumption at the
		  primary server.
		  In particular, if the new version of a zone is completely
		  different from the previous one, the set of differences
		  is of a size comparable to the combined size of the
		  old and new zone versions, and the server needs to
		  temporarily allocate memory to hold this complete
		  difference set.
		</para>
		<para><command>ixfr-from-differences</command>
		  also accepts <command>master</command> and
		  <command>slave</command> at the view and options
		  levels, which causes
		  <command>ixfr-from-differences</command> to be enabled for
		  all primary or secondary zones, respectively.
		  It is off by default.
		</para>
		<para>
		  Note: if inline signing is enabled for a zone, the
		  user-provided <command>ixfr-from-differences</command>
		  setting is ignored for that zone.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>multi-master</command></term>
	      <listitem>
		<para>
		  This should be set when there are multiple primary servers for a zone
		  and the
		  addresses refer to different machines.  If <userinput>yes</userinput>, <command>named</command> does
		  not log
		  when the serial number on the primary is less than what <command>named</command>
		  currently
		  has.  The default is <userinput>no</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>auto-dnssec</command></term>
	      <listitem>
		<para>
		  Zones configured for dynamic DNS may use this
		  option to allow varying levels of automatic DNSSEC key
		  management. There are three possible settings:
		</para>
		<para>
		  <command>auto-dnssec allow;</command> permits
		  keys to be updated and the zone fully re-signed
		  whenever the user issues the command <command>rndc sign
		  <replaceable>zonename</replaceable></command>.
		</para>
		<para>
		  <command>auto-dnssec maintain;</command> includes the
		  above, but also automatically adjusts the zone's DNSSEC
		  keys on a schedule, according to the keys' timing metadata
		  (see <xref linkend="man.dnssec-keygen"/> and
		  <xref linkend="man.dnssec-settime"/>).  The command
		  <command>rndc sign
		  <replaceable>zonename</replaceable></command> causes
		  <command>named</command> to load keys from the key
		  repository and sign the zone with all keys that are
		  active.
		  <command>rndc loadkeys
		  <replaceable>zonename</replaceable></command> causes
		  <command>named</command> to load keys from the key
		  repository and schedule key maintenance events to occur
		  in the future, but it does not sign the full zone
		  immediately.  Note: once keys have been loaded for a
		  zone the first time, the repository is searched
		  for changes periodically, regardless of whether
		  <command>rndc loadkeys</command> is used.  The recheck
		  interval is defined by
		  <command>dnssec-loadkeys-interval</command>.)
		</para>
		<para>
		  The default setting is <command>auto-dnssec off</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dnssec-enable</command></term>
	      <listitem>
		<para>
		  This indicates whether DNSSEC-related resource
		  records are to be returned by <command>named</command>.
		  If set to <userinput>no</userinput>,
		  <command>named</command> does not return DNSSEC-related
		  resource records unless specifically queried for.
		  The default is <userinput>yes</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dnssec-validation</command></term>
	      <listitem>
		<para>
		  This option enables DNSSEC validation in <command>named</command>.
		  Note that <command>dnssec-enable</command> also needs to be
		  set to <userinput>yes</userinput> to be effective.
		  If set to <userinput>no</userinput>, DNSSEC validation
		  is disabled.
		</para>
	        <para>
		  If set to <userinput>auto</userinput>, DNSSEC validation
		  is enabled and a default trust anchor for the DNS root
		  zone is used.  If set to <userinput>yes</userinput>,
		  DNSSEC validation is enabled, but a trust anchor must be
		  manually configured using a <command>trusted-keys</command>
		  or <command>managed-keys</command> statement.  The default
		  is <userinput>yes</userinput>.
		</para>
		<para>
		  The default root trust anchor is stored in the file
		  <filename>bind.keys</filename>.
		  <command>named</command> loads that key at
		  startup if <command>dnssec-validation</command> is
		  set to <constant>auto</constant>.  A copy of the file is
		  installed along with BIND 9, and is current as of the
		  release date.  If the root key expires, a new copy of
		  <filename>bind.keys</filename> can be downloaded
		  from <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/bind-keys">https://www.isc.org/bind-keys</link>.
		</para>
		<para>
		  (To prevent problems if <filename>bind.keys</filename> is
		  not found, the current trust anchor is also compiled in
		  to <command>named</command>.  Relying on this is not
		  recommended, however, as it requires <command>named</command>
		  to be recompiled with a new key when the root key expires.)
		</para>
		<note>
		  <para>
		    <command>named</command> loads <emphasis>only</emphasis>
		    the root key from <filename>bind.keys</filename>.
		    The file cannot be used to store keys for other zones.
		    The root key in <filename>bind.keys</filename> is ignored
		    if <command>dnssec-validation auto</command> is not in
		    use.
		  </para>
		  <para>
		    Whenever the resolver sends out queries to an
		    EDNS-compliant server, it always sets the DO bit
		    indicating it can support DNSSEC responses, even if
		    <command>dnssec-validation</command> is off.
		  </para>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dnssec-accept-expired</command></term>
	      <listitem>
		<para>
		  This accepts expired signatures when verifying DNSSEC signatures.
		  The default is <userinput>no</userinput>.
		  Setting this option to <userinput>yes</userinput>
		  leaves <command>named</command> vulnerable to
		  replay attacks.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>querylog</command></term>
	      <listitem>
		<para>
		  Query logging provides a complete log of all incoming
		  queries and all query errors. This provides more insight
		  into the server's activity, but with a cost to
		  performance which may be significant on heavily loaded
		  servers.
		</para>
		<para>
		  The <command>querylog</command> option specifies
		  whether query logging should be active when
		  <command>named</command> first starts.
		  If <command>querylog</command> is not specified, then
		  query logging is determined by the presence of the
		  logging category <command>queries</command>.
		  Query logging can also be activated at runtime using the
		  command <command>rndc querylog on</command>, or
		  deactivated with <command>rndc querylog off</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-names</command></term>
	      <listitem>
		<para>
		  This option is used to restrict the character set and syntax
		  of
		  certain domain names in zone files and/or DNS responses
		  received
		  from the network.  The default varies according to usage
		  area.  For primary zones (i.e.,
		  <command>type master</command>),
		  the default is <command>fail</command>.
		  For secondary zones (<command>type slave</command>), the
		  default is <command>warn</command>.
		  For answers received from the network (<command>response</command>),
		  the default is <command>ignore</command>.
		</para>
		<para>
		  The rules for legal hostnames and mail domains are derived
		  from RFC 952 and RFC 821 as modified by RFC 1123.
		</para>
		<para><command>check-names</command>
		  applies to the owner names of A, AAAA, and MX records.
		  It also applies to the domain names in the RDATA of NS, SOA,
		  MX, and SRV records.
		  It further applies to the RDATA of PTR records where the owner
		  name indicates that it is a reverse lookup of a hostname
		  (the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-dup-records</command></term>
	      <listitem>
		<para>
		  This checks primary zones for records that are treated as different
		  by DNSSEC but are semantically equal in plain DNS.  The
		  default is to <command>warn</command>.  Other possible
		  values are <command>fail</command> and
		  <command>ignore</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-mx</command></term>
	      <listitem>
		<para>
		  This checks whether the MX record appears to refer to a IP address.
		  The default is to <command>warn</command>.  Other possible
		  values are <command>fail</command> and
		  <command>ignore</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-wildcard</command></term>
	      <listitem>
		<para>
		  This option is used to check for non-terminal wildcards.
		  The use of non-terminal wildcards is almost always as a
		  result of a failure
		  to understand the wildcard matching algorithm (RFC 1034).
		  This option
		  affects primary zones.  The default (<command>yes</command>) is to check
		  for non-terminal wildcards and issue a warning.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-integrity</command></term>
	      <listitem>
		<para>
		  This performs post-load zone integrity checks on primary
		  zones.  It checks that MX and SRV records refer
		  to address (A or AAAA) records and that glue
		  address records exist for delegated zones.  For
		  MX and SRV records, only in-zone hostnames are
		  checked (for out-of-zone hostnames, use
		  <command>named-checkzone</command>).
		  For NS records, only names below top-of-zone are
		  checked (for out-of-zone names and glue consistency
		  checks, use <command>named-checkzone</command>).
		  The default is <command>yes</command>.
		</para>
		<para>
		  The use of the SPF record to publish Sender
		  Policy Framework is deprecated, as the migration
		  from using TXT records to SPF records was abandoned.
		  Enabling this option also checks that a TXT Sender
		  Policy Framework record exists (starts with "v=spf1")
		  if there is an SPF record. Warnings are emitted if the
		  TXT record does not exist; they can be suppressed with
		  <command>check-spf</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-mx-cname</command></term>
	      <listitem>
		<para>
		  If <command>check-integrity</command> is set, then
		  fail, warn, or ignore MX records that refer
		  to CNAMES.  The default is to <command>warn</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-srv-cname</command></term>
	      <listitem>
		<para>
		  If <command>check-integrity</command> is set, then
		  fail, warn, or ignore SRV records that refer
		  to CNAMES.  The default is to <command>warn</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-sibling</command></term>
	      <listitem>
		<para>
		  When performing integrity checks, also check that
		  sibling glue exists.  The default is <command>yes</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>check-spf</command></term>
	      <listitem>
		<para>
		  If <command>check-integrity</command> is set,
		  check that there is a TXT Sender Policy Framework
		  record present (starts with "v=spf1") if there is an
		  SPF record present. The default is
		  <command>warn</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>zero-no-soa-ttl</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, when returning authoritative negative responses to
		  SOA queries, set the TTL of the SOA record returned in
		  the authority section to zero.
		  The default is <command>yes</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>zero-no-soa-ttl-cache</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, when caching a negative response to an SOA query
		  set the TTL to zero.
		  The default is <command>no</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>update-check-ksk</command></term>
	      <listitem>
		<para>
		  When set to the default value of <literal>yes</literal>,
		  check the KSK bit in each key to determine how the key
		  should be used when generating RRSIGs for a secure zone.
		</para>
		<para>
		  Ordinarily, zone-signing keys (that is, keys without the
		  KSK bit set) are used to sign the entire zone, while
		  key-signing keys (keys with the KSK bit set) are only
		  used to sign the DNSKEY RRset at the zone apex.
		  However, if this option is set to <literal>no</literal>,
		  then the KSK bit is ignored; KSKs are treated as if they
		  were ZSKs and are used to sign the entire zone.  This is
		  similar to the <command>dnssec-signzone -z</command>
		  command-line option.
		</para>
		<para>
		  When this option is set to <literal>yes</literal>, there
		  must be at least two active keys for every algorithm
		  represented in the DNSKEY RRset: at least one KSK and one
		  ZSK per algorithm.  If there is any algorithm for which
		  this requirement is not met, this option is ignored
		  for that algorithm.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dnssec-dnskey-kskonly</command></term>
	      <listitem>
		<para>
		  When this option and <command>update-check-ksk</command>
		  are both set to <literal>yes</literal>, only key-signing
		  keys (that is, keys with the KSK bit set) are used
		  to sign the DNSKEY RRset at the zone apex.  Zone-signing
		  keys (keys without the KSK bit set) are used to sign
		  the remainder of the zone, but not the DNSKEY RRset.
		  This is similar to the
		  <command>dnssec-signzone -x</command> command-line option.
		</para>
		<para>
		  The default is <command>no</command>.  If
		  <command>update-check-ksk</command> is set to
		  <literal>no</literal>, this option is ignored.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>try-tcp-refresh</command></term>
	      <listitem>
		<para>
		  If <userinput>yes</userinput>, try to refresh the zone using TCP if UDP queries fail.
		  The default is
		  <command>yes</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>dnssec-secure-to-insecure</command></term>
	      <listitem>
		<para>
		  This allows a dynamic zone to transition from secure to
		  insecure (i.e., signed to unsigned) by deleting all
		  of the DNSKEY records.  The default is <command>no</command>.
		  If set to <command>yes</command>, and if the DNSKEY RRset
		  at the zone apex is deleted, all RRSIG and NSEC records
		  are removed from the zone as well.
		</para>
		<para>
		  If the zone uses NSEC3, it is also necessary to
		  delete the NSEC3PARAM RRset from the zone apex; this
		  causes the removal of all corresponding NSEC3 records.
		  (It is expected that this requirement will be eliminated
		  in a future release.)
		</para>
		<para>
		  Note that if a zone has been configured with
		  <command>auto-dnssec maintain</command> and the
		  private keys remain accessible in the key repository,
		  then the zone will be automatically signed again the
		  next time <command>named</command> is started.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="forwarding"><info><title>Forwarding</title></info>

	  <para>
	    The forwarding facility can be used to create a large site-wide
	    cache on a few servers, reducing traffic over links to external
	    name servers. It can also be used to allow queries by servers that
	    do not have direct access to the Internet, but wish to look up
	    exterior
	    names anyway. Forwarding occurs only on those queries for which
	    the server is not authoritative and does not have the answer in
	    its cache.
	  </para>

	  <variablelist>
	    <varlistentry>
	      <term><command>forward</command></term>
	      <listitem>
		<para>
		  This option is only meaningful if the
		  forwarders list is not empty. A value of <varname>first</varname> is
		  the default and causes the server to query the forwarders
		  first;
		  if that does not answer the question, the server then
		  looks for
		  the answer itself. If <varname>only</varname> is
		  specified, the
		  server only queries the forwarders.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>forwarders</command></term>
	      <listitem>
		<para>
		  This specifies a list of IP addresses to which queries are
		  forwarded. The default is the empty list (no forwarding).
		  Each address in the list can be associated with an optional
		  port number and/or DSCP value, and a default port number and
		  DSCP value can be set for the entire list.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	  <para>
	    Forwarding can also be configured on a per-domain basis, allowing
	    for the global forwarding options to be overridden in a variety
	    of ways. Particular domains can be set to use different
	    forwarders,
	    or have a different <command>forward only/first</command> behavior,
	    or not forward at all; see <xref linkend="zone_statement_grammar"/>.
	  </para>
	</section>

	<section xml:id="dual_stack"><info><title>Dual-stack Servers</title></info>

	  <para>
	    Dual-stack servers are used as servers of last resort, to work
	    around
	    problems in reachability due the lack of support for either IPv4
	    or IPv6
	    on the host machine.
	  </para>

	  <variablelist>
	    <varlistentry>
	      <term><command>dual-stack-servers</command></term>
	      <listitem>
		<para>
		  This specifies host names or addresses of machines with access to
		  both IPv4 and IPv6 transports. If a hostname is used, the
		  server must be able
		  to resolve the name using only the transport it has.  If the
		  machine is dual-stacked, the <command>dual-stack-servers</command> parameter has no effect unless
		  access to a transport has been disabled on the command line
		  (e.g., <command>named -4</command>).
		</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</section>

	<section xml:id="access_control"><info><title>Access Control</title></info>


	  <para>
	    Access to the server can be restricted based on the IP address
	    of the requesting system. See <xref linkend="address_match_lists"/> for
	    details on how to specify IP address lists.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>allow-notify</command></term>
	      <listitem>
		<para>
		  This ACL specifies which hosts are allowed to
		  notify this secondary server of zone changes in addition
		  to the zone primaries.
		  <command>allow-notify</command> may also be
		  specified in the
		  <command>zone</command> statement, in which case
		  it overrides the
		  <command>options allow-notify</command>
		  statement.  It is only meaningful
		  for a secondary zone.  If not specified, the default is to
		  process notify messages
		  only from a zone's primary.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-query</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to ask ordinary
		  DNS questions. <command>allow-query</command> may
		  also be specified in the <command>zone</command>
		  statement, in which case it overrides the
		  <command>options allow-query</command> statement.
		  If not specified, the default is to allow queries
		  from all hosts.
		</para>
		<note>
		  <para>
		    <command>allow-query-cache</command> is
		    used to specify access to the cache.
		  </para>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-query-on</command></term>
	      <listitem>
		<para>
		  This specifies which local addresses can accept ordinary
		  DNS questions. This makes it possible, for instance,
		  to allow queries on internal-facing interfaces but
		  disallow them on external-facing ones, without
		  necessarily knowing the internal network's addresses.
		</para>
		<para>
		  Note that <command>allow-query-on</command> is only
		  checked for queries that are permitted by
		  <command>allow-query</command>.  A query must be
		  allowed by both ACLs, or it is refused.
		</para>
		<para>
		  <command>allow-query-on</command> may
		  also be specified in the <command>zone</command>
		  statement, in which case it overrides the
		  <command>options allow-query-on</command> statement.
		</para>
		<para>
		  If not specified, the default is to allow queries
		  on all addresses.
		</para>
		<note>
		  <para>
		    <command>allow-query-cache</command> is
		    used to specify access to the cache.
		  </para>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-query-cache</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to get answers
		  from the cache.  If <command>allow-query-cache</command>
		  is not set, BIND checks to see if the following parameters
		  are set, in order: <command>allow-recursion</command> and
		  <command>allow-query</command>
		  (unless <command>recursion no;</command> is
		  set, in which case <command>none;</command> is used).
		  If neither of those parameters is set, the default (<command>localnets;</command>
		  <command>localhost;</command>) is used.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-query-cache-on</command></term>
	      <listitem>
		<para>
		  This specifies which local addresses can send answers
		  from the cache.  If not specified, the default is
		  to allow cache queries on any address,
		  <command>localnets</command>, and
		  <command>localhost</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-recursion</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to make recursive
		  queries through this server. BIND checks to see if the
		  following parameters are set, in order:
		  <command>allow-recursion</command>, <command>allow-query-cache</command>,
		  and <command>allow-query</command>.
		  If none of those parameters are set, the default
		  (<command>localnets;</command>
		  <command>localhost;</command>) is used.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-recursion-on</command></term>
	      <listitem>
		<para>
		  This specifies which local addresses can accept recursive
		  queries.  If not specified, the default is to allow
		  recursive queries on all addresses.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-update</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to
		  submit Dynamic DNS updates for primary zones. The default is
		  to deny
		  updates from all hosts.  Note that allowing updates based
		  on the requestor's IP address is insecure; see
		  <xref linkend="dynamic_update_security"/> for details.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-update-forwarding</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to
		  submit Dynamic DNS updates to secondary zones to be forwarded to
		  the
		  primary.  The default is <userinput>{ none; }</userinput>,
		  which
		  means that no update forwarding is performed.  To
		  enable
		  update forwarding, specify
		  <userinput>allow-update-forwarding { any; };</userinput>.
		  Specifying values other than <userinput>{ none; }</userinput> or
		  <userinput>{ any; }</userinput> is usually
		  counterproductive;
		  the responsibility for update access control should rest
		  with the
		  primary server, not the secondaries.
		</para>
		<para>
		  Note that enabling the update forwarding feature on a secondary
		  server
		  may expose primary servers to attacks if they rely on insecure
		  IP-address-based
		  access control; see <xref linkend="dynamic_update_security"/>
		  for more details.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-v6-synthesis</command></term>
	      <listitem>
		<para>
		  This option was introduced for the smooth transition from
		  AAAA
		  to A6 and from "nibble labels" to binary labels.
		  However, since both A6 and binary labels were then
		  deprecated,
		  this option was also deprecated.
		  It is now ignored with some warning messages.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>allow-transfer</command></term>
	      <listitem>
		<para>
		  This specifies which hosts are allowed to
		  receive zone transfers from the server. <command>allow-transfer</command> may
		  also be specified in the <command>zone</command>
		  statement, in which
		  case it overrides the <command>options allow-transfer</command> statement.
		  If not specified, the default is to allow transfers to all
		  hosts.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>blackhole</command></term>
	      <listitem>
		<para>
		  This specifies a list of addresses which the
		  server does accept queries from or use to resolve a
		  query. Queries
		  from these addresses are not responded to. The default
		  is <userinput>none</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>filter-aaaa</command></term>
	      <listitem>
		<para>
		  This specifies a list of addresses to which
		  <command>filter-aaaa-on-v4</command>
		  and <command>filter-aaaa-on-v6</command>
		  apply.  The default is <userinput>any</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>keep-response-order</command></term>
	      <listitem>
		<para>
		  This specifies a list of addresses to which the server
		  sends responses to TCP queries, in the same order
		  in which they were received.  This disables the
		  processing of TCP queries in parallel. The default
		  is <userinput>none</userinput>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>no-case-compress</command></term> <listitem>
		<para>
		  This specifies a list of addresses which require responses
		  to use case-insensitive compression.  This ACL can be
		  used when <command>named</command> needs to work with
		  clients that do not comply with the requirement in RFC
		  1034 to use case-insensitive name comparisons when
		  checking for matching domain names.
		</para>
		<para>
		  If left undefined, the ACL defaults to
		  <command>none</command>: case-insensitive compression
		  is used for all clients.  If the ACL is defined and
		  matches a client, case is ignored when
		  compressing domain names in DNS responses sent to that
		  client.
		</para>
		<para>
		  This can result in slightly smaller responses; if
		  a response contains the names "example.com" and
		  "example.COM", case-insensitive compression treats
		  the second one as a duplicate.  It also ensures
		  that the case of the query name exactly matches the
		  case of the owner names of returned records, rather
		  than matches the case of the records entered in
		  the zone file.  This allows responses to exactly
		  match the query, which is required by some clients
		  due to incorrect use of case-sensitive comparisons.
		</para>
		<para>
		  Case-insensitive compression is <emphasis>always</emphasis>
		  used in AXFR and IXFR responses, regardless of whether
		  the client matches this ACL.
		</para>
		<para>
		  There are circumstances in which <command>named</command>
		  does not preserve the case of owner names of records:
		  if a zone file defines records of different types with
		  the same name, but the capitalization of the name is
		  different (e.g., "www.example.com/A" and
		  "WWW.EXAMPLE.COM/AAAA"), then all responses for that
		  name use the <emphasis>first</emphasis> version
		  of the name that was used in the zone file.  This
		  limitation may be addressed in a future release.  However,
		  domain names specified in the rdata of resource records
		  (i.e., records of type NS, MX, CNAME, etc.) always
		  have their case preserved unless the client matches this
		  ACL.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>resolver-query-timeout</command></term>
	      <listitem>
		<para>
		  This is the amount of time in seconds that the
		  resolver spends attempting to resolve a recursive
		  query before failing.  The default and minimum
		  is <literal>10</literal> and the maximum is
		  <literal>30</literal>.  Setting it to
		  <literal>0</literal> results in the default
		  being used.
		</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>

	</section>

	<section xml:id="interfaces"><info><title>Interfaces</title></info>

	  <para>
	    The interfaces and ports that the server answers queries
	    from may be specified using the <command>listen-on</command> option. <command>listen-on</command> takes
	    an optional port and an <varname>address_match_list</varname>
	    of IPv4 addresses.  (IPv6 addresses are ignored, with a
	    logged warning.)
	    The server listens on all interfaces allowed by the address
	    match list. If a port is not specified, port 53 is used.
	  </para>
	  <para>
	    Multiple <command>listen-on</command> statements are
	    allowed.
	    For example:
	  </para>

<programlisting>listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</programlisting>

	  <para>
	    enables the name server on port 53 for the IP address
	    5.6.7.8, and on port 1234 of an address on the machine in net
	    1.2 that is not 1.2.3.4.
	  </para>

	  <para>
	    If no <command>listen-on</command> is specified, the
	    server listens on port 53 on all IPv4 interfaces.
	  </para>

	  <para>
	    The <command>listen-on-v6</command> option is used to
	    specify the interfaces and the ports on which the server
	    listens for incoming queries sent using IPv6.  If not specified,
	    the server listens on port 53 on all IPv6 interfaces.
	  </para>

	  <para>
	    When <programlisting>{ any; }</programlisting> is
	    specified
	    as the <varname>address_match_list</varname> for the
	    <command>listen-on-v6</command> option,
	    the server does not bind a separate socket to each IPv6 interface
	    address as it does for IPv4, if the operating system has enough API
	    support for IPv6 (specifically, if it conforms to RFC 3493 and RFC
	    3542).
	    Instead, it listens on the IPv6 wildcard address.
	    If the system only has incomplete API support for IPv6, however,
	    the behavior is the same as that for IPv4.
	  </para>

	  <para>
	    A list of particular IPv6 addresses can also be specified, in
	    which case
	    the server listens on a separate socket for each specified
	    address,
	    regardless of whether the desired API is supported by the system.
	    IPv4 addresses specified in <command>listen-on-v6</command>
	    are ignored, with a logged warning.
	  </para>

	  <para>
	    Multiple <command>listen-on-v6</command> options can
	    be used.
	    For example:
	  </para>

<programlisting>listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</programlisting>

	  <para>
	    enables the name server on port 53 for any IPv6 addresses
	    (with a single wildcard socket),
	    and on port 1234 of IPv6 addresses that are not in the prefix
	    2001:db8::/32 (with separate sockets for each matched address).
	  </para>

	  <para>
	    To instruct the server not to listen on any IPv6 address, use:
	  </para>

<programlisting>listen-on-v6 { none; };
</programlisting>

	</section>

	<section xml:id="query_address"><info><title>Query Address</title></info>

	  <para>
	    If the server does not know the answer to a question, it
	    queries other name servers. <command>query-source</command> specifies
	    the address and port used for such queries. For queries sent over
	    IPv6, there is a separate <command>query-source-v6</command> option.
	    If <command>address</command> is <command>*</command> (asterisk) or is omitted,
	    a wildcard IP address (<command>INADDR_ANY</command>)
	    is used.
	  </para>

	  <para>
	    If <command>port</command> is <command>*</command> or is omitted,
	    a random port number from a pre-configured
	    range is picked up and used for each query.
	    The port range(s) is specified in
	    the <command>use-v4-udp-ports</command> (for IPv4)
	    and <command>use-v6-udp-ports</command> (for IPv6)
	    options, excluding the ranges specified in
	    the <command>avoid-v4-udp-ports</command>
	    and <command>avoid-v6-udp-ports</command> options, respectively.
	  </para>

	  <para>
	    The defaults of the <command>query-source</command> and
	    <command>query-source-v6</command> options
	    are:
	  </para>

<programlisting>query-source address * port *;
query-source-v6 address * port *;
</programlisting>

	  <para>
	    If <command>use-v4-udp-ports</command> or
	    <command>use-v6-udp-ports</command> is unspecified,
	    <command>named</command> checks whether the operating
	    system provides a programming interface to retrieve the
	    system's default range for ephemeral ports.
	    If such an interface is available,
	    <command>named</command> uses the corresponding system
	    default range; otherwise, it uses its own defaults:
	 </para>

<programlisting>use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</programlisting>

	  <para>
	    Note: make sure the ranges are sufficiently large for
	    security.  A desirable size depends on several parameters,
	    but we generally recommend it contain at least 16384 ports
	    (14 bits of entropy).
	    Note also that the system's default range when used may be
	    too small for this purpose, and that the range may even be
	    changed while <command>named</command> is running; the new
	    range is automatically applied when <command>named</command>
	    is reloaded.
	    Explicit
	    configuration of <command>use-v4-udp-ports</command> and
	    <command>use-v6-udp-ports</command> is encouraged, so that the
	    ranges are sufficiently large and are reasonably
	    independent from the ranges used by other applications.
	  </para>

	  <para>
	    Note: the operational configuration
	    where <command>named</command> runs may prohibit the use
	    of some ports.  For example, Unix systems do not allow
	    <command>named</command>, if run without root privilege,
	    to use ports less than 1024.
	    If such ports are included in the specified (or detected)
	    set of query ports, the corresponding query attempts will
	    fail, resulting in resolution failures or delay.
	    It is therefore important to configure the set of ports
	    that can be safely used in the expected operational environment.
	  </para>

	  <para>
	    The defaults of the <command>avoid-v4-udp-ports</command> and
	    <command>avoid-v6-udp-ports</command> options
	    are:
	  </para>

<programlisting>avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</programlisting>

	  <para>
	    Note: BIND 9.5.0 introduced
	    the <command>use-queryport-pool</command>
	    option to support a pool of such random ports, but this
	    option is now obsolete because reusing the same ports in
	    the pool may not be sufficiently secure.
	    For the same reason, it is generally strongly discouraged to
	    specify a particular port for the
	    <command>query-source</command> or
	    <command>query-source-v6</command> options;
	    it implicitly disables the use of randomized port numbers.
	  </para>

	  <variablelist>
	    <varlistentry>
	      <term><command>use-queryport-pool</command></term>
	      <listitem>
		<para>
		  This option is obsolete.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>queryport-pool-ports</command></term>
	      <listitem>
		<para>
		  This option is obsolete.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>queryport-pool-updateinterval</command></term>
	      <listitem>
		<para>
		  This option is obsolete.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>
	  <note>
	    <para>
	      The address specified in the <command>query-source</command> option
	      is used for both UDP and TCP queries, but the port applies only
	      to UDP queries.  TCP queries always use a random
	      unprivileged port.
	    </para>
	  </note>
	  <note>
	    <para>
	      Solaris 2.5.1 and earlier does not support setting the source
	      address for TCP sockets.
	    </para>
	  </note>
	  <note>
	    <para>
	      See also <command>transfer-source</command> and
	      <command>notify-source</command>.
	    </para>
	  </note>
	</section>

	<section xml:id="zone_transfers"><info><title>Zone Transfers</title></info>

	  <para>
	    <acronym>BIND</acronym> has mechanisms in place to
	    facilitate zone transfers
	    and set limits on the amount of load that transfers place on the
	    system. The following options apply to zone transfers.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>also-notify</command></term>
	      <listitem>
		<para>
		  This option defines a global list of IP addresses of name servers
		  that are also sent NOTIFY messages whenever a fresh copy of
		  the
		  zone is loaded, in addition to the servers listed in the
		  zone's NS records.
		  This helps to ensure that copies of the zones
		  quickly converge on stealth servers.
		  Optionally, a port may be specified with each
		  <command>also-notify</command> address to send
		  the notify messages to a port other than the
		  default of 53.
		  An optional TSIG key can also be specified with each
		  address to cause the notify messages to be signed; this
		  can be useful when sending notifies to multiple views.
		  In place of explicit addresses, one or more named
		  <command>masters</command> lists can be used.
		</para>
		<para>
		  If an <command>also-notify</command> list
		  is given in a <command>zone</command> statement,
		  it overrides
		  the <command>options also-notify</command>
		  statement. When a <command>zone notify</command>
		  statement
		  is set to <command>no</command>, the IP
		  addresses in the global <command>also-notify</command> list are
		  not sent NOTIFY messages for that zone. The default is
		  the empty
		  list (no global notification list).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-transfer-time-in</command></term>
	      <listitem>
		<para>
		  Inbound zone transfers running longer than
		  this many minutes are terminated. The default is 120
		  minutes
		  (2 hours).  The maximum value is 28 days (40320 minutes).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-transfer-idle-in</command></term>
	      <listitem>
		<para>
		  Inbound zone transfers making no progress
		  in this many minutes are terminated. The default is 60
		  minutes
		  (1 hour).  The maximum value is 28 days (40320 minutes).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-transfer-time-out</command></term>
	      <listitem>
		<para>
		  Outbound zone transfers running longer than
		  this many minutes are terminated. The default is 120
		  minutes
		  (2 hours).  The maximum value is 28 days (40320 minutes).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-transfer-idle-out</command></term>
	      <listitem>
		<para>
		  Outbound zone transfers making no progress
		  in this many minutes are terminated.  The default is 60
		  minutes (1
		  hour).  The maximum value is 28 days (40320 minutes).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify-rate</command></term>
	      <listitem>
		<para>
		  This specifies the rate at which NOTIFY requests are sent
		  during normal zone maintenance operations. (NOTIFY
		  requests due to initial zone loading are subject
		  to a separate rate limit; see below.) The default is
		  20 per second.
		  The lowest possible rate is one per second; when set
		  to zero, it is silently raised to one.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>startup-notify-rate</command></term>
	      <listitem>
		<para>
		  This is the rate at which NOTIFY requests are sent
		  when the name server is first starting up, or when
		  zones have been newly added to the name server.
		  The default is 20 per second.
		  The lowest possible rate is one per second; when set
		  to zero, it is silently raised to one.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>serial-query-rate</command></term>
	      <listitem>
		<para>
		  Secondary servers periodically query primary
		  servers to find out if zone serial numbers have
		  changed. Each such query uses a minute amount of
		  the secondary server's network bandwidth.  To limit
		  the amount of bandwidth used, BIND 9 limits the
		  rate at which queries are sent.  The value of the
		  <command>serial-query-rate</command> option, an
		  integer, is the maximum number of queries sent
		  per second.  The default is 20 per second.
		  The lowest possible rate is one per second; when set
		  to zero, it is silently raised to one.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>serial-queries</command></term>
	      <listitem>
		<para>
		  BIND 9 does not limit the number of outstanding
		  serial queries and ignores the <command>serial-queries</command> option.
		  Instead, it limits the rate at which the queries are sent
		  as defined using the <command>serial-query-rate</command> option.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfer-format</command></term>
	      <listitem>

		<para>
		  Zone transfers can be sent using two different formats,
		  <command>one-answer</command> and
		  <command>many-answers</command>.
		  The <command>transfer-format</command> option is used
		  on the primary server to determine which format it sends.
		  <command>one-answer</command> uses one DNS message per
		  resource record transferred.
		  <command>many-answers</command> packs as many resource
		  records as possible into one message.
		  <command>many-answers</command> is more efficient; the default is <command>many-answers</command>.
		  The <command>many-answers</command> format is also supported by
		  recent Microsoft Windows name servers.
		  <command>transfer-format</command> may be overridden on a
		  per-server basis by using the <command>server</command>
		  statement.
		</para>

