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bind9/doc/arm/Bv9ARM-book.xml
Michał Kępień 33bddbb5d1 Clarify relationship between ACLs and RPZ 
In the ARM section about RPZ, add text explicitly stating that ACLs take
precedence over RPZ to prevent users from expecting RPZ actions to be
applied to queries coming from clients which are not permitted access to
the resolver by ACLs.
2019-08-12 09:46:34 +02:00

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<!--
- Copyright (C) Internet Systems Consortium, Inc. ("ISC")
-
- This Source Code Form is subject to the terms of the Mozilla Public
- License, v. 2.0. If a copy of the MPL was not distributed with this
- file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
- See the COPYRIGHT file distributed with this work for additional
- information regarding copyright ownership.
-->
<!-- Converted by db4-upgrade version 1.0 -->
<book xmlns:db="http://docbook.org/ns/docbook" version="5.0">
<info>
<title>BIND 9 Administrator Reference Manual</title>
<!-- insert copyright start -->
<copyright>
<year>2000</year>
<year>2001</year>
<year>2002</year>
<year>2003</year>
<year>2004</year>
<year>2005</year>
<year>2006</year>
<year>2007</year>
<year>2008</year>
<year>2009</year>
<year>2010</year>
<year>2011</year>
<year>2012</year>
<year>2013</year>
<year>2014</year>
<year>2015</year>
<year>2016</year>
<year>2017</year>
<year>2018</year>
<year>2019</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
<!-- insert copyright end -->
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="releaseinfo.xml"/>
</info>
<chapter xml:id="Bv9ARM.ch01"><info><title>Introduction</title></info>
<para>
The Internet Domain Name System (<acronym>DNS</acronym>)
consists of the syntax
to specify the names of entities in the Internet in a hierarchical
manner, the rules used for delegating authority over names, and the
system implementation that actually maps names to Internet
addresses. <acronym>DNS</acronym> data is maintained in a
group of distributed
hierarchical databases.
</para>
<section xml:id="doc_scope"><info><title>Scope of Document</title></info>
<para>
The Berkeley Internet Name Domain
(<acronym>BIND</acronym>) implements a
domain name server for a number of operating systems. This
document provides basic information about the installation and
care of the Internet Systems Consortium (<acronym>ISC</acronym>)
<acronym>BIND</acronym> version 9 software package for
system administrators.
</para>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="pkgversion.xml"/>
</section>
<section xml:id="organization"><info><title>Organization of This Document</title></info>
<para>
In this document, <emphasis>Chapter 1</emphasis> introduces
the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Chapter 2</emphasis>
describes resource requirements for running <acronym>BIND</acronym> in various
environments. Information in <emphasis>Chapter 3</emphasis> is
<emphasis>task-oriented</emphasis> in its presentation and is
organized functionally, to aid in the process of installing the
<acronym>BIND</acronym> 9 software. The task-oriented
section is followed by
<emphasis>Chapter 4</emphasis>, which contains more advanced
concepts that the system administrator may need for implementing
certain options. The contents of <emphasis>Chapter 5</emphasis> are
organized as in a reference manual to aid in the ongoing
maintenance of the software. <emphasis>Chapter 6</emphasis> addresses
security considerations, and
<emphasis>Chapter 7</emphasis> contains troubleshooting help. The
main body of the document is followed by several
<emphasis>appendices</emphasis> which contain useful reference
information, such as a <emphasis>bibliography</emphasis> and
historic information related to <acronym>BIND</acronym>
and the Domain Name
System.
</para>
</section>
<section xml:id="conventions"><info><title>Conventions Used in This Document</title></info>
<para>
In this document, we use the following general typographic
conventions:
</para>
<informaltable>
<tgroup cols="2">
<colspec colname="1" colnum="1" colwidth="3.000in"/>
<colspec colname="2" colnum="2" colwidth="2.625in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>To describe:</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>We use the style:</emphasis>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
a pathname, filename, URL, hostname,
mailing list name, or new term or concept
</para>
</entry>
<entry colname="2">
<para>
<filename>Fixed width</filename>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
literal user
input
</para>
</entry>
<entry colname="2">
<para>
<userinput>Fixed Width Bold</userinput>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
program output
</para>
</entry>
<entry colname="2">
<para>
<computeroutput>Fixed Width</computeroutput>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The following conventions are used in descriptions of the
<acronym>BIND</acronym> configuration file:<informaltable colsep="0" frame="all" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="3.000in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
<emphasis>To describe:</emphasis>
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<emphasis>We use the style:</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
keywords
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<literal>Fixed Width</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
variables
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<varname>Fixed Width</varname>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1">
<para>
Optional input
</para>
</entry>
<entry colname="2">
<para>
<optional>Text is enclosed in square brackets</optional>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</section>
<section xml:id="dns_overview"><info><title>The Domain Name System (<acronym>DNS</acronym>)</title></info>
<para>
The purpose of this document is to explain the installation
and upkeep of the <acronym>BIND</acronym> (Berkeley Internet
Name Domain) 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>
<section xml:id="dns_fundamentals"><info><title>DNS Fundamentals</title></info>
<para>
The Domain Name System (DNS) is a hierarchical, distributed
database. It stores information for mapping Internet host names to
IP
addresses and vice versa, mail routing information, and other data
used by Internet applications.
