
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.0//EN"
               "http://www.oasis-open.org/docbook/xml/4.0/docbookx.dtd">

<!-- File: $Id: Bv9ARM-book.xml,v 1.159 2001/09/15 14:23:29 marka Exp $ -->

<book>
<title>BIND 9 Administrator Reference Manual</title>

<bookinfo>
<copyright>
<year>2000</year>
<year>2001</year>
<holder>Internet Software Consortium</holder>
</copyright>
</bookinfo>

  <chapter id="ch01">
  <title>Introduction </title>
  <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>

  <sect1>
    <title>Scope of Document</title>

    <para>The Berkeley Internet Name Domain (<acronym>BIND</acronym>) implements an
    domain name server for a number of operating systems. This
    document provides basic information about the installation and
    care of the Internet Software Consortium (<acronym>ISC</acronym>)
    <acronym>BIND</acronym> version 9 software package for system
    administrators.</para>

    <para>This version of the manual corresponds to BIND version 9.2.</para>
    
  </sect1>
  <sect1><title>Organization of This Document</title>
    <para>In this document, <emphasis>Section 1</emphasis> introduces
    the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Section 2</emphasis>
    describes resource requirements for running <acronym>BIND</acronym> in various
    environments. Information in <emphasis>Section 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>Section 4</emphasis>, which contains more advanced
    concepts that the system administrator may need for implementing
    certain options. <emphasis>Section 5</emphasis>
    describes the <acronym>BIND</acronym> 9 lightweight
    resolver.  The contents of <emphasis>Section 6</emphasis> are
    organized as in a reference manual to aid in the ongoing
    maintenance of the software. <emphasis>Section 7
    </emphasis>addresses security considerations, and
    <emphasis>Section 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>
  </sect1>
  <sect1><title>Conventions Used in This Document</title>

    <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></sect1>
<sect1><title>The Domain Name System (<acronym>DNS</acronym>)</title>
<para>The purpose of this document is to explain the installation
and upkeep of the <acronym>BIND</acronym> software package, and we
begin by reviewing the fundamentals of the Domain Name System
(<acronym>DNS</acronym>) as they relate to <acronym>BIND</acronym>.
</para>

<sect2>
<title>DNS Fundamentals</title>

<para>The Domain Name System (DNS) is the 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 9</acronym> software distribution contains both a 
name server and a resolver library.</para>

</sect2><sect2>
<title>Domains and Domain Names</title>

<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>mail.example.net</literal>,
were <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>
</sect2>

<sect2><title>Zones</title>
<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 we 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 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 that you read 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 master and slave
declarations in the <filename>named.conf</filename> file specify
zones, not domains. When you ask some other site if it is willing to
be a slave server for your <emphasis>domain</emphasis>, you are
actually asking for slave service for some collection of zones.</para>
</sect2>

<sect2><title>Authoritative Name Servers</title>

<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.
</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>

<sect3><title>The Primary Master</title>

<para>
The authoritative server where the master copy of the zone data is maintained is
called the <emphasis>primary master</emphasis> server, or simply the
<emphasis>primary</emphasis>.  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>
</sect3>

<sect3><title>Slave Servers</title>
<para>The other authoritative servers, the <emphasis>slave</emphasis>
servers (also known as <emphasis>secondary</emphasis> servers) load
the zone contents from another server using a replication process
known as a <emphasis>zone transfer</emphasis>.  Typically the data are
transferred directly from the primary master, but it is also possible
to transfer it from another slave.  In other words, a slave server
may itself act as a master to a subordinate slave server.</para>
</sect3>

<sect3><title>Stealth Servers</title>

<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.  You can list servers in the zone's top-level NS
records that are not in the parent's NS delegation, but you cannot
list servers in the parent's delegation that are not present at
the zone's top level.</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 master server itself is a
stealth server is often referred to as a "hidden primary"
configuration.  One use for this configuration is when the primary master
is behind a firewall and therefore unable to communicate directly
with the outside world.</para>

</sect3>

</sect2>
<sect2>

<title>Caching Name Servers</title>

<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
in the cache of a caching name server is controlled by the 
Time To Live (TTL) field associated with each resource record.
</para>

<sect3><title>Forwarding</title>

<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>There may be one or more forwarders,
and they are queried in turn until the list is exhausted or an answer
is found. Forwarders are typically used when you do not
wish all the servers at a given site to interact directly with the rest of
the Internet servers. A typical scenario would involve a number
of internal <acronym>DNS</acronym> servers and an Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <acronym>DNS</acronym> servers
on the internal server's behalf. An added benefit of using the forwarding
feature is that the central machine develops a much more complete
cache of information that all the clients can take advantage
of.</para>
</sect3>

</sect2>

<sect2><title>Name Servers in Multiple Roles</title>

<para>The <acronym>BIND</acronym> name server can simultaneously act as
a master for some zones, a slave for other zones, and as 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>

    </sect2>
  </sect1>

</chapter>

<chapter id="ch02"><title><acronym>BIND</acronym> Resource Requirements</title>

<sect1>
<title>Hardware requirements</title>

<para><acronym>DNS</acronym> hardware requirements have traditionally been quite modest.
For many installations, servers that have been pensioned off from
active duty have performed admirably as <acronym>DNS</acronym> servers.</para>
<para>The DNSSEC and IPv6 features of <acronym>BIND</acronym> 9 may prove to be quite
CPU intensive however, so organizations that make heavy use of these
features may wish to consider larger systems for these applications.
<acronym>BIND</acronym> 9 is now fully multithreaded, allowing full utilization of
multiprocessor systems for installations that need it.</para></sect1>
<sect1><title>CPU Requirements</title>
<para>CPU requirements for <acronym>BIND</acronym> 9 range from i486-class machines
for serving of static zones without caching, to enterprise-class
machines if you intend to process many dynamic updates and DNSSEC
signed zones, serving many thousands of queries per second.</para></sect1>

<sect1><title>Memory Requirements</title>
<para>The memory of the server has to be large enough to fit the
cache and zones loaded off disk.  The <command>max-cache-size</command>
option can be used to limit the amount of memory used by the cache,
at the expense of reducing cache hit rates and causing more <acronym>DNS</acronym>
traffic. It is still good practice to have enough memory to load
all zone and cache data into memory &mdash; unfortunately, the best way
to determine this for a given installation is to watch the nameserver
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. Ideally, the resource limits should
be set higher than this stable size.</para></sect1>

<sect1><title>Nameserver Intensive Environment Issues</title>
<para>For nameserver intensive environments, there are two alternative
configurations that may be used. The first is where clients and
any second-level internal nameservers query a main nameserver, 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 nameservers to make queries independently.
In this configuration, none of the individual machines needs 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 nameservers share their cached data.</para></sect1>
<sect1><title>Supported Operating Systems</title>
<para>ISC <acronym>BIND</acronym> 9 compiles and runs on the following operating
systems:</para>
    <itemizedlist>
      <listitem>
        <simpara>IBM AIX 4.3</simpara>
      </listitem>
      <listitem>
        <simpara>Compaq Digital/Tru64 UNIX 4.0D</simpara>
      </listitem>
      <listitem>
        <simpara>Compaq Digital/Tru64 UNIX 5 (with IPv6 EAK)</simpara>
      </listitem>
      <listitem>
        <simpara>HP HP-UX 11</simpara>
      </listitem>
      <listitem>
        <simpara>IRIX64 6.5</simpara>
      </listitem>
      <listitem>
        <simpara>Sun Solaris 2.6, 7, 8</simpara>
      </listitem>
      <listitem>
        <simpara>NetBSD 1.5 (with unproven-pthreads 0.17)</simpara>
      </listitem>
      <listitem>
        <simpara>FreeBSD 3.4-STABLE, 3.5, 4.0, 4.1</simpara>
      </listitem>
      <listitem>
        <simpara>Red Hat Linux 6.0, 6.1, 6.2, 7.0</simpara>
      </listitem>
    </itemizedlist>
  </sect1>
  </chapter>

  <chapter id="ch03">
  <title>Nameserver Configuration</title>
<para>In this section we provide some suggested configurations along
with guidelines for their use. We also address the topic of reasonable
option setting.</para>
  <sect1 id="sample_configuration">
    <title>Sample Configurations</title>
    <sect2>
      <title>A Caching-only Nameserver</title>
      <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.</para>
      <programlisting>
// Two corporate subnets we wish to allow queries from.
acl "corpnets" { 192.168.4.0/24; 192.168.7.0/24; };
options {
     directory "/etc/namedb";           // Working directory
     pid-file "named.pid";              // Put pid file in working dir
     allow-query { "corpnets"; };
};
// Root server hints
zone "." { type hint; file "root.hint"; };
// 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>
    </sect2>
    <sect2>
      <title>An Authoritative-only Nameserver</title>
      <para>This sample configuration is for an authoritative-only server
that is the master server for "<filename>example.com</filename>"
and a slave for the subdomain "<filename>eng.example.com</filename>".</para>
      <programlisting>
options {
     directory "/etc/namedb";           // Working directory
     pid-file "named.pid";              // Put pid file in working dir
     allow-query { any; };              // This is the default
     recursion no;                      // Do not provide recursive service
};
// Root server hints
zone "." { type hint; file "root.hint"; };

// 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 master server for example.com
zone "example.com" {
     type master;
     file "example.com.db";
     // IP addresses of slave servers allowed to transfer example.com
     allow-transfer {
          192.168.4.14;
          192.168.5.53;
     };
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
     type slave;
     file "eng.example.com.bk";
     // IP address of eng.example.com master server
     masters { 192.168.4.12; };
};
</programlisting>
    </sect2>
  </sect1>
  <sect1>
    <title>Load Balancing</title>
    <para>Primitive load balancing can be achieved in <acronym>DNS</acronym> using multiple
A records for one name.</para>
<para>For example, if you have three WWW 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></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></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> will rotate
    them and respond to the query with the records in a different
    order.  In the example above, clients will randomly receive
    records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
    will use the first record returned and discard the rest.</para>
    <para>For more detail on ordering responses, check the
    <command>rrset-order</command> substatement in the
    <command>options</command> statement, see
    <xref endterm="rrset_ordering_title" linkend="rrset_ordering"/>.
    This substatement is not supported in
    <acronym>BIND</acronym> 9, and only the ordering scheme described above is
    available.</para>

  </sect1>
  <sect1 id="notify">
    <title>Notify</title>

    <para><acronym>DNS</acronym> Notify is a mechanism that allows master nameservers to
    notify their slave servers of changes to a zone's data. In
    response to a <command>NOTIFY</command> from a master server, the
    slave will check to see that its version of the zone is the
    current version and, if not, initiate a transfer.</para> <para><acronym>DNS</acronym>
    Notify is fully documented in RFC 1996. See also the description
    of the zone option <command>also-notify</command>, see
    <xref linkend="zone_transfers"/>. For more information about
    <command>notify</command>, see <xref
    linkend="boolean_options"/>.</para>

  </sect1>
  <sect1>
    <title>Nameserver Operations</title>
    <sect2>
      <title>Tools for Use With the Nameserver Daemon</title>
      <para>There are several indispensable diagnostic, administrative
and monitoring tools available to the system administrator for controlling
and debugging the nameserver daemon. We describe several in this
section </para>
      <sect3 id="diagnostic_tools">
        <title>Diagnostic Tools</title>
        <variablelist>
          <varlistentry>
            <term id="dig"><command>dig</command></term>
            <listitem>
              <para>The domain information groper (<command>dig</command>) is
a command line tool that can be used to gather information from
the Domain Name System servers. Dig 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">
                        <command>dig</command>
                        <arg>@<replaceable>server</replaceable></arg>
                        <arg choice="plain"><replaceable>domain</replaceable></arg>
                        <arg><replaceable>query-type</replaceable></arg>
                        <arg><replaceable>query-class</replaceable></arg>
                        <arg>+<replaceable>query-option</replaceable></arg>
                        <arg>-<replaceable>dig-option</replaceable></arg>
                        <arg>%<replaceable>comment</replaceable></arg>
                <!-- one of (SBR GROUP ARG COMMAND) -->
              </cmdsynopsis>
              <para>The usual simple use of dig will take 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
provides a simple <acronym>DNS</acronym> lookup using a command-line interface for
looking up Internet hostnames. By default, the utility converts
between host names and Internet addresses, but its functionality
can be extended with the use of options.</para>
              <cmdsynopsis label="Usage">
                <!-- one of (SBR GROUP ARG COMMAND) -->
                <command>host</command>
                <arg>-aCdlrTwv</arg>
                <arg>-c <replaceable>class</replaceable></arg>
                <arg>-N <replaceable>ndots</replaceable></arg>
                <arg>-t <replaceable>type</replaceable></arg>
                <arg>-W <replaceable>timeout</replaceable></arg>
                <arg>-R <replaceable>retries</replaceable></arg>
                <arg choice="plain"><replaceable>hostname</replaceable></arg>
                <arg><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> is a program used to query Internet
domain nameservers. <command>nslookup</command> has two modes: interactive
and non-interactive. Interactive mode allows the user to query nameservers
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">
                <command>nslookup</command>
                <arg rep="repeat">-option</arg>
                <group>
                  <arg><replaceable>host-to-find</replaceable></arg>
                  <arg>- <arg>server</arg></arg>
                </group>
              </cmdsynopsis>
<para>Interactive mode is entered when no arguments are given (the
default nameserver will be used) or when the first argument is a
hyphen (`-') and the second argument is the host name or Internet address
of a nameserver.</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 nameserver.</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>
</sect3>

<sect3 id="admin_tools">
        <title>Administrative Tools</title>
        <para>Administrative tools play an integral part in the management
of a server.</para>
        <variablelist>
          <varlistentry 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">
                <command>named-checkconf</command>
                <arg>-t <replaceable>directory</replaceable></arg>
                <arg><replaceable>filename</replaceable></arg>
              </cmdsynopsis>
            </listitem>
          </varlistentry>
          <varlistentry id="named-checkzone" xreflabel="Zone Checking application">
            <term><command>named-checkzone</command></term>
            <listitem>
              <para>The <command>named-checkzone</command> program checks a master file for
              syntax and consistency.</para>
              <cmdsynopsis label="Usage">
                <command>check-zone</command>
                <arg>-dq</arg>
                <arg>-c <replaceable>class</replaceable></arg>
                <arg choice="plain"><replaceable>zone</replaceable></arg>
                <arg><replaceable>filename</replaceable></arg>
              </cmdsynopsis>
            </listitem>
          </varlistentry>
          <varlistentry 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 nameserver.
              If you run <command>rndc</command> without any options
              it will display a usage message as follows:</para>
              <cmdsynopsis label="Usage">
                <command>rndc</command>
                <arg>-c <replaceable>config</replaceable></arg>
                <arg>-s <replaceable>server</replaceable></arg>
                <arg>-p <replaceable>port</replaceable></arg>
                <arg>-y <replaceable>key</replaceable></arg>
                <arg choice="plain"><replaceable>command</replaceable></arg>
                <arg rep="repeat"><replaceable>command</replaceable></arg>
              </cmdsynopsis>
              <para><command>command</command> is one of the following:</para>

<variablelist>

   <varlistentry><term><userinput>reload</userinput></term>
   <listitem><para>Reload configuration file and zones.</para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>reload <replaceable>zone</replaceable>
       <optional><replaceable>class</replaceable>
           <optional><replaceable>view</replaceable></optional></optional></userinput></term>
   <listitem><para>Reload the given zone.</para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>refresh <replaceable>zone</replaceable>
       <optional><replaceable>class</replaceable>
           <optional><replaceable>view</replaceable></optional></optional></userinput></term>
   <listitem><para>Schedule zone maintenance for the given zone.</para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>retransfer <replaceable>zone</replaceable>
       <optional><replaceable>class</replaceable>
           <optional><replaceable>view</replaceable></optional></optional></userinput></term>
   <listitem><para>Retransfer the given zone from the master.</para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>reconfig</userinput></term>
   <listitem><para>Reload the configuration file and load new zones,
   but do not reload existing zone files even if they have changed.
   This is faster than a full <command>reload</command> when there
   is a large number of zones because it avoids the need to examine the
   modification times of the zones files.
   </para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>stats</userinput></term>
   <listitem><para>Write server statistics to the statistics file.</para></listitem>
   </varlistentry>

   <varlistentry><term><userinput>querylog</userinput></term>
   <listitem><para>Toggle query logging.</para></listitem></varlistentry>

   <varlistentry><term><userinput>dumpdb</userinput></term>
   <listitem><para>Dump the server's caches to the dump file. </para></listitem></varlistentry>

   <varlistentry><term><userinput>stop</userinput></term>
   <listitem><para>Stop the server,
   making sure any recent changes
   made through dynamic update or IXFR are first saved to the master files
   of the updated zones.</para></listitem></varlistentry>

   <varlistentry><term><userinput>halt</userinput></term>
   <listitem><para>Stop the server immediately.  Recent changes
   made through dynamic update or IXFR are not saved to the master files,
   but will be rolled forward from the journal files when the server
   is restarted.</para></listitem></varlistentry>

   <varlistentry><term><userinput>trace</userinput></term>
   <listitem><para>Increment the servers debugging level by one. </para></listitem></varlistentry>

   <varlistentry><term><userinput>trace <replaceable>level</replaceable></userinput></term>
   <listitem><para>Sets the server's debugging level to an explicit
   value.</para></listitem></varlistentry>

   <varlistentry><term><userinput>notrace</userinput></term>
   <listitem><para>Sets the server's debugging level to 0.</para></listitem></varlistentry>