	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfer-message-size</command></term>
	      <listitem>
		<para>
		  This is an upper bound on the uncompressed size of DNS
		  messages used in zone transfers over TCP.  If a message
		  grows larger than this size, additional messages are
		  used to complete the zone transfer.  (Note, however,
		  that this is a hint, not a hard limit; if a message
		  contains a single resource record whose RDATA does not
		  fit within the size limit, a larger message will be
		  permitted so the record can be transferred.)
		</para>
		<para>
		  Valid values are between 512 and 65535 octets; any
		  values outside that range are adjusted to the nearest
		  value within it.  The default is <literal>20480</literal>,
		  which was selected to improve message compression;
		  most DNS messages of this size will compress to less
		  than 16536 bytes.  Larger messages cannot be compressed
		  as effectively, because 16536 is the largest permissible
		  compression offset pointer in a DNS message.
		</para>
		<para>
		  This option is mainly intended for server testing;
		  there is rarely any benefit in setting a value other
		  than the default.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfers-in</command></term>
	      <listitem>
		<para>
		  This is the maximum number of inbound zone transfers
		  that can run concurrently. The default value is <literal>10</literal>.
		  Increasing <command>transfers-in</command> may
		  speed up the convergence
		  of secondary zones, but it also may increase the load on the
		  local system.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfers-out</command></term>
	      <listitem>
		<para>
		  This is the maximum number of outbound zone transfers
		  that can run concurrently. Zone transfer requests in
		  excess
		  of the limit are refused. The default value is <literal>10</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfers-per-ns</command></term>
	      <listitem>
		<para>
		  This is the maximum number of inbound zone transfers
		  that can concurrently transfer from a given remote
		  name server.
		  The default value is <literal>2</literal>.
		  Increasing <command>transfers-per-ns</command>
		  may
		  speed up the convergence of secondary zones, but it also may
		  increase
		  the load on the remote name server. <command>transfers-per-ns</command> may
		  be overridden on a per-server basis by using the <command>transfers</command> phrase
		  of the <command>server</command> statement.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfer-source</command></term>
	      <listitem>
		<para><command>transfer-source</command>
		  determines which local address is bound to IPv4
		  TCP connections used to fetch zones transferred
		  inbound by the server.  It also determines the
		  source IPv4 address, and optionally the UDP port,
		  used for the refresh queries and forwarded dynamic
		  updates.  If not set, it defaults to a
		  system-controlled value which is usually the address
		  of the interface "closest to" the remote end. This
		  address must appear in the remote end's
		  <command>allow-transfer</command> option for the
		  zone being transferred, if one is specified. This
		  statement sets the
		  <command>transfer-source</command> for all zones,
		  but can be overridden on a per-view or per-zone
		  basis by including a
		  <command>transfer-source</command> statement within
		  the <command>view</command> or
		  <command>zone</command> block in the configuration
		  file.
		</para>
		<note>
		  <para>
		    Solaris 2.5.1 and earlier does not support setting the
		    source address for TCP sockets.
		  </para>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>transfer-source-v6</command></term>
	      <listitem>
		<para>
		  This option is the same as <command>transfer-source</command>,
		  except zone transfers are performed using IPv6.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>alt-transfer-source</command></term>
	      <listitem>
		<para>
		  This indicates an alternate transfer source if the one listed in
		  <command>transfer-source</command> fails and
		  <command>use-alt-transfer-source</command> is
		  set.
		</para>
		<note><simpara>
		  To avoid using the alternate transfer source,
		  set <command>use-alt-transfer-source</command>
		  appropriately and do not depend upon
		  getting an answer back to the first refresh
		  query.
		</simpara></note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>alt-transfer-source-v6</command></term>
	      <listitem>
		<para>
		  This indicates an alternate transfer source if the one listed in
		  <command>transfer-source-v6</command> fails and
		  <command>use-alt-transfer-source</command> is
		  set.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>use-alt-transfer-source</command></term>
	      <listitem>
		<para>
		  This indicates whether the alternate transfer sources should be used.  If views are
		  specified, this defaults to <command>no</command>;
		  otherwise, it defaults to
		  <command>yes</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify-source</command></term>
	      <listitem>
		<para><command>notify-source</command>
		  determines which local source address, and
		  optionally UDP port, is used to send NOTIFY
		  messages.  This address must appear in the secondary
		  server's <command>masters</command> zone clause or
		  in an <command>allow-notify</command> clause.  This
		  statement sets the <command>notify-source</command>
		  for all zones, but can be overridden on a per-zone or
		  per-view basis by including a
		  <command>notify-source</command> statement within
		  the <command>zone</command> or
		  <command>view</command> block in the configuration
		  file.
		</para>
		<note>
		  <para>
		    Solaris 2.5.1 and earlier does not support setting the
		    source address for TCP sockets.
		  </para>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify-source-v6</command></term>
	      <listitem>
		<para>
		  This option acts like <command>notify-source</command>,
		  but applies to notify messages sent to IPv6 addresses.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="port_lists"><info><title>UDP Port Lists</title></info>

	  <para>
	    <command>use-v4-udp-ports</command>,
	    <command>avoid-v4-udp-ports</command>,
	    <command>use-v6-udp-ports</command>, and
	    <command>avoid-v6-udp-ports</command>
	    specify a list of IPv4 and IPv6 UDP ports that are
	    or are not used as source ports for UDP messages.
	    See <xref linkend="query_address"/> about how the
	    available ports are determined.
	    For example, with the following configuration:
	  </para>

<programlisting>
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</programlisting>

	   <para>
	     UDP ports of IPv6 messages sent
	     from <command>named</command> are in one
	     of the following ranges: 32768 to 39999, 40001 to 49999,
	     and 60001 to 65535.
	   </para>

	   <para>
	     <command>avoid-v4-udp-ports</command> and
	     <command>avoid-v6-udp-ports</command> can be used
	     to prevent <command>named</command> from choosing as its random source port a
	     port that is blocked by a firewall or a port that is
	     used by other applications;
	     if a query went out with a source port blocked by a
	     firewall, the
	     answer would not pass through the firewall and the name server would
	     have to query again.
	     Note: the desired range can also be represented only with
	     <command>use-v4-udp-ports</command> and
	     <command>use-v6-udp-ports</command>, and the
	     <command>avoid-</command> options are redundant in that
	     sense; they are provided for backward compatibility and
	     to possibly simplify the port specification.
	   </para>
	</section>

	<section xml:id="resource_limits"><info><title>Operating System Resource Limits</title></info>

	  <para>
	    The server's usage of many system resources can be limited.
	    Scaled values are allowed when specifying resource limits.  For
	    example, <command>1G</command> can be used instead of
	    <command>1073741824</command> to specify a limit of
	    one
	    gigabyte. <command>unlimited</command> requests
	    unlimited use, or the
	    maximum available amount. <command>default</command>
	    uses the limit
	    that was in force when the server was started. See the description
	    of <command>size_spec</command> in <xref linkend="configuration_file_elements"/>.
	  </para>

	  <para>
	    The following options set operating system resource limits for
	    the name server process.  Some operating systems do not support
	    some or
	    any of the limits; on such systems, a warning is issued if
	    an
	    unsupported limit is used.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>coresize</command></term>
	      <listitem>
		<para>
		  This sets the maximum size of a core dump. The default
		  is <literal>default</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>datasize</command></term>
	      <listitem>
		<para>
		  This sets the maximum amount of data memory the server
		  may use. The default is <literal>default</literal>.
		  This is a hard limit on server memory usage;
		  if the server attempts to allocate memory in excess of this
		  limit, the allocation will fail, which may in turn leave
		  the server unable to perform DNS service.  Therefore,
		  this option is rarely useful as a way to limit the
		  amount of memory used by the server, but it can be used
		  to raise an operating system data size limit that is
		  too small by default.  To limit the amount
		  of memory used by the server, use the
		  <command>max-cache-size</command> and
		  <command>recursive-clients</command>
		  options instead.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>files</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of files the server
		  may have open concurrently. The default is <literal>unlimited</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>stacksize</command></term>
	      <listitem>
		<para>
		  This sets the maximum amount of stack memory the server
		  may use. The default is <literal>default</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="server_resource_limits"><info><title>Server Resource Limits</title></info>

	  <para>
	    The following options set limits on the server's
	    resource consumption that are enforced internally by the
	    server rather than by the operating system.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>max-ixfr-log-size</command></term>
	      <listitem>
		<para>
		  This option is obsolete; it is accepted
		  and ignored for BIND 8 compatibility.  The option
		  <command>max-journal-size</command> performs a
		  similar function in BIND 9.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-journal-size</command></term>
	      <listitem>
		<para>
		  This sets a maximum size for each journal file
		  (see <xref linkend="journal"/>).  When the journal file
		  approaches
		  the specified size, some of the oldest transactions in the
		  journal
		  are automatically removed.  The largest permitted
		  value is 2 gigabytes. The default is
		  <literal>unlimited</literal>, which also
		  means 2 gigabytes.
		  This option may also be set on a per-zone basis.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-records</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of records permitted in a zone.
		  The default is zero, which means the maximum is unlimited.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>host-statistics-max</command></term>
	      <listitem>
		<para>
		  In BIND 8, this specified the maximum number of host statistics
		  entries to be kept.
		  It is not implemented in BIND 9.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>recursive-clients</command></term>
	      <listitem>
		<para>
		  This sets the maximum number (a "hard quota") of simultaneous
		  recursive lookups the server performs on behalf
		  of clients.  The default is
		  <literal>1000</literal>.  Because each recursing
		  client uses a fair
		  bit of memory (on the order of 20 kilobytes), the
		  value of the
		  <command>recursive-clients</command> option may
		  have to be decreased on hosts with limited memory.
		</para>
		<para>
		  <option>recursive-clients</option> defines a "hard
		  quota" limit for pending recursive clients; when more
		  clients than this are pending, new incoming requests
		  are not accepted, and for each incoming request
		  a previous pending request is dropped.
		</para>
		<para>
		  A "soft quota" is also set.  When this lower
		  quota is exceeded, incoming requests are accepted, but
		  for each one, a pending request is dropped.
		  If <option>recursive-clients</option> is greater than
		  1000, the soft quota is set to
		  <option>recursive-clients</option> minus 100;
		  otherwise it is set to 90% of
		  <option>recursive-clients</option>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>tcp-clients</command></term>
	      <listitem>
		<para>
		  This is the maximum number of simultaneous client TCP
		  connections that the server accepts.
		  The default is <literal>150</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry xml:id="clients-per-query">
	      <term xml:id="cpq_term"><command>clients-per-query</command></term>;
	      <term><command>max-clients-per-query</command></term>
	      <listitem>
		<para>These set the
		  initial value (minimum) and maximum number of recursive
		  simultaneous clients for any given query
		  (&lt;qname,qtype,qclass&gt;) that the server accepts
		  before dropping additional clients.  <command>named</command> attempts to
		  self-tune this value and changes are logged.  The
		  default values are 10 and 100.
		</para>
		<para>
		  This value should reflect how many queries come in for
		  a given name in the time it takes to resolve that name.
		  If the number of queries exceeds this value, <command>named</command>
		  assumes that it is dealing with a non-responsive zone
		  and drops additional queries.  If it gets a response
		  after dropping queries, it raises the estimate.  The
		  estimate is then lowered in 20 minutes if it has
		  remained unchanged.
		</para>
		<para>
		  If <command>clients-per-query</command> is set to zero,
		  there is no limit on the number of clients per query
		  and no queries are dropped.
		</para>
		<para>
		  If <command>max-clients-per-query</command> is set to zero,
		  there is no upper bound other than imposed by
		  <command>recursive-clients</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry xml:id="fetches-per-zone">
	      <term><command>fetches-per-zone</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of simultaneous iterative
		  queries to any one domain that the server
		  permits before blocking new queries for data
		  in or beneath that zone.
		  This value should reflect how many fetches would
		  normally be sent to any one zone in the time it
		  would take to resolve them.  It should be smaller
		  than <option>recursive-clients</option>.
		</para>
		<para>
		  When many clients simultaneously query for the
		  same name and type, the clients are all attached
		  to the same fetch, up to the
		  <option>max-clients-per-query</option> limit,
		  and only one iterative query is sent.
		  However, when clients are simultaneously
		  querying for <emphasis>different</emphasis> names
		  or types, multiple queries are sent and
		  <option>max-clients-per-query</option> is not
		  effective as a limit.
		</para>
		<para>
		  Optionally, this value may be followed by the keyword
		  <literal>drop</literal> or <literal>fail</literal>,
		  indicating whether queries which exceed the fetch
		  quota for a zone are dropped with no response,
		  or answered with SERVFAIL.  The default is
		  <literal>drop</literal>.
		</para>
		<para>
		  If <command>fetches-per-zone</command> is set to zero,
		  there is no limit on the number of fetches per query
		  and no queries are dropped.  The default is zero.
		</para>
		<para>
		  The current list of active fetches can be dumped by
		  running <command>rndc recursing</command>.  The list
		  includes the number of active fetches for each
		  domain and the number of queries that have been
		  passed or dropped as a result of the
		  <option>fetches-per-zone</option> limit.  (Note:
		  these counters are not cumulative over time; whenever
		  the number of active fetches for a domain drops to
		  zero, the counter for that domain is deleted, and the
		  next time a fetch is sent to that domain, it is
		  recreated with the counters set to zero.)
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry xml:id="fetches-per-server">
	      <term><command>fetches-per-server</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of simultaneous iterative
		  queries that the server allows to be sent to
		  a single upstream name server before blocking
		  additional queries.
		  This value should reflect how many fetches would
		  normally be sent to any one server in the time it
		  would take to resolve them.  It should be smaller
		  than <option>recursive-clients</option>.
		</para>
		<para>
		  Optionally, this value may be followed by the keyword
		  <literal>drop</literal> or <literal>fail</literal>,
		  indicating whether queries are dropped with no
		  response or answered with SERVFAIL, when all of the
		  servers authoritative for a zone are found to have
		  exceeded the per-server quota.  The default is
		  <literal>fail</literal>.
		</para>
		<para>
		  If <command>fetches-per-server</command> is set to zero,
		  there is no limit on the number of fetches per query
		  and no queries are dropped.  The default is zero.
		</para>
		<para>
		  The <command>fetches-per-server</command> quota is
		  dynamically adjusted in response to detected
		  congestion. As queries are sent to a server
		  and are either answered or time out, an
		  exponentially weighted moving average is calculated
		  of the ratio of timeouts to responses.  If the
		  current average timeout ratio rises above a "high"
		  threshold, then <command>fetches-per-server</command>
		  is reduced for that server.  If the timeout ratio
		  drops below a "low" threshold, then
		  <command>fetches-per-server</command> is increased.
		  The <command>fetch-quota-params</command> options
		  can be used to adjust the parameters for this
		  calculation.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>fetch-quota-params</command></term>
	      <listitem>
		<para>
		  This sets the parameters to use for dynamic resizing of
		  the <option>fetches-per-server</option> quota in
		  response to detected congestion.
		</para>
		<para>
		  The first argument is an integer value indicating
		  how frequently to recalculate the moving average
		  of the ratio of timeouts to responses for each
		  server.  The default is 100, meaning that BIND recalculates
		  the average ratio after every 100 queries have either
		  been answered or timed out.
		</para>
		<para>
		  The remaining three arguments represent the "low"
		  threshold (defaulting to a timeout ratio of 0.1),
		  the "high" threshold (defaulting to a timeout
		  ratio of 0.3), and the discount rate for
		  the moving average (defaulting to 0.7).
		  A higher discount rate causes recent events to
		  weigh more heavily when calculating the moving
		  average; a lower discount rate causes past
		  events to weigh more heavily, smoothing out
		  short-term blips in the timeout ratio.
		  These arguments are all fixed-point numbers with
		  precision of 1/100; at most two places after
		  the decimal point are significant.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>reserved-sockets</command></term>
	      <listitem>
		<para>
		  This sets the number of file descriptors reserved for TCP, stdio,
		  etc.  This needs to be big enough to cover the number of
		  interfaces <command>named</command> listens on plus
		  <command>tcp-clients</command>, as well as
		  to provide room for outgoing TCP queries and incoming zone
		  transfers.  The default is <literal>512</literal>.
		  The minimum value is <literal>128</literal> and the
		  maximum value is <literal>128</literal> fewer than
		  maxsockets (-S).  This option may be removed in the future.
		</para>
		<para>
		  This option has little effect on Windows.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-cache-size</command></term>
	      <listitem>
		<para>
		  This sets the maximum amount of memory to use for the
		  server's cache, in bytes or percentage of total physical memory.
		  When the amount of data in the cache
		  reaches this limit, the server causes records to
		  expire prematurely, following an LRU-based strategy, so
		  that the limit is not exceeded.
		  The keyword <userinput>unlimited</userinput>,
		  or the value 0, places no limit on the cache size;
		  records are purged from the cache only when their
		  TTLs expire.
		  Any positive values less than 2MB are ignored
		  and reset to 2MB.
		  In a server with multiple views, the limit applies
		  separately to the cache of each view.
		  The default is <userinput>90%</userinput>.
		  On systems where detection of the amount of physical
		  memory is not supported, values represented as a percentage
		  fall back to unlimited.
		  Note that the detection of physical memory is done only
		  once at startup, so <command>named</command> does not
		  adjust the cache size if the amount of physical memory
		  is changed during runtime.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>tcp-listen-queue</command></term>
	      <listitem>
		<para>
		  This sets the listen-queue depth.  The default and minimum is 10.
		  If the kernel supports the accept filter "dataready", this
		  also controls how
		  many TCP connections are queued in kernel space
		  waiting for
		  some data before being passed to accept.  Non-zero values
		  less than 10 are silently raised. A value of 0 may also
		  be used; on most platforms this sets the listen-queue
		  length to a system-defined default value.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="intervals"><info><title>Periodic Task Intervals</title></info>

	  <variablelist>

	    <varlistentry>
	      <term><command>cleaning-interval</command></term>
	      <listitem>
		<para>
		  This interval is effectively obsolete.  Previously,
		  the server removed expired resource records
		  from the cache every <command>cleaning-interval</command> minutes.
		  <acronym>BIND</acronym> 9 now manages cache
		  memory in a more sophisticated manner and does not
		  rely on periodic cleaning anymore.
		  Specifying this option therefore has no effect on
		  the server's behavior.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>heartbeat-interval</command></term>
	      <listitem>
		<para>
		  The server performs zone maintenance tasks
		  for all zones marked as <command>dialup</command> whenever this
		  interval expires. The default is 60 minutes. Reasonable
		  values are up
		  to 1 day (1440 minutes).  The maximum value is 28 days
		  (40320 minutes).
		  If set to 0, no zone maintenance for these zones occurs.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>interface-interval</command></term>
	      <listitem>
		<para>
		  The server scans the network interface list
		  every <command>interface-interval</command>
		  minutes. The default
		  is 60 minutes; the maximum value is 28 days (40320 minutes).
		  If set to 0, interface scanning only occurs when
		  the configuration file is loaded, or when
		  <command>automatic-interface-scan</command> is enabled
		  and supported by the operating system. After the scan, the
		  server begins listening for queries on any newly
		  discovered interfaces (provided they are allowed by the
		  <command>listen-on</command> configuration), and
		  stops listening on interfaces that have gone away.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>statistics-interval</command></term>
	      <listitem>
		<para>
		  Name server statistics are logged
		  every <command>statistics-interval</command>
		  minutes. The default is
		  60, and the maximum value is 28 days (40320 minutes).
		  If set to 0, no statistics are logged.
		  </para><note>
		  <simpara>
		    This option is not implemented in
		    <acronym>BIND</acronym> 9.
		  </simpara>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>topology</command></term>
	      <listitem>
		<para>
		  In BIND 8, this option indicated network topology
		  so that preferential treatment could be given to
		  the topologically closest name servers when sending
		  queries. It is not implemented in BIND 9.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="the_sortlist_statement"><info><title>The <command>sortlist</command> Statement</title></info>

	  <para>
	    The response to a DNS query may consist of multiple resource
	    records (RRs) forming a resource record set (RRset).  The name
	    server normally returns the RRs within the RRset in an
	    indeterminate order (but see the <command>rrset-order</command>
	    statement in <xref linkend="rrset_ordering"/>).  The client
	    resolver code should rearrange the RRs as appropriate: that is,
	    using any addresses on the local net in preference to other
	    addresses.  However, not all resolvers can do this or are
	    correctly configured.  When a client is using a local server,
	    the sorting can be performed in the server, based on the
	    client's address. This only requires configuring the name
	    servers, not all the clients.
	  </para>

	  <para>
	    The <command>sortlist</command> statement (see below) takes an
	    <command>address_match_list</command> and interprets it in a
	    special way.  Each top-level statement in the
	    <command>sortlist</command> must itself be an explicit
	    <command>address_match_list</command> with one or two elements.
	    The first element (which may be an IP address, an IP prefix, an
	    ACL name, or a nested <command>address_match_list</command>) of
	    each top-level list is checked against the source address of
	    the query until a match is found. When the addresses in the
	    first element overlap, the first rule to match is selected.
	  </para>
	  <para>
	    Once the source address of the query has been matched, if the
	    top-level statement contains only one element, the actual
	    primitive element that matched the source address is used to
	    select the address in the response to move to the beginning of
	    the response. If the statement is a list of two elements, then
	    the second element is interpreted as a topology preference
	    list.  Each top-level element is assigned a distance, and the
	    address in the response with the minimum distance is moved to
	    the beginning of the response.
	  </para>
	  <para>
	    In the following example, any queries received from any of the
	    addresses of the host itself get responses preferring
	    addresses on any of the locally connected networks. Next most
	    preferred are addresses on the 192.168.1/24 network, and after
	    that either the 192.168.2/24 or 192.168.3/24 network, with no
	    preference shown between these two networks. Queries received
	    from a host on the 192.168.1/24 network prefer other
	    addresses on that network to the 192.168.2/24 and 192.168.3/24
	    networks. Queries received from a host on the 192.168.4/24 or
	    the 192.168.5/24 network only prefer other addresses on
	    their directly connected networks.
	  </para>

<programlisting>sortlist {
    // IF the local host
    // THEN first fit on the following nets
    { localhost;
	{ localnets;
	    192.168.1/24;
	    { 192.168.2/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.1 THEN use .1, or .2 or .3
    { 192.168.1/24;
	{ 192.168.1/24;
	    { 192.168.2/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.2 THEN use .2, or .1 or .3
    { 192.168.2/24;
	{ 192.168.2/24;
	    { 192.168.1/24; 192.168.3/24; }; }; };
    // IF on class C 192.168.3 THEN use .3, or .1 or .2
    { 192.168.3/24;
	{ 192.168.3/24;
	    { 192.168.1/24; 192.168.2/24; }; }; };
    // IF .4 or .5 THEN prefer that net
    { { 192.168.4/24; 192.168.5/24; };
    };
};</programlisting>

	  <para>
	    The following example illustrates reasonable behavior for the
	    local host and hosts on directly connected networks. Responses sent to queries from
	    the local host favor any of the directly connected
	    networks. Responses sent to queries from any other hosts on a
	    directly connected network prefer addresses on that same
	    network.  Responses to other queries are not sorted.
	  </para>

<programlisting>sortlist {
	   { localhost; localnets; };
	   { localnets; };
};
</programlisting>

	</section>
	<section xml:id="rrset_ordering"><info><title xml:id="rrset_ordering_title">RRset Ordering</title></info>

          <note>
            <simpara>
              While alternating the order of records in a DNS response between
              subsequent queries is a known load distribution technique, certain
              caveats apply (mostly stemming from caching) which usually make it
              a suboptimal choice for load balancing purposes when used on its
              own.
            </simpara>
          </note>

          <para>
            The <command>rrset-order</command> statement permits configuration
            of the ordering of the records in a multiple-record response.  See
            also: <xref linkend="the_sortlist_statement"/>.
          </para>

          <para>
            Each rule in an <command>rrset-order</command> statement is defined
            as follows:
          </para>

          <para>
            <optional>class <replaceable>&lt;class_name&gt;</replaceable></optional>
            <optional>type <replaceable>&lt;type_name&gt;</replaceable></optional>
            <optional>name <replaceable>"&lt;domain_name&gt;"</replaceable></optional>
            order <replaceable>&lt;ordering&gt;</replaceable>
          </para>

          <para>
            The default qualifiers for each rule are:
            <itemizedlist>
              <listitem>
                If no <command>class</command> is specified, the default is
                <command>ANY</command>.
              </listitem>
              <listitem>
                If no <command>type</command> is specified, the default is
                <command>ANY</command>.
              </listitem>
              <listitem>
                If no <command>name</command> is specified, the default is
                <command>*</command> (asterisk).
              </listitem>
            </itemizedlist>
          </para>

          <para>
            <replaceable>&lt;domain_name&gt;</replaceable> only matches the name
            itself, not any of its subdomains.  To make a rule match all
            subdomains of a given name, a wildcard name
            (<replaceable>*.&lt;domain_name&gt;</replaceable>) must be used.
            Note that <replaceable>*.&lt;domain_name&gt;</replaceable> does
            <emphasis>not</emphasis> match
            <replaceable>&lt;domain_name&gt;</replaceable> itself; to specify
            RRset ordering for a name and all of its subdomains, two separate
            rules must be defined: one for
            <replaceable>&lt;domain_name&gt;</replaceable> and one for
            <replaceable>*.&lt;domain_name&gt;</replaceable>.
          </para>

          <para>
            The legal values for <replaceable>&lt;ordering&gt;</replaceable>
            are:
          </para>

          <variablelist>

            <varlistentry>
              <term><command>fixed</command></term>
              <listitem>
                <para>
                  Records are returned in the order they are defined in the zone
                  file.
                </para>
                <note>
                  <simpara>
                    The <command>fixed</command> option is only available if
                    BIND is configured with
                    <command>--enable-fixed-rrset</command> at compile time.
                  </simpara>
                </note>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><command>random</command></term>
              <listitem>
                <para>
                  Records are returned in a random order.
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><command>cyclic</command></term>
              <listitem>
                <para>
                  Records are returned in a cyclic round-robin order, rotating
                  by one record per query.
                </para>
              </listitem>
            </varlistentry>

          </variablelist>

          <para>
            By default, records are returned in random order.
          </para>

          <para>
            Note that if multiple <command>rrset-order</command> statements are
            present in the configuration file (at both the
            <command>options</command> and <command>view</command> levels), they
            are <emphasis>not</emphasis> combined; instead, the more-specific
            one (<command>view</command>) replaces the less-specific one
            (<command>options</command>).
          </para>

          <para>
            If multiple rules within a single <command>rrset-order</command>
            statement match a given RRset, the first matching rule is applied.
          </para>

          <para>
            Example:
          </para>

<programlisting>rrset-order {
    type A name "foo.isc.org" order random;
    type AAAA name "foo.isc.org" order cyclic;
    name "bar.isc.org" order fixed;
    name "*.bar.isc.org" order random;
    name "*.baz.isc.org" order cyclic;
};
</programlisting>

          <para>
            With the above configuration, the following RRset ordering is used:
          </para>

          <informaltable>
            <tgroup cols="3">
              <thead>
                <row>
                  <entry><para>QNAME</para></entry>
                  <entry><para>QTYPE</para></entry>
                  <entry><para>RRset Order</para></entry>
                </row>
              </thead>
              <tbody>
                <row>
                  <entry><para><userinput>foo.isc.org</userinput></para></entry>
                  <entry><para><userinput>A</userinput></para></entry>
                  <entry><para><command>random</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>foo.isc.org</userinput></para></entry>
                  <entry><para><userinput>AAAA</userinput></para></entry>
                  <entry><para><command>cyclic</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>foo.isc.org</userinput></para></entry>
                  <entry><para><userinput>TXT</userinput></para></entry>
                  <entry><para><command>random</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>sub.foo.isc.org</userinput></para></entry>
                  <entry><para>all</para></entry>
                  <entry><para><command>random</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>bar.isc.org</userinput></para></entry>
                  <entry><para>all</para></entry>
                  <entry><para><command>fixed</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>sub.bar.isc.org</userinput></para></entry>
                  <entry><para>all</para></entry>
                  <entry><para><command>random</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>baz.isc.org</userinput></para></entry>
                  <entry><para>all</para></entry>
                  <entry><para><command>random</command></para></entry>
                </row>
                <row>
                  <entry><para><userinput>sub.baz.isc.org</userinput></para></entry>
                  <entry><para>all</para></entry>
                  <entry><para><command>cyclic</command></para></entry>
                </row>
              </tbody>
            </tgroup>
          </informaltable>

	</section>

	<section xml:id="tuning"><info><title>Tuning</title></info>

	  <variablelist>

	    <varlistentry>
	      <term><command>lame-ttl</command></term>
	      <listitem>
		<para>
		  This sets the number of seconds to cache a
		  lame server indication. 0 disables caching. (This is
		  <emphasis role="bold">NOT</emphasis> recommended.)
		  The default is <literal>600</literal> (10 minutes) and the
		  maximum value is
		  <literal>1800</literal> (30 minutes).
		</para>