   <varlistentry><term><userinput>flush</userinput></term>
   <listitem><para>Flushes the server's cache.</para></listitem></varlistentry>

   <varlistentry><term><userinput>status</userinput></term>
   <listitem><para>Display status of the server.</para></listitem></varlistentry>

</variablelist>

<para>In <acronym>BIND</acronym> 9.2, <command>rndc</command>
supports all the commands of the BIND 8 <command>ndc</command>
utility except <command>ndc start</command>, which was also
not supported in <command>ndc</command>'s channel mode.</para>

<para>A configuration file is required, 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> will also look 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 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 will
be contacted if no <option>-s</option>
option is provided on the command line.  
<command>default-key</command> takes
the name of 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 names a key with its
string argument. The string is required by the server to 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 will accept any string as the argument
to algorithm, currently only the string "<userinput>hmac-md5</userinput>"
has any meaning.  The secret is a base-64 encoded string.</para>

<para>The <command>server</command> statement uses the key clause
to associate a <command>key</command>-defined key with a server.
The argument to the <command>server</command> statement is a
host name or address (addresses must be double quoted).  The argument
to the key clause is the name of the key as defined by the <command>key</command> statement.
The <command>port</command> clause can be used to 
specify the port to which <command>rndc</command> should connect
on the given server.</para>

<para>A sample minimal configuration file is as follows:</para>
<programlisting>
key rndc_key {
     algorithm "hmac-md5";
     secret "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
     default-server localhost;
     default-key    rndc_key;
};
</programlisting>

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

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

<para>to connect to 127.0.0.1 port 953 and cause the nameserver
to reload, if a nameserver on the local machine were running with
following controls statements:</para>
<programlisting>
controls {
        inet 127.0.0.1 allow { localhost; } keys { rndc_key; };
};
</programlisting>
<para>and it had an identical key statement for
<literal>rndc_key</literal>.</para>

<para>Running the <command>rndc-confgen</command> program will
conveniently create a <filename>rndc.conf</filename>
file for you, and also display the
corresponding <command>controls</command> statement that you need to
add to <filename>named.conf</filename>.  Alternatively,
you can run <command>rndc-confgen -a</command> to set up
a <filename>rndc.key</filename> file and not modify 
<filename>named.conf</filename> at all.
</para>

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

      </sect3>
    </sect2>
<sect2>

<title>Signals</title>
<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>
    </sect2>
  </sect1>
  </chapter>

  <chapter id="ch04">
  <title>Advanced Concepts</title>

<sect1 id="dynamic_update">
    <title>Dynamic Update</title>

    <para>Dynamic update is the term used for the ability under
    certain specified conditions to add, modify or delete records or
    RRsets in the master zone files. Dynamic update is fully described
    in RFC 2136.</para>

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

    <para>Updating of secure zones (zones using DNSSEC) follows
    RFC 3007: SIG and NXT 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>

    <sect2 id="journal">
    <title>The journal file</title>

    <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 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.  The journal file is in a
    binary format and should not be edited manually.</para>

    <para>The server will also occasionally write ("dump")
    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 15
    minutes, allowing additional updates to take place.</para>

    <para>When a server is restarted after a shutdown or crash, it will replay
    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
    journalled 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>If you have to make changes to a dynamic zone
    manually, the following procedure will work: Shut down
    the server using <command>rndc stop</command> (sending a signal
    or using <command>rndc halt</command> is <emphasis>not</emphasis>
    sufficient). Wait for the server to exit,
    then <emphasis>remove</emphasis> the zone's 
    <filename>.jnl</filename> file, edit the zone file,
    and restart the server.  Removing the <filename>.jnl</filename>
    file is necessary because the manual edits will not be
    present in the journal, rendering it inconsistent with the
    contents of the zone file.</para>

  </sect2>
    
</sect1>
    
<sect1 id="incremental_zone_transfers">
<title>Incremental Zone Transfers (IXFR)</title>

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

<para>When acting as a master, <acronym>BIND</acronym> 9
supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR.  For manually maintained master
zones, and for slave 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 slave, <acronym>BIND</acronym> 9 will 
attempt 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>
</sect1>

<sect1><title>Split DNS</title>
<para>Setting up different views, or visibility, of DNS space to
internal and external resolvers is usually referred to as a <emphasis>Split
DNS</emphasis> setup. There are several reasons an organization
would want to set up its DNS this way.</para>
<para>One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not 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.</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 in to the internal network.</para>
<para>Here is an example of a split DNS setup:</para>
<para>Let's say a company named <emphasis>Example, Inc.</emphasis> (example.com)
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 will set up two sets
of nameservers. One set will be on the inside network (in the reserved
IP space) and the other set will be on bastion hosts, which are "proxy"
hosts that can talk to both sides of its network, in the DMZ.</para>
<para>The internal servers will be 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>,<emphasis> </emphasis><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 nameservers 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, will
be configured to serve the "public" version of the <filename>site1</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</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 will
be 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><literal>*   IN MX 10 external1.example.com.</literal></programlisting>
<para>Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers on
the bastion hosts will need to be configured to point to the internal
nameservers for DNS resolution.</para>
<para>Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.</para>
<para>In order for all this to work properly, internal clients will
need to be configured to query <emphasis>only</emphasis> the internal
nameservers 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 will now be able to:</para>
<itemizedlist><listitem>
        <simpara>Look up any hostnames in the <literal>site1</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 internal AND external people.</simpara></listitem></itemizedlist>
<para>Hosts on the Internet will be able to:</para>
<itemizedlist><listitem>
        <simpara>Look up any hostnames in the <literal>site1</literal> and 
<literal>site2.example.com</literal> zones.</simpara></listitem>
<listitem>
        <simpara>Exchange mail with anyone in the <literal>site1</literal> and 
<literal>site2.example.com</literal> zones.</simpara></listitem></itemizedlist>

    <para>Here is an example configuration for the setup we just
    described above. Note that this is only configuration information;
    for information on how to configure your 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;
    forwarders {                                // forward to external servers
        <varname>bastion-ips-go-here</varname>; 
    };
    allow-transfer { none; };                   // sample allow-transfer (no one)
    allow-query { internals; externals; };      // restrict query access
    allow-recursion { internals; };             // restrict recursion
    ...
    ...
};

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

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

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

zone "site2.example.com" {
  type slave;
  file "s/site2.foo.com";
  masters { another_bastion_host_maybe; };
  allow-query { any; };
  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>
</sect1>
<sect1 id="tsig"><title>TSIG</title>
<para>This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym>BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym>BIND</acronym>.</para>
<para><acronym>BIND</acronym> primarily supports TSIG for server to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym>BIND</acronym> 8 have limited support
for TSIG.</para>

    <para>TSIG might be most useful for dynamic update. A primary
    server for a dynamic zone should use access control to control
    updates, but IP-based access control is insufficient. Key-based
    access control is far superior, see <xref
    linkend="proposed_standards"/>. The <command>nsupdate</command>
    program supports TSIG via the <option>-k</option> and
    <option>-y</option> command line options.</para>

<sect2><title>Generate Shared Keys for Each Pair of Hosts</title>
<para>A shared secret is generated to be shared between <emphasis>host1</emphasis> and <emphasis>host2</emphasis>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.</para>
<sect3><title>Automatic Generation</title>
<para>The following command will generate a 128 bit (16 byte) HMAC-MD5
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is 512 bits;
keys longer than that will be digested with MD5 to produce a 128
bit key.</para>
        <para><userinput>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</userinput></para>
<para>The key is in the file <filename>Khost1-host2.+157+00000.private</filename>.
Nothing directly uses this file, but the base-64 encoded string
following "<literal>Key:</literal>"
can be extracted from the file and used as a shared secret:</para>
<programlisting>Key: La/E5CjG9O+os1jq0a2jdA==</programlisting>
<para>The string "<literal>La/E5CjG9O+os1jq0a2jdA==</literal>" can
be used as the shared secret.</para></sect3>
<sect3><title>Manual Generation</title>
<para>The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.</para>
<para>Also, a known string can be run through <command>mmencode</command> or
a similar program to generate base-64 encoded data.</para></sect3></sect2>
<sect2><title>Copying the Shared Secret to Both Machines</title>
<para>This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.</para></sect2>
<sect2><title>Informing the Servers of the Key's Existence</title>
<para>Imagine <emphasis>host1</emphasis> and <emphasis>host 2</emphasis> are
both servers. The following is added to each server's <filename>named.conf</filename> file:</para>
<programlisting>
key host1-host2. {
  algorithm hmac-md5;
  secret "La/E5CjG9O+os1jq0a2jdA==";
};
</programlisting>
<para>The algorithm, hmac-md5, is the only one supported by <acronym>BIND</acronym>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <filename>named.conf</filename> be non-world
readable, or the key directive be added to a non-world readable
file that is included by <filename>named.conf</filename>.</para>
<para>At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature succeeds, the response is signed by
the same key.</para></sect2>
<sect2><title>Instructing the Server to Use the Key</title>
<para>Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <filename>named.conf</filename> file
for <emphasis>host1</emphasis>, if the IP address of <emphasis>host2</emphasis> is
10.1.2.3:</para>
<programlisting>
server 10.1.2.3 {
  keys { host1-host2. ;};
};
</programlisting>
<para>Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a world-readable
file.</para>
<para>If <emphasis>host1</emphasis> sends a message that is a request
to that address, the message will be signed with the specified key. <emphasis>host1</emphasis> will
expect any responses to signed messages to be signed with the same
key.</para>
<para>A similar statement must be present in <emphasis>host2</emphasis>'s
configuration file (with <emphasis>host1</emphasis>'s address) for <emphasis>host2</emphasis> to
sign request messages to <emphasis>host1</emphasis>.</para></sect2>
<sect2><title>TSIG Key Based Access Control</title>
<para><acronym>BIND</acronym> allows IP addresses and ranges to be specified in ACL
definitions and
<command>allow-{ query | transfer | update }</command> directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <command>key host1-host2.</command></para>
<para>An example of an allow-update directive would be:</para>
<programlisting>
allow-update { key host1-host2. ;};
</programlisting>

      <para>This allows dynamic updates to succeed only if the request
      was signed by a key named
      "<command>host1-host2.</command>".</para> <para>You may want to read about the more
      powerful <command>update-policy</command> statement in <xref
      linkend="dynamic_update_policies"/>.</para>

    </sect2>
    <sect2>
      <title>Errors</title>

      <para>The processing of TSIG signed messages can result in
      several errors. If a signed message is sent to a non-TSIG aware
      server, a FORMERR will be returned, since the server will not
      understand the record. This is a result of misconfiguration,
      since the server must be explicitly configured to send a TSIG
      signed message to a specific server.</para>

      <para>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. If a TSIG aware server
      receives a message with a signature that does not validate, the
      response will be unsigned with the TSIG extended error code set
      to BADSIG. If a TSIG aware server receives a message with a time
      outside of the allowed range, the response will be signed with
      the TSIG extended error code set to BADTIME, and the time values
      will be adjusted so that the response can be successfully
      verified. In any of these cases, the message's rcode is set to
      NOTAUTH.</para>

    </sect2>
  </sect1>
  <sect1>
    <title>TKEY</title>

    <para><command>TKEY</command> is a mechanism for automatically
    generating a shared secret between two hosts.  There are several
    "modes" of <command>TKEY</command> that specify how the key is
    generated or assigned.  <acronym>BIND</acronym> implements only one of these modes,
    the Diffie-Hellman key exchange.  Both hosts are required to have
    a Diffie-Hellman KEY record (although this record is not required
    to be present in a zone).  The <command>TKEY</command> process
    must use signed messages, signed either by TSIG or SIG(0).  The
    result of <command>TKEY</command> is a shared secret that can be
    used to sign messages with TSIG.  <command>TKEY</command> can also
    be used to delete shared secrets that it had previously
    generated.</para>

    <para>The <command>TKEY</command> process is initiated by a client
    or server by sending a signed <command>TKEY</command> query
    (including any appropriate KEYs) to a TKEY-aware server.  The
    server response, if it indicates success, will contain a
    <command>TKEY</command> record and any appropriate keys.  After
    this exchange, both participants have enough information to
    determine the shared secret; the exact process depends on the
    <command>TKEY</command> mode.  When using the Diffie-Hellman
    <command>TKEY</command> mode, Diffie-Hellman keys are exchanged,
    and the shared secret is derived by both participants.</para>
  
  </sect1>
  <sect1>
    <title>SIG(0)</title>

    <para><acronym>BIND</acronym> 9 partially supports DNSSEC SIG(0) transaction
    signatures as specified in RFC 2535.  SIG(0) uses public/private
    keys to authenticate messages.  Access control is performed in the
    same manner as TSIG keys; privileges can be granted or denied
    based on the key name.</para>

    <para>When a SIG(0) signed message is received, it will only be
    verified if the key is known and trusted by the server; the server
    will not attempt to locate and/or validate the key.</para>

    <para>SIG(0) signing of multiple-message TCP streams is not
    supported.</para>

    <para><acronym>BIND</acronym> 9 does not ship with any tools that generate SIG(0)
    signed messages.</para>

  </sect1>
  <sect1 id="DNSSEC">
    <title>DNSSEC</title>

    <para>Cryptographic authentication of DNS information is possible
    through the DNS Security (<emphasis>DNSSEC</emphasis>) extensions,
    defined in RFC 2535. 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 and signedkey files to be in the working directory, and
    that the tools shipped with BIND 9.0.x are not fully compatible
    with the current ones.</para>

    <para>There must also be communication with the administrators of
    the parent and/or child zone to transmit keys and signatures.  A
    zone's security status must be indicated by the parent zone for a
    DNSSEC capable resolver to trust its data.</para>

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

    <sect2>
      <title>Generating Keys</title>

      <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, a name type of
      <command>ZONE</command>, and must be usable for authentication.
      It is recommended that zone keys be mandatory to implement a
      cryptographic algorithm; currently the only key mandatory to
      implement an algorithm is DSA.</para>

      <para>The following command will generate a 768 bit DSA key for
      the <filename>child.example</filename> zone:</para>

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

      <para>Two output files will be produced:
      <filename>Kchild.example.+003+12345.key</filename> and
      <filename>Kchild.example.+003+12345.private</filename> (where
      12345 is an example of a key tag).  The key file names contain
      the key name (<filename>child.example.</filename>), algorithm (3
      is DSA, 1 is RSA, 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 public keys should be inserted into the zone file with
      <command>$INCLUDE</command> statements, including the
      <filename>.key</filename> files.</para>

    </sect2>
    <sect2>
      <title>Creating a Keyset</title>

      <para>The <command>dnssec-makekeyset</command> program is used
      to create a key set from one or more keys.</para>

      <para>Once the zone keys have been generated, a key set must be
      built for transmission to the administrator of the parent zone,
      so that the parent zone can sign the keys with its own zone key
      and correctly indicate the security status of this zone.  When
      building a key set, the list of keys to be included and the TTL
      of the set must be specified, and the desired signature validity
      period of the parent's signature may also be specified.</para>

      <para>The list of keys to be inserted into the key set may also
      included non-zone keys present at the top of the zone.
      <command>dnssec-makekeyset</command> may also be used at other
      names in the zone.</para>

      <para>The following command generates a key set containing the
      above key and another key similarly generated, with a TTL of
      3600 and a signature validity period of 10 days starting from
      now.</para>

<para><userinput>dnssec-makekeyset -t 3600 -e +864000 Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>

      <para>One output file is produced:
      <filename>keyset-child.example.</filename>.  This file should be
      transmitted to the parent to be signed.  It includes the keys,
      as well as signatures over the key set generated by the zone
      keys themselves, which are used to prove ownership of the
      private keys and encode the desired validity period.</para>

    </sect2>
    <sect2>
      <title>Signing the Child's Keyset</title>

      <para>The <command>dnssec-signkey</command> program is used to
      sign one child's keyset.</para>

      <para>If the <filename>child.example</filename> zone has any
      delegations which are secure, for example,
      <filename>grand.child.example</filename>, the
      <filename>child.example</filename> administrator should receive
      keyset files for each secure subzone.  These keys must be signed
      by this zone's zone keys.</para>

      <para>The following command signs the child's key set with the
      zone keys:</para>

<para><userinput>dnssec-signkey keyset-grand.child.example. Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>

      <para>One output file is produced:
      <filename>signedkey-grand.child.example.</filename>.  This file
      should be both transmitted back to the child and retained.  It
      includes all keys (the child's keys) from the keyset file and
      signatures generated by this zone's zone keys.</para>

    </sect2>
    <sect2>
      <title>Signing the Zone</title>

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

      <para>Any <filename>signedkey</filename> files corresponding to
      secure subzones should be present, as well as a
      <filename>signedkey</filename> file for this zone generated by
      the parent (if there is one). The zone signer will generate
      <literal>NXT</literal> and <literal>SIG</literal> records for
      the zone, as well as incorporate the zone key signature from the
      parent and indicate the security status at all delegation
      points.</para>

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

    </sect2>

<sect2><title>Configuring Servers</title>

<para>Unlike in <acronym>BIND</acronym> 8, 
data is not verified on load in <acronym>BIND</acronym> 9,
so zone keys for authoritative zones do not need to be specified
in the configuration file.</para>

<para>The public key for any security root must be present in
the configuration file's <command>trusted-keys</command>
statement, as described later in this document. </para>

</sect2>

</sect1>
  <sect1>
    <title>IPv6 Support in <acronym>BIND</acronym> 9</title>

    <para><acronym>BIND</acronym> 9 fully supports all currently defined forms of IPv6
    name to address and address to name lookups.  It will also use
    IPv6 addresses to make queries when running on an IPv6 capable
    system.</para>

    <para>For forward lookups, <acronym>BIND</acronym> 9 supports both A6 and AAAA
    records.  The use of AAAA records is deprecated, but it is still
    useful for hosts to have both AAAA and A6 records to maintain
    backward compatibility with installations where AAAA records are
    still used.  In fact, the stub resolvers currently shipped with
    most operating system support only AAAA lookups, because following
    A6 chains is much harder than doing A or AAAA lookups.</para>

    <para>For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports the new
    "bitstring" format used in the <emphasis>ip6.arpa</emphasis>
    domain, as well as the older, deprecated "nibble" format used in
    the <emphasis>ip6.int</emphasis> domain.</para>

    <para><acronym>BIND</acronym> 9 includes a new lightweight resolver library and
    resolver daemon which new applications may choose to use to avoid
    the complexities of A6 chain following and bitstring labels, see <xref
    linkend="ch05"/>.</para>

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

    <sect2>
      <title>Address Lookups Using AAAA Records</title>

      <para>The AAAA record is a parallel to the IPv4 A record.  It
      specifies the entire address in a single record.  For
      example,</para>

<programlisting>
$ORIGIN example.com.
host            3600    IN      AAAA    3ffe:8050:201:1860:42::1
</programlisting>

      <para>While their use is deprecated, they are useful to support
      older IPv6 applications.  They should not be added where they
      are not absolutely necessary.</para>

    </sect2>
    <sect2>
      <title>Address Lookups Using A6 Records</title>

      <para>The A6 record is more flexible than the AAAA record, and
      is therefore more complicated.  The A6 record can be used to
      form a chain of A6 records, each specifying part of the IPv6
      address. It can also be used to specify the entire record as
      well.  For example, this record supplies the same data as the
      AAAA record in the previous example:</para>

<programlisting>
$ORIGIN example.com.
host            3600    IN      A6      0 3ffe:8050:201:1860:42::1
</programlisting>
      <sect3>
        <title>A6 Chains</title>

        <para>A6 records are designed to allow network
        renumbering. This works when an A6 record only specifies the
        part of the address space the domain owner controls.  For
        example, a host may be at a company named "company."  It has
        two ISPs which provide IPv6 address space for it.  These two
        ISPs fully specify the IPv6 prefix they supply.</para>

        <para>In the company's address space:</para>

<programlisting>
$ORIGIN example.com.
host            3600    IN      A6      64 0:0:0:0:42::1 company.example1.net.
host            3600    IN      A6      64 0:0:0:0:42::1 company.example2.net.
</programlisting>

        <para>ISP1 will use:</para>

<programlisting>
$ORIGIN example1.net.
company         3600    IN      A6      0 3ffe:8050:201:1860::
</programlisting>

<para>ISP2 will use:</para>

<programlisting>
$ORIGIN example2.net.
company         3600    IN      A6      0 1234:5678:90ab:fffa::
</programlisting>

        <para>When <literal
       >host.example.com</literal> is looked up,
        the resolver (in the resolver daemon or caching name server)
        will find two partial A6 records, and will use the additional
        name to find the remainder of the data.</para>

      </sect3>
      <sect3>
        <title>A6 Records for DNS Servers</title>

        <para>When an A6 record specifies the address of a name
        server, it should use the full address rather than specifying
        a partial address.  For example:</para>

<programlisting>
$ORIGIN example.com.
@               14400           IN      NS              ns0
                14400           IN      NS              ns1
ns0             14400           IN      A6              0 3ffe:8050:201:1860:42::1
ns1             14400           IN      A               192.168.42.1
</programlisting>

        <para>It is recommended that IPv4-in-IPv6 mapped addresses not
        be used.  If a host has an IPv4 address, use an A record, not
        an A6, with <literal>::ffff:192.168.42.1</literal> as the
        address.</para>

      </sect3>
    </sect2>
    <sect2>
      <title>Address to Name Lookups Using Nibble Format</title>

      <para>While the use of nibble format to look up names is
      deprecated, it is supported for backwards compatiblity with
      existing IPv6 applications.</para>

      <para>When looking up an address in nibble format, the address
      components are simply reversed, just as in IPv4, and
      <literal>ip6.int.</literal> is appended to the resulting name.
      For example, the following would provide reverse name lookup for
      a host with address
      <literal>3ffe:8050:201:1860:42::1</literal>.</para>

<programlisting>
$ORIGIN 0.6.8.1.1.0.2.0.0.5.0.8.e.f.f.3.ip6.int.
1.0.0.0.0.0.0.0.0.0.0.0.2.4.0.0   14400 IN      PTR     host.example.com.
</programlisting>
    </sect2>
    <sect2>
      <title>Address to Name Lookups Using Bitstring Format</title>

      <para>Bitstring labels can start and end on any bit boundary,
      rather than on a multiple of 4 bits as in the nibble
      format. They also use <emphasis>ip6.arpa</emphasis> rather than
      <emphasis>ip6.int</emphasis>.</para>

      <para>To replicate the previous example using bitstrings:</para>

<programlisting>
$ORIGIN \[x3ffe805002011860/64].ip6.arpa.
\[x0042000000000001/64]         14400   IN      PTR     host.example.com.
</programlisting>
    </sect2>
    <sect2>
      <title>Using DNAME for Delegation of IPv6 Reverse Addresses</title>

      <para>In IPV6, the same host may have many addresses from many
      network providers.  Since the trailing portion of the address
      usually remains constant, <command>DNAME</command> can help
      reduce the number of zone files used for reverse mapping that
      need to be maintained.</para>

      <para>For example, consider a host which has two providers
      (<literal>example.net</literal> and
      <literal>example2.net</literal>) and
      therefore two IPv6 addresses.  Since the host chooses its own 64
      bit host address portion, the provider address is the only part
      that changes:</para>

<programlisting>
$ORIGIN example.com.
host                    IN      A6      64      ::1234:5678:1212:5675 cust1.example.net.
                        IN      A6      64      ::1234:5678:1212:5675 subnet5.example2.net.
$ORIGIN example.net.
cust1                   IN      A6      48      0:0:0:dddd:: ipv6net.example.net.
ipv6net                 IN      A6      0       aa:bb:cccc::
$ORIGIN example2.net.
subnet5                 IN      A6      48      0:0:0:1:: ipv6net2.example2.net.
ipv6net2                IN      A6      0       6666:5555:4::
</programlisting>

<para>This sets up forward lookups.  To handle the reverse lookups,
the provider <literal>example.net</literal>
would have:</para>

<programlisting>
$ORIGIN \[x00aa00bbcccc/48].ip6.arpa.
\[xdddd/16]             IN      DNAME           ipv6-rev.example.com.
</programlisting>

      <para>and <literal
     >example2.net</literal> would have:</para>

<programlisting>
$ORIGIN \[x666655550004/48].ip6.arpa.
\[x0001/16]             IN      DNAME           ipv6-rev.example.com.
</programlisting>

      <para><literal>example.com</literal>
      needs only one zone file to handle both of these reverse
      mappings:</para>

<programlisting>
$ORIGIN ipv6-rev.example.com.
\[x1234567812125675/64] IN      PTR             host.example.com. 
</programlisting>
    </sect2>
  </sect1>
  </chapter>

  <chapter id="ch05"><title>The <acronym>BIND</acronym> 9 Lightweight Resolver</title>
<sect1><title>The Lightweight Resolver Library</title>
<para>Traditionally applications have been linked with a stub resolver
library that sends recursive DNS queries to a local caching name
server.</para>
<para>IPv6 introduces new complexity into the resolution process,
such as following A6 chains and DNAME records, and simultaneous
lookup of IPv4 and IPv6 addresses.  These are hard or impossible
to implement in a traditional stub resolver.</para>
<para>Instead, <acronym>BIND</acronym> 9 provides 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></sect1>
<sect1 id="lwresd"><title>Running a Resolver Daemon</title>
<para>To use the lightweight resolver interface, the system must
run the resolver daemon <command>lwresd</command>.</para>
<para>By default, applications using the lightweight resolver library will make
UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.  The
address can be overriden by <command>lwserver</command> lines in
<filename>/etc/resolv.conf</filename>.
The daemon will try to find the answer to the questions "what are the
addresses for host
<literal>foo.example.com</literal>?" and "what are
the names for IPv4 address 10.1.2.3?"</para>
<para>The daemon currently only looks in the DNS, but in the future
it may use other sources such as <filename>/etc/hosts</filename>,
NIS, etc.</para>
<para>The <command>lwresd</command> daemon is essentially a
caching-only name server that answers 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 configured otherwise, 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>

</sect1></chapter>

<chapter id="ch06"><title><acronym>BIND</acronym> 9 Configuration Reference</title>
<para><acronym>BIND</acronym> 9 configuration is broadly similar to <acronym>BIND</acronym> 8.x; however,
there are a few new areas of configuration, such as views. <acronym>BIND</acronym>
8.x configuration files should work with few alterations in <acronym>BIND</acronym>
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in <acronym>BIND</acronym> 9.</para>
<para><acronym>BIND</acronym> 4 configuration files can be converted to the new format
using the shell script
<filename>contrib/named-bootconf/named-bootconf.sh</filename>.</para>
<sect1 id="configuration_file_elements"><title>Configuration File Elements</title>
<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>domain_name</varname></para></entry>
<entry colname = "2"><para>A quoted string which will be used as
a DNS name, for example "<literal>my.test.domain</literal>".</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>dotted_decimal</varname></para></entry>
<entry colname = "2"><para>One or more integers valued 0 through
255 separated only by dots (`.'), such as <command>123</command>, <command>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>fe80::200:f8ff:fe01:9742</command>.</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_port</varname></para></entry>
<entry colname = "2"><para>An IP port <varname>number</varname>.
 <varname>number</varname> is limited to 0 through 65535, with values
below 1024 typically restricted to root-owned processes. 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 a <varname>ip_addr</varname> may 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></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 integer with an entire
range limited by the range of a C language signed integer (2,147,483,647
on a machine with 32 bit integers). Its acceptable value might further
be limited by the context in which it is 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 will be used as
a pathname, such as <filename>zones/master/my.test.domain</filename>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>size_spec</varname></para></entry>
<entry colname = "2"><para>A number, the word <userinput>unlimited</userinput>,
or the word <userinput>default</userinput>.</para><para>The maximum
value of <varname>size_spec</varname> is that of unsigned long integers
on the machine. An <varname>unlimited</varname> <varname>size_spec</varname> requests unlimited
use, or the maximum available amount. A <varname>default size_spec</varname> uses
the limit that was in force when the server was started.</para><para>A <varname>number</varname> 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>Integer
storage overflow is currently silently ignored during conversion
of scaled values, resulting in values less than intended, possibly
even negative. Using <varname>unlimited</varname> is the best way
to safely set a really large number.</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 slave and stub zones.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<sect2 id="address_match_lists"><title>Address Match Lists</title>
<sect3><title>Syntax</title>
        <programlisting><varname>address_match_list</varname> = address_match_list_element ;
  <optional> address_match_list_element; ... </optional>
<varname>address_match_list_element</varname> = <optional> ! </optional> (ip_address <optional>/length</optional> |
   key key_id | acl_name | { address_match_list } )
</programlisting>
</sect3>
<sect3><title>Definition and Usage</title>
<para>Address match lists are primarily used to determine access
control for various server operations. They are also used to define
priorities for querying other nameservers and to set the addresses
on which <command>named</command> will listen for queries. 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 the `/'-notation)</simpara></listitem>
<listitem>
            <simpara>a key ID, as defined by the key statement</simpara></listitem>
<listitem>
            <simpara>the name of an address match list previously 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 acl 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 list is traversed in order until an element matches.
The interpretation of a match depends on whether the list is being used
for access control, defining listen-on ports, or as a topology,
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-query</command>, <command>allow-transfer</command>,
<command>allow-update</command> and <command>blackhole</command> all
use address match lists  this. Similarly, the listen-on option will cause
the server to not accept queries on any of the machine's addresses
which do not match the list.</para>
<para>When used with the topology clause, a non-negated match returns
a distance based on its position on the list (the closer the match
is to the start of the list, the shorter the distance is between
it and the server). A negated match will be assigned the maximum
distance from the server. If there is no match, the address will
get a distance which is further than any non-negated list element,
and closer than any negated element.</para>
<para>Because of the first-match aspect of the algorithm, 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 will match 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 having 1.2.3.13 blocked by the negation but all
other 1.2.3.* hosts fall through.</para></sect3></sect2>
    <sect2>
      <title>Comment Syntax</title>

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

      <sect3>
        <title>Syntax</title>

        <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>
      </sect3>
      <sect3>
        <title>Definition and Usage</title>
<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.</para>
<para>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, if you prefer) comments start
with the character <literal>#</literal> (number sign) and continue to the end of the
physical line, as in C++ comments.</para>
<para>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>WARNING: you cannot use the semicolon (`;') character
          to start a comment such as you would in a zone file. The
          semicolon indicates the end of a configuration
          statement.</para>
        </warning>
      </sect3>
    </sect2>
  </sect1>
  <sect1 id="Configuration_File_Grammar">
    <title>Configuration File Grammar</title>

    <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 substatements, 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 the server logs, and where
the log messages are sent.</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>trusted-keys</command></para></entry>
            <entry colname = "2"><para>defines trusted DNSSEC keys.</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>

    <sect2>
      <title><command>acl</command> Statement Grammar</title>

      <programlisting><command>acl</command> acl-name { 
    address_match_list 
};
</programlisting>
    </sect2>
    <sect2 id="acl">
      <title><command>acl</command> Statement Definition and
Usage</title>

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

      <para>Note that an address match list's name must be defined
      with <command>acl</command> before it can be used elsewhere; no
      forward references are allowed.</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 IP addresses of all interfaces
on the system.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>localnets</command></para></entry>
<entry colname = "2"><para>Matches any host on a network for which
the system has an interface.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
    </sect2>
    <sect2>
      <title><command>controls</command> Statement Grammar</title>
<programlisting><command>controls</command> {
   inet ( ip_addr | * ) <optional> port ip_port </optional> allow { <replaceable> address_match_list </replaceable> }
                keys { <replaceable> key_list </replaceable> };
   <optional> inet ...; </optional>
};
</programlisting>
</sect2>

<sect2 id="controls_statement_definition_and_usage">
<title><command>controls</command> Statement Definition and Usage</title>

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

      <para>An <command>inet</command> control channel is a TCP/IP
      socket accessible to the Internet, created at the specified
      <command>ip_port</command> on the specified
      <command>ip_addr</command>.  If no port is specified, port 953
      is used by default.  "*" 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 address permissions in
      <command>address_match_list</command>. <command>key_id</command>
      members of the <command>address_match_list</command> are
      ignored, and instead are interpreted independently based the
      <command>key_list</command>.  Each <command>key_id</command> in
      the <command>key_list</command> is allowed to be used to
      authenticate commands and responses given over the control
      channel by digitally signing each message between the server and
      a command client (See <xref linkend="rndc"/> in
      <xref linkend="admin_tools"/>). All commands to the control channel
      must be signed by one of its specified keys to
      be honored.</para>

<para>
If no <command>controls</command> statement is present,
<command>named</command> will set 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> will attempt to load the command channel key
from the file <filename>rndc.key</filename> in
<filename>/etc</filename> (or whatever <varname>sysconfdir</varname>
was specified as when <acronym>BIND</acronym> was built).
To create a <filename>rndc.key</filename> file, run
<userinput>rndc-confgen -a</userinput>.
</para>

      <para>The <filename>rndc.key</filename> feature was created to
      ease the transition of systems from <acronym>BIND</acronym> 8,
      which did not have digital signatures on its command channel messages
      and thus did not have a <command>keys</command> clause.