	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>servfail-ttl</command></term>
	      <listitem>
		<para>
		  This sets the number of seconds to cache a
		  SERVFAIL response due to DNSSEC validation failure or
		  other general server failure.  If set to
		  <literal>0</literal>, SERVFAIL caching is disabled.
		  The SERVFAIL cache is not consulted if a query has
		  the CD (Checking Disabled) bit set; this allows a
		  query that failed due to DNSSEC validation to be retried
		  without waiting for the SERVFAIL TTL to expire.
		</para>
		<para>
		  The maximum value is <literal>30</literal>
		  seconds; any higher value is silently
		  reduced. The default is <literal>1</literal>
		  second.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-ncache-ttl</command></term>
	      <listitem>
		<para>
		  To reduce network traffic and increase performance,
		  the server stores negative answers. <command>max-ncache-ttl</command> is
		  used to set a maximum retention time for these answers in
		  the server,
		  in seconds. The default
		  <command>max-ncache-ttl</command> is <literal>10800</literal> seconds (3 hours).
		  <command>max-ncache-ttl</command> cannot exceed
		  7 days and is
		  silently truncated to 7 days if set to a greater value.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-cache-ttl</command></term>
	      <listitem>
		<para>
		  This sets the maximum time for which the server
		  caches ordinary (positive) answers, in seconds.
		  The default is 604800 (one week).
		  A value of zero may cause all queries to return
		  SERVFAIL, because of lost caches of intermediate
		  RRsets (such as NS and glue AAAA/A records) in the
		  resolution process.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>min-roots</command></term>
	      <listitem>
		<para>
		  This sets the minimum number of root servers that
		  is required for a request for the root servers to be
		  accepted. The default
		  is <userinput>2</userinput>.
		</para>
		<note>
		  <simpara>
		    This is not implemented in <acronym>BIND</acronym> 9.
		  </simpara>
		</note>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>sig-validity-interval</command></term>
	      <listitem>
		<para>
		  This specifies the number of days into the future that
		  DNSSEC signatures that are automatically generated as a
		  result of dynamic updates (<xref linkend="dynamic_update"/>) will expire.  There
		  is an optional second field which specifies how
		  long before expiry that the signatures are
		  regenerated.  If not specified, the signatures are
		  regenerated at 1/4 of base interval.  The second
		  field is specified in days if the base interval is
		  greater than 7 days; otherwise it is specified in hours.
		  The default base interval is <literal>30</literal> days,
		  giving a re-signing interval of 7 1/2 days.  The maximum
		  value is 10 years (3660 days).
		</para>
		<para>
		  The signature inception time is unconditionally
		  set to one hour before the current time, to allow
		  for a limited amount of clock skew.
		</para>
		<para>
		  The <command>sig-validity-interval</command>
		  should be at least several multiples of the SOA
		  expire interval, to allow for reasonable interaction
		  between the various timer and expiry dates.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>sig-signing-nodes</command></term>
	      <listitem>
		<para>
		  This specifies the maximum number of nodes to be
		  examined in each quantum, when signing a zone with
		  a new DNSKEY. The default is
		  <literal>100</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>sig-signing-signatures</command></term>
	      <listitem>
		<para>
		  This specifies a threshold number of signatures that
		  terminates processing a quantum, when signing
		  a zone with a new DNSKEY.  The default is
		  <literal>10</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>sig-signing-type</command></term>
	      <listitem>
		<para>
		  This specifies a private RDATA type to be used when generating
		  signing-state records.  The default is
		  <literal>65534</literal>.
		</para>
		<para>
		  This parameter may be removed
		  in a future version, once there is a standard type.
		</para>
		<para>
		  Signing-state records are used internally by
		  <command>named</command> to track the current state of
		  a zone-signing process, i.e., whether it is still active
		  or has been completed.  The records can be inspected
		  using the command
		  <command>rndc signing -list <replaceable>zone</replaceable></command>.
		  Once <command>named</command> has finished signing
		  a zone with a particular key, the signing-state
		  record associated with that key can be removed from
		  the zone by running
		  <command>rndc signing -clear <replaceable>keyid/algorithm</replaceable> <replaceable>zone</replaceable></command>.
		  To clear all of the completed signing-state
		  records for a zone, use
		  <command>rndc signing -clear all <replaceable>zone</replaceable></command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>min-refresh-time</command></term>
	      <term><command>max-refresh-time</command></term>
	      <term><command>min-retry-time</command></term>
	      <term><command>max-retry-time</command></term>
	      <listitem>
		<para>
		  These options control the server's behavior on refreshing a
		  zone (querying for SOA changes) or retrying failed
		  transfers.  Usually the SOA values for the zone are used,
		  up to a hard-coded maximum expiry of 24 weeks. However,
		  these values are set by the primary, giving secondary server
		  administrators little control over their contents.
		</para>
		<para>
		  These options allow the administrator to set a minimum and
		  maximum refresh and retry time in seconds per-zone,
		  per-view, or globally.  These options are valid for
		  secondary and stub zones, and clamp the SOA refresh and
		  retry times to the specified values.
		</para>
		<para>
		  The following defaults apply:
		  <command>min-refresh-time</command> 300 seconds,
		  <command>max-refresh-time</command> 2419200 seconds
		  (4 weeks), <command>min-retry-time</command> 500 seconds,
		  and <command>max-retry-time</command> 1209600 seconds
		  (2 weeks).
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>edns-udp-size</command></term>
	      <listitem>
		<para>
		  This sets the maximum advertised EDNS UDP buffer size, in
		  bytes, to control the size of packets received from
		  authoritative servers in response to recursive queries.
		  Valid values are 512 to 4096; values outside this range
		  are silently adjusted to the nearest value within
		  it.  The default value is 1232.
		</para>
		<para>
		  The usual reason for setting
		  <command>edns-udp-size</command> to a non-default value
		  is to get UDP answers to pass through broken firewalls
		  that block fragmented packets and/or block UDP DNS
		  packets that are greater than 512 bytes.
		</para>
		<para>
		  When <command>named</command> first queries a remote
		  server, it advertises a UDP buffer size of 512, as
		  this has the greatest chance of success on the first try.
		</para>
		<para>
		  If the initial response times out, <command>named</command>
		  tries again with plain DNS; if that is successful,
		  it is taken as evidence that the server does not
		  support EDNS. After enough failures using EDNS and
		  successes using plain DNS, <command>named</command>
		  defaults to plain DNS for future communications
		  with that server.  If that happens, <command>named</command>
		  periodically sends an EDNS query to see if the situation has
		  improved.
		</para>
		<para>
		  However, if the initial query is successful with
		  EDNS advertising a buffer size of 512, then
		  <command>named</command> advertises progressively
		  larger buffer sizes on successive queries, until
		  responses begin timing out or
		  <command>edns-udp-size</command> is reached.
		</para>
		<para>
		  The default buffer sizes used by <command>named</command>
		  are 512, 1232, 1432, and 4096, but never exceed
		  <command>edns-udp-size</command>.  (The values 1232 and
		  1432 are chosen to allow for an IPv4-/IPv6-encapsulated
		  UDP message to be sent without fragmentation at the
		  minimum MTU sizes for Ethernet and IPv6 networks.)
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-udp-size</command></term>
	      <listitem>
		<para>
		  This sets the maximum EDNS UDP message size that
		  <command>named</command> sends, in bytes.
		  Valid values are 512 to 4096; values outside this
		  range are silently adjusted to the nearest
		  value within it.  The default value is 1232.
		</para>
		<para>
		  This value applies to responses sent by a server; to
		  set the advertised buffer size in queries, see
		  <command>edns-udp-size</command>.
		</para>
		<para>
		  The usual reason for setting
		  <command>max-udp-size</command> to a non-default
		  value is to allow UDP answers to pass through broken
		  firewalls that block fragmented packets and/or
		  block UDP packets that are greater than 512 bytes.
		  This is independent of the advertised receive
		  buffer (<command>edns-udp-size</command>).
		</para>
		<para>
		  Setting this to a low value encourages additional
		  TCP traffic to the name server.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>masterfile-format</command></term>
	      <listitem>
		<para>This specifies
		  the file format of zone files (see
		  <xref linkend="zonefile_format"/>).
		  The default value is <constant>text</constant>, which is the
		  standard textual representation, except for secondary zones,
		  in which the default value is <constant>raw</constant>.
		  Files in formats other than <constant>text</constant> are
		  typically expected to be generated by the
		  <command>named-compilezone</command> tool, or dumped by
		  <command>named</command>.
		</para>
		<para>
		  Note that when a zone file in a format other than
		  <constant>text</constant> is loaded, <command>named</command>
		  may omit some of the checks which would be performed for a
		  file in <constant>text</constant> format.  In particular,
		  <command>check-names</command> checks do not apply
		  for the <constant>raw</constant> format.  This means
		  a zone file in the <constant>raw</constant> format
		  must be generated with the same check level as that
		  specified in the <command>named</command> configuration
		  file.  Also, <constant>map</constant> format files are
		  loaded directly into memory via memory mapping, with only
		  minimal checking.
		</para>
		<para>
		  This statement sets the
		  <command>masterfile-format</command> for all zones,
		  but can be overridden on a per-zone or per-view basis
		  by including a <command>masterfile-format</command>
		  statement within the <command>zone</command> or
		  <command>view</command> block in the configuration
		  file.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>masterfile-style</command></term>
	      <listitem>
		<para>
		  This specifies the formatting of zone files during dump,
		  when the <option>masterfile-format</option> is
		  <constant>text</constant>. This option is ignored
		  with any other <option>masterfile-format</option>.
		</para>
		<para>
		  When set to <constant>relative</constant>,
		  records are printed in a multi-line format, with owner
		  names expressed relative to a shared origin.  When set
		  to <constant>full</constant>, records are printed in
		  a single-line format with absolute owner names.
		  The <constant>full</constant> format is most suitable
		  when a zone file needs to be processed automatically
		  by a script.  The <constant>relative</constant> format
		  is more human-readable, and is thus suitable when a
		  zone is to be edited by hand.  The default is
		  <constant>relative</constant>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry xml:id="max-recursion-depth">
	      <term><command>max-recursion-depth</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of levels of recursion
		  that are permitted at any one time while servicing
		  a recursive query. Resolving a name may require
		  looking up a name server address, which in turn
		  requires resolving another name, etc.; if the number
		  of recursions exceeds this value, the recursive
		  query is terminated and returns SERVFAIL.  The
		  default is 7.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry xml:id="max-recursion-queries">
	      <term><command>max-recursion-queries</command></term>
	      <listitem>
		<para>
		  This sets the maximum number of iterative queries that
		  may be sent while servicing a recursive query.
		  If more queries are sent, the recursive query
		  is terminated and returns SERVFAIL.  The default is 75.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>notify-delay</command></term>
	      <listitem>
		<para>
		  This sets the delay, in seconds, between sending sets of NOTIFY
		  messages for a zone.  The default is 5 seconds.
		</para>
		<para>
		  The overall rate at which NOTIFY messages are sent for all
		  zones is controlled by <command>serial-query-rate</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-rsa-exponent-size</command></term>
	      <listitem>
		<para>
		  This sets the maximum RSA exponent size, in bits, that is
		  accepted when validating.  Valid values are 35
		  to 4096 bits.  The default, zero, is also accepted
		  and is equivalent to 4096.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>prefetch</command></term>
	      <listitem>
		<para>
		  When a query is received for cached data which
		  is to expire shortly, <command>named</command> can
		  refresh the data from the authoritative server
		  immediately, ensuring that the cache always has an
		  answer available.
		</para>
		<para>
		  <option>prefetch</option> specifies the
		  "trigger" TTL value at which prefetch of the current
		  query takes place; when a cache record with a
		  lower TTL value is encountered during query processing,
		  it is refreshed.  Valid trigger TTL values are 1 to
		  10 seconds.  Values larger than 10 seconds are silently
		  reduced to 10.
		  Setting a trigger TTL to zero causes
		  prefetch to be disabled.
		  The default trigger TTL is <literal>2</literal>.
		</para>
		<para>
		  An optional second argument specifies the "eligibility"
		  TTL: the smallest <emphasis>original</emphasis>
		  TTL value that is accepted for a record to be
		  eligible for prefetching.  The eligibility TTL must
		  be at least six seconds longer than the trigger TTL;
		  if not, <command>named</command> silently
		  adjusts it upward.
		  The default eligibility TTL is <literal>9</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>v6-bias</command></term>
	      <listitem>
		<para>
		  When determining the next name server to try,
		  this indicates by how many milliseconds to prefer IPv6 name servers.
		  The default is <literal>50</literal> milliseconds.
		</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>

	</section>

	<section xml:id="builtin"><info><title>Built-in Server Information Zones</title></info>

	  <para>
	    The server provides some helpful diagnostic information
	    through a number of built-in zones under the
	    pseudo-top-level-domain <literal>bind</literal> in the
	    <command>CHAOS</command> class.  These zones are part
	    of a
	    built-in view (see <xref linkend="view_statement_grammar"/>) of
	    class
	    <command>CHAOS</command>, which is separate from the
	    default view of class <command>IN</command>. Most global
	    configuration options (<command>allow-query</command>,
	    etc.) apply to this view, but some are locally
	    overridden: <command>notify</command>,
	    <command>recursion</command>, and
	    <command>allow-new-zones</command> are
	    always set to <userinput>no</userinput>, and
	    <command>rate-limit</command> is set to allow
	    three responses per second.
	  </para>
	  <para>
	    To disable these zones, use the options
	    below or hide the built-in <command>CHAOS</command>
	    view by
	    defining an explicit view of class <command>CHAOS</command>
	    that matches all clients.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>version</command></term>
	      <listitem>
		<para>
		  This is the version the server should report
		  via a query of the name <literal>version.bind</literal>
		  with type <command>TXT</command> and class <command>CHAOS</command>.
		  The default is the real version number of this server.
		  Specifying <command>version none</command>
		  disables processing of the queries.
		</para>
		<para>
		  Setting <command>version</command> to any value
		  (including <literal>none</literal>) also
		  disables queries for <literal>authors.bind TXT CH</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>hostname</command></term>
	      <listitem>
		<para>
		  This is the hostname the server should report via a query of
		  the name <filename>hostname.bind</filename>
		  with type <command>TXT</command> and class <command>CHAOS</command>.
		  This defaults to the hostname of the machine hosting the
		  name server, as
		  found by the <command>gethostname()</command> function.  The primary purpose of such queries
		  is to
		  identify which of a group of anycast servers is actually
		  answering the queries.  Specifying <command>hostname none;</command>
		  disables processing of the queries.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>server-id</command></term>
	      <listitem>
		<para>
		  This is the ID the server should report when receiving a Name
		  Server Identifier (NSID) query, or a query of the name
		  <filename>ID.SERVER</filename> with type
		  <command>TXT</command> and class <command>CHAOS</command>.
		  The primary purpose of such queries is to
		  identify which of a group of anycast servers is actually
		  answering the queries.  Specifying <command>server-id none;</command>
		  disables processing of the queries.
		  Specifying <command>server-id hostname;</command> causes <command>named</command> to
		  use the hostname as found by the <command>gethostname()</command> function.
		  The default <command>server-id</command> is <command>none</command>.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="empty"><info><title>Built-in Empty Zones</title></info>

	  <para>
	    The <command>named</command> server has some built-in
	    empty zones, for SOA and NS records only.
	    These are for zones that should normally be answered locally
	    and which queries should not be sent to the Internet's root
	    servers.  The official servers which cover these namespaces
	    return NXDOMAIN responses to these queries.  In particular,
	    these cover the reverse namespaces for addresses from
	    RFC 1918, RFC 4193, RFC 5737, and RFC 6598.  They also include the
	    reverse namespace for the IPv6 local address (locally assigned),
	    IPv6 link local addresses, the IPv6 loopback address, and the
	    IPv6 unknown address.
	  </para>
	  <para>
	    The server attempts to determine if a built-in zone
	    already exists or is active (covered by a forward-only
	    forwarding declaration) and does not create an empty
	    zone if either is true.
	  </para>
	  <para>
	    The current list of empty zones is:
	    <itemizedlist>
	      <listitem>10.IN-ADDR.ARPA</listitem>
	      <listitem>16.172.IN-ADDR.ARPA</listitem>
	      <listitem>17.172.IN-ADDR.ARPA</listitem>
	      <listitem>18.172.IN-ADDR.ARPA</listitem>
	      <listitem>19.172.IN-ADDR.ARPA</listitem>
	      <listitem>20.172.IN-ADDR.ARPA</listitem>
	      <listitem>21.172.IN-ADDR.ARPA</listitem>
	      <listitem>22.172.IN-ADDR.ARPA</listitem>
	      <listitem>23.172.IN-ADDR.ARPA</listitem>
	      <listitem>24.172.IN-ADDR.ARPA</listitem>
	      <listitem>25.172.IN-ADDR.ARPA</listitem>
	      <listitem>26.172.IN-ADDR.ARPA</listitem>
	      <listitem>27.172.IN-ADDR.ARPA</listitem>
	      <listitem>28.172.IN-ADDR.ARPA</listitem>
	      <listitem>29.172.IN-ADDR.ARPA</listitem>
	      <listitem>30.172.IN-ADDR.ARPA</listitem>
	      <listitem>31.172.IN-ADDR.ARPA</listitem>
	      <listitem>168.192.IN-ADDR.ARPA</listitem>
	      <listitem>64.100.IN-ADDR.ARPA</listitem>
	      <listitem>65.100.IN-ADDR.ARPA</listitem>
	      <listitem>66.100.IN-ADDR.ARPA</listitem>
	      <listitem>67.100.IN-ADDR.ARPA</listitem>
	      <listitem>68.100.IN-ADDR.ARPA</listitem>
	      <listitem>69.100.IN-ADDR.ARPA</listitem>
	      <listitem>70.100.IN-ADDR.ARPA</listitem>
	      <listitem>71.100.IN-ADDR.ARPA</listitem>
	      <listitem>72.100.IN-ADDR.ARPA</listitem>
	      <listitem>73.100.IN-ADDR.ARPA</listitem>
	      <listitem>74.100.IN-ADDR.ARPA</listitem>
	      <listitem>75.100.IN-ADDR.ARPA</listitem>
	      <listitem>76.100.IN-ADDR.ARPA</listitem>
	      <listitem>77.100.IN-ADDR.ARPA</listitem>
	      <listitem>78.100.IN-ADDR.ARPA</listitem>
	      <listitem>79.100.IN-ADDR.ARPA</listitem>
	      <listitem>80.100.IN-ADDR.ARPA</listitem>
	      <listitem>81.100.IN-ADDR.ARPA</listitem>
	      <listitem>82.100.IN-ADDR.ARPA</listitem>
	      <listitem>83.100.IN-ADDR.ARPA</listitem>
	      <listitem>84.100.IN-ADDR.ARPA</listitem>
	      <listitem>85.100.IN-ADDR.ARPA</listitem>
	      <listitem>86.100.IN-ADDR.ARPA</listitem>
	      <listitem>87.100.IN-ADDR.ARPA</listitem>
	      <listitem>88.100.IN-ADDR.ARPA</listitem>
	      <listitem>89.100.IN-ADDR.ARPA</listitem>
	      <listitem>90.100.IN-ADDR.ARPA</listitem>
	      <listitem>91.100.IN-ADDR.ARPA</listitem>
	      <listitem>92.100.IN-ADDR.ARPA</listitem>
	      <listitem>93.100.IN-ADDR.ARPA</listitem>
	      <listitem>94.100.IN-ADDR.ARPA</listitem>
	      <listitem>95.100.IN-ADDR.ARPA</listitem>
	      <listitem>96.100.IN-ADDR.ARPA</listitem>
	      <listitem>97.100.IN-ADDR.ARPA</listitem>
	      <listitem>98.100.IN-ADDR.ARPA</listitem>
	      <listitem>99.100.IN-ADDR.ARPA</listitem>
	      <listitem>100.100.IN-ADDR.ARPA</listitem>
	      <listitem>101.100.IN-ADDR.ARPA</listitem>
	      <listitem>102.100.IN-ADDR.ARPA</listitem>
	      <listitem>103.100.IN-ADDR.ARPA</listitem>
	      <listitem>104.100.IN-ADDR.ARPA</listitem>
	      <listitem>105.100.IN-ADDR.ARPA</listitem>
	      <listitem>106.100.IN-ADDR.ARPA</listitem>
	      <listitem>107.100.IN-ADDR.ARPA</listitem>
	      <listitem>108.100.IN-ADDR.ARPA</listitem>
	      <listitem>109.100.IN-ADDR.ARPA</listitem>
	      <listitem>110.100.IN-ADDR.ARPA</listitem>
	      <listitem>111.100.IN-ADDR.ARPA</listitem>
	      <listitem>112.100.IN-ADDR.ARPA</listitem>
	      <listitem>113.100.IN-ADDR.ARPA</listitem>
	      <listitem>114.100.IN-ADDR.ARPA</listitem>
	      <listitem>115.100.IN-ADDR.ARPA</listitem>
	      <listitem>116.100.IN-ADDR.ARPA</listitem>
	      <listitem>117.100.IN-ADDR.ARPA</listitem>
	      <listitem>118.100.IN-ADDR.ARPA</listitem>
	      <listitem>119.100.IN-ADDR.ARPA</listitem>
	      <listitem>120.100.IN-ADDR.ARPA</listitem>
	      <listitem>121.100.IN-ADDR.ARPA</listitem>
	      <listitem>122.100.IN-ADDR.ARPA</listitem>
	      <listitem>123.100.IN-ADDR.ARPA</listitem>
	      <listitem>124.100.IN-ADDR.ARPA</listitem>
	      <listitem>125.100.IN-ADDR.ARPA</listitem>
	      <listitem>126.100.IN-ADDR.ARPA</listitem>
	      <listitem>127.100.IN-ADDR.ARPA</listitem>
	      <listitem>0.IN-ADDR.ARPA</listitem>
	      <listitem>127.IN-ADDR.ARPA</listitem>
	      <listitem>254.169.IN-ADDR.ARPA</listitem>
	      <listitem>2.0.192.IN-ADDR.ARPA</listitem>
	      <listitem>100.51.198.IN-ADDR.ARPA</listitem>
	      <listitem>113.0.203.IN-ADDR.ARPA</listitem>
	      <listitem>255.255.255.255.IN-ADDR.ARPA</listitem>
	      <listitem>0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
	      <listitem>1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
	      <listitem>8.B.D.0.1.0.0.2.IP6.ARPA</listitem>
	      <listitem>D.F.IP6.ARPA</listitem>
	      <listitem>8.E.F.IP6.ARPA</listitem>
	      <listitem>9.E.F.IP6.ARPA</listitem>
	      <listitem>A.E.F.IP6.ARPA</listitem>
	      <listitem>B.E.F.IP6.ARPA</listitem>
	      <listitem>EMPTY.AS112.ARPA</listitem>
	      <listitem>HOME.ARPA</listitem>
	    </itemizedlist>
	  </para>
	  <para>
	    Empty zones can be set at the view level and only apply to
	    views of class IN.  Disabled empty zones are only inherited
	    from options if there are no disabled empty zones specified
	    at the view level.  To override the options list of disabled
	    zones, disable the root zone at the view level. For example:
<programlisting>
	    disable-empty-zone ".";
</programlisting>
	  </para>
	  <para>
	    If using the address ranges covered here,
	    reverse zones covering the addresses should already be in place.
	    In practice this appears to not be the case, with many queries
	    being made to the infrastructure servers for names in these
	    spaces.  So many, in fact, that sacrificial servers had
	    to be deployed to channel the query load away from the
	    infrastructure servers.
	  </para>
	  <note><simpara>
	    The real parent servers for these zones should disable all
	    empty zones under the parent zone they serve.  For the real
	    root servers, this is all built-in empty zones.  This
	    enables them to return referrals to deeper in the tree.
	  </simpara></note>
	  <variablelist>
	    <varlistentry>
	      <term><command>empty-server</command></term>
	      <listitem>
		<para>
		  This specifies the server name that appears in the returned
		  SOA record for empty zones.  If none is specified,
		  the zone's name is used.
		</para>
	       </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>empty-contact</command></term>
	      <listitem>
		<para>
		  This specifies the contact name that appears in the returned
		  SOA record for empty zones.  If none is specified,
		  "." is used.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>empty-zones-enable</command></term>
	      <listitem>
		<para>
		  This enables or disables all empty zones.  By default, they
		  are enabled.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	    <term><command>disable-empty-zone</command></term>
	      <listitem>
		<para>
		  This disables individual empty zones.  By default, none are
		  disabled.  This option can be specified multiple times.
		</para>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</section>

	<section xml:id="acache"><info><title>Additional Section Caching</title></info>


	  <para>
	    The additional section cache, also called <command>acache</command>,
	    is an internal cache to improve the response performance of BIND 9.
	    When additional section caching is enabled, BIND 9
	    caches an internal shortcut to the additional section content for
	    each answer RR.
	    Note that <command>acache</command> is an internal caching
	    mechanism of BIND 9, and is not related to the DNS caching
	    server function.
	  </para>

	  <para>
	    Additional section caching does not change the
	    response content (except the RRsets ordering of the additional
	    section; see below), but can improve the response performance
	    significantly.
	    It is particularly effective when BIND 9 acts as an authoritative
	    server for a zone that has many delegations with many glue RRs.
	  </para>

	  <para>
	    To obtain the maximum performance improvement
	    from additional section caching, setting
	    <command>additional-from-cache</command>
	    to <command>no</command> is recommended, since the current
	    implementation of <command>acache</command>
	    does not shortcut additional section information from the
	    DNS cache data.
	  </para>

	  <para>
	    One obvious disadvantage of <command>acache</command> is
	    that it requires much more
	    memory for the internal cached data.
	    Thus, if the response performance does not matter and memory
	    consumption is more critical, the
	    <command>acache</command> mechanism can be
	    disabled by setting <command>acache-enable</command> to
	    <command>no</command>.
	    It is also possible to specify the upper limit of memory
	    consumption
	    for <command>acache</command> by using <command>max-acache-size</command>.
	  </para>

	  <para>
	    Additional section caching also has a minor effect on the
	    RRset ordering in the additional section.
	    Without <command>acache</command>,
	    <command>cyclic</command> order is effective for the additional
	    section as well as for the answer and authority sections.
	    However, additional section caching fixes the ordering when it
	    first caches an RRset for the additional section, and the same
	    ordering is kept in succeeding responses, regardless of the
	    setting of <command>rrset-order</command>.
	    The effect of this should be minor, however, since an
	    RRset in the additional section
	    typically only contains a small number of RRs (and in many cases
	    only a single RR), so the
	    ordering is not significant.
	  </para>

	  <para>
	    The following is a summary of options related to
	    <command>acache</command>.
	  </para>

	  <variablelist>

	    <varlistentry>
	      <term><command>acache-enable</command></term>
	      <listitem>
		<para>
		  If <command>yes</command>, additional section caching is
		  enabled.  The default value is <command>no</command>.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>acache-cleaning-interval</command></term>
	      <listitem>
		<para>
		  The server removes stale cache entries, based on an LRU-based
		  algorithm, every <command>acache-cleaning-interval</command> minutes.
		  The default is 60 minutes.
		  If set to 0, no periodic cleaning occurs.
		</para>
	      </listitem>
	    </varlistentry>

	    <varlistentry>
	      <term><command>max-acache-size</command></term>
	      <listitem>
		<para>
		  This is the maximum amount of memory, in bytes, to use for the server's acache.
		  When the amount of data in the acache reaches this limit,
		  the server
		  cleans more aggressively so that the limit is not
		  exceeded.
		  In a server with multiple views, the limit applies
		  separately to the
		  <command>acache</command> of each view.
		  The default is <literal>16M</literal>.
		</para>
	      </listitem>
	    </varlistentry>

	  </variablelist>

	</section>

	<section xml:id="content_filtering"><info><title>Content Filtering</title></info>

	  <para>
	    <acronym>BIND</acronym> 9 provides the ability to filter
	    out responses from external DNS servers containing
	    certain types of data in the answer section.
	    Specifically, it can reject address (A or AAAA) records if
	    the corresponding IPv4 or IPv6 addresses match the given
	    <varname>address_match_list</varname> of the
	    <command>deny-answer-addresses</command> option.
	    It can also reject CNAME or DNAME records if the "alias"
	    name (i.e., the CNAME alias or the substituted query name
	    due to DNAME) matches the
	    given <varname>namelist</varname> of the
	    <command>deny-answer-aliases</command> option, where
	    "match" means the alias name is a subdomain of one of
	    the <varname>name_list</varname> elements.
	    If the optional <varname>namelist</varname> is specified
	    with <command>except-from</command>, records whose query name
	    matches the list are accepted regardless of the filter
	    setting.
	    Likewise, if the alias name is a subdomain of the
	    corresponding zone, the <command>deny-answer-aliases</command>
	    filter does not apply;
	    for example, even if "example.com" is specified for
	    <command>deny-answer-aliases</command>,
	  </para>
<programlisting>www.example.com. CNAME xxx.example.com.</programlisting>

	  <para>
	    returned by an "example.com" server is accepted.
	  </para>

	  <para>
	    In the <varname>address_match_list</varname> of the
	    <command>deny-answer-addresses</command> option, only
	    <varname>ip_addr</varname>
	    and <varname>ip_prefix</varname>
	    are meaningful;
	    any <varname>key_id</varname> is silently ignored.
	  </para>

	  <para>
	    If a response message is rejected due to the filtering,
	    the entire message is discarded without being cached, and
	    a SERVFAIL error is returned to the client.
	  </para>

	  <para>
	    This filtering is intended to prevent "DNS rebinding attacks," in
	    which an attacker, in response to a query for a domain name the
	    attacker controls, returns an IP address within the user's own network or
	    an alias name within the user's own domain.
	    A naive web browser or script could then serve as an
	    unintended proxy, allowing the attacker
	    to get access to an internal node of the local network
	    that could not be externally accessed otherwise.
	    See the paper available at
	    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://dl.acm.org/doi/10.1145/1315245.1315298">
	    https://dl.acm.org/doi/10.1145/1315245.1315298
	    </link>
	    for more details about these attacks.
	  </para>

	  <para>
	    For example, with a domain named "example.net" and
	    an internal network using an IPv4 prefix 192.0.2.0/24,
	    an administrator might specify the following rules:
	  </para>

<programlisting>deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</programlisting>

	  <para>
	    If an external attacker let a web browser in the local
	    network look up an IPv4 address of "attacker.example.com",
	    the attacker's DNS server would return a response like this:
	  </para>

<programlisting>attacker.example.com. A 192.0.2.1</programlisting>

	  <para>
	    in the answer section.
	    Since the rdata of this record (the IPv4 address) matches
	    the specified prefix 192.0.2.0/24, this response would be
	    ignored.
	  </para>

	  <para>
	    On the other hand, if the browser looked up a legitimate
	    internal web server "www.example.net" and the
	    following response were returned to
	    the <acronym>BIND</acronym> 9 server:
	  </para>

<programlisting>www.example.net. A 192.0.2.2</programlisting>

	  <para>
	    it would be accepted, since the owner name "www.example.net"
	    matches the <command>except-from</command> element,
	    "example.net".
	  </para>

	  <para>
	    Note that this is not really an attack on the DNS per se.
	    In fact, there is nothing wrong with having an "external" name
	    mapped to an "internal" IP address or domain name
	    from the DNS point of view;
	    it might actually be provided for a legitimate purpose,
	    such as for debugging.
	    As long as the mapping is provided by the correct owner,
	    it either is not possible or does not make sense to detect
	    whether the intent of the mapping is legitimate
	    within the DNS.
	    The "rebinding" attack must primarily be protected at the
	    application that uses the DNS.
	    For a large site, however, it may be difficult to protect
	    all possible applications at once.
	    This filtering feature is provided only to help such an
	    operational environment;
	    turning it on is generally discouraged unless there is
	    no other choice and the attack is a
	    real threat to applications.
	  </para>

	  <para>
	    Care should be particularly taken if using this
	    option for addresses within 127.0.0.0/8.
	    These addresses are obviously "internal," but many
	    applications conventionally rely on a DNS mapping from
	    some name to such an address.
	    Filtering out DNS records containing this address
	    spuriously can break such applications.
	  </para>
	</section>

	<section xml:id="rpz"><info><title>Response Policy Zone (RPZ) Rewriting</title></info>

	  <para>
	    <acronym>BIND</acronym> 9 includes a limited
	    mechanism to modify DNS responses for requests
	    analogous to email anti-spam DNS rejection lists.
	    Responses can be changed to deny the existence of domains (NXDOMAIN),
	    deny the existence of IP addresses for domains (NODATA),
	    or contain other IP addresses or data.
	  </para>

	  <para>
	    Response policy zones are named in the
	    <command>response-policy</command> option for the view or among the
	    global options if there is no <command>response-policy</command> option for the view.
	    Response policy zones are ordinary DNS zones containing RRsets
	    that can be queried normally if allowed.
	    It is usually best to restrict those queries with something like
	    <command>allow-query { localhost; };</command>.
	    Note that zones using <command>masterfile-format map</command>
	    cannot be used as policy zones.
	  </para>

	  <para>
	    A <command>response-policy</command> option can support
	    multiple policy zones.  To maximize performance, a radix
	    tree is used to quickly identify response policy zones
	    containing triggers that match the current query.  This
	    imposes an upper limit of 32 on the number of policy zones
	    in a single <command>response-policy</command> option; more
	    than that is a configuration error.
	  </para>

	  <para>
	    Rules encoded in response policy zones are processed after
	    those defined in <link linkend="access_control">Access Control Lists
	    (ACLs)</link>.  All queries from clients which are not
	    permitted access to the resolver are answered with a
	    status code of REFUSED, regardless of configured RPZ rules.
	  </para>

	  <para>
	    Five policy triggers can be encoded in RPZ records.
	    <variablelist>
	      <varlistentry>
		<term><command>RPZ-CLIENT-IP</command></term>
		<listitem>
		  <para>
		    IP records are triggered by the IP address of the
		    DNS client.
		    Client IP address triggers are encoded in records that have
		    owner names that are subdomains of
		    <command>rpz-client-ip</command>, relativized to the
		    policy zone origin name,
		    and encode an address or address block.
		    IPv4 addresses are represented as
		    <userinput>prefixlength.B4.B3.B2.B1.rpz-client-ip</userinput>.
		    The IPv4 prefix length must be between 1 and 32.
		    All four bytes - B4, B3, B2, and B1 - must be present.
		    B4 is the decimal value of the least significant byte of the
		    IPv4 address as in IN-ADDR.ARPA.
		  </para>

		  <para>
		    IPv6 addresses are encoded in a format similar
		    to the standard IPv6 text representation,
		    <userinput>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip</userinput>.
		    Each of W8,...,W1 is a one- to four-digit hexadecimal number
		    representing 16 bits of the IPv6 address as in the standard
		    text representation of IPv6 addresses, but reversed as in
		    IP6.ARPA. (Note that this representation of IPv6
		    address is different from IP6.ARPA where each hex
		    digit occupies a label.)
		    All 8 words must be present except when one set of consecutive
		    zero words is replaced with <userinput>.zz.</userinput>,
		    analogous to double colons (::) in standard IPv6 text
		    encodings.
		    The IPv6 prefix length must be between 1 and 128.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>QNAME</command></term>
		<listitem>
		  <para>
		    QNAME policy records are triggered by query names of
		    requests and targets of CNAME records resolved to generate
		    the response.
		    The owner name of a QNAME policy record is
		    the query name relativized to the policy zone.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>RPZ-IP</command></term>
		<listitem>
		  <para>
		    IP triggers are IP addresses in an
		    A or AAAA record in the ANSWER section of a response.
		    They are encoded like client-IP triggers, except as
		    subdomains of <command>rpz-ip</command>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>RPZ-NSDNAME</command></term>
		<listitem>
		  <para>
		    NSDNAME triggers match names of authoritative servers
		    for the query name, a parent of the query name, a CNAME for
		    the query name, or a parent of a CNAME.
		    They are encoded as subdomains of
		    <command>rpz-nsdname</command>, relativized
		    to the RPZ origin name.
		    NSIP triggers match IP addresses in A and
		    AAAA RRsets for domains that can be checked against NSDNAME
		    policy records.  The
		    <command>nsdname-enable</command> phrase turns NSDNAME
		    triggers off or on for a single policy zone or for all
		    zones.
		  </para>
		</listitem>
		<listitem>
		  <para>
		    If authoritative nameservers for the query name are not
		    yet known, <command>named</command> recursively
		    looks up the authoritative servers for the query name
		    before applying an RPZ-NSDNAME rule,
		    which can cause a processing delay. To speed up
		    processing at the cost of precision, the
		    <command>nsdname-wait-recurse</command> option
		    can be used; when set to <userinput>no</userinput>,
		    RPZ-NSDNAME rules are only applied when authoritative
		    servers for the query name have already been looked up and
		    cached.  If authoritative servers for the query name
		    are not in the cache, the RPZ-NSDNAME rule is
		    ignored, but the authoritative servers for the query name
		    are looked up in the background and the rule is
		    applied to subsequent queries. The default is
		    <userinput>yes</userinput>, meaning RPZ-NSDNAME
		    rules are always applied, even if authoritative
		    servers for the query name need to be looked up first.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>RPZ-NSIP</command></term>
		<listitem>
		  <para>
		    NSIP triggers match the IP addresses of authoritative
		    servers.  They are enncoded like IP triggers, except as
		    subdomains of <command>rpz-nsip</command>.
		    NSDNAME and NSIP triggers are checked only for names with at
		    least <command>min-ns-dots</command> dots.
		    The default value of <command>min-ns-dots</command> is
		    1, to exclude top-level domains.
		  </para>
		  <para>
		    If a name server's IP address is not yet known,
		    <command>named</command> recursively looks up
		    the IP address before applying an RPZ-NSIP rule,
		    which can cause a processing delay. To speed up
		    processing at the cost of precision, the
		    <command>nsip-wait-recurse</command> option
		    can be used: when set to <userinput>no</userinput>,
		    RPZ-NSIP rules are only applied when a name
		    server's IP address has already been looked up and
		    cached.  If a server's IP address is not in the
		    cache, the RPZ-NSIP rule is ignored,
		    but the address is looked up in the
		    background and the rule is applied
		    to subsequent queries.  The default is
		    <userinput>yes</userinput>, meaning RPZ-NSIP
		    rules are always applied, even if an
		    address needs to be looked up first.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </para>