It makes it possible to use an existing <acronym>BIND</acronym> 8
configuration file in <acronym>BIND</acronym> 9 unchanged,
and still have <command>rndc</command> work the same way
<command>ndc</command> worked in BIND 8, simply by executing the
command <userinput>rndc-keygen -a</userinput> after BIND 9 is
installed.
</para>

      <para>
      Since the <filename>rndc.key</filename> feature
      is only intended to allow the backward-compatible usage of
      <acronym>BIND</acronym> 8 configuration files, this feature does not
      have a high degree of configurability.  You cannot easily change
      the key name or the size of the secret, so you should make a
      <filename>rndc.conf</filename> with your own key if you wish to change
      those things.  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.  If you
      desire greater flexibility in allowing other users to access
      <command>rndc</command> commands then you need to create an
      <filename>rndc.conf</filename> and make it group readable by a group
      that contains the users who should have access.</para>

      <para>The UNIX control channel type of <acronym>BIND</acronym> 8 is not supported
      in <acronym>BIND</acronym> 9, and is not expected to be added in future
      releases.  If it is present in the controls statement from a
      <acronym>BIND</acronym> 8 configuration file, it is ignored
      and a warning is logged.</para>

    </sect2>
    <sect2>
      <title><command>include</command> Statement Grammar</title>
      <programlisting>include <replaceable>filename</replaceable>;</programlisting>
    </sect2>
    <sect2>
      <title><command>include</command> Statement Definition and Usage</title>

      <para>The <command>include</command> statement inserts the
      specified file at the point that 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 a nameserver.</para>

    </sect2>
    <sect2>
      <title><command>key</command> Statement Grammar</title>
<programlisting>key <replaceable>key_id</replaceable> {
    algorithm <replaceable>string</replaceable>;
    secret <replaceable>string</replaceable>;
};
</programlisting>
    </sect2>

<sect2>
<title><command>key</command> Statement Definition and Usage</title>

<para>The <command>key</command> statement defines a shared
secret key for use with TSIG, see <xref linkend="tsig"/>.</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 uniquely identifying the key. It can
be used in a "server" 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 only
algorithm currently supported with TSIG authentication is
<literal>hmac-md5</literal>.  The
<replaceable>secret_string</replaceable> is the secret to be
used by the algorithm, and is treated as a base-64 encoded
string.</para>

</sect2>
    <sect2>
      <title><command>logging</command> Statement Grammar</title>
      <programlisting><command>logging</command> {
   [ <command>channel</command> <replaceable>channel_name</replaceable> {
     ( <command>file</command> <replaceable>path name</replaceable>
         [ <command>versions</command> ( <replaceable>number</replaceable> | <literal>unlimited</literal> ) ]
         [ <command>size</command> <replaceable>size spec</replaceable> ]
       | <command>syslog</command> <replaceable>syslog_facility</replaceable>
       | <command>stderr</command>
       | <command>null</command> );
     [ <command>severity</command> (<option>critical</option> | <option>error</option> | <option>warning</option> | <option>notice</option> |
                 <option>info</option> | <option>debug</option> [ <replaceable>level</replaceable> ] | <option>dynamic</option> ); ]
     [ <command>print-category</command> <option>yes</option> or <option>no</option>; ]
     [ <command>print-severity</command> <option>yes</option> or <option>no</option>; ]
     [ <command>print-time</command> <option>yes</option> or <option>no</option>; ]
   }; ]
   [ <command>category</command> <replaceable>category_name</replaceable> {
     <replaceable>channel_name</replaceable> ; [ <replaceable>channel_nam</replaceable>e ; ... ]
   }; ]
   ...
};
</programlisting>
</sect2>

<sect2>
<title><command>logging</command> Statement Definition and Usage</title>

<para>The <command>logging</command> statement configures a wide
variety of logging options for the nameserver. 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 are wanted. If there is no <command>logging</command> statement,
the logging configuration will be:</para>

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

<para>In <acronym>BIND</acronym> 9, the logging configuration is only established when
the entire configuration file has been parsed.  In <acronym>BIND</acronym> 8, it was
established as soon as the <command>logging</command> statement
was parsed. When the server is starting 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>

<sect3>
<title>The <command>channel</command> Phrase</title>

<para>All log output goes to one or more <emphasis>channels</emphasis>;
you can make as many of them as you want.</para>

<para>Every channel definition must include a destination clause that
says whether messages selected for the channel go to a file, to a
particular syslog facility, to the standard error stream, or are
discarded. It can optionally also limit the message severity level
that will be 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 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 how many versions
of the file will be saved each time the file is opened.</para>

<para>If you use the <command>versions</command> log file option, then
<command>named</command> will retain that many backup versions of the file by
renaming them when opening.  For example, if you choose to keep 3 old versions
of the file <filename>lamers.log</filename> then 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>.
You can say <command>versions unlimited;</command> 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> will
stop writing to the file unless it 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 will be 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>Example usage of 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. How <command>syslog</command> will handle messages sent to
this facility is described in the <command>syslog.conf</command> man
page. If you have a system which uses a very old version of <command>syslog</command> that
only uses two arguments to the <command>openlog()</command> function,
then this clause is silently ignored.</para>
<para>The <command>severity</command> clause works like <command>syslog</command>'s
"priorities," except that they can also be used if you are writing
straight to a file rather than using <command>syslog</command>.
Messages which are not at least of the severity level given will
not be selected for the channel; messages of higher severity levels
will be accepted.</para>
<para>If you are using <command>syslog</command>, then the <command>syslog.conf</command> priorities
will 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> will
cause 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, for example
when debugging a configuration.</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, then debugging mode will be 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>ndc
notrace</command>. All debugging messages in the server have a debug
level, and 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>will 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 level to determine what messages to print.</para>
        <para>If <command>print-time</command> has been turned on, then
the date and time will be logged. <command>print-time</command> may
be specified for a <command>syslog</command> channel, but is usually
pointless since <command>syslog</command> also prints the date and
time. If <command>print-category</command> is requested, then the
category of the message will be logged as well. Finally, if <command>print-severity</command> is
on, then the severity level of the message will be logged. The <command>print-</command> options may
be used in any combination, and will always be 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>There are four predefined channels that are used for
<command>named</command>'s default logging as follows. How they are
used is described in <xref linkend="the_category_phrase"/>.
</para>

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

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

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

channel "null" {
   null;                                // toss anything sent to
                                        // this channel
};
</programlisting>

<para>The <command>default_debug</command> channel has the special
property that it only produces output when the server's debug level is
nonzero.  It normally writes to a file <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 up and still running as root is discarded.  If you need
to capture this output, you must run the server with the "<option>-g</option>"
option and redirect standard error to a file.</para>

<para>Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have defined.</para>
</sect3>

<sect3 id="the_category_phrase"><title>The <command>category</command> Phrase</title>

<para>There are many categories, so you can send the logs you want
to see wherever you want, without seeing logs you don't want. If
you don't specify a list of channels for a category, then log messages
in that category will be sent to the <command>default</command> category
instead. If you don't specify a default category, the following
"default default" is used:</para>
<programlisting>category "default" { "default_syslog"; "default_debug"; };
</programlisting>
<para>As an example, let's say you want to log security events to
a file, but you also want keep the default logging behavior. You'd
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>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>
<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><command>default</command></para></entry>
<entry colname = "2"><para>The default category defines the logging
options for those categories where no specific configuration has been
defined.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>general</command></para></entry>
<entry colname = "2"><para>The catch-all. Many things still aren't
classified into categories, and they all end up here.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>database</command></para></entry>
<entry colname = "2"><para>Messages relating to the databases used
internally by the name server to store zone and cache data.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>security</command></para></entry>
<entry colname = "2"><para>Approval and denial of requests.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>config</command></para></entry>
<entry colname = "2"><para>Configuration file parsing and processing.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>resolver</command></para></entry>
<entry colname = "2"><para>DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name server.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>xfer-in</command></para></entry>
<entry colname = "2"><para>Zone transfers the server is receiving.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>xfer-out</command></para></entry>
<entry colname = "2"><para>Zone transfers the server is sending.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>notify</command></para></entry>
<entry colname = "2"><para>The NOTIFY protocol.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>client</command></para></entry>
<entry colname = "2"><para>Processing of client requests.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>unmatched</command></para></entry>
<entry colname = "2"><para>Messages that named was unable to determine the
class of or for which there was no matching <command>view</command>.
A one line summary is also logged to the <command>client</command> category.
This category is best sent to a file or stderr, by default it is sent to
the <command>null</command> channel.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>network</command></para></entry>
<entry colname = "2"><para>Network operations.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>update</command></para></entry>
<entry colname = "2"><para>Dynamic updates.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>queries</command></para></entry>
<entry colname = "2"><para>Queries.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>dispatch</command></para></entry>
<entry colname = "2"><para>Dispatching of incoming packets to the
server modules where they are to be processed.
</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>dnssec</command></para></entry>
<entry colname = "2"><para>DNSSEC and TSIG protocol processing.
</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>lame-servers</command></para></entry>
<entry colname = "2"><para>Lame servers.  These are misconfigurations
in remote servers, discovered by BIND 9 when trying to query
those servers during resolution.
</para></entry>
</row>
</tbody>
</tgroup></informaltable>
</sect3>
</sect2>

<sect2>
<title><command>lwres</command> Statement Grammar</title>

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

<programlisting><command>lwres</command> {
    <optional> listen-on { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
    <optional> view <replaceable>view_name</replaceable>; </optional>
    <optional> search { <replaceable>domain_name</replaceable> ; <optional> <replaceable>domain_name</replaceable> ; ... </optional> }; </optional>
    <optional> ndots <replaceable>number</replaceable>; </optional>
};
</programlisting>

</sect2>
<sect2>
<title><command>lwres</command> Statement Definition and Usage</title>

<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 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
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 will be 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 will be constructed in the same manner as a normal DNS query
matching this view.  If this statement is omitted, the default view is
used, and 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>
</sect2>
<sect2>
<title><command>options</command> Statement Grammar</title>

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

<programlisting>options {
    <optional> version <replaceable>version_string</replaceable>; </optional>
    <optional> directory <replaceable>path_name</replaceable>; </optional>
    <optional> named-xfer <replaceable>path_name</replaceable>; </optional>
    <optional> tkey-domain <replaceable>domainname</replaceable>; </optional>
    <optional> tkey-dhkey <replaceable>key_name</replaceable> <replaceable>key_tag</replaceable>; </optional>
    <optional> dump-file <replaceable>path_name</replaceable>; </optional>
    <optional> memstatistics-file <replaceable>path_name</replaceable>; </optional>
    <optional> pid-file <replaceable>path_name</replaceable>; </optional>
    <optional> statistics-file <replaceable>path_name</replaceable>; </optional>
    <optional> zone-statistics <replaceable>yes_or_no</replaceable>; </optional>
    <optional> auth-nxdomain <replaceable>yes_or_no</replaceable>; </optional>
    <optional> deallocate-on-exit <replaceable>yes_or_no</replaceable>; </optional>
    <optional> dialup <replaceable>dialup_option</replaceable>; </optional>
    <optional> fake-iquery <replaceable>yes_or_no</replaceable>; </optional>
    <optional> fetch-glue <replaceable>yes_or_no</replaceable>; </optional>
    <optional> has-old-clients <replaceable>yes_or_no</replaceable>; </optional>
    <optional> host-statistics <replaceable>yes_or_no</replaceable>; </optional>
    <optional> minimal-responses <replaceable>yes_or_no</replaceable>; </optional>
    <optional> multiple-cnames <replaceable>yes_or_no</replaceable>; </optional>
    <optional> notify <replaceable>yes_or_no</replaceable> | <replaceable>explicit</replaceable>; </optional>
    <optional> recursion <replaceable>yes_or_no</replaceable>; </optional>
    <optional> rfc2308-type1 <replaceable>yes_or_no</replaceable>; </optional>
    <optional> use-id-pool <replaceable>yes_or_no</replaceable>; </optional>
    <optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable>; </optional>
    <optional> forward ( <replaceable>only</replaceable> | <replaceable>first</replaceable> ); </optional>
    <optional> forwarders { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
    <optional> check-names ( <replaceable>master</replaceable> | <replaceable>slave</replaceable> | <replaceable> response</replaceable> )( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
    <optional> allow-notify { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> allow-transfer { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> allow-recursion { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> allow-v6-synthesis { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> blackhole { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> listen-on <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> listen-on-v6 <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
    <optional> query-source <optional> address ( <replaceable>ip_addr</replaceable> | <replaceable>*</replaceable> ) </optional> <optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional>; </optional>
    <optional> max-transfer-time-in <replaceable>number</replaceable>; </optional>
    <optional> max-transfer-time-out <replaceable>number</replaceable>; </optional>
    <optional> max-transfer-idle-in <replaceable>number</replaceable>; </optional>
    <optional> max-transfer-idle-out <replaceable>number</replaceable>; </optional>
    <optional> tcp-clients <replaceable>number</replaceable>; </optional>
    <optional> recursive-clients <replaceable>number</replaceable>; </optional>
    <optional> serial-query-rate <replaceable>number</replaceable>; </optional>
    <optional> serial-queries <replaceable>number</replaceable>; </optional>
    <optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable>; </optional>
    <optional> transfers-in  <replaceable>number</replaceable>; </optional>
    <optional> transfers-out <replaceable>number</replaceable>; </optional>
    <optional> transfers-per-ns <replaceable>number</replaceable>; </optional>
    <optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> also-notify { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
    <optional> max-ixfr-log-size <replaceable>number</replaceable>; </optional>
    <optional> coresize <replaceable>size_spec</replaceable> ; </optional>
    <optional> datasize <replaceable>size_spec</replaceable> ; </optional>
    <optional> files <replaceable>size_spec</replaceable> ; </optional>
    <optional> stacksize <replaceable>size_spec</replaceable> ; </optional>
    <optional> cleaning-interval <replaceable>number</replaceable>; </optional>
    <optional> heartbeat-interval <replaceable>number</replaceable>; </optional>
    <optional> interface-interval <replaceable>number</replaceable>; </optional>
    <optional> statistics-interval <replaceable>number</replaceable>; </optional>
    <optional> topology { <replaceable>address_match_list</replaceable> }</optional>;
    <optional> sortlist { <replaceable>address_match_list</replaceable> }</optional>;
    <optional> rrset-order { <replaceable>order_spec</replaceable> ; <optional> <replaceable>order_spec</replaceable> ; ... </optional> </optional> };
    <optional> lame-ttl <replaceable>number</replaceable>; </optional>
    <optional> max-ncache-ttl <replaceable>number</replaceable>; </optional>
    <optional> max-cache-ttl <replaceable>number</replaceable>; </optional>
    <optional> sig-validity-interval <replaceable>number</replaceable> ; </optional>
    <optional> min-roots <replaceable>number</replaceable>; </optional>
    <optional> use-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> treat-cr-as-space <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
    <optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
    <optional> min-retry-time <replaceable>number</replaceable> ; </optional>
    <optional> max-retry-time <replaceable>number</replaceable> ; </optional>
    <optional> port <replaceable>ip_port</replaceable>; </optional>
    <optional> additional-from-auth <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> additional-from-cache <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> random-device <replaceable>path_name</replaceable> ; </optional>
    <optional> max-cache-size <replaceable>size_spec</replaceable> ; </optional>
    <optional> match-mapped-addresses <replaceable>yes_or_no</replaceable>; </optional>
};
</programlisting>
</sect2>

<sect2><title><command>options</command> Statement Definition and Usage</title>

<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 more than one occurrence is found,
the first occurrence determines the actual options used, and a warning
will be generated.  If there is no <command>options</command>
statement, an options block with each option set to its default will
be used.</para>

<variablelist>

<varlistentry><term><command>version</command></term>
<listitem><para>The version the server should report
via a query of name <filename>version.bind</filename> in
class <command>CHAOS</command>.
The default is the real version number of this server.</para>
</listitem></varlistentry>

<varlistentry><term><command>directory</command></term>
<listitem><para>The working directory of the server.
Any non-absolute pathnames in the configuration file will be 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.</para>
</listitem></varlistentry>

<varlistentry><term><command>named-xfer</command></term>
<listitem><para><emphasis>This option is obsolete.</emphasis>
It was used in <acronym>BIND</acronym> 8 to
specify the pathname to the <command>named-xfer</command> program.
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-domain</command></term>
<listitem><para>The domain 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 will be "<varname>client specified part</varname>" + 
"<varname>tkey-domain</varname>".
Otherwise, the name of the shared key will be "<varname>random hex
digits</varname>" + "<varname>tkey-domain</varname>". In most cases,
the <command>domainname</command> should be the server's domain
name.</para>
</listitem></varlistentry>

<varlistentry><term><command>tkey-dhkey</command></term>
<listitem><para>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 keyname should be the server's host name.</para>
</listitem></varlistentry>

<varlistentry><term><command>dump-file</command></term>
<listitem><para>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>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>
<note><para>Not yet implemented in <acronym>BIND</acronym> 9.</para></note>
</listitem></varlistentry>

<varlistentry><term><command>pid-file</command></term>
<listitem><para>The pathname of the file the server writes its process ID
in. If not specified, the default is <filename>/var/run/named.pid</filename>.
The pid-file is used by programs that want to send signals to the running
nameserver.</para>
</listitem></varlistentry>

<varlistentry><term><command>statistics-file</command></term>
<listitem><para>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>port</command></term>
<listitem><para>
The UDP/TCP port number the server uses for 
receiving and sending DNS protocol traffic.
The default is 53.  This option is mainly intended for server testing;
a server using a port other than 53 will not be able to communicate with
the global DNS.
The <command>port</command> option should be placed at
the beginning of the options block, before
any other options that take port numbers or IP addresses,
to ensure that the port value takes effect for all addresses
used by the server.</para>
</listitem></varlistentry>

<varlistentry><term><command>random-device</command></term>
<listitem><para>
The 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 options specifies the device (or file) from which to read
entropy.  If this is a file, operations requiring entropy will fail when the
file has been exhausted.  If 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>

</variablelist>


<sect3 id="boolean_options"><title>Boolean Options</title>

<variablelist>

<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>; this is
a change from <acronym>BIND</acronym> 8. If you are using very old DNS software, you
may need to set it to <userinput>yes</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>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. This has different effects according
to zone type and concentrates the zone maintenance so that it all
happens in a short interval, once every <command>heartbeat-interval</command> and
hopefully during the one call. It also suppresses some of the normal
zone maintenance traffic. The default is <userinput>no</userinput>.</para>
<para>The <command>dialup</command> option
may also be specified in the <command>view</command> and 
<command>zone</command> statements,
in which case it overrides the global <command>dialup</command>
option.</para>
<para>If the zone is a master zone then the server will send out a NOTIFY 
request to all the slaves. This will trigger the zone serial number check
in the slave (providing it supports NOTIFY) allowing the slave to
verify the zone while the connection is active.</para><para>If the
zone is a slave or stub zone, then the server will suppress the regular
"zone up to date" (refresh) queries and only perform 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 send refresh queries 
when the <command>heartbeat-interval</command> expires and
<userinput>passive</userinput> which just disables normal refresh
processing.</para></listitem></varlistentry>

<varlistentry><term><command>fake-iquery</command></term>
<listitem><para>In <acronym>BIND</acronym> 8, this option was used to
enable 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
didn't 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>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 enables keeping of
statistics for every host that the nameserver interacts with.
Not implemented in BIND 9.
</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.  If you need to disable outgoing incremental zone
transfers, use <command>provide-ixfr</command> <userinput>no</userinput>.
</para></listitem></varlistentry>

<varlistentry><term><command>minimal-responses</command></term>
<listitem><para>If <userinput>yes</userinput>, then when generating
responses the server will only add 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.
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 allow multiple CNAME records in violation of the
DNS standards.  <acronym>BIND</acronym> 9.2 always strictly
enforces the CNAME rules both in master 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 master server identified
in the SOA MNAME field), and to any servers listed in the
<command>also-notify</command> option.
</para><para>
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 slaves
to crash.</para></listitem></varlistentry>

<varlistentry><term><command>recursion</command></term>
<listitem><para>If <userinput>yes</userinput>, and a
DNS query requests recursion, then the server will attempt to do
all the work required to answer the query. If recursion is off
and the server does not already know the answer, it will return 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.
See also <command>fetch-glue</command> above.
</para></listitem></varlistentry>

<varlistentry><term><command>rfc2308-type1</command></term>
<listitem><para>Setting this to <userinput>yes</userinput> will
cause the server to send NS records along with the SOA record for negative
answers. The default is <userinput>no</userinput>.</para>
<note><simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</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>zone-statistics</command></term>
<listitem><para>If <userinput>yes</userinput>, the server will, by default, collect
statistical data on all zones in the server.  These statistics may be accessed
using <command>rndc stats</command>, which will dump them to the file listed
in the <command>statistics-file</command>.  See also <xref linkend="statsfile"/>.
</para></listitem></varlistentry>

<varlistentry><term><command>use-ixfr</command></term>
<listitem><para><emphasis>This option is obsolete</emphasis>.
If you need 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>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 will be 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 slave zones may be added and modified by
untrusted third parties.  Also, avoiding
the search for this additional data will speed 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, A6, and AAAA) for <literal>mail.example.net</literal> will be provided as well,
if known.  Setting these options to <command>no</command> disables this behavior.
</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 will not be able to provide upwards
referrals when <command>additional-from-cache no</command>
has been specified.  Instead, it will respond 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 will match any address match
list entries that match the corresponding IPv4 address.
Enabling this option is sometimes useful on IPv6-enabled Linux
systems, to work around a kernel quirk that causes IPv4
TCP connections such as zone transfers to be accepted
on an IPv6 socket using mapped addresses, causing
address match lists designed for IPv4 to fail to match.
The use of this option for any other purpose is discouraged.
</para></listitem></varlistentry>

<varlistentry><term><command>ixfr-from-differences</command></term>
<listitem>
<para>
When 'yes' and the server loads a new version of a master
zone from its zone file or receives a new version of a slave
file by a non-incremental zone transfer, it will compare
the new version to the previous one and calculate a set
of differences.  The differences are then logged in the
zone's journal file such that the changes can be transmitted
to downstream slaves 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 master.
In particular, if the new version of a zone is completely
different from the previous one, the set of differences
will be of a size comparable to the combined size of the
old and new zone version, and the server will need to
temporarily allocate memory to hold this complete
difference set.
</para></listitem></varlistentry>

</variablelist>

</sect3>

<sect3><title>Forwarding</title>
<para>The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
nameservers. 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>,
the default, causes the server to query the forwarders first, and
if that doesn't answer the question the server will then look for
the answer itself. If <varname>only</varname> is specified, the
server will only query the forwarders.
</para></listitem></varlistentry>

<varlistentry><term><command>forwarders</command></term>
<listitem><para>Specifies the IP addresses to be used
for forwarding. The default is the empty list (no forwarding).
</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. You can set particular domains 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>
</sect3>

<sect3 id="access_control"><title>Access Control</title>

<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>Specifies which hosts are allowed to
notify slaves of a zone change in addition to the zone masters.
<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 slave zone.  If not specified, the default is to process notify messages
only from a zone's master.</para>
</listitem></varlistentry>

<varlistentry><term><command>allow-query</command></term>
<listitem><para>Specifies which hosts are allowed to
ask ordinary 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>
</listitem></varlistentry>


<varlistentry><term><command>allow-recursion</command></term>
<listitem><para>Specifies which hosts are allowed to
make recursive queries through this server. If not specified, the
default is to allow recursive queries from all hosts. 
Note that disallowing recursive queries for a host does not prevent the
host from retrieving data that is already in the server's cache.
</para>
</listitem></varlistentry>

<varlistentry><term><command>allow-v6-synthesis</command></term>
<listitem><para>Specifies which hosts are to receive
synthetic responses to IPv6 queries as described in
<xref linkend="synthesis"/>.
</para>
</listitem></varlistentry>

<varlistentry><term><command>allow-transfer</command></term>
<listitem><para>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 from all hosts.</para>
</listitem></varlistentry>

<varlistentry><term><command>blackhole</command></term>
<listitem><para>Specifies a list of addresses that the
server will not accept queries from or use to resolve a query. Queries
from these addresses will not be responded to. The default is <userinput>none</userinput>.</para>
</listitem></varlistentry>

</variablelist>

</sect3>

<sect3><title>Interfaces</title>
<para>The interfaces and ports that the server will answer 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>.
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be 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>will enable the nameserver 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 will listen on port 53 on all interfaces.</para>

<para>The <command>listen-on-v6</command> option is used to
specify the ports on which the server will listen for incoming
queries sent using IPv6.</para>

<para>The server does not bind a separate socket to each IPv6
interface address as it does for IPv4. Instead, it always
listens on the IPv6 wildcard address. Therefore, the only
values allowed for the <varname>address_match_list</varname>
argument to the <command>listen-on-v6</command> statement are
<programlisting>{ any; }</programlisting> and
<programlisting>{ none;}</programlisting></para>

<para>Multiple <command>listen-on-v6</command> options can be
used to listen on multiple ports:</para>

<programlisting>listen-on-v6 port 53 { any; };
listen-on-v6 port 1234 { any; };
</programlisting>
<para>To make the server not listen on any IPv6 address, use</para>
<programlisting>listen-on-v6 { none; };
</programlisting>
<para>If no <command>listen-on-v6</command> statement is specified,
the server will not listen on any IPv6 address.</para></sect3>
<sect3><title>Query Address</title>
<para>If the server doesn't know the answer to a question, it will
query other nameservers. <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> or is omitted,
a wildcard IP address (<command>INADDR_ANY</command>) will be used.
If <command>port</command> is <command>*</command> or is omitted,
a random unprivileged port will be used. The defaults are</para>
<programlisting>query-source address * port *;
query-source-v6 address * port *
</programlisting>
<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></sect3>

<sect3 id="zone_transfers"><title>Zone Transfers</title>
<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>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 will
quickly converge on stealth servers. If an <command>also-notify</command> list
is given in a <command>zone</command> statement, it will override
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 will
not be 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 will be terminated. The default is 120 minutes
(2 hours).</para>
</listitem></varlistentry>

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

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

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

<varlistentry><term><command>serial-query-rate</command></term>
<listitem><para>Slave servers will periodically query master servers
to find out if zone serial numbers have changed. Each such query uses
a minute amount of the slave server's network bandwidth.  To limit the
amount of bandwith 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.
</para>
</listitem></varlistentry>

<varlistentry><term><command>serial-queries</command></term>
<listitem><para>In BIND 8, the <command>serial-queries</command> option
set the maximum number of concurrent serial number queries
allowed to be outstanding at any given time.
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 master 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 a message. <command>many-answers</command> is more
efficient, but is only supported by relatively new slave servers,
such as <acronym>BIND</acronym> 9, <acronym>BIND</acronym> 8.x and patched
versions of <acronym>BIND</acronym> 4.9.5. The default is
<command>many-answers</command>. <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>transfers-in</command></term>
<listitem><para>The maximum number of inbound zone transfers
that can be running concurrently. The default value is <literal>10</literal>.
Increasing <command>transfers-in</command> may speed up the convergence
of slave zones, but it also may increase the load on the local system.</para>
</listitem></varlistentry>

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

<varlistentry><term><command>transfers-per-ns</command></term>
<listitem><para>The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote nameserver.
The default value is <literal>2</literal>. Increasing <command>transfers-per-ns</command> may
speed up the convergence of slave zones, but it also may increase
the load on the remote nameserver. <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 will be 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 will usually be 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>
</listitem></varlistentry>

<varlistentry><term><command>transfer-source-v6</command></term>
<listitem><para>The same as <command>transfer-source</command>,
except zone transfers are performed using IPv6.</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, will be used to
send NOTIFY messages.
This address must appear in the slave 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 / 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>
</listitem></varlistentry>

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

</variablelist>

</sect3>

<sect3>
<title>Operating System Resource Limits</title>

<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 don't support some or
any of the limits. On such systems, a warning will be issued if the
unsupported limit is used.</para>

<variablelist>

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

<varlistentry><term><command>datasize</command></term>
<listitem><para>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 of limiting 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.  If you wish 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>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>The maximum amount of stack memory the server
may use. The default is <literal>default</literal>.</para>
</listitem></varlistentry>

</variablelist>

</sect3>

<sect3>
<title>Server  Resource Limits</title>

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

<varlistentry><term><command>recursive-clients</command></term>
<listitem><para>The maximum number of simultaneous recursive lookups
the server will perform on behalf of clients.  The default is
<literal>1000</literal>.  Because each recursing clients 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>
</listitem></varlistentry>

<varlistentry><term><command>tcp-clients</command></term>
<listitem><para>The maximum number of simultaneous client TCP
connections that the server will accept.
The default is <literal>100</literal>.</para>
</listitem></varlistentry>

<varlistentry><term><command>max-cache-size</command></term>
<listitem><para>The maximum amount of memory to use for the
server's cache, in bytes.  When the amount of data in the cache
reaches this limit, the server will cause records to expire
prematurely so that the limit is not exceeded.  In a server with
multiple views, the limit applies separately to the cache of each
view.  The default is <literal>unlimited</literal>, meaning that 
records are purged from the cache only when their TTLs expire.
</para>
</listitem></varlistentry>

</variablelist>

</sect3>

<sect3><title>Periodic Task Intervals</title>

<variablelist>

<varlistentry><term><command>cleaning-interval</command></term>
<listitem><para>The server will remove expired resource records
from the cache every <command>cleaning-interval</command> minutes.
The default is 60 minutes.
If set to 0, no  periodic cleaning will occur.</para>
</listitem></varlistentry>

<varlistentry><term><command>heartbeat-interval</command></term>
<listitem><para>The server will perform 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). If set to 0, no zone maintenance for these zones will occur.</para>
</listitem></varlistentry>

<varlistentry><term><command>interface-interval</command></term>
<listitem><para>The server will scan the network interface list
every <command>interface-interval</command> minutes. The default
is 60 minutes. If set to 0, interface scanning will only occur when
the configuration file is  loaded. After the scan, listeners will be
started on any new interfaces (provided they are allowed by the
<command>listen-on</command> configuration). Listeners on interfaces
that have gone away will be cleaned up.</para>
</listitem></varlistentry>

<varlistentry><term><command>statistics-interval</command></term>
<listitem><para>Nameserver statistics will be logged
every <command>statistics-interval</command> minutes. The default is 
60. If set to 0, no statistics will be logged.</para><note>
<simpara>Not yet implemented in <acronym>BIND</acronym>9.</simpara></note>
</listitem></varlistentry>

</variablelist>

</sect3>

<sect3 id="topology"><title>Topology</title>

<para>All other things being equal, when the server chooses a nameserver
to query from a list of nameservers, it prefers the one that is
topologically closest to itself. The <command>topology</command> statement
takes an <command>address_match_list</command> and interprets it
in a special way. Each top-level list element is assigned a distance.
Non-negated elements get a distance based on their position in the
list, where the closer the match is to the start of the list, the
shorter the distance is between it and the server. A negated match
will be assigned the maximum distance from the server. If there
is no match, the address will get a distance which is further than
any non-negated list element, and closer than any negated element.
For example,</para>
<programlisting>topology {
    10/8;
    !1.2.3/24;
    { 1.2/16; 3/8; };
};</programlisting>
<para>will prefer servers on network 10 the most, followed by hosts
on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the
exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
is preferred least of all.</para>
<para>The default topology is</para>
<programlisting>    topology { localhost; localnets; };
</programlisting>
<note><simpara>The <command>topology</command> option
is not implemented in <acronym>BIND</acronym> 9.
</simpara></note>
</sect3>

<sect3 id="the_sortlist_statement">

<title>The <command>sortlist</command> Statement</title>

<para>The response to a DNS query may consist of multiple resource
records (RRs) forming a resource records set (RRset).
The name server will normally return 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 nameservers, not all the clients.</para>

<para>The <command>sortlist</command> statement (see below) takes
an <command>address_match_list</command> and interprets it even
more specifically than the <command>topology</command> statement
does (<xref linkend="topology"/>).
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.</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
treated the same as the <command>address_match_list</command> in
a <command>topology</command> statement. 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 will 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
will 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 will only prefer other addresses on
their directly connected networks.</para>
<programlisting>sortlist {
    { localhost;                                   // IF   the local host
        { localnets;                               // THEN first fit on the
            192.168.1/24;                          //   following nets
            { 192.168.2/24; 192.168.3/24; }; }; };
    { 192.168.1/24;                                // IF   on class C 192.168.1
        { 192.168.1/24;                            // THEN use .1, or .2 or .3
            { 192.168.2/24; 192.168.3/24; }; }; };
    { 192.168.2/24;                                // IF   on class C 192.168.2
        { 192.168.2/24;                            // THEN use .2, or .1 or .3
            { 192.168.1/24; 192.168.3/24; }; }; };
    { 192.168.3/24;                                // IF   on class C 192.168.3
        { 192.168.3/24;                            // THEN use .3, or .1 or .2
            { 192.168.1/24; 192.168.2/24; }; }; };
    { { 192.168.4/24; 192.168.5/24; };             // if .4 or .5, prefer that net
    };
};</programlisting>
<para>The following example will give reasonable behavior for the
local host and hosts on directly connected networks. It is similar
to the behavior of the address sort in <acronym>BIND</acronym> 4.9.x. Responses sent
to queries from the local host will favor any of the directly connected
networks. Responses sent to queries from any other hosts on a directly
connected network will prefer addresses on that same network. Responses
to other queries will not be sorted.</para>
<programlisting>sortlist {
           { localhost; localnets; };
           { localnets; };
};
</programlisting>
</sect3>
<sect3 id="rrset_ordering"><title id="rrset_ordering_title">RRset Ordering</title>
<para>When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the response.
The <command>rrset-order</command> statement permits configuration
of the ordering of the records in a multiple record response.
See also the <command>sortlist</command> statement,
<xref linkend="the_sortlist_statement"/>.
</para>

<para>An <command>order_spec</command> is defined as follows:</para>
<programlisting><optional> class <replaceable>class_name</replaceable> </optional><optional> type <replaceable>type_name</replaceable> </optional><optional> name <replaceable>"domain_name"</replaceable></optional>
      order <replaceable>ordering</replaceable>
</programlisting>
<para>If no class is specified, the default is <command>ANY</command>.
If no type is specified, the default is <command>ANY</command>.
If no name is specified, the default is "<command>*</command>".</para>
<para>The legal values for <command>ordering</command> 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 = "0.750in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.750in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>fixed</command></para></entry>
<entry colname = "2"><para>Records are returned in the order they
are defined in the zone file.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>random</command></para></entry>
<entry colname = "2"><para>Records are returned in some random order.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>cyclic</command></para></entry>
<entry colname = "2"><para>Records are returned in a round-robin
order.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>For example:</para>
<programlisting>rrset-order {
   class IN type A name "host.example.com" order random;
   order cyclic;
};
</programlisting>
<para>will cause any responses for type A records in class IN that
have "<literal>host.example.com</literal>" as a suffix, to always be returned
in random order. All other records are returned in cyclic order.</para>
<para>If multiple <command>rrset-order</command> statements appear,
they are not combined &mdash; the last one applies.</para>

<note>
<simpara>The <command>rrset-order</command> statement
is not yet implemented in <acronym>BIND</acronym> 9.
BIND 9 currently supports only a "random-cyclic" ordering,
where the server randomly chooses a starting point within
the RRset and returns the records in order starting at
that point, wrapping around the end of the RRset if 
necessary.</simpara></note>
</sect3>

<sect3 id="synthesis"><title>Synthetic IPv6 responses</title>

<para>Many existing stub resolvers support IPv6 DNS lookups as defined in
RFC1886, using AAAA records for forward lookups and "nibble labels" in
the <literal>ip6.int</literal> domain for reverse lookups, but do not support
RFC2874-style lookups (using A6 records and binary labels in the
<literal>ip6.arpa</literal> domain).</para>

<para>For those who wish to continue to use such stub resolvers rather than
switching to the BIND 9 lightweight resolver, BIND 9 provides a way
to automatically convert RFC1886-style lookups into
RFC2874-style lookups and return the results as "synthetic" AAAA and
PTR records.</para>