	  <para>
	    The query response is checked against all response policy zones,
	    so two or more policy records can be triggered by a response.
	    Because DNS responses are rewritten according to at most one
	    policy record, a single record encoding an action (other than
	    <command>DISABLED</command> actions) must be chosen.
	    Triggers, or the records that encode them, are chosen for
	    rewriting in the following order:
	    <orderedlist inheritnum="ignore" continuation="restarts">
	      <listitem>Choose the triggered record in the zone that appears
		first in the <command>response-policy</command> option.
	      </listitem>
	      <listitem>Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP
		triggers in a single zone.
	      </listitem>
	      <listitem>Among NSDNAME triggers, prefer the
		trigger that matches the smallest name under the DNSSEC ordering.
	      </listitem>
	      <listitem>Among IP or NSIP triggers, prefer the trigger
		with the longest prefix.
	      </listitem>
	      <listitem>Among triggers with the same prefix length,
		prefer the IP or NSIP trigger that matches
		the smallest IP address.
	      </listitem>
	    </orderedlist>
	  </para>

	  <para>
	    When the processing of a response is restarted to resolve
	    DNAME or CNAME records and a policy record set has
	    not been triggered,
	    all response policy zones are again consulted for the
	    DNAME or CNAME names and addresses.
	  </para>

	  <para>
	    RPZ record sets are any types of DNS record, except
	    DNAME or DNSSEC, that encode actions or responses to
	    individual queries.
	    Any of the policies can be used with any of the triggers.
	    For example, while the <command>TCP-only</command> policy is
	    commonly used with <command>client-IP</command> triggers,
	    it can be used with any type of trigger to force the use of
	    TCP for responses with owner names in a zone.
	    <variablelist>
	      <varlistentry>
		<term><command>PASSTHRU</command></term>
		<listitem>
		  <para>
		    The auto-acceptance policy is specified
		    by a CNAME whose target is <command>rpz-passthru</command>.
		    It causes the response to not be rewritten
		    and is most often used to "poke holes" in policies for
		    CIDR blocks.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>DROP</command></term>
		<listitem>
		  <para>
		    The auto-rejection policy is specified
		    by a CNAME whose target is <command>rpz-drop</command>.
		    It causes the response to be discarded.
		    Nothing is sent to the DNS client.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>TCP-Only</command></term>
		<listitem>
		  <para>
		    The "slip" policy is specified
		    by a CNAME whose target is <command>rpz-tcp-only</command>.
		    It changes UDP responses to short, truncated DNS responses
		    that require the DNS client to try again with TCP.
		    It is used to mitigate distributed DNS reflection attacks.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>NXDOMAIN</command></term>
		<listitem>
		  <para>
		    The "domain undefined" response is encoded
		    by a CNAME whose target is the root domain (.)
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>NODATA</command></term>
		<listitem>
		  <para>
		    The empty set of resource records is specified by a
		    CNAME whose target is the wildcard top-level
		    domain (<literal>*.</literal>).
		    It rewrites the response to NODATA or ANCOUNT=0.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>Local Data</command></term>
		<listitem>
		  <para>
		    A set of ordinary DNS records can be used to answer queries.
		    Queries for record types not the set are answered with
		    NODATA.
		  </para>

		  <para>
		    A special form of local data is a CNAME whose target is a
		    wildcard such as *.example.com.
		    It is used as if an ordinary CNAME after the asterisk (*)
		    has been replaced with the query name.
		    This special form is useful for query logging in the
		    walled garden's authoritative DNS server.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </para>

	  <para>
	    All of the actions specified in all of the individual records
	    in a policy zone
	    can be overridden with a <command>policy</command> clause in the
	    <command>response-policy</command> option.
	    An organization using a policy zone provided by another
	    organization might use this mechanism to redirect domains
	    to its own walled garden.
	    <variablelist>
	      <varlistentry>
		<term><command>GIVEN</command></term>
		<listitem>
		  <para>The placeholder policy says "do not override but
		    perform the action specified in the zone."
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>DISABLED</command></term>
		<listitem>
		  <para>
		    The testing override policy causes policy zone records to do
		    nothing but log what they would have done if the
		    policy zone were not disabled.
		    The response to the DNS query is written (or not)
		    according to any triggered policy records that are not
		    disabled.
		    Disabled policy zones should appear first,
		    because they are often not logged
		    if a higher-precedence trigger is found first.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>PASSTHRU</command></term>,
		<term><command>DROP</command></term>,
		<term><command>TCP-Only</command></term>,
		<term><command>NXDOMAIN</command></term>,
		and
		<term><command>NODATA</command></term>
		<listitem>
		  <para>
		    each override the corresponding per-record policy.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		  <term><command>CNAME domain</command></term>
		  <listitem>
		    <para>
		      causes all RPZ policy records to act as if they were
		      "cname domain" records.
		    </para>
		  </listitem>
		</varlistentry>
	    </variablelist>
	  </para>

	  <para>
	    By default, the actions encoded in a response policy zone
	    are applied only to queries that ask for recursion (RD=1).
	    That default can be changed for a single policy zone, or for
	    all response policy zones in a view,
	    with a <command>recursive-only no</command> clause.
	    This feature is useful for serving the same zone files
	    both inside and outside an RFC 1918 cloud and using RPZ to
	    delete answers that would otherwise contain RFC 1918 values
	    on the externally visible name server or view.
	  </para>

	  <para>
	    Also by default, RPZ actions are applied only to DNS requests
	    that either do not request DNSSEC metadata (DO=0) or when no
	    DNSSEC records are available for the requested name in the original
	    zone (not the response policy zone).  This default can be
	    changed for all response policy zones in a view with a
	    <command>break-dnssec yes</command> clause.  In that case, RPZ
	    actions are applied regardless of DNSSEC.  The name of the
	    clause option reflects the fact that results rewritten by RPZ
	    actions cannot verify.
	  </para>

	  <para>
	    No DNS records are needed for a QNAME or Client-IP trigger;
	    the name or IP address itself is sufficient,
	    so in principle the query name need not be recursively resolved.
	    However, not resolving the requested
	    name can leak the fact that response policy rewriting is in use,
	    and that the name is listed in a policy zone, to operators of
	    servers for listed names.  To prevent that information leak, by
	    default any recursion needed for a request is done before any
	    policy triggers are considered.  Because listed domains often
	    have slow authoritative servers, this behavior can cost
	    significant time.
	    The <command>qname-wait-recurse no</command> option
	    overrides that default behavior when recursion cannot
	    change a non-error response.
	    The option does not affect QNAME or client-IP triggers
	    in policy zones listed
	    after other zones containing IP, NSIP, and NSDNAME triggers, because
	    those may depend on the A, AAAA, and NS records that would be
	    found during recursive resolution.  It also does not affect
	    DNSSEC requests (DO=1) unless <command>break-dnssec yes</command>
	    is in use, because the response would depend on whether
	    RRSIG records were found during resolution.
	    Using this option can cause error responses such as SERVFAIL to
	    appear to be rewritten, since no recursion is being done to
	    discover problems at the authoritative server.
	  </para>

	  <para>
	    The TTL of a record modified by RPZ policies is set from the
	    TTL of the relevant record in the policy zone.  It is then limited
	    to a maximum value.
	    The <command>max-policy-ttl</command> clause changes the
	    maximum number of seconds from its default of 5.
	  </para>

	  <para>
	    For example, an administrator might use this option statement:
	  </para>
<programlisting>    response-policy { zone "badlist"; };</programlisting>
	  <para>
	    and this zone statement:
	  </para>
<programlisting>    zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</programlisting>
	  <para>
	    with this zone file:
	  </para>
<programlisting>$TTL 1H
@                       SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
			NS  LOCALHOST.

; QNAME policy records.  There are no periods (.) after the owner names.
nxdomain.domain.com     CNAME   .               ; NXDOMAIN policy
*.nxdomain.domain.com   CNAME   .               ; NXDOMAIN policy
nodata.domain.com       CNAME   *.              ; NODATA policy
*.nodata.domain.com     CNAME   *.              ; NODATA policy
bad.domain.com          A       10.0.0.1        ; redirect to a walled garden
			AAAA    2001:2::1
bzone.domain.com        CNAME   garden.example.com.

; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com           CNAME   rpz-passthru.

; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com      CNAME   *.garden.example.com.


; IP policy records that rewrite all responses containing A records in 127/8
;       except 127.0.0.1
8.0.0.0.127.rpz-ip      CNAME   .
32.1.0.0.127.rpz-ip     CNAME   rpz-passthru.

; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname   CNAME   .
48.zz.2.2001.rpz-nsip       CNAME   .

; auto-reject and auto-accept some DNS clients
112.zz.2001.rpz-client-ip    CNAME   rpz-drop.
8.0.0.0.127.rpz-client-ip    CNAME   rpz-drop.

; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip   CNAME   rpz-tcp-only.
example.com                 CNAME   rpz-tcp-only.
*.example.com               CNAME   rpz-tcp-only.

</programlisting>
	  <para>
	    RPZ can affect server performance.
	    Each configured response policy zone requires the server to
	    perform one to four additional database lookups before a
	    query can be answered.
	    For example, a DNS server with four policy zones, each with all
	    four kinds of response triggers (QNAME, IP, NSIP, and
	    NSDNAME), requires a total of 17 times as many database
	    lookups as a similar DNS server with no response policy zones.
	    A <acronym>BIND</acronym> 9 server with adequate memory and one
	    response policy zone with QNAME and IP triggers might achieve a
	    maximum queries-per-second (QPS) rate about 20% lower.
	    A server with four response policy zones with QNAME and IP
	    triggers might have a maximum QPS rate about 50% lower.
	  </para>

	  <para>
	    Responses rewritten by RPZ are counted in the
	    <command>RPZRewrites</command> statistics.
	  </para>

	  <para>
	    The <command>log</command> clause can be used to optionally
	    turn off rewrite logging for a particular response policy
	    zone. By default, all rewrites are logged.
	  </para>
	</section>

	<section xml:id="rrl"><info><title>Response Rate Limiting</title></info>

	  <para>
	    Excessive, almost identical UDP <emphasis>responses</emphasis>
	    can be controlled by configuring a
	    <command>rate-limit</command> clause in an
	    <command>options</command> or <command>view</command> statement.
	    This mechanism keeps authoritative BIND 9 from being used
	    to amplify reflection denial of service (DoS) attacks.
	    Short, truncated (TC=1) responses can be sent to provide
	    rate-limited responses to legitimate clients within
	    a range of forged, attacked IP addresses.
	    Legitimate clients react to dropped or truncated responses
	    by retrying with UDP or with TCP, respectively.
	  </para>

	  <para>
	    This mechanism is intended for authoritative DNS servers.
	    It can be used on recursive servers, but can slow
	    applications such as SMTP servers (mail receivers) and
	    HTTP clients (web browsers) that repeatedly request the
	    same domains.
	    When possible, closing "open" recursive servers is better.
	  </para>

	  <para>
	    Response rate limiting uses a "credit" or "token bucket" scheme.
	    Each combination of identical response and client
	    has a conceptual "account" that earns a specified number
	    of credits every second.
	    A prospective response debits its account by one.
	    Responses are dropped or truncated
	    while the account is negative.
	    Responses are tracked within a rolling window of time
	    which defaults to 15 seconds, but which can be configured with
	    the <command>window</command> option to any value from
	    1 to 3600 seconds (1 hour).
	    The account cannot become more positive than
	    the per-second limit
	    or more negative than <command>window</command>
	    times the per-second limit.
	    When the specified number of credits for a class of
	    responses is set to 0, those responses are not rate-limited.
	  </para>

	  <para>
	    The notions of "identical response" and "DNS client"
	    for rate limiting are not simplistic.
	    All responses to an address block are counted as if to a
	    single client.
	    The prefix lengths of address blocks are
	    specified with <command>ipv4-prefix-length</command> (default 24)
	    and <command>ipv6-prefix-length</command> (default 56).
	  </para>

	  <para>
	    All non-empty responses for a valid domain name (qname)
	    and record type (qtype) are identical and have a limit specified
	    with <command>responses-per-second</command>
	    (default 0 or no limit).
	    All empty (NODATA) responses for a valid domain,
	    regardless of query type, are identical.
	    Responses in the NODATA class are limited by
	    <command>nodata-per-second</command>
	    (default <command>responses-per-second</command>).
	    Requests for any and all undefined subdomains of a given
	    valid domain result in NXDOMAIN errors, and are identical
	    regardless of query type.
	    They are limited by <command>nxdomains-per-second</command>
	    (default <command>responses-per-second</command>).
	    This controls some attacks using random names, but
	    can be relaxed or turned off (set to 0)
	    on servers that expect many legitimate
	    NXDOMAIN responses, such as from anti-spam rejection lists.
	    Referrals or delegations to the server of a given
	    domain are identical and are limited by
	    <command>referrals-per-second</command>
	    (default <command>responses-per-second</command>).
	  </para>

	  <para>
	    Responses generated from local wildcards are counted and limited
	    as if they were for the parent domain name.
	    This controls flooding using random.wild.example.com.
	  </para>

	  <para>
	    All requests that result in DNS errors other
	    than NXDOMAIN, such as SERVFAIL and FORMERR, are identical
	    regardless of requested name (qname) or record type (qtype).
	    This controls attacks using invalid requests or distant,
	    broken authoritative servers.
	    By default the limit on errors is the same as the
	    <command>responses-per-second</command> value,
	    but it can be set separately with
	    <command>errors-per-second</command>.
	  </para>

	  <para>
	    Many attacks using DNS involve UDP requests with forged source
	    addresses.
	    Rate limiting prevents the use of BIND 9 to flood a network
	    with responses to requests with forged source addresses,
	    but could let a third party block responses to legitimate requests.
	    There is a mechanism that can answer some legitimate
	    requests from a client whose address is being forged in a flood.
	    Setting <command>slip</command> to 2 (its default) causes every
	    other UDP request to be answered with a small truncated (TC=1)
	    response.
	    The small size and reduced frequency, and resulting lack of
	    amplification, of "slipped" responses make them unattractive
	    for reflection DoS attacks.
	    <command>slip</command> must be between 0 and 10.
	    A value of 0 does not "slip";
	    no truncated responses are sent due to rate limiting.
	    Rather, all responses are dropped.
	    A value of 1 causes every response to slip;
	    values between 2 and 10 cause every nth response to slip.
	    Some error responses, including REFUSED and SERVFAIL,
	    cannot be replaced with truncated responses and are instead
	    leaked at the <command>slip</command> rate.
	  </para>

	  <para>
	    (Note: dropped responses from an authoritative server may
	    reduce the difficulty of a third party successfully forging
	    a response to a recursive resolver. The best security
	    against forged responses is for authoritative operators
	    to sign their zones using DNSSEC and for resolver operators
	    to validate the responses. When this is not an option,
	    operators who are more concerned with response integrity
	    than with flood mitigation may consider setting
	    <command>slip</command> to 1, causing all rate-limited
	    responses to be truncated rather than dropped.  This reduces
	    the effectiveness of rate-limiting against reflection attacks.)
	  </para>

	  <para>
	    When the approximate query-per-second rate exceeds
	    the <command>qps-scale</command> value,
	    the <command>responses-per-second</command>,
	    <command>errors-per-second</command>,
	    <command>nxdomains-per-second</command>, and
	    <command>all-per-second</command> values are reduced by the
	    ratio of the current rate to the <command>qps-scale</command> value.
	    This feature can tighten defenses during attacks.
	    For example, with
	    <command>qps-scale 250; responses-per-second 20;</command> and
	    a total query rate of 1000 queries/second for all queries from
	    all DNS clients including via TCP,
	    then the effective responses/second limit changes to
	    (250/1000)*20, or 5.
	    Responses sent via TCP are not limited
	    but are counted to compute the query-per-second rate.
	  </para>

	  <para>
	    Communities of DNS clients can be given their own parameters or no
	    rate limiting by putting
	    <command>rate-limit</command> statements in <command>view</command>
	    statements instead of in the global <command>option</command>
	    statement.
	    A <command>rate-limit</command> statement in a view replaces,
	    rather than supplements, a <command>rate-limit</command>
	    statement among the main options.
	    DNS clients within a view can be exempted from rate limits
	    with the <command>exempt-clients</command> clause.
	  </para>

	  <para>
	    UDP responses of all kinds can be limited with the
	    <command>all-per-second</command> phrase.  This rate
	    limiting is unlike the rate limiting provided by
	    <command>responses-per-second</command>,
	    <command>errors-per-second</command>, and
	    <command>nxdomains-per-second</command> on a DNS server,
	    which are often invisible to the victim of a DNS
	    reflection attack.  Unless the forged requests of the
	    attack are the same as the legitimate requests of the
	    victim, the victim's requests are not affected.  Responses
	    affected by an <command>all-per-second</command> limit
	    are always dropped; the <command>slip</command> value
	    has no effect.  An <command>all-per-second</command>
	    limit should be at least 4 times as large as the other
	    limits, because single DNS clients often send bursts
	    of legitimate requests.  For example, the receipt of a
	    single mail message can prompt requests from an SMTP
	    server for NS, PTR, A, and AAAA records as the incoming
	    SMTP/TCP/IP connection is considered.  The SMTP server
	    can need additional NS, A, AAAA, MX, TXT, and SPF records
	    as it considers the SMTP <command>Mail From</command>
	    command.  Web browsers often repeatedly resolve the
	    same names that are duplicated in HTML &lt;IMG&gt; tags
	    in a page.  <command>all-per-second</command> is similar
	    to the rate limiting offered by firewalls but is often
	    inferior.  Attacks that justify ignoring the contents
	    of DNS responses are likely to be attacks on the DNS
	    server itself.  They usually should be discarded before
	    the DNS server spends resources make TCP connections
	    or parsing DNS requests, but that rate limiting must
	    be done before the DNS server sees the requests.
	  </para>

	  <para>
	    The maximum size of the table used to track requests and
	    rate-limit responses is set with <command>max-table-size</command>.
	    Each entry in the table is between 40 and 80 bytes.
	    The table needs approximately as many entries as the number
	    of requests received per second.
	    The default is 20,000.
	    To reduce the cold start of growing the table,
	    <command>min-table-size</command> (default 500)
	    can set the minimum table size.
	    Enable <command>rate-limit</command> category logging to monitor
	    expansions of the table and inform
	    choices for the initial and maximum table size.
	  </para>

	  <para>
	    Use <command>log-only yes</command> to test rate-limiting parameters
	    without actually dropping any requests.
	  </para>

	  <para>
	    Responses dropped by rate limits are included in the
	    <command>RateDropped</command> and <command>QryDropped</command>
	    statistics.
	    Responses that truncated by rate limits are included in
	    <command>RateSlipped</command> and <command>RespTruncated</command>.
	  </para>
	</section>

	<section xml:id="nxdomain_redirect"><info><title>NXDOMAIN Redirection</title></info>
	  <para>
	    <command>named</command> supports NXDOMAIN redirection via two methods:
	    <itemizedlist>
	      <listitem>Redirect zone <xref linkend="zone_statement_grammar"/></listitem>
	      <listitem>Redirect namespace</listitem>
	    </itemizedlist>
	  </para>
	  <para>
	    With either method, when <command>named</command> gets an NXDOMAIN response
	    it examines a separate namespace to see if the NXDOMAIN
	    response should be replaced with an alternative response.
	  </para>
	  <para>
	    With a redirect zone (<command>zone "." { type redirect; };</command>), the
	    data used to replace the NXDOMAIN is held in a single
	    zone which is not part of the normal namespace.  All the
	    redirect information is contained in the zone; there are
	    no delegations.
	  </para>
	  <para>
	    With a redirect namespace (<command>option { nxdomain-redirect
	    &lt;suffix&gt; };</command>), the data used to replace the
	    NXDOMAIN is part of the normal namespace and is looked up by
	    appending the specified suffix to the original query name.
	    This roughly doubles the cache required to process NXDOMAIN
	    responses, as both the original NXDOMAIN response and
	    the replacement data (or a NXDOMAIN indicating that there
	    is no replacement) must be stored.
	  </para>
	  <para>
	    If both a redirect zone and a redirect namespace are configured,
	    the redirect zone is tried first.
	  </para>
	</section>
      </section>

      <section xml:id="server_statement_grammar"><info><title><command>server</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="server.grammar.xml"/>
	</section>

	<section xml:id="server_statement_definition_and_usage"><info><title><command>server</command> Statement Definition and
	    Usage</title></info>

	  <para>
	    The <command>server</command> statement defines
	    characteristics
	    to be associated with a remote name server.  If a prefix length is
	    specified, then a range of servers is covered.  Only the most
	    specific
	    server clause applies, regardless of the order in
	    <filename>named.conf</filename>.
	  </para>

	  <para>
	    The <command>server</command> statement can occur at
	    the top level of the
	    configuration file or inside a <command>view</command>
	    statement.
	    If a <command>view</command> statement contains
	    one or more <command>server</command> statements, only
	    those
	    apply to the view and any top-level ones are ignored.
	    If a view contains no <command>server</command>
	    statements,
	    any top-level <command>server</command> statements are
	    used as
	    defaults.
	  </para>

	  <para>
	    If a remote server is giving out bad data,
	    marking it as bogus prevents further queries to it. The
	    default
	    value of <command>bogus</command> is <command>no</command>.
	  </para>
	  <para>
	    The <command>provide-ixfr</command> clause determines
	    whether
	    the local server, acting as primary, responds with an
	    incremental
	    zone transfer when the given remote server, a secondary, requests it.
	    If set to <command>yes</command>, incremental transfer
	    is provided
	    whenever possible. If set to <command>no</command>,
	    all transfers
	    to the remote server are non-incremental. If not set, the
	    value
	    of the <command>provide-ixfr</command> option in the
	    view or
	    global options block is used as a default.
	  </para>

	  <para>
	    The <command>request-ixfr</command> clause determines
	    whether
	    the local server, acting as a secondary, requests incremental zone
	    transfers from the given remote server, a primary. If not set, the
	    value of the <command>request-ixfr</command> option in
	    the view or global options block is used as a default. It may
	    also be set in the zone block; if set there, it
	    overrides the global or view setting for that zone.
	  </para>

	  <para>
	    IXFR requests to servers that do not support IXFR
	    automatically
	    fall back to AXFR.  Therefore, there is no need to manually list
	    which servers support IXFR and which ones do not; the global
	    default
	    of <command>yes</command> should always work.
	    The purpose of the <command>provide-ixfr</command> and
	    <command>request-ixfr</command> clauses is
	    to make it possible to disable the use of IXFR even when both
	    primary
	    and secondary claim to support it: for example, if one of the servers
	    is buggy and crashes or corrupts data when IXFR is used.
	  </para>

	  <para>
	    The <command>request-expire</command> clause determines
	    whether the local server, when acting as a secondary,
	    requests the EDNS EXPIRE value.  The EDNS EXPIRE value
	    indicates the remaining time before the zone data
	    expires and needs to be refreshed.  This is used
	    when a secondary server transfers a zone from another
	    secondary server; when transferring from the primary, the
	    expiration timer is set from the EXPIRE field of the SOA
	    record instead.
	    The default is <command>yes</command>.
	  </para>

	  <para>
	    The <command>edns</command> clause determines whether
	    the local server attempts to use EDNS when communicating
	    with the remote server.  The default is <command>yes</command>.
	  </para>

	  <para>
	    The <command>edns-udp-size</command> option sets the
	    EDNS UDP size that is advertised by <command>named</command>
	    when querying the remote server.  Valid values are 512
	    to 4096 bytes; values outside this range are silently
	    adjusted to the nearest value within it.  This option
	    is useful when advertising a different value
	    to this server than the value advertised globally:
	    for example, when there is a firewall at the remote
	    site that is blocking large replies. Note: currently,
	    this sets a single UDP size for all packets sent to the
	    server; <command>named</command> does not deviate from
	    this value.  This differs from the behavior of
	    <command>edns-udp-size</command> in <command>options</command>
	    or <command>view</command> statements, where it specifies
	    a maximum value. The <command>server</command> statement
	    behavior may be brought into conformance with the
	    <command>options/view</command> behavior in future releases.
	  </para>

	  <para>
	    The <command>edns-version</command> option sets the
	    maximum EDNS VERSION that is sent to the server(s)
	    by the resolver.  The actual EDNS version sent is still
	    subject to normal EDNS version-negotiation rules (see
	    RFC 6891), the maximum EDNS version supported by the
	    server, and any other heuristics that indicate that a
	    lower version should be sent.  This option is intended
	    to be used when a remote server reacts badly to a given
	    EDNS version or higher; it should be set to the highest
	    version the remote server is known to support.  Valid
	    values are 0 to 255; higher values are silently
	    adjusted.  This option is not needed until higher
	    EDNS versions than 0 are in use.
	  </para>

	  <para>
	    The <command>max-udp-size</command> option sets the
	    maximum EDNS UDP message size <command>named</command>
	    sends.  Valid values are 512 to 4096 bytes; values
	    outside this range are silently adjusted.  This
	    option is useful when there is a firewall
	    that is blocking large replies from <command>named</command>.
	  </para>

	  <para>
	    The <command>tcp-only</command> option sets the transport
	    protocol to TCP. The default is to use the UDP transport
	    and to fallback on TCP only when a truncated response
	    is received.
	  </para>

	  <para>
	    The server supports two zone transfer methods. The first, <command>one-answer</command>,
	    uses one DNS message per resource record transferred. <command>many-answers</command> packs
	    as many resource records as possible into a single message, which is
	    more efficient. It is possible to specify which method
	    to use for a server via the <command>transfer-format</command> option;
	    If not set there, the <command>transfer-format</command>
	    specified
	    by the <command>options</command> statement is
	    used.
	  </para>

	  <para><command>transfers</command>
	    is used to limit the number of concurrent inbound zone
	    transfers from the specified server. If no
	    <command>transfers</command> clause is specified, the
	    limit is set according to the
	    <command>transfers-per-ns</command> option.
	  </para>

	  <para>
	    The <command>keys</command> clause identifies a
	    <command>key_id</command> defined by the <command>key</command> statement,
	    to be used for transaction security (TSIG, <xref linkend="tsig"/>)
	    when talking to the remote server.
	    When a request is sent to the remote server, a request signature
	    is generated using the key specified here and appended to the
	    message. A request originating from the remote server is not
	    required
	    to be signed by this key.
	  </para>

	  <para>
	    Only a single key per server is currently supported.
	  </para>

	  <para>
	    The <command>transfer-source</command> and
	    <command>transfer-source-v6</command> clauses specify
	    the IPv4 and IPv6 source
	    address, respectively, to be used for zone transfer with the remote server.
	    For an IPv4 remote server, only <command>transfer-source</command> can
	    be specified.
	    Similarly, for an IPv6 remote server, only
	    <command>transfer-source-v6</command> can be
	    specified.
	    For more details, see the description of
	    <command>transfer-source</command> and
	    <command>transfer-source-v6</command> in
	    <xref linkend="zone_transfers"/>.
	  </para>

	  <para>
	    The <command>notify-source</command> and
	    <command>notify-source-v6</command> clauses specify the
	    IPv4 and IPv6 source address, respectively, to be used for notify
	    messages sent to remote servers.  For an
	    IPv4 remote server, only <command>notify-source</command>
	    can be specified.  Similarly, for an IPv6 remote server,
	    only <command>notify-source-v6</command> can be specified.
	  </para>

	  <para>
	    The <command>query-source</command> and
	    <command>query-source-v6</command> clauses specify the
	    IPv4 and IPv6 source address, respectively, to be used for queries
	    sent to remote servers.  For an IPv4
	    remote server, only <command>query-source</command> can
	    be specified.  Similarly, for an IPv6 remote server,
	    only <command>query-source-v6</command> can be specified.
	  </para>

	  <para>
	    The <command>request-nsid</command> clause determines
	    whether the local server adds an NSID EDNS option
	    to requests sent to the server.  This overrides
	    <command>request-nsid</command> set at the view or
	    option level.
	  </para>

	  <para>
	    The <command>send-cookie</command> clause determines
	    whether the local server adds a COOKIE EDNS option
	    to requests sent to the server.  This overrides
	    <command>send-cookie</command> set at the view or
	    option level.  The <command>named</command> server may
	    determine that COOKIE is not supported by the remote server
	    and not add a COOKIE EDNS option to requests.
	  </para>
	</section>

      <section xml:id="statschannels"><info><title><command>statistics-channels</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="statistics-channels.grammar.xml"/>
      </section>

      <section xml:id="statistics_channels"><info><title><command>statistics-channels</command> Statement Definition and
	    Usage</title></info>

	<para>
	  The <command>statistics-channels</command> statement
	  declares communication channels to be used by system
	  administrators to get access to statistics information on
	  the name server.
	</para>

	<para>
	  This statement is intended to be flexible to support multiple
	  communication protocols in the future, but currently only
	  HTTP access is supported.
	  It requires that BIND 9 be compiled with libxml2 and/or
	  json-c (also known as libjson0); the
	  <command>statistics-channels</command> statement is
	  still accepted even if it is built without the library,
	  but any HTTP access fails with an error.
	</para>

	<para>
	  An <command>inet</command> control channel is a TCP socket
	  listening at the specified <command>ip_port</command> on the
	  specified <command>ip_addr</command>, which can be an IPv4 or IPv6
	  address.  An <command>ip_addr</command> of <literal>*</literal>
	  (asterisk) is
	  interpreted as the IPv4 wildcard address; connections are
	  accepted on any of the system's IPv4 addresses.
	  To listen on the IPv6 wildcard address,
	  use an <command>ip_addr</command> of <literal>::</literal>.
	</para>

	<para>
	  If no port is specified, port 80 is used for HTTP channels.
	  The asterisk (<literal>*</literal>) cannot be used for
	  <command>ip_port</command>.
	</para>

	<para>
	  Attempts to open a statistics channel are
	  restricted by the optional <command>allow</command> clause.
	  Connections to the statistics channel are permitted based on the
	  <command>address_match_list</command>.
	  If no <command>allow</command> clause is present,
	  <command>named</command> accepts connection
	  attempts from any address; since the statistics may
	  contain sensitive internal information, it is highly
	  recommended to restrict the source of connection requests
	  appropriately.
	</para>

	<para>
	  If no <command>statistics-channels</command> statement is present,
	  <command>named</command> does not open any communication channels.
	</para>

	<para>
	  The statistics are available in various formats and views,
	  depending on the URI used to access them.  For example, if
	  the statistics channel is configured to listen on 127.0.0.1
	  port 8888, then the statistics are accessible in XML format at
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/">http://127.0.0.1:8888/</link> or
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml">http://127.0.0.1:8888/xml</link>. A CSS file is
	  included, which can format the XML statistics into tables
	  when viewed with a stylesheet-capable browser, and into
	  charts and graphs using the Google Charts API when using a
	  JavaScript-capable browser.
	</para>

	<para>
	  Broken-out subsets of the statistics can be viewed at
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/status">http://127.0.0.1:8888/xml/v3/status</link>
	  (server uptime and last reconfiguration time),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/server">http://127.0.0.1:8888/xml/v3/server</link>
	  (server and resolver statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/zones">http://127.0.0.1:8888/xml/v3/zones</link>
	  (zone statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/net">http://127.0.0.1:8888/xml/v3/net</link>
	  (network status and socket statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/mem">http://127.0.0.1:8888/xml/v3/mem</link>
	  (memory manager statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/tasks">http://127.0.0.1:8888/xml/v3/tasks</link>
	  (task manager statistics), and
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/traffic">http://127.0.0.1:8888/xml/v3/traffic</link>
	  (traffic sizes).
	</para>

	<para>
	  The full set of statistics can also be read in JSON format at
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json">http://127.0.0.1:8888/json</link>,
	  with the broken-out subsets at
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/status">http://127.0.0.1:8888/json/v1/status</link>
	  (server uptime and last reconfiguration time),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/server">http://127.0.0.1:8888/json/v1/server</link>
	  (server and resolver statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/zones">http://127.0.0.1:8888/json/v1/zones</link>
	  (zone statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/net">http://127.0.0.1:8888/json/v1/net</link>
	  (network status and socket statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/mem">http://127.0.0.1:8888/json/v1/mem</link>
	  (memory manager statistics),
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/tasks">http://127.0.0.1:8888/json/v1/tasks</link>
	  (task manager statistics), and
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/traffic">http://127.0.0.1:8888/json/v1/traffic</link>
	  (traffic sizes).
	</para>
      </section>