<para>This feature is disabled by default and can be enabled on a per-client
basis by adding a
<command>allow-v6-synthesis { <replaceable>address_match_list</replaceable> };</command>
clause to the <command>options</command> or <command>view</command> statement.
 When it is enabled, recursive
AAAA queries cause the server to first try an A6 lookup and if that
fails, an AAAA lookups.  No matter which one succeeds, the results are
returned as a set of synthetic AAAA records.  Similarly, recursive PTR
queries in <literal>ip6.int</literal> will cause a
lookup in <literal>ip6.arpa</literal> using binary
labels, and if that fails, another lookup in <literal>ip6.int</literal>.
The results are returned as a synthetic PTR record in
<literal>ip6.int</literal>.</para>

<para>The synthetic records have a TTL of zero.  DNSSEC validation of
synthetic responses is not currently supported; therefore responses
containing synthetic RRs will not have the AD flag set.</para>
</sect3>

<sect3 id="tuning"><title>Tuning</title>

<variablelist>

<varlistentry><term><command>lame-ttl</command></term>
<listitem><para>Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
<emphasis role="bold">NOT</emphasis> recommended.)
Default is <literal>600</literal> (10 minutes). Maximum value is 
<literal>1800</literal> (30 minutes).</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 will
be silently truncated to 7 days if set to a greater value.</para>
</listitem></varlistentry>

<varlistentry><term><command>max-cache-ttl</command></term>
<listitem><para><command>max-cache-ttl</command> sets
the maximum time for which the server will cache ordinary (positive)
answers. The default is one week (7 days).</para>
</listitem></varlistentry>

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

<varlistentry><term><command>sig-validity-interval</command></term>
<listitem><para>Specifies the number of days into the
future when DNSSEC signatures automatically generated as a result
of dynamic updates (<xref linkend="dynamic_update"/>)
will expire. The default is <literal>30</literal> days. The signature
inception time is unconditionally set to one hour before the current time
to allow for a limited amount of clock skew.</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, but these values
are set by the master, giving slave server administrators little
control over their contents.
</para><para>
These options allow the administrator to set a minimum and maximum
refresh and retry time either per-zone, per-view, or per-server.
These options are valid for master, slave and stub zones, 
and clamp the SOA refresh and retry times to the specified values.
</para></listitem></varlistentry>

</variablelist>

</sect3>

<sect3 id="statsfile">
<title>The Statistics File</title>

<para>The statistics file generated by <acronym>BIND</acronym> 9
is similar, but not identical, to that
generated by <acronym>BIND</acronym> 8.
</para>
<para>The statistics dump begins with the line <command>+++ Statistics Dump
+++ (973798949)</command>, where the number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970.  Following
that line are a series of lines containing a counter type, the value of the
counter, optionally a zone name, and optionally a view name.
The lines without view and zone listed are global statistics for the entire server.
Lines with a zone and view name for the given view and zone (the view name is
omitted for the default view).  The statistics dump ends
with the line <command>--- Statistics Dump --- (973798949)</command>, where the
number is identical to the number in the beginning line.</para>
<para>The following statistics counters are maintained:</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><command>success</command></para></entry>
<entry colname = "2"><para>The number of
successful queries made to the server or zone.  A successful query
is defined as query which returns a NOERROR response other than
a referral response.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>referral</command></para></entry>
<entry colname = "2"><para>The number of queries which resulted
in referral responses.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>nxrrset</command></para></entry>
<entry colname = "2"><para>The number of queries which resulted in
NOERROR responses with no data.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>nxdomain</command></para></entry>
<entry colname = "2"><para>The number
of queries which resulted in NXDOMAIN responses.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>recursion</command></para></entry>
<entry colname = "2"><para>The number of queries which caused the server
to perform recursion in order to find the final answer.</para></entry>
</row
><row rowsep = "0">
<entry colname = "1"><para><command>failure</command></para></entry>
<entry colname = "2"><para>The number of queries which resulted in a
failure response other than those above.</para></entry>
</row>
</tbody>
</tgroup></informaltable>

</sect3>

</sect2>

<sect2 id="server_statement_grammar">
<title><command>server</command> Statement Grammar</title>

<programlisting>server <replaceable>ip_addr</replaceable> {
    <optional> bogus <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> provide-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> request-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> edns <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> transfers <replaceable>number</replaceable> ; </optional>
    <optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable> ; ]</optional>
    <optional> keys <replaceable>{ string ; <optional> string ; <optional>...</optional></optional> }</replaceable> ; </optional>
};
</programlisting>

</sect2>

<sect2 id="server_statement_definition_and_usage">
<title><command>server</command> Statement Definition and Usage</title>

<para>The <command>server</command> statement defines characteristics
to be associated with a remote nameserver.</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 you discover that a remote server is giving out bad data,
marking it as bogus will prevent 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 master, will respond with an incremental
zone transfer when the given remote server, a slave, requests it.
If set to <command>yes</command>, incremental transfer will be provided
whenever possible. If set to <command>no</command>, all transfers
to the remote server will be nonincremental. If not set, the value
of the <command>provide-ixfr</command> option in the global options block
is used as a default.</para>

<para>The <command>request-ixfr</command> clause determines whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the <command>request-ixfr</command> option in the global
options block is used as a default.</para>

<para>IXFR requests to servers that do not support IXFR will 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 master
and slave 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>edns</command> clause determines whether the local server
will attempt to use EDNS when communicating with the remote server.  The
default is <command>yes</command>.</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 message. <command>many-answers</command> is
more efficient, but is only known to be understood by <acronym>BIND</acronym> 9, <acronym>BIND</acronym>
8.x, and patched versions of <acronym>BIND</acronym> 4.9.5. You can specify which method
to use for a server with the <command>transfer-format</command> option.
If <command>transfer-format</command> is not specified, the <command>transfer-format</command> specified
by the <command>options</command> statement will be 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 is used to identify a <command>key_id</command> defined
by the <command>key</command> statement, to be used for transaction
security when talking to the remote server. The <command>key</command> statement
must come before the <command>server</command> statement that references
it. When a request is sent to the remote server, a request signature
will be 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>Although the grammar of the <command>keys</command> clause
allows for multiple keys, only a single key per server is currently
supported.</para>

</sect2>

<sect2><title><command>trusted-keys</command> Statement Grammar</title>
<programlisting>trusted-keys {
    <replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ;
    <optional> <replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; <optional>...</optional></optional>
};
</programlisting>
</sect2>
<sect2><title><command>trusted-keys</command> Statement Definition
and Usage</title>
<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 its parent zone is unsigned.
Once a key has been configured as a trusted key, it is treated as
if it had been validated and proven secure. The resolver attempts
DNSSEC validation on all DNS data in subdomains of a security root.</para>
<para>The <command>trusted-keys</command> statement can contain
multiple key entries, each consisting of the key's domain name,
flags, protocol, algorithm, and the base-64 representation of the
key data.</para></sect2>
<sect2><title><command>view</command> Statement Grammar</title>
<programlisting>view <replaceable>view_name</replaceable> <optional><replaceable>class</replaceable></optional> {
      match-clients { <replaceable>address_match_list</replaceable> } ;
      match-destinations { <replaceable>address_match_list</replaceable> } ;
      match-recursive-only { <replaceable>yes_or_no</replaceable> } ;
      <optional> <replaceable>view_option</replaceable>; ...</optional>
      <optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
      <optional> <replaceable>zone_statement</replaceable>; ...</optional>
};
</programlisting></sect2>
<sect2><title><command>view</command> Statement Definition and Usage</title>

<para>The <command>view</command> statement is a powerful new 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 will be 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.  A view can also be specified
as <command>match-recursive-only</command>, which means that only recursive
requests from matching clients will match that view.
The order of the <command>view</command> statements is significant &mdash; 
a client request will be resolved in the context of the first
<command>view</command> that it matches.</para>

<para>Zones defined within a <command>view</command> statement will
be only be 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, and any <command>zone</command> statements specified on
the top level of the configuration file are considered to be part of
this 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-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>
</sect2>
<sect2 id="zone_statement_grammar"><title><command>zone</command>
Statement Grammar</title>
      <programlisting>zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> <optional>{ 
    type ( master | slave | hint | stub | forward ) ;
    <optional> allow-notify { <replaceable>address_match_list</replaceable> } ; </optional>
    <optional> allow-query { <replaceable>address_match_list</replaceable> } ; </optional>
    <optional> allow-transfer { <replaceable>address_match_list</replaceable> } ; </optional>
    <optional> allow-update { <replaceable>address_match_list</replaceable> } ; </optional>
    <optional> update-policy { <replaceable>update_policy_rule</replaceable> <optional>...</optional> } ; </optional>
    <optional> allow-update-forwarding { <replaceable>address_match_list</replaceable> } ; </optional>
    <optional> also-notify { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
    <optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
    <optional> dialup <replaceable>dialup_option</replaceable> ; </optional>
    <optional> file <replaceable>string</replaceable> ; </optional>
    <optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
    <optional> forwarders { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
    <optional> ixfr-base <replaceable>string</replaceable> ; </optional>
    <optional> ixfr-tmp-file <replaceable>string</replaceable> ; </optional>
    <optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> masters <optional>port <replaceable>ip_port</replaceable></optional> { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> <optional>key <replaceable>key</replaceable></optional>; <optional>...</optional> } ; </optional>
    <optional> max-ixfr-log-size <replaceable>number</replaceable> ; </optional>
    <optional> max-transfer-idle-in <replaceable>number</replaceable> ; </optional>
    <optional> max-transfer-idle-out <replaceable>number</replaceable> ; </optional>
    <optional> max-transfer-time-in <replaceable>number</replaceable> ; </optional>
    <optional> max-transfer-time-out <replaceable>number</replaceable> ; </optional>
    <optional> notify <replaceable>yes_or_no</replaceable> | <replaceable>explicit</replaceable> ; </optional>
    <optional> pubkey <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; </optional>
    <optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
    <optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
    <optional> sig-validity-interval <replaceable>number</replaceable> ; </optional>
    <optional> database <replaceable>string</replaceable> ; </optional>
    <optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
    <optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
    <optional> min-retry-time <replaceable>number</replaceable> ; </optional>
    <optional> max-retry-time <replaceable>number</replaceable> ; </optional>

}</optional>;
</programlisting>
</sect2>
<sect2><title><command>zone</command> Statement Definition and Usage</title>
<sect3><title>Zone Types</title>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0"
    tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.908in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.217in"/>
<tbody>
<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 will be 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 slave zone is a replica of a master
zone. The <command>masters</command> list specifies one or more IP addresses
of master servers that the slave contacts to update its copy of the zone.
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 master can also be done with per-server TSIG keys.
If a file is specified, then the
replica will be 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 start-up 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 file names. For example,
a slave 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 you put 100K files into a single directory.)</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 slave zone,
except that it replicates only the NS records of a master 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 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.
In <acronym>BIND</acronym> 4/8, zone transfers of a parent zone
included the NS records from stub children of that zone. This meant
that, in some cases, users could get away with configuring child stubs
only in the master server for the parent zone. <acronym>BIND</acronym>
9 never mixes together zone data from different zones in this
way. Therefore, if a <acronym>BIND</acronym> 9 master serving a parent
zone has child stub zones configured, all the slave 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 of forcing 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
RFC2157 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>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 will apply 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 will be done for the domain, cancelling the effects of
any forwarders in the <command>options</command> statement. Thus
if you want 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 want to use the same
servers as set globally) you need to respecify the global forwarders.</para>
</entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>hint</varname></para></entry>
<entry colname = "2"><para>The initial set of root nameservers is
specified using a "hint zone". When the server starts up, it uses
the root hints to find a root nameserver and get the most recent
list of root nameservers. 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 defaults hints.</para></entry>
</row>
</tbody>
</tgroup></informaltable></sect3>

<sect3><title>Class</title>
<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 is
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></sect3>
<sect3>

<title>Zone Options</title>

<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-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>Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is to deny
updates from all hosts.</para>
</listitem></varlistentry>

<varlistentry><term><command>update-policy</command></term>
<listitem><para>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>Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to the
master.  The default is <userinput>{ none; }</userinput>, which 
means that no update forwarding will be 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, since
the responsibility for update access control should rest with the 
master server, not the slaves.</para>
<para>Note that enabling the update forwarding feature on a slave server
may expose master servers relying on insecure IP address based
access control to attacks; see <xref linkend="dynamic_update_security"/>
for more details.</para>
</listitem></varlistentry>

<varlistentry><term><command>also-notify</command></term>
<listitem><para>Only meaningful if <command>notify</command> is
active for this zone. The set of machines that will receive a 
<literal>DNS NOTIFY</literal> message
for this zone is made up of all the listed nameservers (other than
the primary master) 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.
<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 was used in BIND 8 to restrict the character set of
domain names in master files and/or DNS responses received from the
netowrk.  BIND 9 does not restrict the character set of domain names
and does not implement the <command>check-names</command> option.
</para>
</listitem></varlistentry>

<varlistentry><term><command>database</command></term>
<listitem><para>Specify the type of database to be used for storing 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>forward</command></term>
<listitem><para>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> would
allow a normal lookup to be tried.</para>
</listitem></varlistentry>

<varlistentry><term><command>forwarders</command></term>
<listitem><para>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; the global options are not used.</para>
</listitem></varlistentry>

<varlistentry><term><command>ixfr-base</command></term>
<listitem><para>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>Was an undocumented option in <acronym>BIND</acronym> 8.
Ignored in <acronym>BIND</acronym> 9.</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>pubkey</command></term>
<listitem><para>In <acronym>BIND</acronym> 8, this option was intended for specifying
a public zone key for verification of signatures in DNSSEC signed
zones when they are loaded from disk. <acronym>BIND</acronym> 9 does not verify signatures
on loading and ignores the option.</para>
</listitem></varlistentry>

<varlistentry><term><command>zone-statistics</command></term>
<listitem><para>If <userinput>yes</userinput>, the server will keep statistical
information for this zone, which can be dumped to the
<command>statistics-file</command> defined in the server options.</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>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>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 description 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"/>.</para>
</listitem></varlistentry>

</variablelist>

</sect3>
<sect3 id="dynamic_update_policies"><title>Dynamic Update Policies</title>
<para><acronym>BIND</acronym> 9 supports two alternative 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> option, respectively.</para>
<para>The <command>allow-update</command> clause works the same
way as in previous versions of <acronym>BIND</acronym>. It grants given clients the
permission to update any record of any name in the zone.</para>
<para>The <command>update-policy</command> clause is new in <acronym>BIND</acronym>
9 and allows more fine-grained control over what updates are allowed.
A set of rules is specified, where each rule either grants or denies
permissions for one or more names to be updated by one or more identities.
 If the dynamic update request message is signed (that is, it includes
either a TSIG or SIG(0) record), the identity of the signer can
be determined.</para>
<para>Rules are specified in the <command>update-policy</command> zone
option, and are only meaningful for master zones.  When the <command>update-policy</command> statement
is present, it is a configuration error for the <command>allow-update</command> statement
to be present.  The <command>update-policy</command> statement only
examines the signer of a message; the source address is not relevant.</para>
<para>This is how a rule definition looks:</para>
<programlisting>
( <command>grant</command> | <command>deny</command> ) <replaceable>identity</replaceable> <replaceable>nametype</replaceable> <replaceable>name</replaceable> <optional> <replaceable>types</replaceable> </optional>
</programlisting>
<para>Each rule grants or denies privileges.  Once a message has
successfully matched a rule, the operation is immediately granted
or denied and no further rules are examined.  A rule is matched
when the signer matches the identity field, the name matches the
name field, and the type is specified in the type field.</para>
<para>The identity field specifies a name or a wildcard name.  The
nametype field has 4 values: <varname>name</varname>, <varname>subdomain</varname>, <varname>wildcard</varname>,
and <varname>self</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>Matches when the updated name is the
same as the name in the name field.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>subdomain</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is a subdomain
of the name in the name field (which includes the name itself).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>wildcard</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is a valid
expansion of the wildcard name in the name field.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>self</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is the
same as the message signer. The name field is ignored.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>If no types are specified, the rule matches all types except
SIG, NS, SOA, and NXT. Types may be specified by name, including
"ANY" (ANY matches all types except NXT, which can never be updated).
</para>
      </sect3>
    </sect2>
  </sect1>
  <sect1>
    <title>Zone File</title>
    <sect2 id="types_of_resource_records_and_when_to_use_them">
      <title>Types of Resource Records and When to Use Them</title>
<para>This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been identified
and implemented in the DNS. These are also included.</para>
      <sect3>
        <title>Resource Records</title>

        <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 nameservers, 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 in this resource record. Types refer to
abstract resources.</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 instance of a protocol.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RDATA</para></entry>
<entry colname = "2"><para>the type and sometimes class-dependent
data that describes the resource.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The following are <emphasis>types</emphasis> of valid RRs
(some of these listed, although not obsolete, are experimental (x)
or historical (h) and no longer in general use):</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>A</para></entry>
<entry colname = "2"><para>a host address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>A6</para></entry>
<entry colname = "2"><para>an IPv6 address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>AAAA</para></entry>
<entry colname = "2"><para>Obsolete format of IPv6 address</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>AFSDB</para></entry>
<entry colname = "2"><para>(x) location of AFS database servers.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>CNAME</para></entry>
<entry colname = "2"><para>identifies the canonical name of an alias.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>DNAME</para></entry>
<entry colname = "2"><para>for delegation of reverse addresses.
Replaces the domain name specified with another name to be looked
up. Described in RFC 2672.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>HINFO</para></entry>
<entry colname = "2"><para>identifies the CPU and OS used by a host.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>ISDN</para></entry>
<entry colname = "2"><para>(x) representation of ISDN addresses.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>KEY</para></entry>
<entry colname = "2"><para>stores a public key associated with a
DNS name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>LOC</para></entry>
<entry colname = "2"><para>(x) for storing GPS info. See RFC 1876.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>MX</para></entry>
<entry colname = "2"><para>identifies a mail exchange for the domain.
 See RFC 974 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NS</para></entry>
<entry colname = "2"><para>the authoritative nameserver for the
domain.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NXT</para></entry>
<entry colname = "2"><para>used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do not exist in
a zone and indicate what RR types are present for an existing name.
See RFC 2535 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>PTR</para></entry>
<entry colname = "2"><para>a pointer to another part of the domain
name space.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RP</para></entry>
<entry colname = "2"><para>(x) information on persons responsible
for the domain. Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RT</para></entry>
<entry colname = "2"><para>(x) route-through binding for hosts that
do not have their own direct wide area network addresses. Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SIG</para></entry>
<entry colname = "2"><para>("signature") contains data authenticated
in the secure DNS. See RFC 2535 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SOA</para></entry>
<entry colname = "2"><para>identifies the start of a zone of authority.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SRV</para></entry>
<entry colname = "2"><para>information about well known network
services (replaces WKS).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>WKS</para></entry>
<entry colname = "2"><para>(h) information about which well known
network services, such as SMTP, that a domain supports. Historical,
replaced by newer RR SRV.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>X25</para></entry>
<entry colname = "2"><para>(x) representation of X.25 network addresses. Experimental.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<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 system.</para></entry>
</row>
<row rowsep = "0">
<entry nameend = "2" namest = "1"><para>For information about other,
older classes of RRs, see <xref linkend="classes_of_resource_records"/>.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para><emphasis>RDATA</emphasis> is the type-dependent or class-dependent
data that describes the resource:</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>A</para></entry>
<entry colname = "2"><para>for the IN class, a 32 bit IP address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>A6</para></entry>
<entry colname = "2"><para>maps a domain name to an IPv6 address,
with a provision for indirection for leading "prefix" bits.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>CNAME</para></entry>
<entry colname = "2"><para>a domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>DNAME</para></entry>
<entry colname = "2"><para>provides alternate naming to an entire
subtree of the domain name space, rather than to a single node.
 It causes some suffix of a queried name to be substituted with
a name from the DNAME record's RDATA.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>MX</para></entry>
<entry colname = "2"><para>a 16 bit preference value (lower is better)
followed by a host name willing to act as a mail exchange for the
owner domain.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NS</para></entry>
<entry colname = "2"><para>a fully qualified domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>PTR</para></entry>
<entry colname = "2"><para>a fully qualified domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SOA</para></entry>
<entry colname = "2"><para>several fields.</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 nameservers 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 meaning of 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; it is also timed out, but by 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
during the change, 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></sect3>
<sect3><title>Textual expression of RRs</title>
<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 nameserver or resolver.  In the examples provided in
RFC 1034, a style similar to that used in master 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, we 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.  In order 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 interests of clarity.</para>
<para>The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.</para>
<para>For example, we might show the RRs carried in a message 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></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></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></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>This example shows six RRs, with two RRs at each of three
domain names.</para>
<para>Similarly we might see:</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. IN</literal></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>10.0.0.44</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>CH</literal></para></entry>
<entry colname = "2"><para><literal>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></sect3></sect2>
<sect2><title>Discussion of MX Records</title>
<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 datum, a domain name matched with relevant data,
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 will fall back to the next largest priority.
Priority numbers do not have any absolute meaning &mdash; they are relevant
only respective to other MX records for that domain name. The domain
name given is the machine to which the mail will be delivered. It <emphasis>must</emphasis> have
an associated A record &mdash; 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 will be ignored. Instead,
the mail will be delivered to the server specified in the MX record
pointed to by the CNAME.</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></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></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></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></para></entry>
</row>
</tbody>
</tgroup></informaltable><para>For example:</para>
<para>Mail delivery will be attempted to <literal>mail.example.com</literal> and
<literal>mail2.example.com</literal> (in
any order), and if neither of those succeed, delivery to <literal>mail.backup.org</literal> will
be attempted.</para></sect2>
<sect2 id="Setting_TTLs"><title>Setting TTLs</title>
<para>The time to live 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 a RR can be cached before it
should be discarded. The following three types of TTL 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 will cache no-such-domain
(NXDOMAIN) responses from you.</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 $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every RR without
a specific TTL set.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RR TTLs</para></entry>
<entry colname = "2"><para>Each RR can have a TTL as the second
field in the RR, which will control how long other servers can cache
the it.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, <literal>1h30m</literal>. </para></sect2>
<sect2><title>Inverse Mapping in IPv4</title>
<para>Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the <emphasis>in-addr.arpa</emphasis> domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally, multiple
PTR records if the machine has more than one name. For example,
in the <optional>example.com</optional> domain:</para>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0"
    tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.125in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><literal>$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>$ORIGIN</command> lines in the examples
are for providing context to the examples only-they do not necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.</para></note></sect2>
<sect2><title>Other Zone File Directives</title>
<para>The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format itself
is class independent all records in a Master File must be of the same
class.</para>
<para>Master File Directives include <command>$ORIGIN</command>, <command>$INCLUDE</command>,
and <command>$TTL.</command></para>
<sect3><title>The <command>$ORIGIN</command> Directive</title>
<para>Syntax: <command>$ORIGIN
</command><replaceable>domain-name</replaceable> <optional> <replaceable>comment</replaceable></optional></para>
<para><command>$ORIGIN</command> sets the domain name that will
be appended to any unqualified records. When a zone is first read
in there is an implicit <command>$ORIGIN</command> &#60;<varname>zone-name</varname>><command>.</command> The
current <command>$ORIGIN</command> is appended to the domain specified
in the <command>$ORIGIN</command> argument if it is not absolute.</para>
<programlisting><literal>$ORIGIN example.com.
WWW     CNAME   MAIN-SERVER</literal></programlisting>
<para>is equivalent to</para>
<programlisting><literal>WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.</literal></programlisting></sect3>
<sect3><title>The <command>$INCLUDE</command> Directive</title>
<para>Syntax: <command>$INCLUDE</command>
<replaceable>filename</replaceable> <optional>
<replaceable>origin</replaceable> </optional> <optional> <replaceable>comment</replaceable> </optional></para>
<para>Read and process the file <filename>filename</filename> as
if it were included into the file at this point.  If <command>origin</command> is
specified the file is processed with <command>$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>$INCLUDE</command>, but it is silent on whether the current
domain name should also be restored.  BIND 9 restores both of them.
This could be construed as a deviation from RFC 1035, a feature, or both.
</para></note>
</sect3>
<sect3><title>The <command>$TTL</command> Directive</title>
<para>Syntax: <command>$TTL</command>
<replaceable>default-ttl</replaceable> <optional>
<replaceable>comment</replaceable> </optional></para>
<para>Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647 seconds.</para>
<para><command>$TTL</command> is defined in RFC 2308.</para></sect3></sect2>
<sect2><title><acronym>BIND</acronym> Master File Extension: the  <command>$GENERATE</command> Directive</title>
        <para>Syntax: <command>$GENERATE</command> <replaceable>range</replaceable> <replaceable>lhs</replaceable> <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><literal>$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 0 NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</literal></programlisting>
<para>is equivalent to</para>
<programlisting><literal>0.0.0.192.IN-ADDR.ARPA NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA CNAME 1.0.0.0.192.IN-ADDR.ARPA
2.0.0.192.IN-ADDR.ARPA CNAME 2.0.0.0.192.IN-ADDR.ARPA
...
127.0.0.192.IN-ADDR.ARPA CNAME 127.0.0.0.192.IN-ADDR.ARPA
.</literal></programlisting>
      <informaltable colsep = "0" rowsep = "0">
        <tgroup cols = "2" colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
          <colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
          <colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.250in"/>
          <tbody>
            <row rowsep = "0">
              <entry colname = "1"><para><command>range</command></para></entry>
              <entry colname = "2"><para>This can be one of two forms: start-stop
or start-stop/step. If the first form is used then step is set to
        1. All of start, stop and step must be positive.</para></entry>
      </row>
        <row rowsep = "0">
          <entry colname = "1"><para><command>lhs</command></para></entry>
          <entry colname = "2"><para><command>lhs</command> describes the
owner name of the resource records to be created.      Any single <command>$</command> symbols
within the <command>lhs</command> side are replaced by the iterator
value.
To get a $ in the output you need to 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 interator, field width and base. 
Modifiers are introduced by a <command>{</command> immediately following the
<command>$</command> as <command>${offset[,width[,base]]}</command>.
e.g. <command>${-20,3,d}</command> which subtracts 20 from the current value,
prints the result as a decimal in a zero padded field of with 3.  Available
output forms are decimal (<command>d</command>), octal (<command>o</command>)
and hexadecimal (<command>x</command> or <command>X</command> for uppercase).
The default modifier is <command>${0,0,d}</command>.
If the <command>lhs</command> is not
absolute, the current <command>$ORIGIN</command> is appended to
the name.</para>
<para>For compatability with earlier versions <command>$$</command> is still
recognised a indicating a literal $ in the output.</para></entry>
        </row>
        <row rowsep = "0">
          <entry colname = "1"><para><command>type</command></para></entry>
          <entry colname = "2"><para>At present the only supported types are
PTR, CNAME, DNAME, A, AAAA and NS.</para></entry>
        </row>
        <row rowsep = "0">
          <entry colname = "1"><para><command>rhs</command></para></entry>
          <entry colname = "2"><para>rhs is a domain name. It is processed
similarly to lhs.</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>
    </sect2>
  </sect1>
</chapter>
<chapter id="ch07"><title><acronym>BIND</acronym> 9 Security Considerations</title>
<sect1 id="Access_Control_Lists"><title>Access Control Lists</title>
<para>Access Control Lists (ACLs), are address match lists that
you can set up and nickname for future use in <command>allow-notify</command>,
<command>allow-query</command>, <command>allow-recursion</command>,
<command>blackhole</command>, <command>allow-transfer</command>,
etc.</para>
<para>Using ACLs allows you to have finer control over who can access
your nameserver, without cluttering up your config files with huge
lists of IP addresses.</para>
<para>It is a <emphasis>good idea</emphasis> to use ACLs, and to
control access to your server. Limiting access to your server by
outside parties can help prevent spoofing and DoS attacks against
your server.</para>
<para>Here is an example of how to properly apply ACLs:</para>
<programlisting>
// Set up an ACL named "bogusnets" that will block RFC1918 space,
// which is commonly used in spoofing attacks.
acl bogusnets { 0.0.0.0/8; 1.0.0.0/8; 2.0.0.0/8; 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 recursive queries of the server from the outside
unless recursion has been previously disabled.</para>
<para>For more information on how to use ACLs to protect your server,
see the <emphasis>AUSCERT</emphasis> advisory at
<ulink url="ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos">ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos</ulink></para></sect1>
<sect1><title><command>chroot</command> and <command>setuid</command> (for
UNIX servers)</title>
<para>On UNIX servers, it is possible to run <acronym>BIND</acronym> in a <emphasis>chrooted</emphasis> environment
(<command>chroot()</command>) by specifying the "<option>-t</option>"
option. This can help improve system security by placing <acronym>BIND</acronym> in
a "sandbox," which will limit 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 a nonprivileged user ( <option>-u</option> <replaceable>user</replaceable> ).
We suggest running as a nonprivileged 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/bin/named -u 202 -t /var/named</userinput></para>

<sect2><title>The <command>chroot</command> Environment</title>

<para>In order for a <command>chroot()</command> environment to
work properly in a particular directory
(for example, <filename>/var/named</filename>),
you will need to set up an environment that includes 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.  You will need to adjust the values of options like
like <command>directory</command> and <command>pid-file</command> to account
for this.
</para>
<para>
Unlike with earlier versions of BIND, you will typically
<emphasis>not</emphasis> need to compile <command>named</command>
statically nor install shared libraries under the new root.
However, depending on your operating system, you may need
to set up things like
<filename>/dev/zero</filename>,
<filename>/dev/random</filename>,
<filename>/dev/log</filename>, and/or
<filename>/etc/localtime</filename>.
</para>
</sect2>

<sect2><title>Using the <command>setuid</command> Function</title>

<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
to which you want <acronym>BIND</acronym>
to write.  Note that if the <command>named</command> daemon is running as a
nonprivileged user, it will not be able to bind to new restricted ports if the
server is reloaded.</para>
</sect2>
</sect1>

<sect1 id="dynamic_update_security"><title>Dynamic Update Security</title> 

<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 slave
server which performs forwarding of dynamic updates, the master can be
trivially attacked by sending the update to the slave, which will
forward it to the master with its own source IP address causing the
master 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 new <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>

</sect1></chapter>

<chapter id="ch08">
  <title>Troubleshooting</title>
  <sect1>
    <title>Common Problems</title>
    <sect2>
      <title>It's not working; how can I figure out what's wrong?</title>

      <para>The best solution to solving installation and
      configuration issues is to take preventative measures by setting
      up logging files beforehand. The log files provide a
      source of hints and information that can be used to figure out
      what went wrong and how to fix the problem.</para>

    </sect2>
  </sect1>
  <sect1>
    <title>Incrementing and Changing the Serial Number</title>

    <para>Zone serial numbers are just numbers-they aren't date
    related.  A lot of people set them to a number that represents a
    date, usually of the form YYYYMMDDRR. A number of people have been
    testing these numbers for Y2K compliance and have set the number
    to the year 2000 to see if it will work. They then try to restore
    the old serial number. This will cause problems because serial
    numbers are used to indicate that a zone has been updated. If the
    serial number on the slave server is lower than the serial number
    on the master, the slave server will attempt to update its copy of
    the zone.</para>

    <para>Setting the serial number to a lower number on the master
    server than the slave server means that the slave 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 slaves have updated to
    the new zone serial number, then reset the number to what you want
    it to be, and reload the zone again.</para>

  </sect1>
  <sect1>
    <title>Where Can I Get Help?</title>

      <para>The Internet Software Consortium (<acronym>ISC</acronym>) offers a wide range
    of support and service agreements for <acronym>BIND</acronym> and <acronym>DHCP</acronym> servers. Four
    levels of premium support are available and each level includes
    support for all <acronym>ISC</acronym> programs, significant discounts on products
    and training, and a recognized priority on bug fixes and
    non-funded feature requests. In addition, <acronym>ISC</acronym> offers a standard
    support agreement package which includes services ranging from bug
    fix announcements to remote support. It also includes training in
    <acronym>BIND</acronym> and <acronym>DHCP</acronym>.</para>

    <para>To discuss arrangements for support, contact
    <ulink url="mailto:info@isc.org">info@isc.org</ulink> or visit the
    <acronym>ISC</acronym> web page at <ulink
    url="http://www.isc.org/services/support/">http://www.isc.org/services/support/</ulink>
    to read more.</para>
  </sect1>
</chapter>
<appendix id="ch09">
  <title>Appendices</title>
  <sect1>
    <title>Acknowledgements</title>
    <sect2>
      <title>A Brief History of the <acronym>DNS</acronym> and <acronym>BIND</acronym></title>