	<section xml:id="trusted-keys"><info><title><command>trusted-keys</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="trusted-keys.grammar.xml"/>
	</section>
	<section xml:id="trusted_keys"><info><title><command>trusted-keys</command> Statement Definition
	    and Usage</title></info>

	  <para>
	    The <command>trusted-keys</command> statement defines
	    DNSSEC security roots. DNSSEC is described in <xref linkend="DNSSEC"/>. A security root is defined when the
	    public key for a non-authoritative zone is known, but
	    cannot be securely obtained through DNS, either because
	    it is the DNS root zone or because its parent zone is
	    unsigned.  Once a key has been configured as a trusted
	    key, it is treated as if it has been validated and
	    proven secure. The resolver attempts DNSSEC validation
	    on all DNS data in subdomains of a security root.
	  </para>
	  <para>
	    All keys (and corresponding zones) listed in
	    <command>trusted-keys</command> are deemed to exist regardless
	    of what parent zones say.  Similarly, for all keys listed in
	    <command>trusted-keys</command>, only those keys are
	    used to validate the DNSKEY RRset.  The parent's DS RRset
	    is not used.
	  </para>
	  <para>
	    The <command>trusted-keys</command> statement can contain
	    multiple key entries, each consisting of the key's
	    domain name, flags, protocol, and algorithm, and the Base64
	    representation of the key data.
	    Spaces, tabs, newlines, and carriage returns are ignored
	    in the key data, so the configuration may be split into
	    multiple lines.
	  </para>
	  <para>
	    <command>trusted-keys</command> may be set at the top level
	    of <filename>named.conf</filename> or within a view.  If it is
	    set in both places, they are additive; keys defined at the top
	    level are inherited by all views, but keys defined in a view
	    are only used within that view.
	  </para>
	  <para>
	    Validation below specified names can be temporarily disabled
	    by using <command>rndc nta</command>.
	  </para>
	</section>

	<section xml:id="managed_keys"><info><title><command>managed-keys</command> Statement Grammar</title></info>
	<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="managed-keys.grammar.xml"/>
	</section>
	<section xml:id="managed-keys"><info><title><command>managed-keys</command> Statement Definition
	    and Usage</title></info>

	  <para>
	    The <command>managed-keys</command> statement, like
	    <command>trusted-keys</command>, defines DNSSEC
	    security roots.  The difference is that
	    <command>managed-keys</command> can be kept up-to-date
	    automatically, without intervention from the resolver
	    operator.
	  </para>
	  <para>
	    Suppose, for example, that a zone's key-signing
	    key was compromised, and the zone owner had to revoke and
	    replace the key.  A resolver which had the old key in a
	    <command>trusted-keys</command> statement would be
	    unable to validate this zone; it would
	    reply with a SERVFAIL response code.  This would
	    continue until the resolver operator updated the
	    <command>trusted-keys</command> statement with the new key.
	  </para>
	  <para>
	    If, however, the zone were listed in a
	    <command>managed-keys</command> statement instead, the
	    zone owner could add a "stand-by" key to the zone in advance.
	    <command>named</command> would store the stand-by key, and
	    when the original key was revoked, <command>named</command>
	    would be able to transition smoothly to the new key.  It would
	    also recognize that the old key had been revoked and cease
	    using that key to validate answers, minimizing the damage that
	    the compromised key could do.
	  </para>
	  <para>
	    A <command>managed-keys</command> statement contains a list of
	    the keys to be managed, along with information about how the
	    keys are to be initialized for the first time.  The only
	    initialization method currently supported is
	    <literal>initial-key</literal>.
	    This means the <command>managed-keys</command> statement must
	    contain a copy of the initializing key.  (Future releases may
	    allow keys to be initialized by other methods, eliminating this
	    requirement.)
	  </para>
	  <para>
	    Consequently, a <command>managed-keys</command> statement
	    appears similar to a <command>trusted-keys</command> statement, differing
	    by the presence of the second field, which contains the keyword
	    <literal>initial-key</literal>.  The difference is, whereas the
	    keys listed in a <command>trusted-keys</command> continue to be
	    trusted until they are removed from
	    <filename>named.conf</filename>, an initializing key listed
	    in a <command>managed-keys</command> statement is only trusted
	    <emphasis>once</emphasis>: for as long as it takes to load the
	    managed-key database and start the RFC 5011 key-maintenance
	    process.
	  </para>
	  <para>
	    The first time <command>named</command> runs with a managed key
	    configured in <filename>named.conf</filename>, it fetches the
	    DNSKEY RRset directly from the zone apex, and validates it
	    using the key specified in the <command>managed-keys</command>
	    statement.  If the DNSKEY RRset is validly signed, then it is
	    used as the basis for a new managed-keys database.
	  </para>
	  <para>
	    From that point on, whenever <command>named</command> runs, it
	    sees the <command>managed-keys</command> statement, checks to
	    make sure RFC 5011 key maintenance has already been initialized
	    for the specified domain, and if so, simply moves on.  The
	    key specified in the <command>managed-keys</command>
	    statement is not used to validate answers; it is
	    superseded by the key or keys stored in the managed-keys database.
	  </para>
	  <para>
	    The next time <command>named</command> runs after a name
	    has been <emphasis>removed</emphasis> from the
	    <command>managed-keys</command> statement, the corresponding
	    zone is removed from the managed-keys database,
	    and RFC 5011 key maintenance is no longer used for that
	    domain.
	  </para>
	  <para>
	    In the current implementation, the managed-keys database
	    is stored as a master-format zone file.
	  </para>
	  <para>
	    On servers which do not use views, this file is named
	    <filename>managed-keys.bind</filename>.  When views are in
	    use, there is a separate managed-keys database for each
	    view; the filename is the view name (or, if a view name
	    contains characters which would make it illegal as a filename,
	    a hash of the view name), followed by
	    the suffix <filename>.mkeys</filename>.
	  </para>
	  <para>
	    When the key database is changed, the zone is updated.
	    As with any other dynamic zone, changes are written
	    into a journal file, e.g.,
	    <filename>managed-keys.bind.jnl</filename> or
	    <filename>internal.mkeys.jnl</filename>.
	    Changes are committed to the zone file as soon as
	    possible afterward, usually within 30
	    seconds.  Whenever <command>named</command> is using
	    automatic key maintenance, the zone file and journal file
	    can be expected to exist in the working directory.
	    (For this reason, among others, the working directory
	    should be always be writable by <command>named</command>.)
	  </para>
	  <para>
	    If the <command>dnssec-validation</command> option is
	    set to <userinput>auto</userinput>, <command>named</command>
	    automatically initializes a managed key for the
	    root zone.  The key that is used to initialize the
		key-maintenance process is stored in <filename>bind.keys</filename>;
	    the location of this file can be overridden with the
	    <command>bindkeys-file</command> option. As a fallback
	    in the event no <filename>bind.keys</filename> can be
	    found, the initializing key is also compiled directly
	    into <command>named</command>.
	  </para>
	</section>

	<section xml:id="view_statement_grammar"><info><title><command>view</command> Statement Grammar</title></info>

<programlisting><command>view</command> <replaceable>view_name</replaceable> [ <replaceable>class</replaceable> ] <command>{</command>
    <command>match-clients {</command> <replaceable>address_match_list</replaceable> <command>}</command> ;
    <command>match-destinations {</command> <replaceable>address_match_list</replaceable> <command>}</command> ;
    <command>match-recursive-only</command> <replaceable>yes_or_no</replaceable> ;
  [ <replaceable>view_option</replaceable> ; ... ]
  [ <replaceable>zone_statement</replaceable> ; ... ]
<command>} </command>;
</programlisting>

	</section>
	<section xml:id="view_statement"><info><title><command>view</command> Statement Definition and Usage</title></info>

	  <para>
	    The <command>view</command> statement is a powerful
	    feature
	    of <acronym>BIND</acronym> 9 that lets a name server
	    answer a DNS query differently
	    depending on who is asking. It is particularly useful for
	    implementing
	    split DNS setups without having to run multiple servers.
	  </para>

	  <para>
	    Each <command>view</command> statement defines a view
	    of the
	    DNS namespace that is seen by a subset of clients.  A client
	    matches
	    a view if its source IP address matches the
	    <varname>address_match_list</varname> of the view's
	    <command>match-clients</command> clause and its
	    destination IP address matches
	    the <varname>address_match_list</varname> of the
	    view's
	    <command>match-destinations</command> clause.  If not
	    specified, both
	    <command>match-clients</command> and <command>match-destinations</command>
	    default to matching all addresses.  In addition to checking IP
	    addresses,
	    <command>match-clients</command> and <command>match-destinations</command>
	    can also take <command>keys</command> which provide an
	    mechanism for the
	    client to select the view.  A view can also be specified
	    as <command>match-recursive-only</command>, which
	    means that only recursive
	    requests from matching clients match that view.
	    The order of the <command>view</command> statements is
	    significant;
	    a client request is resolved in the context of the first
	    <command>view</command> that it matches.
	  </para>

	  <para>
	    Zones defined within a <command>view</command>
	    statement are
	    only accessible to clients that match the <command>view</command>.
	    By defining a zone of the same name in multiple views, different
	    zone data can be given to different clients: for example,
	    "internal"
	    and "external" clients in a split DNS setup.
	  </para>

	  <para>
	    Many of the options given in the <command>options</command> statement
	    can also be used within a <command>view</command>
	    statement, and then
	    apply only when resolving queries with that view.  When no
	    view-specific
	    value is given, the value in the <command>options</command> statement
	    is used as a default.  Also, zone options can have default values
	    specified
	    in the <command>view</command> statement; these
	    view-specific defaults
	    take precedence over those in the <command>options</command> statement.
	  </para>

	  <para>
	    Views are class-specific.  If no class is given, class IN
	    is assumed.  Note that all non-IN views must contain a hint zone,
	    since only the IN class has compiled-in default hints.
	  </para>

	  <para>
	    If there are no <command>view</command> statements in
	    the config
	    file, a default view that matches any client is automatically
	    created
	    in class IN. Any <command>zone</command> statements
	    specified on
	    the top level of the configuration file are considered to be part
	    of
	    this default view, and the <command>options</command>
	    statement
	    applies to the default view. If any explicit <command>view</command>
	    statements are present, all <command>zone</command>
	    statements must
	    occur inside <command>view</command> statements.
	  </para>

	  <para>
	    Here is an example of a typical split DNS setup implemented
	    using <command>view</command> statements:
	  </para>

<programlisting>view "internal" {
      // This should match our internal networks.
      match-clients { 10.0.0.0/8; };

      // Provide recursive service to internal
      // clients only.
      recursion yes;

      // Provide a complete view of the example.com
      // zone including addresses of internal hosts.
      zone "example.com" {
	    type master;
	    file "example-internal.db";
      };
};

view "external" {
      // Match all clients not matched by the
      // previous view.
      match-clients { any; };

      // Refuse recursive service to external clients.
      recursion no;

      // Provide a restricted view of the example.com
      // zone containing only publicly accessible hosts.
      zone "example.com" {
	   type master;
	   file "example-external.db";
      };
};
</programlisting>

	</section>
	<section xml:id="zone_statement_grammar"><info><title><command>zone</command>
	    Statement Grammar</title></info>

<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="master.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="slave.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="hint.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="stub.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="static-stub.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="forward.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="redirect.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="delegation-only.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="in-view.zoneopt.xml"/>

	</section>
	<section xml:id="zone_statement"><info><title><command>zone</command> Statement Definition and Usage</title></info>

	  <section xml:id="zone_types"><info><title>Zone Types</title></info>
	    <para>
	      The <command>type</command> keyword is required
	      for the <command>zone</command> configuration unless
	      it is an <command>in-view</command> configuration. Its
	      acceptable values are: <varname>master</varname>,
	      <varname>slave</varname>, <varname>hint</varname>,
	      <varname>stub</varname>, <varname>static-stub</varname>,
	      <varname>forward</varname>, <varname>redirect</varname>,
	      or <varname>delegation-only</varname>.
	    </para>
	    <note>
	      Later versions of BIND added <command>type primary</command>
	      and <command>type secondary</command> as synonyms for
	      <command>type master</command> and <command>type slave</command>,
	      as those terms are in more common use now. BIND 9.11's
	      configuration syntax predates this change.
	    </note>

	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
		<!--colspec colname="1" colnum="1" colsep="0" colwidth="1.108in"/-->
		<!--colspec colname="2" colnum="2" colsep="0" colwidth="4.017in"/-->
		<colspec colname="1" colnum="1" colsep="0" colwidth="*"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="4*"/>
		<tbody valign="top">
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>master</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The server has a master copy of the data
			for the zone and is able to provide authoritative
			answers for it.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>slave</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			A secondary zone, replicating a primary zone
			provided by another authoritative server.
			The <command>masters</command> list
			specifies one or more IP addresses
			of primary servers that the secondary contacts to update
			its copy of the zone.
			Masters list elements can also be names of other
			masters lists.
			By default, transfers are made from port 53 on the
			servers; this can
			be changed for all servers by specifying a port number
			before the
			list of IP addresses, or on a per-server basis after
			the IP address.
			Authentication to the primary can also be done with
			per-server TSIG keys.
			If a file is specified, then the
			replica is written to this file whenever the zone
			is changed,
			and reloaded from this file on a server restart. Use
			of a file is
			recommended, since it often speeds server startup and
			eliminates
			a needless waste of bandwidth. Note that for large
			numbers (in the
			tens or hundreds of thousands) of zones per server, it
			is best to
			use a two-level naming scheme for zone filenames. For
			example,
			a secondary server for the zone <literal>example.com</literal> might place
			the zone contents into a file called
			<filename>ex/example.com</filename> where <filename>ex/</filename> is
			just the first two letters of the zone name. (Most
			operating systems
			behave very slowly if there are 100000 files in
			a single directory.)
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>hint</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The initial set of root name servers is
			specified using a hint zone. When the server starts,
			it uses
			the root hints to find a root name server and get the
			most recent
			list of root name servers. If no hint zone is
			specified for class
			IN, the server uses a compiled-in default set of root
			servers hints.
			Classes other than IN have no built-in default hints.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>stub</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			A stub zone is similar to a secondary zone,
			except that it replicates only the NS records of a
			primary zone instead
			of the entire zone. Stub zones are not a standard part
			of the DNS;
			they are a feature specific to the <acronym>BIND</acronym> implementation.
		      </para>

		      <para>
			Stub zones can be used to eliminate the need for a glue
			NS record
			in a parent zone, at the expense of maintaining a stub
			zone entry and
			a set of name server addresses in <filename>named.conf</filename>.
			This usage is not recommended for new configurations,
			and BIND 9
			supports it only in a limited way.
			If a <acronym>BIND</acronym> 9 primary, serving a parent
			zone, has child stub zones configured, all the secondary
			servers for the
			parent zone also need to have the same child stub
			zones
			configured.
		      </para>

		      <para>
			Stub zones can also be used as a way to force the
			resolution
			of a given domain to use a particular set of
			authoritative servers.
			For example, the caching name servers on a private
			network using
			RFC 1918 addressing may be configured with stub zones
			for
			<literal>10.in-addr.arpa</literal>
			to use a set of internal name servers as the
			authoritative
			servers for that domain.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>static-stub</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			A static-stub zone is similar to a stub zone
			with the following exceptions:
			the zone data is statically configured, rather
			than transferred from a primary server; and
			when recursion is necessary for a query that
			matches a static-stub zone, the locally
			configured data (name server names and glue addresses)
			is always used, even if different authoritative
			information is cached.
		      </para>
		      <para>
			Zone data is configured via the
			<command>server-addresses</command> and
			<command>server-names</command> zone options.
		      </para>
		      <para>
			The zone data is maintained in the form of NS
			and (if necessary) glue A or AAAA RRs
			internally, which can be seen by dumping zone
			databases by <command>rndc dumpdb -all</command>.
			The configured RRs are considered local configuration
			parameters rather than public data.
			Non-recursive queries (i.e., those with the RD
			bit off) to a static-stub zone are therefore
			prohibited and are responded to with REFUSED.
		      </para>
		      <para>
			Since the data is statically configured, no
			zone maintenance action takes place for a static-stub
			zone.
			For example, there is no periodic refresh
			attempt, and an incoming notify message
			will be rejected with an rcode of NOTAUTH.
		      </para>
		      <para>
			Each static-stub zone is configured with
			internally generated NS and (if necessary)
			glue A or AAAA RRs.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>forward</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			A forward zone is a way to configure
			forwarding on a per-domain basis.  A <command>zone</command> statement
			of type <command>forward</command> can
			contain a <command>forward</command>
			and/or <command>forwarders</command>
			statement,
			which applies to queries within the domain given by
			the zone
			name. If no <command>forwarders</command>
			statement is present, or
			an empty list for <command>forwarders</command> is given, then no
			forwarding is done for the domain, canceling the
			effects of
			any forwarders in the <command>options</command> statement. Thus,
			to use this type of zone to change the
			behavior of the
			global <command>forward</command> option
			(that is, "forward first"
			to, then "forward only", or vice versa), but
			use the same
			servers as set globally, re-specify the
			global forwarders.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>redirect</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			Redirect zones are used to provide answers to
			queries when normal resolution would result in
			NXDOMAIN being returned.
			Only one redirect zone is supported
			per view.  <command>allow-query</command> can be
			used to restrict which clients see these answers.
		      </para>
		      <para>
			If the client has requested DNSSEC records (DO=1) and
			the NXDOMAIN response is signed, no substitution
			occurs.
		      </para>
		      <para>
			To redirect all NXDOMAIN responses to
			100.100.100.2 and
			2001:ffff:ffff::100.100.100.2,
			configure a type <varname>redirect</varname> zone named ".",
			with the zone file containing wildcard records
			that point to the desired addresses:
			<literal>*. IN A 100.100.100.2</literal>
			and
			<literal>*. IN AAAA 2001:ffff:ffff::100.100.100.2</literal>.
		      </para>
		      <para>
			As another example, to redirect all Spanish names (under .ES),
			use similar entries but with the names
			"*.ES." instead of "*.".  To redirect all
			commercial Spanish names (under COM.ES),
			use wildcard entries called "*.COM.ES.".
		      </para>
		      <para>
			Note that the redirect zone supports all
			possible types; it is not limited to A and
			AAAA records.
		      </para>
		      <para>
			Because redirect zones are not referenced
			directly by name, they are not kept in the
			zone lookup table with normal primary and secondary
			zones. Consequently, it is not currently possible
			to use
			<command>rndc reload
				<replaceable>zonename</replaceable></command>
			to reload a redirect zone.  However, when using
			<command>rndc reload</command> without specifying
			a zone name, redirect zones are reloaded along
			with other zones.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>delegation-only</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			This zone type is used to enforce the delegation-only
			status of infrastructure zones (e.g., COM,
			NET, ORG).  Any answer that is received
			without an explicit or implicit delegation
			in the authority section is treated
			as NXDOMAIN.  This does not apply to the
			zone apex, and should not be applied to
			leaf zones.
		      </para>
		      <para>
			<varname>delegation-only</varname> has no
			effect on answers received from forwarders.
		      </para>
		      <para>
			See caveats in <xref linkend="root_delegation_only"/>.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>in-view</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
                        When using multiple views, a primary or secondary zone
			configured in one view can be referenced in a
			subsequent view. This allows both views to serve the
			same zone without the overhead of loading it more
			than once. This is configured using a
			<varname>zone</varname> statement, with an
			<varname>in-view</varname> option specifying the
			view in which the zone is defined.
			A <varname>zone</varname> statement containing
			<varname>in-view</varname> does not need to specify
			a type, since that is part of the zone definition
			in the other view.
		      </para>
		      <para>
			See <xref linkend="multiple_views"/> for more information.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </section>

	  <section xml:id="class"><info><title>Class</title></info>

	    <para>
	      The zone's name may optionally be followed by a class. If
	      a class is not specified, class <literal>IN</literal> (for <varname>Internet</varname>),
	      is assumed. This is correct for the vast majority of cases.
	    </para>
	    <para>
	      The <literal>hesiod</literal> class is
	      named for an information service from MIT's Project Athena. It was
	      used to share information about various systems databases, such
	      as users, groups, printers, and so on. The keyword
	      <literal>HS</literal> is
	      a synonym for hesiod.
	    </para>
	    <para>
	      Another MIT development is Chaosnet, a LAN protocol created
	      in the mid-1970s. Zone data for it can be specified with the <literal>CHAOS</literal> class.
	    </para>
	  </section>

	  <section xml:id="zone_options"><info><title>Zone Options</title></info>

	    <variablelist>

	      <varlistentry>
		<term><command>allow-notify</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>allow-notify</command> in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>allow-query</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>allow-query</command> in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>allow-query-on</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>allow-query-on</command> in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>allow-transfer</command></term>
		<listitem>
		  <para>
		    See the description of <command>allow-transfer</command>
		    in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>allow-update</command></term>
		<listitem>
		  <para>
		    See the description of <command>allow-update</command>
		    in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>update-policy</command></term>
		<listitem>
		  <para>
		    This specifies a "Simple Secure Update" policy. See
		    <xref linkend="dynamic_update_policies"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>allow-update-forwarding</command></term>
		<listitem>
		  <para>
		    See the description of <command>allow-update-forwarding</command>
		    in <xref linkend="access_control"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>also-notify</command></term>
		<listitem>
		  <para>
		    This option is only meaningful if <command>notify</command>
		    is
		    active for this zone. The set of machines that
		    receive a
		    <literal>DNS NOTIFY</literal> message
		    for this zone is made up of all the listed name servers
		    (other than
		    the primary) for the zone, plus any IP addresses
		    specified
		    with <command>also-notify</command>. A port
		    may be specified
		    with each <command>also-notify</command>
		    address to send the notify
		    messages to a port other than the default of 53.
		    A TSIG key may also be specified to cause the
		    <literal>NOTIFY</literal> to be signed by the
		    given key.
		    <command>also-notify</command> is not
		    meaningful for stub zones.
		    The default is the empty list.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-names</command></term>
		<listitem>
		  <para>
		    This option is used to restrict the character set and
		    syntax of
		    certain domain names in zone files and/or DNS responses
		    received from the
		    network.  The default varies according to zone type.
		    For primary zones the default is <command>fail</command>;
		    for secondary zones the default is <command>warn</command>.
		    It is not implemented for <command>hint</command> zones.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-mx</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>check-mx</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-spf</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>check-spf</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-wildcard</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>check-wildcard</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-integrity</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>check-integrity</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>check-sibling</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>check-sibling</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>zero-no-soa-ttl</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>zero-no-soa-ttl</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>update-check-ksk</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>update-check-ksk</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>dnssec-loadkeys-interval</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>dnssec-loadkeys-interval</command> in <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>dnssec-update-mode</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>dnssec-update-mode</command> in <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>dnssec-dnskey-kskonly</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>dnssec-dnskey-kskonly</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>try-tcp-refresh</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>try-tcp-refresh</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>database</command></term>
		<listitem>
		  <para>
		    This specifies the type of database to be used to store the
		    zone data.  The string following the <command>database</command> keyword
		    is interpreted as a list of whitespace-delimited words.
		    The first word
		    identifies the database type, and any subsequent words are
		    passed
		    as arguments to the database to be interpreted in a way
		    specific
		    to the database type.
		  </para>
		  <para>
		    The default is <userinput>"rbt"</userinput>, BIND 9's
		    native in-memory
		    red-black tree database.  This database does not take
		    arguments.
		  </para>
		  <para>
		    Other values are possible if additional database drivers
		    have been linked into the server.  Some sample drivers are
		    included
		    with the distribution but none are linked in by default.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>dialup</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>dialup</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>delegation-only</command></term>
		<listitem>
		  <para>
		    This flag only applies to forward, hint, and stub
		    zones.  If set to <userinput>yes</userinput>,
		    then the zone is treated as if it is
		    also a delegation-only type zone.
		  </para>
		  <para>
		    See caveats in <xref linkend="root_delegation_only"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>file</command></term>
		<listitem>
		  <para>
		    This sets the zone's filename. In <command>master</command>,
		    <command>hint</command>, and <command>redirect</command>
		    zones which do not have <command>masters</command>
		    defined, zone data is loaded from this file. In
		    <command>slave</command>, <command>stub</command>, and
		    <command>redirect</command> zones which do have
		    <command>masters</command> defined, zone data is
		    retrieved from another server and saved in this file.
		    This option is not applicable to other zone types.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>forward</command></term>
		<listitem>
		  <para>
		    This option is only meaningful if the zone has a forwarders
		    list. The <command>only</command> value causes
		    the lookup to fail
		    after trying the forwarders and getting no answer, while <command>first</command>
		    allows a normal lookup to be tried.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>forwarders</command></term>
		<listitem>
		  <para>
		    This is used to override the list of global forwarders.
		    If it is not specified in a zone of type <command>forward</command>,
		    no forwarding is done for the zone and the global options are
		    not used.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>ixfr-base</command></term>
		<listitem>
		  <para>
		    This was used in <acronym>BIND</acronym> 8 to
		    specify the name
		    of the transaction log (journal) file for dynamic update
		    and IXFR.
		    <acronym>BIND</acronym> 9 ignores the option
		    and constructs the name of the journal
		    file by appending "<filename>.jnl</filename>"
		    to the name of the
		    zone file.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>ixfr-tmp-file</command></term>
		<listitem>
		  <para>
		    This was an undocumented option in <acronym>BIND</acronym> 8.
		    It is ignored in <acronym>BIND</acronym> 9.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>journal</command></term>
		<listitem>
		  <para>
		    This allows the default journal's filename to be overridden.
		    The default is the zone's filename with "<filename>.jnl</filename>" appended.
		    This is applicable to primary (<command>master</command>)
		    and secondary (<command>slave</command>) zones.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-journal-size</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-journal-size</command> in <xref linkend="server_resource_limits"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-records</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-records</command> in <xref linkend="server_resource_limits"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-transfer-time-in</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-transfer-time-in</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-transfer-idle-in</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-transfer-idle-in</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-transfer-time-out</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-transfer-time-out</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-transfer-idle-out</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>max-transfer-idle-out</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>notify</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>notify</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>notify-delay</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>notify-delay</command> in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>notify-to-soa</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>notify-to-soa</command> in
		    <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>pubkey</command></term>
		<listitem>
		  <para>
		    In <acronym>BIND</acronym> 8, this option was
		    intended to specify
		    a public zone key for verification of signatures in DNSSEC-signed
		    zones when they were loaded from disk. <acronym>BIND</acronym> 9 does not verify signatures
		    on load and ignores the option.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>zone-statistics</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>zone-statistics</command> in
		    <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>server-addresses</command></term>
		<listitem>
		  <para>
		    This option is only meaningful for static-stub zones.
		    This is a list of IP addresses to which queries
		    should be sent in recursive resolution for the
		    zone.
		    A non-empty list for this option internally
		    configures the apex NS RR with associated glue A or
		    AAAA RRs.
		  </para>
		  <para>
		    For example, if "example.com" is configured as a
		    static-stub zone with 192.0.2.1 and 2001:db8::1234
		    in a <command>server-addresses</command> option,
		    the following RRs are internally configured:
		  </para>
<programlisting>example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</programlisting>
		  <para>
		    These records are used internally to resolve
		    names under the static-stub zone.
		    For instance, if the server receives a query for
		    "www.example.com" with the RD bit on, the server
		    initiates recursive resolution and sends
		    queries to 192.0.2.1 and/or 2001:db8::1234.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>server-names</command></term>
		<listitem>
		  <para>
		    This option is only meaningful for static-stub zones.
		    This is a list of domain names of name servers that
		    act as authoritative servers of the static-stub
		    zone.
		    These names are resolved to IP addresses when
		    <command>named</command> needs to send queries to
		    these servers.
		    For this supplemental resolution to be successful,
		    these names must not be a subdomain of the origin
		    name of the static-stub zone.
		    That is, when "example.net" is the origin of a
		    static-stub zone, "ns.example" and
		    "master.example.com" can be specified in the
		    <command>server-names</command> option, but
		    "ns.example.net" cannot; it is rejected by
		    the configuration parser.
		  </para>
		  <para>
		    A non-empty list for this option internally
		    configures the apex NS RR with the specified names.
		    For example, if "example.com" is configured as a
		    static-stub zone with "ns1.example.net" and
		    "ns2.example.net"
		    in a <command>server-names</command> option,
		    the following RRs are internally configured:
		  </para>

<programlisting>example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</programlisting>

		  <para>
		    These records are used internally to resolve
		    names under the static-stub zone.
		    For instance, if the server receives a query for
		    "www.example.com" with the RD bit on, the server
		    initiates recursive resolution,
		    resolves "ns1.example.net" and/or
		    "ns2.example.net" to IP addresses, and then sends
		    queries to one or more of these addresses.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>sig-validity-interval</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>sig-validity-interval</command> in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>sig-signing-nodes</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>sig-signing-nodes</command> in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>sig-signing-signatures</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>sig-signing-signatures</command> in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>sig-signing-type</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>sig-signing-type</command> in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>transfer-source</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>transfer-source</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>transfer-source-v6</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>alt-transfer-source</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>alt-transfer-source-v6</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>alt-transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>use-alt-transfer-source</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>use-alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>


	      <varlistentry>
		<term><command>notify-source</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>notify-source</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>notify-source-v6</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>notify-source-v6</command> in <xref linkend="zone_transfers"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>min-refresh-time</command></term>
		<term><command>max-refresh-time</command></term>
		<term><command>min-retry-time</command></term>
		<term><command>max-retry-time</command></term>
		<listitem>
		  <para>
		    See the descriptions in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>ixfr-from-differences</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>ixfr-from-differences</command> in <xref linkend="boolean_options"/>.
		    (Note that the <command>ixfr-from-differences</command>
		    choices of <userinput>master</userinput> and
		    <userinput>slave</userinput> are not
		    available at the zone level.)
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>key-directory</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>key-directory</command> in <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>auto-dnssec</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>auto-dnssec</command> in
		    <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>serial-update-method</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>serial-update-method</command> in
		    <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>inline-signing</command></term>
		<listitem>
		  <para>
		    If <literal>yes</literal>, this enables
		    "bump in the wire" signing of a zone, where an
		    unsigned zone is transferred in or loaded from
		    disk and a signed version of the zone is served,
		    with, possibly, a different serial number.  This
		    behavior is disabled by default.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>multi-master</command></term>
		<listitem>
		  <para>
		    See the description of <command>multi-master</command> in
		    <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>masterfile-format</command></term>
		<listitem>
		  <para>
		    See the description of <command>masterfile-format</command>
		    in <xref linkend="tuning"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>max-zone-ttl</command></term>
		<listitem>
		  <para>
		    See the description of <command>max-zone-ttl</command>
		    in <xref linkend="options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>dnssec-secure-to-insecure</command></term>
		<listitem>
		  <para>
		    See the description of
		    <command>dnssec-secure-to-insecure</command> in <xref linkend="boolean_options"/>.
		  </para>
		</listitem>
	      </varlistentry>

	    </variablelist>

	  </section>
	  <section xml:id="dynamic_update_policies"><info><title>Dynamic Update Policies</title></info>

	    <para><acronym>BIND</acronym> 9 supports two
	      methods of granting clients the right to perform
	      dynamic updates to a zone, configured by the
	      <command>allow-update</command> and
	      <command>update-policy</command> options.
	    </para>
	    <para>
	      The <command>allow-update</command> clause is a simple
	      access control list.  Any client that matches
	      the ACL is granted permission to update any record
	      in the zone.
	    </para>
	    <para>
	      The <command>update-policy</command> clause
	      allows more fine-grained control over which updates are
	      allowed.  It specifies a set of rules, in which each rule
	      either grants or denies permission for one or more
	      names in the zone to be updated by one or more
	      identities. Identity is determined by the key that
	      signed the update request, using either TSIG or SIG(0).
	      In most cases, <command>update-policy</command> rules
	      only apply to key-based identities.  There is no way
	      to specify update permissions based on client source
	      address.
	    </para>
	    <para>
	      <command>update-policy</command> rules are only meaningful
	      for primary zones (type <command>master</command>), and are
	      not allowed in any other zone type.
	      It is a configuration error to specify both
	      <command>allow-update</command> and
	      <command>update-policy</command> at the same time.
	    </para>
	    <para>
	      A pre-defined <command>update-policy</command> rule can be
	      switched on with the command
	      <command>update-policy local;</command>.
	      <command>named</command> automatically generates a TSIG session
	      key when starting and stores it in a file; this key can then
	      be used by local clients to update the zone while
	      <command>named</command> is running.
	      By default, the session key is stored in the file
	      <filename>/var/run/named/session.key</filename>, the key name
	      is "local-ddns", and the key algorithm is HMAC-SHA256.
	      These values are configurable with the
	      <command>session-keyfile</command>,
	      <command>session-keyname</command>, and
	      <command>session-keyalg</command> options, respectively.
	      A client running on the local system, if run with appropriate
	      permissions, may read the session key from the key file and
	      use it to sign update requests.  The zone's update
	      policy is set to allow that key to change any record
	      within the zone.  Assuming the key name is "local-ddns",
	      this policy is equivalent to:
	    </para>