      <para>Although the "official" beginning of the Domain Name
      System occurred 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 an 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). 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 O. Kure.</para>
      <para><acronym>BIND</acronym> versions 4.9 and 4.9.1 were released by Digital Equipment
Corporation (now Compaq Computer Corporation). Paul Vixie, then
a DEC employee, became <acronym>BIND</acronym>'s primary caretaker. Paul 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><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 the Internet Software Consortium with support being provided
by ISC's sponsors. 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><acronym>BIND</acronym> development work is made possible today by the sponsorship
of several corporations, and by the tireless work efforts of numerous
individuals.</para>
    </sect2>
  </sect1>
  <sect1 id="historical_dns_information">
    <title>Historical <acronym>DNS</acronym> Information</title>
    <sect2 id="classes_of_resource_records">
      <title>Classes of Resource Records</title>
      <sect3>
        <title>HS = hesiod</title>
        <para>The <optional>hesiod</optional> class is an information service
developed by MIT's Project Athena. It is used to share information
about various systems databases, such as users, groups, printers
and so on. The keyword <command>hs</command> is a synonym for
hesiod.</para>
      </sect3>
      <sect3>
        <title>CH = chaos</title>
        <para>The <command>chaos</command> class is used to specify zone
data for the MIT-developed CHAOSnet, a LAN protocol created in the
mid-1970s.</para>
      </sect3>
    </sect2>
  </sect1>
  <sect1>
    <title>General <acronym>DNS</acronym> Reference Information</title>
    <sect2 id="ipv6addresses">
      <title>IPv6 addresses (A6)</title>
      <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 2374.</para>
<para>The aggregatable global Unicast address format is as follows:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "6"
    colsep = "0" rowsep = "0" tgroupstyle = "1Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.477in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.501in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.523in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.731in"/>
<colspec colname = "5" colnum = "5" colsep = "0" colwidth = "1.339in"/>
<colspec colname = "6" colnum = "6" colsep = "0" colwidth = "2.529in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>3</para></entry>
<entry colname = "2" colsep = "1" rowsep = "1"><para>13</para></entry>
<entry colname = "3" colsep = "1" rowsep = "1"><para>8</para></entry>
<entry colname = "4" colsep = "1" rowsep = "1"><para>24</para></entry>
<entry colname = "5" colsep = "1" rowsep = "1"><para>16</para></entry>
<entry colname = "6" rowsep = "1"><para>64 bits</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>FP</para></entry>
<entry colname = "2" colsep = "1"><para>TLA ID</para></entry>
<entry colname = "3" colsep = "1"><para>RES</para></entry>
<entry colname = "4" colsep = "1"><para>NLA ID</para></entry>
<entry colname = "5" colsep = "1"><para>SLA ID</para></entry>
<entry colname = "6"><para>Interface ID</para></entry>
</row>
<row rowsep = "0">
<entry nameend = "4" namest = "1"><para>&#60;------ Public Topology
------></para></entry>
<entry colname = "5"><para></para></entry>
<entry colname = "6"><para></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para></para></entry>
<entry colname = "3"><para></para></entry>
<entry colname = "4"><para></para></entry>
<entry colname = "5"><para>&#60;-Site Topology-></para></entry>
<entry colname = "6"><para></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para></para></entry>
<entry colname = "3"><para></para></entry>
<entry colname = "4"><para></para></entry>
<entry colname = "5"><para></para></entry>
<entry colname = "6"><para>&#60;------ Interface Identifier ------></para></entry>
</row>
</tbody>
</tgroup></informaltable>
      <para>Where
<informaltable colsep = "0"  rowsep = "0"><tgroup
    cols = "3" colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.375in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.250in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "3.500in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>FP</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Format Prefix (001)</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>TLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Top-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RES</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Reserved for future use</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Next-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Site-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>INTERFACE ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Interface Identifier</para></entry>
</row>
</tbody>
</tgroup></informaltable></para>
      <para>The <emphasis>Public Topology</emphasis> is provided by the
upstream provider or ISP, and (roughly) corresponds to the IPv4 <emphasis>network</emphasis> section
of the address range. The <emphasis>Site Topology</emphasis> is
where you can subnet this space, much the same as subnetting an
IPv4 /16 network into /24 subnets. The <emphasis>Interface Identifier</emphasis> is
the address of an individual interface on a given network. (With
IPv6, addresses belong to interfaces rather than machines.)</para>
      <para>The subnetting capability of IPv6 is much more flexible than
that of IPv4: subnetting can now be carried out on bit boundaries,
in much the same way as Classless InterDomain Routing (CIDR).</para>
<para>The internal structure of the Public Topology for an A6 global
unicast address consists of:</para>
<informaltable colsep = "0"  rowsep = "0"><tgroup cols = "4"
    colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.506in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.662in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.556in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.825in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>3</para></entry>
<entry colname = "2" colsep = "1" rowsep = "1"><para>13</para></entry>
<entry colname = "3" colsep = "1" rowsep = "1"><para>8</para></entry>
<entry colname = "4" rowsep = "1"><para>24</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>FP</para></entry>
<entry colname = "2" colsep = "1"><para>TLA ID</para></entry>
<entry colname = "3" colsep = "1"><para>RES</para></entry>
<entry colname = "4"><para>NLA ID</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>A 3 bit FP (Format Prefix) of 001 indicates this is a global
Unicast address. FP lengths for other types of addresses may vary.</para>
<para>13 TLA (Top Level Aggregator) bits give the prefix of your
top-level IP backbone carrier.</para>
<para>8 Reserved bits</para>
<para>24 bits for Next Level Aggregators. This allows organizations
with a TLA to hand out portions of their IP space to client organizations,
so that the client can then split up the network further by filling
in more NLA bits, and hand out IPv6 prefixes to their clients, and
so forth.</para>
<para>There is no particular structure for the Site topology section.
Organizations can allocate these bits in any way they desire.</para>
<para>The Interface Identifier must be unique on that network. On
ethernet networks, one way to ensure this is to set the address
to the first three bytes of the hardware address, "FFFE", then the
last three bytes of the hardware address. The lowest significant
bit of the first byte should then be complemented. Addresses are
written as 32-bit blocks separated with a colon, and leading zeros
of a block may be omitted, for example:</para>
<para><command>3ffe:8050:201:9:a00:20ff:fe81:2b32</command></para>
<para>IPv6 address specifications are likely to 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>
    </sect2>
  </sect1>
  <sect1 id="bibliography">
    <title>Bibliography (and Suggested Reading)</title>
    <sect2 id="rfcs">
      <title>Request for Comments (RFCs)</title>
      <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 via FTP at 
<ulink url="ftp://www.isi.edu/in-notes/">ftp://www.isi.edu/in-notes/RFC<replaceable>xxx</replaceable>.txt</ulink> (where <replaceable>xxx</replaceable> is
the number of the RFC). RFCs are also available via the Web at
<ulink url="http://www.ietf.org/rfc/">http://www.ietf.org/rfc/</ulink>.
</para>
      <bibliography>
        <bibliodiv>
          <!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
          <title>Standards</title>
          <biblioentry>
            <abbrev>RFC974</abbrev>
            <author>
              <surname>Partridge</surname>
              <firstname>C.</firstname>
            </author>
            <title>Mail Routing and the Domain System</title>
            <pubdate>January 1986</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1034</abbrev>
            <author>
              <surname>Mockapetris</surname>
              <firstname>P.V.</firstname>
            </author> 
            <title>Domain Names &mdash; Concepts and Facilities</title>
            <pubdate>November 1987</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1035</abbrev>
            <author>
              <surname>Mockapetris</surname>
              <firstname>P. V.</firstname>
            </author> <title>Domain Names &mdash; Implementation and
Specification</title>
            <pubdate>November 1987</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv id="proposed_standards" xreflabel="Proposed Standards">

          <title>Proposed Standards</title>
          <!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
          <biblioentry>
            <abbrev>RFC2181</abbrev>
            <author>
              <surname>Elz</surname>
              <firstname>R., R. Bush</firstname>
            </author>
            <title>Clarifications to the <acronym>DNS</acronym> Specification</title>
            <pubdate>July 1997</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2308</abbrev>
            <author>
              <surname>Andrews</surname>
              <firstname>M.</firstname>
            </author>
            <title>Negative Caching of <acronym>DNS</acronym> Queries</title>
            <pubdate>March 1998</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1995</abbrev>
            <author>
              <surname>Ohta</surname>
              <firstname>M.</firstname>
            </author>
            <title>Incremental Zone Transfer in <acronym>DNS</acronym></title>
            <pubdate>August 1996</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1996</abbrev>
            <author>
              <surname>Vixie</surname>
              <firstname>P.</firstname>
            </author>
            <title>A Mechanism for Prompt Notification of Zone Changes</title>
            <pubdate>August 1996</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2136</abbrev>
            <authorgroup>
              <author>
                <surname>Vixie</surname>
                <firstname>P.</firstname>
              </author>
              <author>
                <firstname>S.</firstname>
                <surname>Thomson</surname>
              </author>
              <author>
                <firstname>Y.</firstname>
                <surname>Rekhter</surname>
              </author>
              <author>
                <firstname>J.</firstname>
                <surname>Bound</surname>
              </author>
            </authorgroup> 
            <title>Dynamic Updates in the Domain Name System</title>
            <pubdate>April 1997</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2845</abbrev>
            <authorgroup>
              <author>
                <surname>Vixie</surname>
                <firstname>P.</firstname>
              </author>
              <author>
                <firstname>O.</firstname>
                <surname>Gudmundsson</surname>
              </author>
              <author>
                <firstname>D.</firstname>
                <surname>Eastlake</surname>
                <lineage>3rd</lineage></author>
              <author>
                <firstname>B.</firstname>
                <surname>Wellington</surname>
              </author></authorgroup>
            <title>Secret Key Transaction Authentication for <acronym>DNS</acronym> (TSIG)</title>
            <pubdate>May 2000</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title>Proposed Standards Still Under Development</title>
          <note>
            <para><emphasis>Note:</emphasis> the following list of
RFCs are undergoing major revision by the IETF.</para>
          </note>
          <biblioentry>
            <abbrev>RFC1886</abbrev>
            <authorgroup>
              <author>
                <surname>Thomson</surname>
                <firstname>S.</firstname>
              </author>
              <author>
                <firstname>C.</firstname>
                <surname>Huitema</surname>
              </author>
            </authorgroup>
            <title><acronym>DNS</acronym> Extensions to support IP version 6</title>
            <pubdate>December 1995</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2065</abbrev>
            <authorgroup>
              <author>
                <surname>Eastlake</surname>
                <lineage>3rd</lineage>
                <firstname>D.</firstname>
              </author>
              <author>
                <firstname>C.</firstname>
                <surname>Kaufman</surname>
              </author>
            </authorgroup>
            <title>Domain Name System Security Extensions</title>
            <pubdate>January 1997</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2137</abbrev>
            <author>
              <surname>Eastlake</surname>
              <lineage>3rd</lineage>
              <firstname>D.</firstname>
            </author>
            <title>Secure Domain Name System Dynamic Update</title>
            <pubdate>April 1997</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title>Other Important RFCs About <acronym>DNS</acronym> Implementation</title>
          <biblioentry>
            <abbrev>RFC1535</abbrev>
            <author>
              <surname>Gavron</surname>
              <firstname>E.</firstname>
            </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>
                <surname>Kumar</surname>
                <firstname>A.</firstname>
              </author>
              <author>
                <firstname>J.</firstname>
                <surname>Postel</surname>
              </author>
              <author>
                <firstname>C.</firstname>
                <surname>Neuman</surname></author>
              <author>
                <firstname>P.</firstname>
                <surname>Danzig</surname>
              </author>
              <author>
                <firstname>S.</firstname>
                <surname>Miller</surname>
              </author>
            </authorgroup>
            <title>Common <acronym>DNS</acronym> Implementation Errors and Suggested Fixes</title>
            <pubdate>October 1993</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1982</abbrev>
            <authorgroup>
              <author>
                <surname>Elz</surname>
                <firstname>R.</firstname>
              </author>
              <author>
                <firstname>R.</firstname>
                <surname>Bush</surname>
              </author>
            </authorgroup>
            <title>Serial Number Arithmetic</title>
            <pubdate>August 1996</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title>Resource Record Types</title>
          <biblioentry>
            <abbrev>RFC1183</abbrev>
            <authorgroup>
              <author>
                <surname>Everhart</surname>
                <firstname>C.F.</firstname>
              </author>
              <author>
                <firstname>L. A.</firstname>
                <surname>Mamakos</surname>
              </author>
              <author>
                <firstname>R.</firstname>
                <surname>Ullmann</surname>
              </author>
              <author>
                <firstname>P.</firstname>
                <surname>Mockapetris</surname>
              </author>
            </authorgroup>
            <title>New <acronym>DNS</acronym> RR Definitions</title>
            <pubdate>October 1990</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1706</abbrev>
            <authorgroup>
              <author>
                <surname>Manning</surname>
                <firstname>B.</firstname>
              </author>
              <author>
                <firstname>R.</firstname>
                <surname>Colella</surname>
              </author>
            </authorgroup>
            <title><acronym>DNS</acronym> NSAP Resource Records</title>
            <pubdate>October 1994</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2168</abbrev>
            <authorgroup>
              <author>
                <surname>Daniel</surname>
                <firstname>R.</firstname>
              </author>
              <author>
                <firstname>M.</firstname>
                <surname>Mealling</surname>
              </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>
                <surname>Davis</surname>
                <firstname>C.</firstname>
              </author>
              <author>
                <firstname>P.</firstname>
                <surname>Vixie</surname>
              </author>
              <author>
                <firstname>T.</firstname>
                <firstname>Goodwin</firstname>
              </author>
              <author>
                <firstname>I.</firstname>
                <surname>Dickinson</surname>
              </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>
                <surname>Gulbrandsen</surname>
                <firstname>A.</firstname>
              </author>
              <author>
                <firstname>P.</firstname>
                <surname>Vixie</surname>
              </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>
              <surname>Allocchio</surname>
              <firstname>A.</firstname>
            </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>
              <surname>Atkinson</surname>
              <firstname>R.</firstname>
            </author>
            <title>Key Exchange Delegation Record for the <acronym>DNS</acronym></title>
            <pubdate>October 1997</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title><acronym>DNS</acronym> and the Internet</title>
          <biblioentry>
            <abbrev>RFC1101</abbrev>
            <author>
              <surname>Mockapetris</surname>
              <firstname>P. V.</firstname>
            </author>
            <title><acronym>DNS</acronym> Encoding of Network Names and Other Types</title>
            <pubdate>April 1989</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1123</abbrev>
            <author>
              <surname>Braden</surname>
              <surname>R.</surname>
            </author>
            <title>Requirements for Internet Hosts - Application and Support</title>
            <pubdate>October 1989</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1591</abbrev>
            <author>
              <surname>Postel</surname>
              <firstname>J.</firstname></author>
            <title>Domain Name System Structure and Delegation</title>
            <pubdate>March 1994</pubdate></biblioentry>
          <biblioentry>
            <abbrev>RFC2317</abbrev>
            <authorgroup>
              <author>
                <surname>Eidnes</surname>
                <firstname>H.</firstname>
              </author>
              <author>
                <firstname>G.</firstname>
                <surname>de Groot</surname>
              </author>
              <author>
                <firstname>P.</firstname>
                <surname>Vixie</surname>
              </author>
            </authorgroup>
            <title>Classless IN-ADDR.ARPA Delegation</title>
            <pubdate>March 1998</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title><acronym>DNS</acronym> Operations</title>
          <biblioentry>
            <abbrev>RFC1537</abbrev>
            <author>
              <surname>Beertema</surname>
              <firstname>P.</firstname>
            </author>
            <title>Common <acronym>DNS</acronym> Data File Configuration Errors</title>
            <pubdate>October 1993</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1912</abbrev>
            <author>
              <surname>Barr</surname>
              <firstname>D.</firstname>
            </author>
            <title>Common <acronym>DNS</acronym> Operational and Configuration Errors</title>
            <pubdate>February 1996</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1912</abbrev>
            <author>
              <surname>Barr</surname>
              <firstname>D.</firstname>
            </author>
            <title>Common <acronym>DNS</acronym> Operational and Configuration Errors</title>
            <pubdate>February 1996</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2010</abbrev>
            <authorgroup>
              <author>
                <surname>Manning</surname>
                <firstname>B.</firstname>
              </author>
              <author>
                <firstname>P.</firstname>
                <surname>Vixie</surname>
              </author>
            </authorgroup>
            <title>Operational Criteria for Root Name Servers.</title>
            <pubdate>October 1996</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2219</abbrev>
            <authorgroup>
              <author>
                <surname>Hamilton</surname>
                <firstname>M.</firstname>
              </author>
              <author>
                <firstname>R.</firstname>
                <surname>Wright</surname>
              </author>
            </authorgroup>
            <title>Use of <acronym>DNS</acronym> Aliases for Network Services.</title>
            <pubdate>October 1997</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>
              <surname>Rosenbaum</surname>
              <firstname>R.</firstname>
            </author>
            <title>Using the Domain Name System To Store Arbitrary String Attributes</title>
            <pubdate>May 1993</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC1713</abbrev>
            <author>
              <surname>Romao</surname>
              <firstname>A.</firstname>
            </author>
            <title>Tools for <acronym>DNS</acronym> Debugging</title>
            <pubdate>November 1994</pubdate></biblioentry>
          <biblioentry>
            <abbrev>RFC1794</abbrev>
            <author>
              <surname>Brisco</surname>
              <firstname>T.</firstname>
            </author>
            <title><acronym>DNS</acronym> Support for Load Balancing</title>
            <pubdate>April 1995</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2240</abbrev>
            <author>
              <surname>Vaughan</surname>
              <firstname>O.</firstname></author>
            <title>A Legal Basis for Domain Name Allocation</title>
            <pubdate>November 1997</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2345</abbrev>
            <authorgroup>
              <author>
                <surname>Klensin</surname>
                <firstname>J.</firstname>
              </author>
              <author>
                <firstname>T.</firstname>
                <surname>Wolf</surname>
              </author>
              <author>
                <firstname>G.</firstname>
                <surname>Oglesby</surname>
              </author>
            </authorgroup>
            <title>Domain Names and Company Name Retrieval</title>
            <pubdate>May 1998</pubdate>
          </biblioentry>
          <biblioentry>
            <abbrev>RFC2352</abbrev>
            <author>
              <surname>Vaughan</surname>
              <firstname>O.</firstname>
            </author>
            <title>A Convention For Using Legal Names as Domain Names</title>
            <pubdate>May 1998</pubdate>
          </biblioentry>
        </bibliodiv>
        <bibliodiv>
          <title>Obsolete and Unimplemented Experimental RRs</title>
          <biblioentry>
            <abbrev>RFC1712</abbrev>
            <authorgroup>
              <author>
                <surname>Farrell</surname>
                <firstname>C.</firstname>
              </author>
              <author>
                <firstname>M.</firstname>
                <surname>Schulze</surname>
              </author>
              <author>
                <firstname>S.</firstname>
                <surname>Pleitner</surname>
              </author>
              <author>
                <firstname>D.</firstname>
                <surname>Baldoni</surname>
              </author>
            </authorgroup>
            <title><acronym>DNS</acronym> Encoding of Geographical
Location</title>
            <pubdate>November 1994</pubdate>
          </biblioentry>
        </bibliodiv>
      </bibliography>
    </sect2>
    <sect2 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>
    </sect2>
    <sect2>
      <title>Other Documents About <acronym>BIND</acronym></title>
      <para></para>
      <bibliography>
        <biblioentry>
          <authorgroup>
            <author>
              <surname>Albitz</surname>
              <firstname>Paul</firstname>
            </author>
            <author>
              <firstname>Cricket</firstname>
              <surname>Liu</surname>
            </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>
    </sect2>
  </sect1>

</appendix>

</book>