	    <programlisting>update-policy { grant local-ddns zonesub any; };
	    </programlisting>

	    <para>
	      with the additional restriction that only clients
	      connecting from the local system are permitted to send
	      updates.
	    </para>
	    <para>
	      Note that only one session key is generated by
	      <command>named</command>; all zones configured to use
	      <command>update-policy local</command> accept the same key.
	    </para>
	    <para>
	      The command <command>nsupdate -l</command> implements this
	      feature, sending requests to localhost and signing them using
	      the key retrieved from the session key file.
	    </para>

	    <para>
	      Other rule definitions look like this:
	    </para>

<programlisting>
( <command>grant</command> | <command>deny</command> ) <replaceable>identity</replaceable> <replaceable>ruletype</replaceable> <optional> <replaceable>name</replaceable> </optional> <optional> <replaceable>types</replaceable> </optional>
</programlisting>

	    <para>
	      Each rule grants or denies privileges.  Rules are checked
	      in the order in which they are specified in the
	      <command>update-policy</command> statement. Once a message
	      has successfully matched a rule, the operation is immediately
	      granted or denied, and no further rules are examined.  There
	      are 13 types of rules; the rule type is specified by the
	      <command>ruletype</command> field, and the interpretation
	      of other fields varies depending on the rule type.
	    </para>
	    <para>
	      In general, a rule is matched when the
	      key that signed an update request matches the
	      <command>identity</command> field, the name of the record
	      to be updated matches the <command>name</command> field
	      (in the manner specified by the <command>ruletype</command>
	      field), and the type of the record to be updated matches the
	      <command>types</command> field. Details for each rule type
	      are described below.
	    </para>
	    <para>
	      The <command>identity</command> field must be set to
	      a fully qualified domain name.  In most cases, this
	      represents the name of the TSIG or SIG(0) key that must be
	      used to sign the update request.  If the specified name is a
	      wildcard, it is subject to DNS wildcard expansion, and the
	      rule may apply to multiple identities.  When a TKEY exchange
	      has been used to create a shared secret, the identity of
	      the key used to authenticate the TKEY exchange is
	      used as the identity of the shared secret.  Some rule types
	      use identities matching the client's Kerberos principal
	      (e.g, <userinput>"host/machine@REALM"</userinput>) or
	      Windows realm (<userinput>machine$@REALM</userinput>).
	    </para>
	    <para>
	      The <replaceable>name</replaceable> field also specifies
	      a fully qualified domain name. This often
	      represents the name of the record to be updated.
	      Interpretation of this field is dependent on rule type.
	    </para>
	    <para>
	      If no <command>types</command> are explicitly specified,
	      then a rule matches all types except RRSIG, NS, SOA, NSEC,
	      and NSEC3. Types may be specified by name, including
	      "ANY"; ANY matches all types except NSEC and NSEC3,
	      which can never be updated.  Note that when an attempt
	      is made to delete all records associated with a name,
	      the rules are checked for each existing record type.
	    </para>
	    <para>
	      The <replaceable>ruletype</replaceable> field has 16
	      values:
	      <varname>name</varname>, <varname>subdomain</varname>,
	      <varname>zonesub</varname>, <varname>wildcard</varname>,
		  <varname>self</varname>, <varname>selfsub</varname>,
		  <varname>selfwild</varname>, <varname>ms-self</varname>,
	      <varname>ms-selfsub</varname>, <varname>ms-subdomain</varname>,
	      <varname>krb5-self</varname>, <varname>krb5-selfsub</varname>,
	      <varname>krb5-subdomain</varname>, <varname>tcp-self</varname>,
		  <varname>6to4-self</varname>, and <varname>external</varname>.
	    </para>
	    <informaltable>
	      <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="0.819in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="3.681in"/>
		<tbody>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>name</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			With exact-match semantics, this rule matches
			when the name being updated is identical
			to the contents of the
			<replaceable>name</replaceable> field.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>subdomain</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule matches when the name being updated
			is a subdomain of, or identical to, the
			contents of the <replaceable>name</replaceable>
			field.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>zonesub</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule is similar to subdomain, except that
			it matches when the name being updated is a
			subdomain of the zone in which the
			<command>update-policy</command> statement
			appears.  This obviates the need to type the zone
			name twice, and enables the use of a standard
			<command>update-policy</command> statement in
			multiple zones without modification.
		      </para>
		      <para>
			When this rule is used, the
			<replaceable>name</replaceable> field is omitted.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>wildcard</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			The <replaceable>name</replaceable> field
			is subject to DNS wildcard expansion, and
			this rule matches when the name being updated
			is a valid expansion of the wildcard.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>self</varname>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			This rule matches when the name of the record
			being updated matches the contents of the
			<replaceable>identity</replaceable> field.
			The <replaceable>name</replaceable> field
			is ignored. To avoid confusion, it is recommended
			that this field be set to the same value as the
			<replaceable>identity</replaceable> field or to
			"."
		      </para>
		      <para>
			The <varname>self</varname> rule type is
			most useful when allowing one key per
			name to update, where the key has the same
			name as the record to be updated.  In this case,
			the <replaceable>identity</replaceable> field
			can be specified as <constant>*</constant>
			(asterisk).
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>selfsub</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule is similar to <varname>self</varname>,
			except that subdomains of <varname>self</varname>
			can also be updated.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>selfwild</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule is similar to <varname>self</varname>,
			except that only subdomains of
			<varname>self</varname> can be updated.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>ms-self</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			When a client sends an UPDATE using a Windows
			machine principal (for example, "machine$@REALM"),
			this rule allows records with the absolute name
			of "machine.REALM" to be updated.
		      </para>
		      <para>
			The realm to be matched is specified in the
			<replaceable>identity</replaceable> field.
		      </para>
		      <para>
			The <replaceable>name</replaceable> field has
			no effect on this rule; it should be set to "."
			as a placeholder.
		      </para>
		      <para>
			For example,
			<userinput>grant EXAMPLE.COM ms-self . A AAAA</userinput>
			allows any machine with a valid principal in
			the realm <userinput>EXAMPLE.COM</userinput> to update
			its own address records.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>ms-selfsub</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This is similar to <command>ms-self</command>,
			except it also allows updates to any subdomain of
			the name specified in the Windows machine
			principal, not just to the name itself.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>ms-subdomain</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			When a client sends an UPDATE using a Windows
			machine principal (for example, "machine$@REALM"),
			this rule allows any machine in the specified
			realm to update any record in the zone or in a
			specified subdomain of the zone.
		      </para>
		      <para>
			The realm to be matched is specified in the
			<replaceable>identity</replaceable> field.
		      </para>
		      <para>
			The <replaceable>name</replaceable> field
			specifies the subdomain that may be updated.
			If set to "." or any other name at or above
			the zone apex, any name in the zone can be
			updated.
		      </para>
		      <para>
			For example, if <command>update-policy</command>
			for the zone "example.com" includes
			<userinput>grant EXAMPLE.COM ms-subdomain hosts.example.com. A AAAA</userinput>,
			any machine with a valid principal in
			the realm <userinput>EXAMPLE.COM</userinput> is
			able to update address records at or below
			"hosts.example.com".
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>krb5-self</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			When a client sends an UPDATE using a
			Kerberos machine principal (for example,
			"host/machine@REALM"), this rule allows
			records with the absolute name of "machine"
			to be updated, provided it has been authenticated
			by REALM.  This is similar but not identical
			to <command>ms-self</command>, due to the
			"machine" part of the Kerberos principal
			being an absolute name instead of an unqualified
			name.
		      </para>
		      <para>
			The realm to be matched is specified in the
			<replaceable>identity</replaceable> field.
		      </para>
		      <para>
			The <replaceable>name</replaceable> field has
			no effect on this rule; it should be set to "."
			as a placeholder.
		      </para>
		      <para>
			For example,
			<userinput>grant EXAMPLE.COM krb5-self . A AAAA</userinput>
			allows any machine with a valid principal in
			the realm <userinput>EXAMPLE.COM</userinput> to update
			its own address records.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>krb5-selfsub</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This is similar to <command>krb5-self</command>,
			except it also allows updates to any subdomain of
			the name specified in the "machine" part of the
			Kerberos principal, not just to the name itself.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>krb5-subdomain</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule is identical to
			<command>ms-subdomain</command>, except that it works
			with Kerberos machine principals (i.e.,
			"host/machine@REALM") rather than Windows machine
			principals.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>tcp-self</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule allows updates that have been sent via
			TCP and for which the standard mapping from the
			client's IP address into the
			<literal>in-addr.arpa</literal> and
			<literal>ip6.arpa</literal>
			namespaces matches the name to be updated.
			The <command>identity</command> field must match
			that name.  The <command>name</command> field
			should be set to ".".
			Note that, since identity is based on the client's
			IP address, it is not necessary for update request
			messages to be signed.
		      </para>
		      <note>
			It is theoretically possible to spoof these TCP
			sessions.
		      </note>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>6to4-self</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This allows the name matching a 6to4 IPv6 prefix,
			as specified in RFC 3056, to be updated by any
			TCP connection from either the 6to4 network or
			from the corresponding IPv4 address.  This is
			intended to allow NS or DNAME RRsets to be added
			to the <literal>ip6.arpa</literal> reverse tree.
		      </para>
		      <para>
			The <command>identity</command> field must match
			the 6to4 prefix in <literal>ip6.arpa</literal>.
			The <command>name</command> field should
			be set to ".".
			Note that, since identity is based on the client's
			IP address, it is not necessary for update request
			messages to be signed.
		      </para>
		      <para>
			In addition, if specified for an
			<literal>ip6.arpa</literal> name outside of the
			<literal>2.0.0.2.ip6.arpa</literal> namespace,
			the corresponding /48 reverse name can be updated.
			For example, TCP/IPv6 connections
			from 2001:DB8:ED0C::/48 can update records at
			<literal>C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa</literal>.
		      </para>
		      <note>
			It is theoretically possible to spoof these TCP
			sessions.
		      </note>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<varname>external</varname>
		      </para>
		    </entry> <entry colname="2">
		      <para>
			This rule allows <command>named</command>
			to defer the decision of whether to allow a
			given update to an external daemon.
		      </para>
		      <para>
			The method of communicating with the daemon is
			specified in the <replaceable>identity</replaceable>
			field, the format of which is
			"<constant>local:</constant><replaceable>path</replaceable>",
			where <replaceable>path</replaceable> is the location
			of a Unix-domain socket.  (Currently, "local" is the
			only supported mechanism.)
		      </para>
		      <para>
			Requests to the external daemon are sent over the
			Unix-domain socket as datagrams with the following
			format:
		      </para>
		      <programlisting>
   Protocol version number (4 bytes, network byte order, currently 1)
   Request length (4 bytes, network byte order)
   Signer (null-terminated string)
   Name (null-terminated string)
   TCP source address (null-terminated string)
   Rdata type (null-terminated string)
   Key (null-terminated string)
   TKEY token length (4 bytes, network byte order)
   TKEY token (remainder of packet)</programlisting>
		      <para>
			The daemon replies with a four-byte value in
			network byte order, containing either 0 or 1; 0
			indicates that the specified update is not
			permitted, and 1 indicates that it is.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </section>

	  <section xml:id="multiple_views"><info><title>Multiple Views</title></info>

	    <para>
	      When multiple views are in use, a zone may be
	      referenced by more than one of them. Often, the views
	      contain different zones with the same name, allowing
	      different clients to receive different answers for the same
	      queries. At times, however, it is desirable for multiple
	      views to contain identical zones.  The
	      <command>in-view</command> zone option provides an efficient
	      way to do this; it allows a view to reference a zone that
	      was defined in a previously configured view. Example:
	    </para>
	    <programlisting>
view internal {
    match-clients { 10/8; };

    zone example.com {
	type master;
	file "example-external.db";
    };
};

view external {
    match-clients { any; };

    zone example.com {
	in-view internal;
    };
};
	    </programlisting>
	    <para>
	      An <command>in-view</command> option cannot refer to a view
	      that is configured later in the configuration file.
	    </para>
	    <para>
	      A <command>zone</command> statement which uses the
	      <command>in-view</command> option may not use any other
	      , with the exception of <command>forward</command>
	      and <command>forwarders</command>. (These options control
	      the behavior of the containing view, rather than change
	      the zone object itself.)
	    </para>
	    <para>
	      Zone-level ACLs (e.g., allow-query, allow-transfer), and
	      other configuration details of the zone, are all set
	      in the view the referenced zone is defined in.  Be
	      careful to ensure that ACLs are wide enough
	      for all views referencing the zone.
	    </para>
	    <para>
	      An <command>in-view</command> zone cannot be used as a
	      response policy zone.
	    </para>
	    <para>
	      An <command>in-view</command> zone is not intended to reference
	      a <command>forward</command> zone.
	    </para>
	  </section>

	</section>
      </section>
      <section xml:id="zone_file"><info><title>Zone File</title></info>

	<section xml:id="types_of_resource_records_and_when_to_use_them"><info><title>Types of Resource Records and When to Use Them</title></info>

	  <para>
	    This section, largely borrowed from RFC 1034, describes the
	    concept of a Resource Record (RR) and explains when each type is used.
	    Since the publication of RFC 1034, several new RRs have been
	    identified
	    and implemented in the DNS. These are also included.
	  </para>
	  <section><info><title>Resource Records</title></info>

	    <para>
	      A domain name identifies a node.  Each node has a set of
	      resource information, which may be empty.  The set of resource
	      information associated with a particular name is composed of
	      separate RRs. The order of RRs in a set is not significant and
	      need not be preserved by name servers, resolvers, or other
	      parts of the DNS. However, sorting of multiple RRs is
	      permitted for optimization purposes: for example, to specify
	      that a particular nearby server be tried first. See <xref linkend="the_sortlist_statement"/> and <xref linkend="rrset_ordering"/>.
	    </para>

	    <para>
	      The components of a Resource Record are:
	    </para>
	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.000in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="3.500in"/>
		<tbody>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			owner name
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The domain name where the RR is found.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			type
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			An encoded 16-bit value that specifies
			the type of the resource record.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			TTL
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The time-to-live of the RR. This field
			is a 32-bit integer in units of seconds, and is
			primarily used by
			resolvers when they cache RRs. The TTL describes how
			long a RR can
			be cached before it should be discarded.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			class
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			An encoded 16-bit value that identifies
			a protocol family or an instance of a protocol.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			RDATA
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The resource data.  The format of the
			data is type- and sometimes class-specific.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
		<para>
		For a complete list of <emphasis>types</emphasis> of valid RRs,
		including those that have been obsoleted,
		please refer to https://en.wikipedia.org/wiki/List_of_DNS_record_types.
		</para>

	    <para>
	      The following <emphasis>classes</emphasis> of resource records
	      are currently valid in the DNS:
	    </para>
	    <informaltable colsep="0" rowsep="0"><tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="3.625in"/>
		<tbody>

		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			IN
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			The Internet.
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			CH
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			Chaosnet, a LAN protocol created at MIT in the
			mid-1970s.
			It was rarely used for its historical purpose, but was reused for
			BIND's
			built-in server information zones, e.g.,
			<literal>version.bind</literal>.
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			HS
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			Hesiod, an information service
			developed by MIT's Project Athena. It was used to share
			information
			about various systems databases, such as users,
			groups, printers,
			etc.
		      </para>
		    </entry>
		  </row>

		</tbody>
	      </tgroup>
	    </informaltable>

	    <para>
	      The owner name is often implicit, rather than forming an
	      integral
	      part of the RR.  For example, many name servers internally form
	      tree
	      or hash structures for the name space, and chain RRs off nodes.
	      The remaining RR parts are the fixed header (type, class, TTL),
	      which is consistent for all RRs, and a variable part (RDATA)
	      that
	      fits the needs of the resource being described.
	    </para>
	    <para>
	      The TTL field is a time limit on how long an
	      RR can be kept in a cache.  This limit does not apply to
	      authoritative
	      data in zones; that also times out, but follows the refreshing
	      policies
	      for the zone.  The TTL is assigned by the administrator for the
	      zone where the data originates.  While short TTLs can be used to
	      minimize caching, and a zero TTL prohibits caching, the
	      realities
	      of Internet performance suggest that these times should be on
	      the
	      order of days for the typical host.  If a change can be
	      anticipated,
	      the TTL can be reduced prior to the change to minimize
	      inconsistency, and then increased back to its former value
	      following
	      the change.
	    </para>
	    <para>
	      The data in the RDATA section of RRs is carried as a combination
	      of binary strings and domain names.  The domain names are
	      frequently
	      used as "pointers" to other data in the DNS.
	    </para>
	  </section>
	  <section xml:id="rr_text"><info><title>Textual Expression of RRs</title></info>

	    <para>
	      RRs are represented in binary form in the packets of the DNS
	      protocol, and are usually represented in highly encoded form
	      when
	      stored in a name server or resolver.  In the examples provided
	      in
	      RFC 1034, a style similar to that used in zone files was
	      employed
	      in order to show the contents of RRs.  In this format, most RRs
	      are shown on a single line, although continuation lines are
	      possible
	      using parentheses.
	    </para>
	    <para>
	      The start of the line gives the owner of the RR.  If a line
	      begins with a blank, then the owner is assumed to be the same as
	      that of the previous RR.  Blank lines are often included for
	      readability.
	    </para>
	    <para>
	      Following the owner are list the TTL, type, and class of the
	      RR.  Class and type use the mnemonics defined above, and TTL is
	      an integer before the type field.  To avoid ambiguity
	      in
	      parsing, type and class mnemonics are disjoint, TTLs are
	      integers,
	      and the type mnemonic is always last. The IN class and TTL
	      values
	      are often omitted from examples in the interest of clarity.
	    </para>
	    <para>
	      The resource data or RDATA section of the RR is given using
	      knowledge of the typical representation for the data.
	    </para>
	    <para>
	      For example, the RRs carried in a message might be shown as:
	    </para>
	    <informaltable colsep="0" rowsep="0"><tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.381in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="1.020in"/>
		<colspec colname="3" colnum="3" colsep="0" colwidth="2.099in"/>
		<tbody>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<literal>ISI.EDU.</literal>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>MX</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>10 VENERA.ISI.EDU.</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para/>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>MX</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>10 VAXA.ISI.EDU</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<literal>VENERA.ISI.EDU</literal>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>128.9.0.32</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para/>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>10.1.0.52</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<literal>VAXA.ISI.EDU</literal>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>10.2.0.27</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para/>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>128.9.0.33</literal>
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	    <para>
	      The MX RRs have an RDATA section which consists of a 16-bit
	      number followed by a domain name.  The address RRs use a
	      standard
	      IP address format to contain a 32-bit Internet address.
	    </para>
	    <para>
	      The above example shows six RRs, with two RRs at each of three
	      domain names.
	    </para>
	    <para>
	      Here is another possible example:
	    </para>
	    <informaltable colsep="0" rowsep="0"><tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.491in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="1.067in"/>
		<colspec colname="3" colnum="3" colsep="0" colwidth="2.067in"/>
		<tbody>
		  <row rowsep="0">
		    <entry colname="1">
		      <para>
			<literal>XX.LCS.MIT.EDU.</literal>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<literal>IN A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>10.0.0.44</literal>
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1"/>
		    <entry colname="2">
		      <para>
			<literal>CH A</literal>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<literal>MIT.EDU. 2420</literal>
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	    <para>
	      This example shows two addresses for
	      <literal>XX.LCS.MIT.EDU</literal>, each of a different class.
	    </para>
	  </section>
	</section>

	<section xml:id="mx_records"><info><title>Discussion of MX Records</title></info>

	  <para>
	    As described above, domain servers store information as a
	    series of resource records, each of which contains a particular
	    piece of information about a given domain name (which is usually,
	    but not always, a host). The simplest way to think of a RR is as
	    a typed pair of data, a domain name matched with a relevant datum
	    and stored with some additional type information, to help systems
	    determine when the RR is relevant.
	  </para>

	  <para>
	    MX records are used to control delivery of email. The data
	    specified in the record is a priority and a domain name. The
	    priority
	    controls the order in which email delivery is attempted, with the
	    lowest number first. If two priorities are the same, a server is
	    chosen randomly. If no servers at a given priority are responding,
	    the mail transport agent falls back to the next largest
	    priority.
	    Priority numbers do not have any absolute meaning; they are
	    relevant
	    only respective to other MX records for that domain name. The
	    domain
	    name given is the machine to which the mail is delivered.
	    It <emphasis>must</emphasis> have an associated address record
	    (A or AAAA); CNAME is not sufficient.
	  </para>
	  <para>
	    For a given domain, if there is both a CNAME record and an
	    MX record, the MX record is in error, and is ignored.
	    Instead,
	    the mail is delivered to the server specified in the MX
	    record
	    pointed to by the CNAME.
	    For example:
	  </para>
	  <informaltable colsep="0" rowsep="0">
	    <tgroup cols="5" colsep="0" rowsep="0" tgroupstyle="3Level-table">
	      <colspec colname="1" colnum="1" colsep="0" colwidth="1.708in"/>
	      <colspec colname="2" colnum="2" colsep="0" colwidth="0.444in"/>
	      <colspec colname="3" colnum="3" colsep="0" colwidth="0.444in"/>
	      <colspec colname="4" colnum="4" colsep="0" colwidth="0.976in"/>
	      <colspec colname="5" colnum="5" colsep="0" colwidth="1.553in"/>
	      <tbody>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      <literal>example.com.</literal>
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN</literal>
		    </para>
		  </entry>
		  <entry colname="3">
		    <para>
		      <literal>MX</literal>
		    </para>
		  </entry>
		  <entry colname="4">
		    <para>
		      <literal>10</literal>
		    </para>
		  </entry>
		  <entry colname="5">
		    <para>
		      <literal>mail.example.com.</literal>
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para/>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN</literal>
		    </para>
		  </entry>
		  <entry colname="3">
		    <para>
		      <literal>MX</literal>
		    </para>
		  </entry>
		  <entry colname="4">
		    <para>
		      <literal>10</literal>
		    </para>
		  </entry>
		  <entry colname="5">
		    <para>
		      <literal>mail2.example.com.</literal>
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para/>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN</literal>
		    </para>
		  </entry>
		  <entry colname="3">
		    <para>
		      <literal>MX</literal>
		    </para>
		  </entry>
		  <entry colname="4">
		    <para>
		      <literal>20</literal>
		    </para>
		  </entry>
		  <entry colname="5">
		    <para>
		      <literal>mail.backup.org.</literal>
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      <literal>mail.example.com.</literal>
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN</literal>
		    </para>
		  </entry>
		  <entry colname="3">
		    <para>
		      <literal>A</literal>
		    </para>
		  </entry>
		  <entry colname="4">
		    <para>
		      <literal>10.0.0.1</literal>
		    </para>
		  </entry>
		  <entry colname="5">
		    <para/>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      <literal>mail2.example.com.</literal>
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN</literal>
		    </para>
		  </entry>
		  <entry colname="3">
		    <para>
		      <literal>A</literal>
		    </para>
		  </entry>
		  <entry colname="4">
		    <para>
		      <literal>10.0.0.2</literal>
		    </para>
		  </entry>
		  <entry colname="5">
		    <para/>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	    </informaltable><para>
	    Mail delivery is attempted to <literal>mail.example.com</literal> and
	    <literal>mail2.example.com</literal> (in
	    any order); if neither of those succeeds, delivery to <literal>mail.backup.org</literal>
	    is attempted.
	  </para>
	</section>
	<section xml:id="Setting_TTLs"><info><title>Setting TTLs</title></info>

	  <para>
	    The time-to- (TTL) of the RR field is a 32-bit integer represented
	    in units of seconds, and is primarily used by resolvers when they
	    cache RRs. The TTL describes how long an RR can be cached before it
	    should be discarded. The following three types of TTLs are
	    currently
	    used in a zone file.
	  </para>
	  <informaltable colsep="0" rowsep="0">
	    <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
	      <colspec colname="1" colnum="1" colsep="0" colwidth="0.750in"/>
	      <colspec colname="2" colnum="2" colsep="0" colwidth="4.375in"/>
	      <tbody>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      SOA
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The last field in the SOA is the negative
		      caching TTL. This controls how long other servers
		      cache no-such-domain
		      (NXDOMAIN) responses from this server.
		    </para>
		    <para>
		      The maximum time for
		      negative caching is 3 hours (3h).
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      $TTL
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      The $TTL directive at the top of the
		      zone file (before the SOA) gives a default TTL for every
		      RR without
		      a specific TTL set.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      RR TTLs
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      Each RR can have a TTL as the second
		      field in the RR, which controls how long other
		      servers can cache it.
		    </para>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	  <para>
	    All of these TTLs default to units of seconds, though units
	    can be explicitly specified: for example, <literal>1h30m</literal>.
	  </para>
	</section>
	<section xml:id="ipv4_reverse"><info><title>Inverse Mapping in IPv4</title></info>

	  <para>
	    Reverse name resolution (that is, translation from IP address
	    to name) is achieved by means of the <emphasis>in-addr.arpa</emphasis> domain
	    and PTR records. Entries in the in-addr.arpa domain are made in
	    least-to-most significant order, read left to right. This is the
	    opposite order to the way IP addresses are usually written. Thus,
	    a machine with an IP address of 10.1.2.3 would have a
	    corresponding
	    in-addr.arpa name of
	    3.2.1.10.in-addr.arpa. This name should have a PTR resource record
	    whose data field is the name of the machine or, optionally,
	    multiple
	    PTR records if the machine has more than one name. For example,
	    in the <optional>example.com</optional> domain:
	  </para>
	  <informaltable colsep="0" rowsep="0">
	    <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
	      <colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
	      <colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
	      <tbody>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      <literal>$ORIGIN</literal>
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>2.1.10.in-addr.arpa</literal>
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para>
		      <literal>3</literal>
		    </para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <literal>IN PTR foo.example.com.</literal>
		    </para>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	  <note>
	    <para>
	      The <command>$ORIGIN</command> line in this example
	      is only to provide context; it does not
	      necessarily
	      appear in the actual usage. It is only used here to indicate
	      that the example is relative to the listed origin.
	    </para>
	  </note>
	</section>
	<section xml:id="zone_directives"><info><title>Other Zone File Directives</title></info>

	  <para>
	    The DNS "master file" format was initially defined in RFC 1035 and
	    has subsequently been extended. While the format
	    itself
	    is class-independent, all records in a zone file must be of the
	    same
	    class.
	  </para>
	  <para>
	    Master file directives include <command>$ORIGIN</command>, <command>$INCLUDE</command>,
	    and <command>$TTL.</command>
	  </para>
	  <section xml:id="atsign"><info><title>The <command>@</command> (at-sign)</title></info>

	    <para>
	      When used in the label (or name) field, the asperand or
	      at-sign (@) symbol represents the current origin.
	      At the start of the zone file, it is the
	      &lt;<varname>zone_name</varname>&gt;, followed by a
	      trailing dot (.).
	    </para>
	  </section>
	  <section xml:id="origin_directive"><info><title>The <command>$ORIGIN</command> Directive</title></info>

	    <para>
	      Syntax: <command>$ORIGIN</command>
	      <replaceable>domain-name</replaceable>
	      <optional><replaceable>comment</replaceable></optional>
	    </para>
	    <para><command>$ORIGIN</command>
	      sets the domain name that is appended to any
	      unqualified records. When a zone is first read, there
	      is an implicit <command>$ORIGIN</command>
	      &lt;<varname>zone_name</varname>&gt;<command>.</command>;
	      note the trailing dot.
	      The current <command>$ORIGIN</command> is appended to
	      the domain specified in the <command>$ORIGIN</command>
	      argument if it is not absolute.
	    </para>

<programlisting>
$ORIGIN example.com.
WWW     CNAME   MAIN-SERVER
</programlisting>

	    <para>
	      is equivalent to
	    </para>

<programlisting>
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
</programlisting>

	  </section>
	  <section xml:id="include_directive"><info><title>The <command>$INCLUDE</command> Directive</title></info>

	    <para>
	      Syntax: <command>$INCLUDE</command>
	      <replaceable>filename</replaceable>
	      <optional>
<replaceable>origin</replaceable> </optional>
	      <optional> <replaceable>comment</replaceable> </optional>
	    </para>
	    <para>
	      This reads and processes the file <filename>filename</filename> as
	      if it were included in the file at this point.  If <command>origin</command> is
	      specified, the file is processed with <command>$ORIGIN</command> set
	      to that value; otherwise, the current <command>$ORIGIN</command> is
	      used.
	    </para>
	    <para>
	      The origin and the current domain name
	      revert to the values they had prior to the <command>$INCLUDE</command> once
	      the file has been read.
	    </para>
	    <note>
	      <para>
		RFC 1035 specifies that the current origin should be restored
		after
		an <command>$INCLUDE</command>, but it is silent
		on whether the current
		domain name should also be restored.  BIND 9 restores both of
		them.
		This could be construed as a deviation from RFC 1035, a
		feature, or both.
	      </para>
	    </note>
	  </section>
	  <section xml:id="ttl_directive"><info><title>The <command>$TTL</command> Directive</title></info>

	    <para>
	      Syntax: <command>$TTL</command>
	      <replaceable>default-ttl</replaceable>
	      <optional>
<replaceable>comment</replaceable> </optional>
	    </para>
	    <para>
	      This sets the default Time-To-Live (TTL) for subsequent records
	      with undefined TTLs. Valid TTLs are of the range 0-2147483647
	      seconds.
	    </para>
	    <para><command>$TTL</command>
	       is defined in RFC 2308.
	    </para>
	  </section>
	</section>
	<section xml:id="generate_directive"><info><title><acronym>BIND</acronym> Primary File Extension: the  <command>$GENERATE</command> Directive</title></info>

	  <para>
	    Syntax: <command>$GENERATE</command>
	    <replaceable>range</replaceable>
	    <replaceable>lhs</replaceable>
	    <optional><replaceable>ttl</replaceable></optional>
	    <optional><replaceable>class</replaceable></optional>
	    <replaceable>type</replaceable>
	    <replaceable>rhs</replaceable>
	    <optional><replaceable>comment</replaceable></optional>
	  </para>
	  <para><command>$GENERATE</command>
	    is used to create a series of resource records that only
	    differ from each other by an
	    iterator. <command>$GENERATE</command> can be used to
	    easily generate the sets of records required to support
	    sub-/24 reverse delegations described in RFC 2317:
	    Classless IN-ADDR.ARPA delegation.
	  </para>

<programlisting>$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</programlisting>

	  <para>
	    is equivalent to
	  </para>

<programlisting>0.0.0.192.IN-ADDR.ARPA. NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.
</programlisting>

	   <para>
	    Both generate a set of A and MX records.  Note the MX's right-hand
	    side is a quoted string.  The quotes are stripped when the
	    right-hand side is processed.
	   </para>

<programlisting>
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."</programlisting>

	  <para>
	    is equivalent to
	  </para>

<programlisting>HOST-1.EXAMPLE.   A  1.2.3.1
HOST-1.EXAMPLE.   MX 0 .
HOST-2.EXAMPLE.   A  1.2.3.2
HOST-2.EXAMPLE.   MX 0 .
HOST-3.EXAMPLE.   A  1.2.3.3
HOST-3.EXAMPLE.   MX 0 .
...
HOST-127.EXAMPLE. A  1.2.3.127
HOST-127.EXAMPLE. MX 0 .
</programlisting>

	  <informaltable colsep="0" rowsep="0">
	    <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
			<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
	      <colspec colname="2" colnum="2" colsep="0" colwidth="4.250in"/>
	      <tbody>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>range</command></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      This can be one of two forms: start-stop
		      or start-stop/step. If the first form is used, then step
		      is set to 1. "start", "stop", and "step" must be positive
		      integers between 0 and (2^31)-1. "start" must not be
		      larger than "stop".
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>lhs</command></para>
		  </entry>
		  <entry colname="2">
		    <para>This
		      describes the owner name of the resource records
		      to be created.  Any single <command>$</command>
		      (dollar sign)
		      symbols within the <command>lhs</command> string
		      are replaced by the iterator value.

		      To get a $ in the output, escape the
		      <command>$</command> using a backslash
		      <command>\</command>,
		      e.g., <command>\$</command>. The
		      <command>$</command> may optionally be followed
		      by modifiers which change the offset from the
		      iterator, field width, and base.

		      Modifiers are introduced by a
		      <command>{</command> (left brace) immediately following the
		      <command>$</command>, as in
		      <command>${offset[,width[,base]]}</command>.
		      For example, <command>${-20,3,d}</command>
		      subtracts 20 from the current value and prints the
		      result as a decimal in a zero-padded field of
		      width 3.

		      Available output forms are decimal
		      (<command>d</command>), octal
		      (<command>o</command>), hexadecimal
		      (<command>x</command> or <command>X</command>
		      for uppercase), and nibble
		      (<command>n</command> or <command>N</command>
		      for uppercase).  The default modifier is
		      <command>${0,0,d}</command>.  If the
		      <command>lhs</command> is not absolute, the
		      current <command>$ORIGIN</command> is appended
		      to the name.
		    </para>
		    <para>
		      In nibble mode, the value is treated as
		      if it were a reversed hexadecimal string,
		      with each hexadecimal digit as a separate
		      label.  The width field includes the label
		      separator.
		    </para>
		    <para>
		      For compatibility with earlier versions,
		      <command>$$</command> is still recognized as
		      indicating a literal $ in the output.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>ttl</command></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      This specifies the time-to-live of the generated records. If
		      not specified, this is inherited using the
		      normal TTL inheritance rules.
		    </para>
		    <para><command>class</command>
		      and <command>ttl</command> can be
		      entered in either order.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>class</command></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      This specifies the class of the generated records.
		      This must match the zone class if it is
		      specified.
		    </para>
		    <para><command>class</command>
		      and <command>ttl</command> can be
		      entered in either order.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>type</command></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      This can be any valid type.
		    </para>
		  </entry>
		</row>
		<row rowsep="0">
		  <entry colname="1">
		    <para><command>rhs</command></para>
		  </entry>
		  <entry colname="2">
		    <para>
		      <command>rhs</command> is an optionally quoted string.
		    </para>
		  </entry>
		</row>
	      </tbody>
	    </tgroup>
	  </informaltable>
	  <para>
	    The <command>$GENERATE</command> directive is a <acronym>BIND</acronym> extension
	    and not part of the standard zone file format.
	  </para>
	  <para>
	    BIND 8 did not support the optional TTL and CLASS fields.
	  </para>
	</section>

	<section xml:id="zonefile_format"><info><title>Additional File Formats</title></info>

	  <para>
	    In addition to the standard text format, BIND 9
	    supports the ability to read or dump to zone files in
	    other formats.
	  </para>
	  <para>
	    The <constant>raw</constant> format is
	    a binary representation of zone data in a manner similar
	    to that used in zone transfers.  Since it does not require
	    parsing text, load time is significantly reduced.
	  </para>
	  <para>
	    An even faster alternative is the <constant>map</constant>
	    format, which is an image of a <acronym>BIND</acronym> 9
	    in-memory zone database; it can be loaded
	    directly into memory via the <command>mmap()</command>
	    function and the zone can begin serving queries almost
	    immediately.
	  </para>
	  <para>
	    For a primary server, a zone file in
	    <constant>raw</constant> or <constant>map</constant>
	    format is expected to be generated from a textual zone
	    file by the <command>named-compilezone</command> command.
	    For a secondary server or for a dynamic zone, the zone file is automatically
	    generated when
	    <command>named</command> dumps the zone contents after
	    zone transfer or when applying prior updates, if one of these formats is specified by the
	    <command>masterfile-format</command> option.
	  </para>
	  <para>
	    If a zone file in a binary format needs manual modification,
	    it first must be converted to a textual form by the
	    <command>named-compilezone</command> command.  Make any
	    necessary modifications to the text file, and
	    then convert it to the binary form via the
	    <command>named-compilezone</command> command again.
	  </para>
	  <para>
	    Note that <command>map</command> format is extremely
	    architecture-specific.  A <constant>map</constant>
	    file <emphasis>cannot</emphasis> be used on a system
	    with different pointer size, endianness, or data alignment
	    than the system on which it was generated, and should in
	    general be used only inside a single system.
	    While <constant>raw</constant> format uses
	    network byte order and avoids architecture-dependent
	    data alignment so that it is as portable as
	    possible, it is also primarily expected to be used
	    inside the same single system.  To export a
	    zone file in either <constant>raw</constant> or
	    <constant>map</constant> format, or make a
	    portable backup of such a file, conversion to
	    <constant>text</constant> format is recommended.
	  </para>
	</section>
      </section>

      <section xml:id="statistics"><info><title>BIND 9 Statistics</title></info>

	<para>
	  <acronym>BIND</acronym> 9 maintains lots of statistics
	  information and provides several interfaces for users to
	  access those statistics.
	  The available statistics include all statistics counters
	  that are meaningful in <acronym>BIND</acronym> 9,
	  and other information that is considered useful.
	</para>

	<para>
	  The statistics information is categorized into the following
	  sections:
	</para>

	<informaltable frame="all">
	  <tgroup cols="2">
	    <colspec colname="1" colnum="1" colsep="0" colwidth="3.300in"/>
	    <colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
	    <tbody>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Incoming Requests</para>
		</entry>
		<entry colname="2">
		  <para>
		    The number of incoming DNS requests for each OPCODE.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Incoming Queries</para>
		</entry>
		<entry colname="2">
		  <para>
		    The number of incoming queries for each RR type.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Outgoing Queries</para>
		</entry>
		<entry colname="2">
		  <para>
		    The number of outgoing queries for each RR
		    type sent from the internal resolver,
		    maintained per view.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Name Server Statistics</para>
		</entry>
		<entry colname="2">
		  <para>
		    Statistics counters for incoming request processing.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Zone Maintenance Statistics</para>
		</entry>
		<entry colname="2">
		  <para>
		    Statistics counters regarding zone maintenance
		    operations, such as zone transfers.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Resolver Statistics</para>
		</entry>
		<entry colname="2">
		  <para>
		    Statistics counters for name resolutions
		    performed in the internal resolver,
		    maintained per view.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Cache DB RRsets</para>
		</entry>
		<entry colname="2">
		  <para>
		    Statistics counters related to cache contents,
		    maintained per view.
		  </para>
		  <para>
		    The "NXDOMAIN" counter is the number of names
		    that have been cached as nonexistent.
		    Counters named for RR types indicate the
		    number of active RRsets for each type in the cache
		    database.
		  </para>
		  <para>
		    If an RR type name is preceded by an exclamation
		    point (!), it represents the number of records in the
		    cache which indicate that the type does not exist
		    for a particular name; this is also known as "NXRRSET".
		    If an RR type name is preceded by a hash mark (#), it
		    represents the number of RRsets for this type that are
		    present in the cache but whose TTLs have expired; these
		    RRsets may only be used if stale answers are enabled.
		    If an RR type name is preceded by a tilde (~), it
		    represents the number of RRsets for this type that are
		    present in the cache database but are marked for garbage
		    collection; these RRsets cannot be used.
		  </para>
		</entry>
	      </row>

	      <row rowsep="0">
		<entry colname="1">
		  <para>Socket I/O Statistics</para>
		</entry>
		<entry colname="2">
		  <para>
		    Statistics counters for network-related events.
		  </para>
		</entry>
	      </row>

	    </tbody>
	  </tgroup>
	</informaltable>

	<para>
	  A subset of Name Server Statistics is collected and shown
	  per zone for which the server has the authority, when
	  <command>zone-statistics</command> is set to
	  <userinput>full</userinput> (or <userinput>yes</userinput>),
	  for backward compatibility. See the description of
	  <command>zone-statistics</command> in <xref linkend="options"/>
	  for further details.
	</para>

	<para>
	  These statistics counters are shown with their zone and
	  view names. The view name is omitted when the server is
	  not configured with explicit views.</para>

	<para>
	  There are currently two user interfaces to get access to the
	  statistics.
	  One is in plain-text format, dumped to the file specified
	  by the <command>statistics-file</command> configuration option;
	  the other is remotely accessible via a statistics channel
	  when the <command>statistics-channels</command> statement
	  is specified in the configuration file
	  (see <xref linkend="statschannels"/>.)
	</para>

	<section xml:id="statsfile"><info><title>The Statistics File</title></info>

	  <para>
	    The text format statistics dump begins with a line, like:
	  </para>
	  <para>
	    <command>+++ Statistics Dump +++ (973798949)</command>
	  </para>
	  <para>
	    The number in parentheses is a standard
	    Unix-style timestamp, measured in seconds since January 1, 1970.

	    Following
	    that line is a set of statistics information, which is categorized
	    as described above.
	    Each section begins with a line, like:
	  </para>

	  <para>
	    <command>++ Name Server Statistics ++</command>
	  </para>

	  <para>
	    Each section consists of lines, each containing the statistics
	    counter value followed by its textual description;
	    see below for available counters.
	    For brevity, counters that have a value of 0 are not shown
	    in the statistics file.
	  </para>

	  <para>
	    The statistics dump ends with the line where the
	    number is identical to the number in the beginning line; for example:
	  </para>
	  <para>
	    <command>--- Statistics Dump --- (973798949)</command>
	  </para>
	</section>

	<section xml:id="statistics_counters"><info><title>Statistics Counters</title></info>

	  <para>
	    The following tables summarize the statistics counters that
	    <acronym>BIND</acronym> 9 provides.
	    For each row of the tables, the leftmost column is the
	    abbreviated symbol name of that counter;
	    these symbols are shown in the statistics information
	    accessed via an HTTP statistics channel.
	    The rightmost column gives the description of the counter,
	    which is also shown in the statistics file,
	    but, in this document, may be slightly modified
	    for better readability.
	    Additional notes may also be provided in this column.
	    When a middle column exists between these two columns,
	    it gives the corresponding counter name of the
	    <acronym>BIND</acronym> 8 statistics, if applicable.
	  </para>

	  <section xml:id="stats_counters"><info><title>Name Server Statistics Counters</title></info>

	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
		<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
		<tbody>
		  <row>
		    <entry colname="1">
		      <para>
			<emphasis>Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<emphasis>BIND 8 Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<emphasis>Description</emphasis>
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Requestv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv4 requests received.
			Note: this also counts non-query requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Requestv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv6 requests received.
			Note: this also counts non-query requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqEdns0</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requests received with EDNS(0).
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqBadEDNSVer</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requests received with an unsupported EDNS version.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqTSIG</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requests received with TSIG.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqSIG0</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requests received with SIG(0).
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqBadSIG</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requests received with an invalid (TSIG or SIG(0)) signature.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ReqTCP</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RTCP</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of TCP requests received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>AuthQryRej</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RUQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of rejected authoritative (non-recursive) queries.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RecQryRej</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RURQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of rejected recursive queries.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>XfrRej</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RUXFR</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of rejected zone transfer requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateRej</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RUUpd</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of rejected dynamic update requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Response</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SAns</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RespTruncated</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of truncated responses sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RespEDNS0</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses sent with EDNS(0).
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RespTSIG</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses sent with TSIG.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RespSIG0</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses sent with SIG(0).
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QrySuccess</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in a successful answer,
			meaning queries which return a NOERROR response
			with at least one answer RR.
			This corresponds to the
			<command>success</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryAuthAns</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in an authoritative answer.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryNoauthAns</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SNaAns</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in a non-authoritative answer.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryReferral</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in a referral answer.
			This corresponds to the
			<command>referral</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryNxrrset</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in NOERROR responses with no data.
			This corresponds to the
			<command>nxrrset</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QrySERVFAIL</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SFail</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in SERVFAIL.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryFORMERR</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SFErr</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in FORMERR.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryNXDOMAIN</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SNXD</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in NXDOMAIN.
			This corresponds to the
			<command>nxdomain</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryRecursion</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RFwdQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that caused the server
			to perform recursion in order to find the final answer.
			This corresponds to the
			<command>recursion</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryDuplicate</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RDupQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries which the server attempted to
			recurse but for which it discovered an existing query with the same
			IP address, port, query ID, name, type, and class
			already being processed.
			This corresponds to the
			<command>duplicate</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryDropped</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of recursive queries for which the server
			discovered an excessive number of existing
			recursive queries for the same name, type, and
			class, and which were subsequently dropped.
			This is the number of dropped queries due to
			the reason explained with the
			<command>clients-per-query</command>
			and
			<command>max-clients-per-query</command>
			options
			(see the description about
			<xref endterm="cpq_term" linkend="clients-per-query"/>.)
			This corresponds to the
			<command>dropped</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryFailure</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of query failures.
			This corresponds to the
			<command>failure</command> counter
			of previous versions of
			<acronym>BIND</acronym> 9.
			Note: this counter is provided mainly for
			backward compatibility with the previous versions;
			normally, more fine-grained counters such as
			<command>AuthQryRej</command> and
			<command>RecQryRej</command>
			that would also fall into this counter are provided,
			so this counter is not of much
			interest in practice.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryNXRedir</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in NXDOMAIN that were redirected.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryNXRedirRLookup</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries that resulted in NXDOMAIN that were redirected
			and resulted in a successful remote lookup.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>XfrReqDone</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of requested and completed zone transfers.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateReqFwd</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of forwarded update requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateRespFwd</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of forwarded update responses.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateFwdFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of forwarded dynamic updates that failed.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateDone</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of completed dynamic updates.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of failed dynamic updates.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>UpdateBadPrereq</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of dynamic updates rejected due to a prerequisite failure.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RateDropped</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses dropped due to rate limits.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RateSlipped</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of responses truncated by rate limits.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>RPZRewrites</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of response policy zone rewrites.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </section>

	  <section xml:id="zone_stats"><info><title>Zone Maintenance Statistics Counters</title></info>

	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
		<tbody>
		  <row>
		    <entry colname="1">
		      <para>
			<emphasis>Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<emphasis>Description</emphasis>
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NotifyOutv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv4 notifies sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NotifyOutv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv6 notifies sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NotifyInv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv4 notifies received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NotifyInv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv6 notifies received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NotifyRej</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of incoming notifies rejected.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>SOAOutv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv4 SOA queries sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>SOAOutv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of IPv6 SOA queries sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>AXFRReqv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of requested IPv4 AXFRs.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>AXFRReqv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of requested IPv6 AXFRs.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>IXFRReqv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of requested IPv4 IXFRs.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>IXFRReqv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of requested IPv6 IXFRs.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>XfrSuccess</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of successful zone transfer requests.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>XfrFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of failed zone transfer requests.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </section>

	  <section xml:id="resolver_stats"><info><title>Resolver Statistics Counters</title></info>

	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
		<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
		<tbody>
		  <row>
		    <entry colname="1">
		      <para>
			<emphasis>Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<emphasis>BIND 8 Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="3">
		      <para>
			<emphasis>Description</emphasis>
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Queryv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SFwdQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv4 queries sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Queryv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SFwdQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv6 queries sent.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Responsev4</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RR</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv4 responses received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Responsev6</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RR</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv6 responses received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>NXDOMAIN</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RNXD</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of NXDOMAINs received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>SERVFAIL</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RFail</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of SERVFAILs received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>FORMERR</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RFErr</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of FORMERRs received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>OtherError</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RErr</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of other errors received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>EDNS0Fail</command></para>
						 </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of EDNS(0) query failures.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Mismatch</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RDupR</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of mismatched responses received,
			meaning the DNS ID, response's source address,
			and/or the response's source port does not
			match what was expected.
			(The port must be 53 or as defined by
			the <command>port</command> option.)
			This may be an indication of a cache
			poisoning attempt.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Truncated</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of truncated responses received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Lame</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>RLame</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of lame delegations received.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>Retry</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SDupQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of query retries performed.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QueryAbort</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of queries aborted due to quota control.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QuerySockFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of failures in opening query sockets.
			One common reason for such failures is a
			due to a limitation on file descriptors.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QueryTimeout</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of query timeouts.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>GlueFetchv4</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SSysQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv4 NS address fetches invoked.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>GlueFetchv6</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command>SSysQ</command></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of IPv6 NS address fetches invoked.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>GlueFetchv4Fail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of failed IPv4 NS address fetches.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>GlueFetchv6Fail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of failed IPv6 NS address fetches.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ValAttempt</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of attempted DNSSEC validations.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ValOk</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of successful DNSSEC validations.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ValNegOk</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of successful DNSSEC validations on negative information.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>ValFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This indicates the number of failed DNSSEC validations.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>QryRTTnn</command></para>
		    </entry>
		    <entry colname="2">
		      <para><command/></para>
		    </entry>
		    <entry colname="3">
		      <para>
			This provides a frequency table on query round-trip times (RTTs).
			Each <command>nn</command> specifies the corresponding
			frequency.
			In the sequence of
			<command>nn_1</command>,
			<command>nn_2</command>,
			...,
			<command>nn_m</command>,
			the value of <command>nn_i</command> is the
			number of queries whose RTTs are between
			<command>nn_(i-1)</command> (inclusive) and
			<command>nn_i</command> (exclusive) milliseconds.
			For the sake of convenience, we define
			<command>nn_0</command> to be 0.
			The last entry should be represented as
			<command>nn_m+</command>, which means the
			number of queries whose RTTs are equal to or greater than
			<command>nn_m</command> milliseconds.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>

	  </section>

	  <section xml:id="socket_stats"><info><title>Socket I/O Statistics Counters</title></info>

	    <para>
	      Socket I/O statistics counters are defined per socket
	      type, which are
	      <command>UDP4</command> (UDP/IPv4),
	      <command>UDP6</command> (UDP/IPv6),
	      <command>TCP4</command> (TCP/IPv4),
	      <command>TCP6</command> (TCP/IPv6),
	      <command>Unix</command> (Unix Domain), and
	      <command>FDwatch</command> (sockets opened outside the
	      socket module).
	      In the following table, <command>&lt;TYPE&gt;</command>
	      represents a socket type.
	      Not all counters are available for all socket types;
	      exceptions are noted in the description field.
	    </para>

	    <informaltable colsep="0" rowsep="0">
	      <tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
		<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
		<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
		<tbody>
		  <row>
		    <entry colname="1">
		      <para>
			<emphasis>Symbol</emphasis>
		      </para>
		    </entry>
		    <entry colname="2">
		      <para>
			<emphasis>Description</emphasis>
		      </para>
		    </entry>
		  </row>

		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;Open</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of sockets opened successfully.
			This counter does not apply to the
			<command>FDwatch</command> type.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;OpenFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of failures to open sockets.
			This counter does not apply to the
			<command>FDwatch</command> type.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;Close</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of closed sockets.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;BindFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of failures to bind sockets.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;ConnFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of failures to connect sockets.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;Conn</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of connections established successfully.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;AcceptFail</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of failures to accept incoming connection requests.
			This counter does not apply to the
			<command>UDP</command> and
			<command>FDwatch</command> types.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;Accept</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of incoming connections successfully accepted.
			This counter does not apply to the
			<command>UDP</command> and
			<command>FDwatch</command> types.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;SendErr</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of errors in socket send operations.
			This counter corresponds
			to the <command>SErr</command> counter of
			<command>BIND</command> 8.
		      </para>
		    </entry>
		  </row>
		  <row rowsep="0">
		    <entry colname="1">
		      <para><command>&lt;TYPE&gt;RecvErr</command></para>
		    </entry>
		    <entry colname="2">
		      <para>
			This indicates the number of errors in socket receive operations,
			including errors of send operations on a
			connected UDP socket, notified by an ICMP error
			message.
		      </para>
		    </entry>
		  </row>
		</tbody>
	      </tgroup>
	    </informaltable>
	  </section>

	  <section xml:id="bind8_compatibility"><info><title>Compatibility with <emphasis>BIND</emphasis> 8 Counters</title></info>

	    <para>
	      Most statistics counters that were available
	      in <command>BIND</command> 8 are also supported in
	      <command>BIND</command> 9, as shown in the above tables.
	      Here are notes about other counters that do not appear
	      in these tables.
	    </para>

	    <variablelist>
	      <varlistentry>
		<term><command>RFwdR,SFwdR</command></term>
		<listitem>
		  <para>
		    These counters are not supported,
		    because <command>BIND</command> 9 does not adopt
		    the notion of <emphasis>forwarding</emphasis>
		    as <command>BIND</command> 8 did.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>RAXFR</command></term>
		<listitem>
		  <para>
		    This counter is accessible in the Incoming Queries section.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>RIQ</command></term>
		<listitem>
		  <para>
		    This counter is accessible in the Incoming Requests section.
		  </para>
		</listitem>
	      </varlistentry>

	      <varlistentry>
		<term><command>ROpts</command></term>
		<listitem>
		  <para>
		    This counter is not supported,
		    because <command>BIND</command> 9 does not care
		    about IP options.
		  </para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </section>
	</section>
      </section>

    </chapter>
    <chapter xml:id="Bv9ARM.ch07"><info><title><acronym>BIND</acronym> 9 Security Considerations</title></info>

      <section xml:id="Access_Control_Lists"><info><title>Access Control Lists</title></info>

	<para>
	  Access Control Lists (ACLs) are address match lists that
	  can be set up and nicknamed for future use in
	  <command>allow-notify</command>, <command>allow-query</command>,
	  <command>allow-query-on</command>, <command>allow-recursion</command>,
	  <command>blackhole</command>, <command>allow-transfer</command>,
	  <command>match-clients</command>, etc.
	</para>
	<para>
	  ACLs give users finer control over who can access
	  the name server, without cluttering up configuration files with huge
	  lists of IP addresses.
	</para>
	<para>
	  It is a <emphasis>good idea</emphasis> to use ACLs, and to
	  control access. Limiting access to the server by
	  outside parties can help prevent spoofing and denial of service
	  (DoS) attacks against the server.
	</para>
	<para>
	  ACLs match clients on the basis of up to three characteristics:
	  1) The client's IP address; 2) the TSIG or SIG(0) key that was
	  used to sign the request, if any; and 3) an address prefix
	  encoded in an EDNS Client-Subnet option, if any.
	</para>
	<para>
	  Here is an example of ACLs based on client addresses:
	</para>

<programlisting>
// Set up an ACL named "bogusnets" that blocks
// RFC 1918 space and some reserved space, which is
// commonly used in spoofing attacks.
acl bogusnets {
	0.0.0.0/8;  192.0.2.0/24; 224.0.0.0/3;
	10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
};

// Set up an ACL called our-nets. Replace this with the
// real IP numbers.
acl our-nets { x.x.x.x/24; x.x.x.x/21; };
options {
  ...
  ...
  allow-query { our-nets; };
  allow-recursion { our-nets; };
  ...
  blackhole { bogusnets; };
  ...
};

zone "example.com" {
  type master;
  file "m/example.com";
  allow-query { any; };
};
</programlisting>

	<para>
	  This allows authoritative queries for "example.com" from any
	  address, but recursive queries only from the networks specified
	  in "our-nets", and no queries at all from the networks
	  specified in "bogusnets".
	</para>
	<para>
	  In addition to network addresses and prefixes, which are
	  matched against the source address of the DNS request, ACLs
	  may include <option>key</option> elements, which specify the
	  name of a TSIG or SIG(0) key, or <option>ecs</option>
	  elements, which specify a network prefix but are only matched
	  if that prefix matches an EDNS client-subnet option included
	  in the request.
	</para>
	<para>
	  The EDNS Client-Subnet (ECS) option is used by a recursive
	  resolver to inform an authoritative name server of the network
	  address block from which the original query was received, enabling
	  authoritative servers to give different answers to the same
	  resolver for different resolver clients.  An ACL containing
	  an element of the form
	  <command>ecs <replaceable>prefix</replaceable></command>
	  will match if a request arrives in containing an ECS option
	  encoding an address within that prefix.  If the request has no
	  ECS option, then "ecs" elements are simply ignored.  Addresses
	  in ACLs that are not prefixed with "ecs" are matched only
	  against the source address.
	</para>
	<note>
	  <simpara>
	    (Note: the authoritative ECS implementation in
	    <command>named</command> is based on an early version of the
	    specification, and is known to have incompatibilities with
	    other implementations.  It is also inefficient, requiring
	    a separate view for each client subnet to be sent different
	    answers, and it is unable to correct for overlapping subnets in
	    the configuration.  It can be used for testing purposes, but is
	    not recommended for production use.)
	  </simpara>
	</note>
	<para>
	  When <acronym>BIND</acronym> 9 is built with GeoIP support,
	  ACLs can also be used for geographic access restrictions.
	  This is done by specifying an ACL element of the form:
	  <command>geoip <optional>db <replaceable>database</replaceable></optional> <replaceable>field</replaceable> <replaceable>value</replaceable></command>
	</para>
	<para>
	  The <replaceable>field</replaceable> parameter indicates which field
	  to search for a match.  Available fields are "country",
	  "region", "city", "continent", "postal" (postal code),
	  "metro" (metro code), "area" (area code), "tz" (timezone),
	  "isp", "asnum", and "domain".
	</para>
	<para>
	  <replaceable>value</replaceable> is the value to search
	  for within the database.  A string may be quoted if it
	  contains spaces or other special characters.  An "asnum"
	  search for autonomous system number can be specified using
	  the string "ASNNNN" or the integer NNNN.
	  When "country" search is specified with a string that is two
	  characters long, it must be a standard ISO-3166-1
	  two-letter country code; otherwise, it is interpreted as
	  the full name of the country.  Similarly, if
	  "region" is the search term and the string is two characters long,
	  it is treated as a standard two-letter state or province
	  abbreviation; otherwise, it is treated as the full name of the
	  state or province.
	</para>
	<para>
	  The <replaceable>database</replaceable> field indicates which
	  GeoIP database to search for a match.  In most cases this is
	  unnecessary, because most search fields can only be found in
	  a single database.  However, searches for "continent" or "country"
	  can be answered from either the "city" or "country" databases,
	  so for these search types, specifying a
	  <replaceable>database</replaceable>
	  forces the query to be answered from that database and no
	  other.  If <replaceable>database</replaceable> is not
	  specified, these queries are first answered from the "city"
	  database if it is installed, and then from the "country" database if it
	  is installed. Valid database names are
	  "country", "city", "asnum", "isp", and "domain". (If using
	  the legacy GeoIP API, "netspeed" and "org" databases are also
	  available.)
	</para>
	<para>
	  By default, if a DNS query includes an EDNS Client-Subnet (ECS)
	  option which encodes a non-zero address prefix, then GeoIP ACL
	  elements are matched against that address prefix.  Otherwise,
	  they are matched against the source address of the query.  To
	  prevent GeoIP ACLs from matching against ECS options, set
	  the <command>geoip-use-ecs</command> to <literal>no</literal>.
	</para>
	<para>
	  Some example GeoIP ACLs:
	</para>
	<programlisting>geoip country US;
geoip country JP;
geoip db country country Canada;
geoip region WA;
geoip city "San Francisco";
geoip region Oklahoma;
geoip postal 95062;
geoip tz "America/Los_Angeles";
geoip org "Internet Systems Consortium";
</programlisting>

	<para>
	  ACLs use a "first-match" logic rather than "best-match";
	  if an address prefix matches an ACL element, then that ACL
	  is considered to have matched even if a later element would
	  have matched more specifically.  For example, the ACL
	  <command>{ 10/8; !10.0.0.1; }</command> would actually
	  match a query from 10.0.0.1, because the first element
	  indicates that the query should be accepted, and the second
	  element is ignored.
	</para>
	<para>
	  When using "nested" ACLs (that is, ACLs included or referenced
	  within other ACLs), a negative match of a nested ACL tells
	  the containing ACL to continue looking for matches.  This
	  enables complex ACLs to be constructed, in which multiple
	  client characteristics can be checked at the same time. For
	  example, to construct an ACL which allows a query only when
	  it originates from a particular network <emphasis>and</emphasis>
	  only when it is signed with a particular key, use:
	</para>
	<programlisting>
allow-query { !{ !10/8; any; }; key example; };
</programlisting>
	<para>
	  Within the nested ACL, any address that is
	  <emphasis>not</emphasis> in the 10/8 network prefix is
	  rejected, which terminates processing of the
	  ACL.  Any address that <emphasis>is</emphasis> in the 10/8
	  network prefix is accepted, but this causes a negative
	  match of the nested ACL, so the containing ACL continues
	  processing. The query is accepted if it is signed
	  by the key "example", and rejected otherwise.  The ACL, then,
	  only matches when <emphasis>both</emphasis> conditions
	  are true.
	</para>
      </section>

      <section xml:id="chroot_and_setuid"><info><title><command>Chroot</command> and <command>Setuid</command></title></info>

	<para>
	  On Unix servers, it is possible to run <acronym>BIND</acronym>
	  in a <emphasis>chrooted</emphasis> environment (using
	  the <command>chroot()</command> function) by specifying
	  the <option>-t</option> option for <command>named</command>.
	  This can help improve system security by placing
	  <acronym>BIND</acronym> in a "sandbox," which limits
	  the damage done if a server is compromised.
	</para>
	<para>
	  Another useful feature in the Unix version of <acronym>BIND</acronym> is the
	  ability to run the daemon as an unprivileged user (<option>-u</option> <replaceable>user</replaceable>).
	  We suggest running as an unprivileged user when using the <command>chroot</command> feature.
	</para>
	<para>
	  Here is an example command line to load <acronym>BIND</acronym> in a <command>chroot</command> sandbox,
	  <command>/var/named</command>, and to run <command>named</command> <command>setuid</command> to
	  user 202:
	</para>
	<para>
	  <userinput>/usr/local/sbin/named -u 202 -t /var/named</userinput>
	</para>

	<section xml:id="chroot"><info><title>The <command>chroot</command> Environment</title></info>

	  <para>
	    For a <command>chroot</command> environment
	    to work properly in a particular directory (for example,
	    <filename>/var/named</filename>), the
	    environment must include everything
	    <acronym>BIND</acronym> needs to run.  From
	    <acronym>BIND</acronym>'s point of view,
	    <filename>/var/named</filename> is the root of the
	    filesystem; the values of
	    options like <command>directory</command> and
	    <command>pid-file</command> must be adjusted to account for this.
	  </para>
	  <para>
	    Unlike with earlier versions of BIND,
	    <command>named</command> does <emphasis>not</emphasis> typically need to be compiled
	    statically, nor do shared libraries need to be installed under the new root.
	    However, depending on the operating system, it may be necessary
	    to set up locations such as
	    <filename>/dev/zero</filename>,
	    <filename>/dev/random</filename>,
	    <filename>/dev/log</filename>, and
	    <filename>/etc/localtime</filename>.
	  </para>
	</section>

	<section xml:id="setuid"><info><title>Using the <command>setuid</command> Function</title></info>

	  <para>
	    Prior to running the <command>named</command> daemon,
	    use
	    the <command>touch</command> utility (to change file
	    access and
	    modification times) or the <command>chown</command>
	    utility (to
	    set the user id and/or group id) on files
	    where <acronym>BIND</acronym>
	    should write.
	  </para>
	  <note><simpara>
	    If the <command>named</command> daemon is running as an
	    unprivileged user, it cannot bind to new restricted
	    ports if the server is reloaded.
	  </simpara></note>
	</section>
      </section>

      <section xml:id="dynamic_update_security"><info><title>Dynamic Update Security</title></info>

	<para>
	  Access to the dynamic
	  update facility should be strictly limited.  In earlier versions of
	  <acronym>BIND</acronym>, the only way to do this was
	  based on the IP
	  address of the host requesting the update, by listing an IP address
	  or
	  network prefix in the <command>allow-update</command>
	  zone option.
	  This method is insecure, since the source address of the update UDP
	  packet
	  is easily forged.  Also note that if the IP addresses allowed by the
	  <command>allow-update</command> option include the
	  address of a secondary
	  server which performs forwarding of dynamic updates, the primary can
	  be
	  trivially attacked by sending the update to the secondary, which
	  forwards it to the primary with its own source IP address - causing the
	  primary to approve it without question.
	</para>

	<para>
	  For these reasons, we strongly recommend that updates be
	  cryptographically authenticated by means of transaction signatures
	  (TSIG).  That is, the <command>allow-update</command>
	  option should
	  list only TSIG key names, not IP addresses or network
	  prefixes. Alternatively, the <command>update-policy</command>
	  option can be used.
	</para>

	<para>
	  Some sites choose to keep all dynamically updated DNS data
	  in a subdomain and delegate that subdomain to a separate zone. This
	  way, the top-level zone containing critical data, such as the IP
	  addresses
	  of public web and mail servers, need not allow dynamic update at
	  all.
	</para>

      </section>
    </chapter>

    <chapter xml:id="Bv9ARM.ch08"><info><title>Troubleshooting</title></info>

      <section xml:id="common_problems"><info><title>Common Problems</title></info>

	<section><info><title>It's Not Working; How Can I Figure Out What's Wrong?</title></info>

	  <para>
	    The best solution to installation and
	    configuration issues is to take preventive measures by setting
	    up logging files beforehand. The log files provide a
	    source of hints and information that can be used to identify
	    what went wrong and fix the problem.
	  </para>

	</section>
      </section>
      <section><info><title>Incrementing and Changing the Serial Number</title></info>

	<para>
	  Zone serial numbers are just numbers — they are not
	  date-related.  However, many people set them to a number that
	  represents a date, usually of the form YYYYMMDDRR.
	  Occasionally they make a mistake and set the serial number to a
	  date in the future, then try to correct it by setting
	  it to the current date.  This causes problems because
	  serial numbers are used to indicate that a zone has been
	  updated.  If the serial number on the secondary server is
	  lower than the serial number on the primary, the secondary
	  server attempts to update its copy of the zone.
	</para>

	<para>
	  Setting the serial number to a lower number on the primary
	  server than the one on the secondary server means that the secondary will not perform
	  updates to its copy of the zone.
	</para>

	<para>
	  The solution to this is to add 2147483647 (2^31-1) to the
	  number, reload the zone and make sure all secondaries have updated to
	  the new zone serial number, then reset it to the desired number
	  and reload the zone again.
	</para>

      </section>
      <section xml:id="more_help"><info><title>Where Can I Get Help?</title></info>

	<para>
	The BIND-users mailing list, at https://lists.isc.org/mailman/listinfo/bind-users,
	is an excellent resource for peer user support. In addition, <acronym>ISC</acronym> maintains a
	Knowledgebase of helpful articles at https://kb.isc.org.
	</para>

	<para>
	  Internet Systems Consortium
	  (<acronym>ISC</acronym>) offers annual
	  support agreements for <acronym>BIND</acronym>9, ISC <acronym>DHCP</acronym>, and Kea DHCP.
	  All paid support contracts include advance security notifications; some levels include
	  service level agreements (SLAs), premium software features, and increased priority on bug fixes
	  and feature requests.
	</para>

	<para>
	  Please contact
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="mailto:info@isc.org">info@isc.org</link> or visit
	  <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/contact/">https://www.isc.org/contact/</link>
	  for more information.
	</para>
      </section>
    </chapter>

    <appendix xml:id="Bv9ARM.ch09"><info><title>Release Notes</title></info>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="notes.xml"/>
    </appendix>

    <appendix xml:id="Bv9ARM.ch10"><info><title>A Brief History of the <acronym>DNS</acronym> and <acronym>BIND</acronym></title></info>
      <para xml:id="historical_dns_information">
	Although the Domain Name
	System "officially" began in 1984 with the publication of RFC 920, the
	core of the new system was described in 1983 in RFCs 882 and
	883. From 1984 to 1987, the ARPAnet (the precursor to today's
	Internet) became a testbed of experimentation for developing the
	new naming/addressing scheme in a rapidly expanding,
	operational network environment.  New RFCs were written and
	published in 1987 that modified the original documents to
	incorporate improvements based on the working model. RFC 1034,
	"Domain Names-Concepts and Facilities," and RFC 1035, "Domain
	Names-Implementation and Specification," were published and
	became the standards upon which all <acronym>DNS</acronym> implementations are
	built.
      </para>

      <para>
	The first working domain name server, called "Jeeves," was
	written in 1983-84 by Paul Mockapetris for operation on DEC
	Tops-20
	machines located at the University of Southern California's
	Information
	Sciences Institute (USC-ISI) and SRI International's Network
	Information
	Center (SRI-NIC). A <acronym>DNS</acronym> server for
	Unix machines, the Berkeley Internet
	Name Domain (<acronym>BIND</acronym>) package, was
	written soon after by a group of
	graduate students at the University of California at Berkeley
	under
	a grant from the US Defense Advanced Research Projects
	Administration
	(DARPA).
      </para>
      <para>
	Versions of <acronym>BIND</acronym> through
	4.8.3 were maintained by the Computer
	Systems Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark
	Painter, David Riggle, and Songnian Zhou made up the initial <acronym>BIND</acronym>
	project team. After that, additional work on the software package
	was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment
	Corporation
	employee on loan to the CSRG, worked on <acronym>BIND</acronym> for 2 years, from 1985
	to 1987. Many other people also contributed to <acronym>BIND</acronym> development
	during that time: Doug Kingston, Craig Partridge, Smoot
	Carl-Mitchell,
	Mike Muuss, Jim Bloom and Mike Schwartz. <acronym>BIND</acronym> maintenance was subsequently
	handled by Mike Karels and Øivind Kure.
      </para>
      <para>
	<acronym>BIND</acronym> versions 4.9 and 4.9.1 were
	released by Digital Equipment
	Corporation (which became Compaq Computer Corporation and eventually merged with Hewlett-Packard). Paul Vixie, then
	a DEC employee, became <acronym>BIND</acronym>'s
	primary caretaker. He was assisted
	by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan
	Beecher, Andrew
	Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat
	Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe
	Wolfhugel, and others.
      </para>
      <para>
	In 1994, <acronym>BIND</acronym> version 4.9.2 was sponsored by
	Vixie Enterprises. Paul
	Vixie became <acronym>BIND</acronym>'s principal
	architect/programmer.
      </para>
      <para>
	<acronym>BIND</acronym> versions from 4.9.3 onward
	have been developed and maintained
	by Internet Systems Consortium and its predecessor,
	the Internet Software Consortium,  with support provided
	by ISC's sponsors.
      </para>
      <para>
	As co-architects/programmers, Bob Halley and
	Paul Vixie released the first production-ready version of
	<acronym>BIND</acronym> version 8 in May 1997.
      </para>
      <para>
	BIND version 9 was released in September 2000 and is a
	major rewrite of nearly all aspects of the underlying
	BIND architecture.
      </para>
      <para>
	BIND versions 4 and 8 are officially deprecated.
	No additional development is done
	on BIND version 4 or BIND version 8.
      </para>
      <para>
	<acronym>BIND</acronym> development work is made
	possible today by the sponsorship
	of corporations who purchase professional support services from ISC
	(https://www.isc.org/contact/) and/or donate to our mission, and by the tireless efforts of
	numerous individuals.
      </para>
    </appendix>

    <appendix xml:id="Bv9ARM.ch11"><info><title>General <acronym>DNS</acronym> Reference Information</title></info>

      <section xml:id="ipv6addresses"><info><title>IPv6 addresses (AAAA)</title></info>

	  <para>
	    IPv6 addresses are 128-bit identifiers, for interfaces and
	    sets of interfaces, which were introduced in the <acronym>DNS</acronym> to facilitate
	    scalable Internet routing. There are three types of addresses: <emphasis>Unicast</emphasis>,
	    an identifier for a single interface;
	    <emphasis>Anycast</emphasis>,
	    an identifier for a set of interfaces; and <emphasis>Multicast</emphasis>,
	    an identifier for a set of interfaces. Here we describe the global
	    Unicast address scheme. For more information, see RFC 3587,
	    "IPv6 Global Unicast Address Format."
	  </para>
	  <para>
	    IPv6 unicast addresses consist of a
	    <emphasis>global routing prefix</emphasis>, a
	    <emphasis>subnet identifier</emphasis>, and an
	    <emphasis>interface identifier</emphasis>.
	  </para>
	  <para>
	    The global routing prefix is provided by the
	    upstream provider or ISP, and roughly corresponds to the
	    IPv4 <emphasis>network</emphasis> section
	    of the address range.

	    The subnet identifier is for local subnetting, much
	    like subnetting an
	    IPv4 /16 network into /24 subnets.

	    The interface identifier is the address of an individual
	    interface on a given network; in IPv6, addresses belong to
	    interfaces rather than to machines.
	  </para>
	  <para>
	    The subnetting capability of IPv6 is much more flexible than
	    that of IPv4; subnetting can be carried out on bit boundaries,
	    in much the same way as Classless InterDomain Routing
	    (CIDR), and the DNS PTR representation ("nibble" format)
	    makes setting up reverse zones easier.
	  </para>
	  <para>
	    The interface identifier must be unique on the local link,
	    and is usually generated automatically by the IPv6
	    implementation, although it is usually possible to
	    override the default setting if necessary.  A typical IPv6
	    address might look like:
	    <command>2001:db8:201:9:a00:20ff:fe81:2b32</command>.
	  </para>
	  <para>
	    IPv6 address specifications often contain long strings
	    of zeros, so the architects have included a shorthand for
	    specifying
	    them. The double colon ("::") indicates the longest possible
	    string
	    of zeros that can fit, and can be used only once in an address.
	  </para>
      </section>
      <section xml:id="bibliography"><info><title>Bibliography (and Suggested Reading)</title></info>

	<section xml:id="rfcs"><info><title>Requests for Comments (RFCs)</title></info>

	  <para>
	    Specification documents for the Internet protocol suite, including
	    the <acronym>DNS</acronym>, are published as part of
	    the Request for Comments (RFCs)
	    series of technical notes. The standards themselves are defined
	    by the Internet Engineering Task Force (IETF) and the Internet
	    Engineering Steering Group (IESG). RFCs can be obtained online at:
	  </para>
	  <para>
	    <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://datatracker.ietf.org/doc/">
	    https://datatracker.ietf.org/doc/
	    </link>
	  </para>

	  <bibliography><title/>
	    <bibliodiv><title>Standards</title>
	      <!-- one of (BIBLIOENTRY BIBLIOMIXED) -->

	      <biblioentry>
		<abbrev>RFC974</abbrev>
		<author><personname><surname>Partridge</surname><firstname>C.</firstname></personname></author>
		<title>Mail Routing and the Domain System</title>
		<pubdate>January 1986</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1034</abbrev>
		<author><personname><surname>Mockapetris</surname><firstname>P.V.</firstname></personname></author>
		<title>Domain Names — Concepts and Facilities</title>
		<pubdate>November 1987</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1035</abbrev>
		<author><personname><surname>Mockapetris</surname><firstname>P. V.</firstname></personname></author> <title>Domain Names — Implementation and
		  Specification</title>
		<pubdate>November 1987</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv xml:id="proposed_standards" xreflabel="Proposed Standards"><title>Proposed Standards</title>

	      <!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
	      <biblioentry>
		<abbrev>RFC2181</abbrev>
		<author><personname><surname>Elz</surname><firstname>R., R. Bush</firstname></personname></author>
		<title>Clarifications to the <acronym>DNS</acronym>
		  Specification</title>
		<pubdate>July 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2308</abbrev>
		<author><personname><surname>Andrews</surname><firstname>M.</firstname></personname></author>
		<title>Negative Caching of <acronym>DNS</acronym>
		  Queries</title>
		<pubdate>March 1998</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1995</abbrev>
		<author><personname><surname>Ohta</surname><firstname>M.</firstname></personname></author>
		<title>Incremental Zone Transfer in <acronym>DNS</acronym></title>
		<pubdate>August 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1996</abbrev>
		<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
		<title>A Mechanism for Prompt Notification of Zone Changes</title>
		<pubdate>August 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2136</abbrev>
		<authorgroup>
		  <author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Thomson</surname></personname></author>
		  <author><personname><firstname>Y.</firstname><surname>Rekhter</surname></personname></author>
		  <author><personname><firstname>J.</firstname><surname>Bound</surname></personname></author>
		</authorgroup>
		<title>Dynamic Updates in the Domain Name System</title>
		<pubdate>April 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2671</abbrev>
		<authorgroup>
		  <author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
		</authorgroup>
		<title>Extension Mechanisms for DNS (EDNS0)</title>
		<pubdate>August 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2672</abbrev>
		<authorgroup>
		  <author><personname><firstname>M.</firstname><surname>Crawford</surname></personname></author>
		</authorgroup>
		<title>Non-Terminal DNS Name Redirection</title>
		<pubdate>August 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2845</abbrev>
		<authorgroup>
		  <author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
		  <author><personname><firstname>O.</firstname><surname>Gudmundsson</surname></personname></author>
		  <author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
		  <author><personname><firstname>B.</firstname><surname>Wellington</surname></personname></author>
		</authorgroup>
		<title>Secret Key Transaction Authentication for <acronym>DNS</acronym> (TSIG)</title>
		<pubdate>May 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2930</abbrev>
		<authorgroup>
		  <author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
		</authorgroup>
		<title>Secret Key Establishment for DNS (TKEY RR)</title>
		<pubdate>September 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2931</abbrev>
		<authorgroup>
		  <author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
		</authorgroup>
		<title>DNS Request and Transaction Signatures (SIG(0)s)</title>
		<pubdate>September 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3007</abbrev>
		<authorgroup>
		  <author><personname><firstname>B.</firstname><surname>Wellington</surname></personname></author>
		</authorgroup>
		<title>Secure Domain Name System (DNS) Dynamic Update</title>
		<pubdate>November 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3645</abbrev>
		<authorgroup>
		  <author><personname><firstname>S.</firstname><surname>Kwan</surname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Garg</surname></personname></author>
		  <author><personname><firstname>J.</firstname><surname>Gilroy</surname></personname></author>
		  <author><personname><firstname>L.</firstname><surname>Esibov</surname></personname></author>
		  <author><personname><firstname>J.</firstname><surname>Westhead</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Hall</surname></personname></author>
		</authorgroup>
		<title>Generic Security Service Algorithm for Secret
		       Key Transaction Authentication for DNS
		       (GSS-TSIG)</title>
		<pubdate>October 2003</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title><acronym>DNS</acronym> Security Proposed Standards</title>

	      <biblioentry>
		<abbrev>RFC3225</abbrev>
		<authorgroup>
		  <author><personname><firstname>D.</firstname><surname>Conrad</surname></personname></author>
		</authorgroup>
		<title>Indicating Resolver Support of DNSSEC</title>
		<pubdate>December 2001</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3833</abbrev>
		<authorgroup>
		  <author><personname><firstname>D.</firstname><surname>Atkins</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
		</authorgroup>
		<title>Threat Analysis of the Domain Name System (DNS)</title>
		<pubdate>August 2004</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC4033</abbrev>
		<authorgroup>
		  <author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
		  <author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
		</authorgroup>
		<title>DNS Security Introduction and Requirements</title>
		<pubdate>March 2005</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC4034</abbrev>
		<authorgroup>
		  <author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
		  <author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
		</authorgroup>
		<title>Resource Records for the DNS Security Extensions</title>
		<pubdate>March 2005</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC4035</abbrev>
		<authorgroup>
		  <author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
		  <author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
		</authorgroup>
		<title>Protocol Modifications for the DNS
		       Security Extensions</title>
		<pubdate>March 2005</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Other Important RFCs About <acronym>DNS</acronym>
		Implementation</title>

	      <biblioentry>
		<abbrev>RFC1535</abbrev>
		<author><personname><surname>Gavron</surname><firstname>E.</firstname></personname></author>
		<title>A Security Problem and Proposed Correction With Widely
		  Deployed <acronym>DNS</acronym> Software</title>
		<pubdate>October 1993</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1536</abbrev>
		<authorgroup>
		  <author><personname><surname>Kumar</surname><firstname>A.</firstname></personname></author>
		  <author><personname><firstname>J.</firstname><surname>Postel</surname></personname></author>
		  <author><personname><firstname>C.</firstname><surname>Neuman</surname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Danzig</surname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Miller</surname></personname></author>
		</authorgroup>
		<title>Common <acronym>DNS</acronym> Implementation
		  Errors and Suggested Fixes</title>
		<pubdate>October 1993</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1982</abbrev>
		<authorgroup>
		  <author><personname><surname>Elz</surname><firstname>R.</firstname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Bush</surname></personname></author>
		</authorgroup>
		<title>Serial Number Arithmetic</title>
		<pubdate>August 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC4074</abbrev>
		<authorgroup>
		  <author><personname><surname>Morishita</surname><firstname>Y.</firstname></personname></author>
		  <author><personname><firstname>T.</firstname><surname>Jinmei</surname></personname></author>
		</authorgroup>
		<title>Common Misbehaviour Against <acronym>DNS</acronym>
		Queries for IPv6 Addresses</title>
		<pubdate>May 2005</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Resource Record Types</title>

	      <biblioentry>
		<abbrev>RFC1183</abbrev>
		<authorgroup>
		  <author><personname><surname>Everhart</surname><firstname>C.F.</firstname></personname></author>
		  <author><personname><firstname>L. A.</firstname><surname>Mamakos</surname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Ullmann</surname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Mockapetris</surname></personname></author>
		</authorgroup>
		<title>New <acronym>DNS</acronym> RR Definitions</title>
		<pubdate>October 1990</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1706</abbrev>
		<authorgroup>
		  <author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Colella</surname></personname></author>
		</authorgroup>
		<title><acronym>DNS</acronym> NSAP Resource Records</title>
		<pubdate>October 1994</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2168</abbrev>
		<authorgroup>
		  <author><personname><surname>Daniel</surname><firstname>R.</firstname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Mealling</surname></personname></author>
		</authorgroup>
		<title>Resolution of Uniform Resource Identifiers using
		  the Domain Name System</title>
		<pubdate>June 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1876</abbrev>
		<authorgroup>
		  <author><personname><surname>Davis</surname><firstname>C.</firstname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
		  <author><personname><firstname>T.</firstname><firstname>Goodwin</firstname></personname></author>
		  <author><personname><firstname>I.</firstname><surname>Dickinson</surname></personname></author>
		</authorgroup>
		<title>A Means for Expressing Location Information in the
		  Domain
		  Name System</title>
		<pubdate>January 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2052</abbrev>
		<authorgroup>
		  <author><personname><surname>Gulbrandsen</surname><firstname>A.</firstname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
		</authorgroup>
		<title>A <acronym>DNS</acronym> RR for Specifying the
		  Location of
		  Services</title>
		<pubdate>October 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2163</abbrev>
		<author><personname><surname>Allocchio</surname><firstname>A.</firstname></personname></author>
		<title>Using the Internet <acronym>DNS</acronym> to
		  Distribute MIXER
		  Conformant Global Address Mapping</title>
		<pubdate>January 1998</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2230</abbrev>
		<author><personname><surname>Atkinson</surname><firstname>R.</firstname></personname></author>
		<title>Key Exchange Delegation Record for the <acronym>DNS</acronym></title>
		<pubdate>October 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2536</abbrev>
		<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		<title>DSA KEYs and SIGs in the Domain Name System (DNS)</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2537</abbrev>
		<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		<title>RSA/MD5 KEYs and SIGs in the Domain Name System (DNS)</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2538</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		  <author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
		</authorgroup>
		<title>Storing Certificates in the Domain Name System (DNS)</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2539</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		</authorgroup>
		<title>Storage of Diffie-Hellman Keys in the Domain Name System (DNS)</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2540</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		</authorgroup>
		<title>Detached Domain Name System (DNS) Information</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2782</abbrev>
		<author><personname><surname>Gulbrandsen</surname><firstname>A.</firstname></personname></author>
		<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
		<author><personname><surname>Esibov</surname><firstname>L.</firstname></personname></author>
		<title>A DNS RR for specifying the location of services (DNS SRV)</title>
		<pubdate>February 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2915</abbrev>
		<author><personname><surname>Mealling</surname><firstname>M.</firstname></personname></author>
		<author><personname><surname>Daniel</surname><firstname>R.</firstname></personname></author>
		<title>The Naming Authority Pointer (NAPTR) DNS Resource Record</title>
		<pubdate>September 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3110</abbrev>
		<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		<title>RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)</title>
		<pubdate>May 2001</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3123</abbrev>
		<author><personname><surname>Koch</surname><firstname>P.</firstname></personname></author>
		<title>A DNS RR Type for Lists of Address Prefixes (APL RR)</title>
		<pubdate>June 2001</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3596</abbrev>
		<authorgroup>
		  <author><personname><surname>Thomson</surname><firstname>S.</firstname></personname></author>
		  <author><personname><firstname>C.</firstname><surname>Huitema</surname></personname></author>
		  <author><personname><firstname>V.</firstname><surname>Ksinant</surname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Souissi</surname></personname></author>
		</authorgroup>
		<title><acronym>DNS</acronym> Extensions to support IP
		  version 6</title>
		<pubdate>October 2003</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3597</abbrev>
		<author><personname><surname>Gustafsson</surname><firstname>A.</firstname></personname></author>
		<title>Handling of Unknown DNS Resource Record (RR) Types</title>
		<pubdate>September 2003</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title><acronym>DNS</acronym> and the Internet</title>

	      <biblioentry>
		<abbrev>RFC1101</abbrev>
		<author><personname><surname>Mockapetris</surname><firstname>P. V.</firstname></personname></author>
		<title><acronym>DNS</acronym> Encoding of Network Names
		  and Other Types</title>
		<pubdate>April 1989</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1123</abbrev>
		<author><personname><surname>Braden</surname><surname>R.</surname></personname></author>
		<title>Requirements for Internet Hosts - Application and
		  Support</title>
		<pubdate>October 1989</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1591</abbrev>
		<author><personname><surname>Postel</surname><firstname>J.</firstname></personname></author>
		<title>Domain Name System Structure and Delegation</title>
		<pubdate>March 1994</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2317</abbrev>
		<authorgroup>
		  <author><personname><surname>Eidnes</surname><firstname>H.</firstname></personname></author>
		  <author><personname><firstname>G.</firstname><surname>de Groot</surname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
		</authorgroup>
		<title>Classless IN-ADDR.ARPA Delegation</title>
		<pubdate>March 1998</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2826</abbrev>
		<authorgroup>
		  <author><personname><surname>Internet Architecture Board</surname></personname></author>
		</authorgroup>
		<title>IAB Technical Comment on the Unique DNS Root</title>
		<pubdate>May 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2929</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
		  <author><personname><surname>Brunner-Williams</surname><firstname>E.</firstname></personname></author>
		  <author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
		</authorgroup>
		<title>Domain Name System (DNS) IANA Considerations</title>
		<pubdate>September 2000</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title><acronym>DNS</acronym> Operations</title>

	      <biblioentry>
		<abbrev>RFC1033</abbrev>
		<author><personname><surname>Lottor</surname><firstname>M.</firstname></personname></author>
		<title>Domain administrators operations guide</title>
		<pubdate>November 1987</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1537</abbrev>
		<author><personname><surname>Beertema</surname><firstname>P.</firstname></personname></author>
		<title>Common <acronym>DNS</acronym> Data File
		  Configuration Errors</title>
		<pubdate>October 1993</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1912</abbrev>
		<author><personname><surname>Barr</surname><firstname>D.</firstname></personname></author>
		<title>Common <acronym>DNS</acronym> Operational and
		  Configuration Errors</title>
		<pubdate>February 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2010</abbrev>
		<authorgroup>
		  <author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
		  <author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
		</authorgroup>
		<title>Operational Criteria for Root Name Servers</title>
		<pubdate>October 1996</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2219</abbrev>
		<authorgroup>
		  <author><personname><surname>Hamilton</surname><firstname>M.</firstname></personname></author>
		  <author><personname><firstname>R.</firstname><surname>Wright</surname></personname></author>
		</authorgroup>
		<title>Use of <acronym>DNS</acronym> Aliases for
		  Network Services</title>
		<pubdate>October 1997</pubdate>
	      </biblioentry>
              <biblioentry>
                <abbrev>RFC8906</abbrev>
                <authorgroup>
		  <author><personname><surname>Andrews</surname><firstname>M.</firstname></personname></author>
		  <author><personname><surname>Bellis</surname><firstname>R.</firstname></personname></author>
                </authorgroup>
                <title>
                  A Common Operational Problem in DNS Servers: Failure to Communicate
                </title>
                <pubdate>September 2020</pubdate>
              </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Internationalized Domain Names</title>

	      <biblioentry>
		<abbrev>RFC2825</abbrev>
		<authorgroup>
		  <author><personname><surname>IAB</surname></personname></author>
		  <author><personname><surname>Daigle</surname><firstname>R.</firstname></personname></author>
		</authorgroup>
		<title>A Tangled Web: Issues of I18N, Domain Names,
		       and the Other Internet protocols</title>
		<pubdate>May 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3490</abbrev>
		<authorgroup>
		  <author><personname><surname>Faltstrom</surname><firstname>P.</firstname></personname></author>
		  <author><personname><surname>Hoffman</surname><firstname>P.</firstname></personname></author>
		  <author><personname><surname>Costello</surname><firstname>A.</firstname></personname></author>
		</authorgroup>
		<title>Internationalizing Domain Names in Applications (IDNA)</title>
		<pubdate>March 2003</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3491</abbrev>
		<authorgroup>
		  <author><personname><surname>Hoffman</surname><firstname>P.</firstname></personname></author>
		  <author><personname><surname>Blanchet</surname><firstname>M.</firstname></personname></author>
		</authorgroup>
		<title>Nameprep: A Stringprep Profile for Internationalized Domain Names</title>
		<pubdate>March 2003</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3492</abbrev>
		<authorgroup>
		  <author><personname><surname>Costello</surname><firstname>A.</firstname></personname></author>
		</authorgroup>
		<title>Punycode: A Bootstring encoding of Unicode
		       for Internationalized Domain Names in
		       Applications (IDNA)</title>
		<pubdate>March 2003</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Other <acronym>DNS</acronym>-related RFCs</title>

	      <note>
		<para>
		  Note: the following list of RFCs, although
		  <acronym>DNS</acronym>-related, are not
		  concerned with implementing software.
		</para>
	      </note>
	      <biblioentry>
		<abbrev>RFC1464</abbrev>
		<author><personname><surname>Rosenbaum</surname><firstname>R.</firstname></personname></author>
		<title>Using the Domain Name System To Store Arbitrary String
		  Attributes</title>
		<pubdate>May 1993</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1713</abbrev>
		<author><personname><surname>Romao</surname><firstname>A.</firstname></personname></author>
		<title>Tools for <acronym>DNS</acronym> Debugging</title>
		<pubdate>November 1994</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC1794</abbrev>
		<author><personname><surname>Brisco</surname><firstname>T.</firstname></personname></author>
		<title><acronym>DNS</acronym> Support for Load
		  Balancing</title>
		<pubdate>April 1995</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2240</abbrev>
		<author><personname><surname>Vaughan</surname><firstname>O.</firstname></personname></author>
		<title>A Legal Basis for Domain Name Allocation</title>
		<pubdate>November 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2345</abbrev>
		<authorgroup>
		  <author><personname><surname>Klensin</surname><firstname>J.</firstname></personname></author>
		  <author><personname><firstname>T.</firstname><surname>Wolf</surname></personname></author>
		  <author><personname><firstname>G.</firstname><surname>Oglesby</surname></personname></author>
		</authorgroup>
		<title>Domain Names and Company Name Retrieval</title>
		<pubdate>May 1998</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2352</abbrev>
		<author><personname><surname>Vaughan</surname><firstname>O.</firstname></personname></author>
		<title>A Convention For Using Legal Names as Domain Names</title>
		<pubdate>May 1998</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3071</abbrev>
		<authorgroup>
		  <author><personname><surname>Klensin</surname><firstname>J.</firstname></personname></author>
		</authorgroup>
		<title>Reflections on the DNS, RFC 1591, and Categories of Domains</title>
		<pubdate>February 2001</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3258</abbrev>
		<authorgroup>
		  <author><personname><surname>Hardie</surname><firstname>T.</firstname></personname></author>
		</authorgroup>
		<title>Distributing Authoritative Name Servers via
		       Shared Unicast Addresses</title>
		<pubdate>April 2002</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3901</abbrev>
		<authorgroup>
		  <author><personname><surname>Durand</surname><firstname>A.</firstname></personname></author>
		  <author><personname><firstname>J.</firstname><surname>Ihren</surname></personname></author>
		</authorgroup>
		<title>DNS IPv6 Transport Operational Guidelines</title>
		<pubdate>September 2004</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Obsolete and Unimplemented Experimental RFC</title>

	      <biblioentry>
		<abbrev>RFC1712</abbrev>
		<authorgroup>
		  <author><personname><surname>Farrell</surname><firstname>C.</firstname></personname></author>
		  <author><personname><firstname>M.</firstname><surname>Schulze</surname></personname></author>
		  <author><personname><firstname>S.</firstname><surname>Pleitner</surname></personname></author>
		  <author><personname><firstname>D.</firstname><surname>Baldoni</surname></personname></author>
		</authorgroup>
		<title><acronym>DNS</acronym> Encoding of Geographical
		  Location</title>
		<pubdate>November 1994</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2673</abbrev>
		<authorgroup>
		  <author><personname><surname>Crawford</surname><firstname>M.</firstname></personname></author>
		</authorgroup>
		<title>Binary Labels in the Domain Name System</title>
		<pubdate>August 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2874</abbrev>
		<authorgroup>
		  <author><personname><surname>Crawford</surname><firstname>M.</firstname></personname></author>
		  <author><personname><surname>Huitema</surname><firstname>C.</firstname></personname></author>
		</authorgroup>
		<title>DNS Extensions to Support IPv6 Address Aggregation
		       and Renumbering</title>
		<pubdate>July 2000</pubdate>
	      </biblioentry>
	    </bibliodiv>
	    <bibliodiv><title>Obsoleted DNS Security RFCs</title>

	      <note>
		<para>
		  Most of these have been consolidated into RFC4033,
		  RFC4034 and RFC4035 which collectively describe DNSSECbis.
		</para>
	      </note>
	      <biblioentry>
		<abbrev>RFC2065</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
		  <author><personname><firstname>C.</firstname><surname>Kaufman</surname></personname></author>
		</authorgroup>
		<title>Domain Name System Security Extensions</title>
		<pubdate>January 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2137</abbrev>
		<author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
		<title>Secure Domain Name System Dynamic Update</title>
		<pubdate>April 1997</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC2535</abbrev>
		<authorgroup>
		  <author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
		</authorgroup>
		<title>Domain Name System Security Extensions</title>
		<pubdate>March 1999</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3008</abbrev>
		<authorgroup>
		  <author><personname><surname>Wellington</surname><firstname>B.</firstname></personname></author>
		</authorgroup>
		<title>Domain Name System Security (DNSSEC)
		       Signing Authority</title>
		<pubdate>November 2000</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3090</abbrev>
		<authorgroup>
		  <author><personname><surname>Lewis</surname><firstname>E.</firstname></personname></author>
		</authorgroup>
		<title>DNS Security Extension Clarification on Zone Status</title>
		<pubdate>March 2001</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3445</abbrev>
		<authorgroup>
		  <author><personname><surname>Massey</surname><firstname>D.</firstname></personname></author>
		  <author><personname><surname>Rose</surname><firstname>S.</firstname></personname></author>
		</authorgroup>
		<title>Limiting the Scope of the KEY Resource Record (RR)</title>
		<pubdate>December 2002</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3655</abbrev>
		<authorgroup>
		  <author><personname><surname>Wellington</surname><firstname>B.</firstname></personname></author>
		  <author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
		</authorgroup>
		<title>Redefinition of DNS Authenticated Data (AD) bit</title>
		<pubdate>November 2003</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3658</abbrev>
		<authorgroup>
		  <author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
		</authorgroup>
		<title>Delegation Signer (DS) Resource Record (RR)</title>
		<pubdate>December 2003</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3755</abbrev>
		<authorgroup>
		  <author><personname><surname>Weiler</surname><firstname>S.</firstname></personname></author>
		</authorgroup>
		<title>Legacy Resolver Compatibility for Delegation Signer (DS)</title>
		<pubdate>May 2004</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3757</abbrev>
		<authorgroup>
		  <author><personname><surname>Kolkman</surname><firstname>O.</firstname></personname></author>
		  <author><personname><surname>Schlyter</surname><firstname>J.</firstname></personname></author>
		  <author><personname><surname>Lewis</surname><firstname>E.</firstname></personname></author>
		</authorgroup>
		<title>Domain Name System KEY (DNSKEY) Resource Record
		      (RR) Secure Entry Point (SEP) Flag</title>
		<pubdate>April 2004</pubdate>
	      </biblioentry>
	      <biblioentry>
		<abbrev>RFC3845</abbrev>
		<authorgroup>
		  <author><personname><surname>Schlyter</surname><firstname>J.</firstname></personname></author>
		</authorgroup>
		<title>DNS Security (DNSSEC) NextSECure (NSEC) RDATA Format</title>
		<pubdate>August 2004</pubdate>
	      </biblioentry>
	    </bibliodiv>
	  </bibliography>
	</section>
	<section xml:id="internet_drafts"><title>Internet Drafts</title>

	  <para>
	    Internet Drafts (IDs) are rough-draft working documents of
	    the Internet Engineering Task Force. They are, in essence, RFCs
	    in the preliminary stages of development. Implementors are
	    cautioned not
	    to regard IDs as archival, and they should not be quoted or cited
	    in any formal documents unless accompanied by the disclaimer that
	    they are "works in progress." IDs have a lifespan of six months
	    after which they are deleted unless updated by their authors.
	  </para>
	</section>
	<section xml:id="more_about_bind"><info><title>Other Documents About <acronym>BIND</acronym></title></info>

	  <para/>
	  <bibliography><title/>
	    <biblioentry>
	      <authorgroup>
		<author><personname><surname>Albitz</surname><firstname>Paul</firstname></personname></author>
		<author><personname><firstname>Cricket</firstname><surname>Liu</surname></personname></author>
	      </authorgroup>
	      <title><acronym>DNS</acronym> and <acronym>BIND</acronym></title>
	      <copyright>
		<year>1998</year>
		<holder>Sebastopol, CA: O'Reilly and Associates</holder>
	      </copyright>
	    </biblioentry>
	  </bibliography>
	</section>
      </section>
    </appendix>

    <appendix xml:id="Bv9ARM.ch12"><info><title>BIND 9 DNS Library Support</title></info>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="libdns.xml"/>
    </appendix>

    <reference xml:id="Bv9ARM.ch13"><info><title>Manual pages</title></info>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/arpaname.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/confgen/ddns-confgen.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/delv/delv.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dig/dig.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/python/dnssec-checkds.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/python/dnssec-coverage.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-dsfromkey.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-importkey.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-keyfromlabel.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-keygen.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/python/dnssec-keymgr.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-revoke.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-settime.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-signzone.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dnssec/dnssec-verify.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/dnstap-read.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/genrandom.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dig/host.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/isc-hmac-fixup.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/named/lwresd.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/mdig.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/check/named-checkconf.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/check/named-checkzone.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/named-journalprint.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/named-nzd2nzf.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/named-rrchecker.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/named/named.conf.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/named/named.docbook"/>
       <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/tools/nsec3hash.docbook"/>
     <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/dig/nslookup.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/nsupdate/nsupdate.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/pkcs11/pkcs11-destroy.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/pkcs11/pkcs11-keygen.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/pkcs11/pkcs11-list.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/pkcs11/pkcs11-tokens.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/confgen/rndc-confgen.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/rndc/rndc.conf.docbook"/>
      <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="../../bin/rndc/rndc.docbook"/>
    </reference>

  </book>