</para>
<para>
Clients look up information in the DNS by calling a
<emphasis>resolver</emphasis> library, which sends queries to one or
more <emphasis>name servers</emphasis> and interprets the responses.
The <acronym>BIND</acronym> 9 software distribution
contains a name server, <command>named</command>, and a set
of associated tools.
</para>
</section>
<section xml:id="domain_names"><info><title>Domains and Domain Names</title></info>
<para>
The data stored in the DNS is identified by <emphasis>domain names</emphasis> that are organized as a tree according to
organizational or administrative boundaries. Each node of the tree,
called a <emphasis>domain</emphasis>, is given a label. The domain
name of the
node is the concatenation of all the labels on the path from the
node to the <emphasis>root</emphasis> node. This is represented
in written form as a string of labels listed from right to left and
separated by dots. A label need only be unique within its parent
domain.
</para>
<para>
For example, a domain name for a host at the
company <emphasis>Example, Inc.</emphasis> could be
<literal>ourhost.example.com</literal>,
where <literal>com</literal> is the
top level domain to which
<literal>ourhost.example.com</literal> belongs,
<literal>example</literal> is
a subdomain of <literal>com</literal>, and
<literal>ourhost</literal> is the
name of the host.
</para>
<para>
For administrative purposes, the name space is partitioned into
areas called <emphasis>zones</emphasis>, each starting at a node and
extending down to the leaf nodes or to nodes where other zones
start.
The data for each zone is stored in a <emphasis>name server</emphasis>, which answers queries about the zone using the
<emphasis>DNS protocol</emphasis>.
</para>
<para>
The data associated with each domain name is stored in the
form of <emphasis>resource records</emphasis> (<acronym>RR</acronym>s).
Some of the supported resource record types are described in
<xref linkend="types_of_resource_records_and_when_to_use_them"/>.
</para>
<para>
For more detailed information about the design of the DNS and
the DNS protocol, please refer to the standards documents listed in
<xref linkend="rfcs"/>.
</para>
</section>
<section xml:id="zones"><info><title>Zones</title></info>
<para>
To properly operate a name server, it is important to understand
the difference between a <emphasis>zone</emphasis>
and a <emphasis>domain</emphasis>.
</para>
<para>
As stated previously, a zone is a point of delegation in
the <acronym>DNS</acronym> tree. A zone consists of
those contiguous parts of the domain
tree for which a name server has complete information and over which
it has authority. It contains all domain names from a certain point
downward in the domain tree except those which are delegated to
other zones. A delegation point is marked by one or more
<emphasis>NS records</emphasis> in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.
</para>
<para>
For instance, consider the <literal>example.com</literal>
domain which includes names
such as <literal>host.aaa.example.com</literal> and
<literal>host.bbb.example.com</literal> even though
the <literal>example.com</literal> zone includes
only delegations for the <literal>aaa.example.com</literal> and
<literal>bbb.example.com</literal> zones. A zone can
map
exactly to a single domain, but could also include only part of a
domain, the rest of which could be delegated to other
name servers. Every name in the <acronym>DNS</acronym>
tree is a
<emphasis>domain</emphasis>, even if it is
<emphasis>terminal</emphasis>, that is, has no
<emphasis>subdomains</emphasis>. Every subdomain is a domain and
every domain except the root is also a subdomain. The terminology is
not intuitive and we suggest 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>
</section>
<section xml:id="auth_servers"><info><title>Authoritative Name Servers</title></info>
<para>
Each zone is served by at least
one <emphasis>authoritative name server</emphasis>,
which contains the complete data for the zone.
To make the DNS tolerant of server and network failures,
most zones have two or more authoritative servers, on
different networks.
</para>
<para>
Responses from authoritative servers have the "authoritative
answer" (AA) bit set in the response packets. This makes them
easy to identify when debugging DNS configurations using tools like
<command>dig</command> (<xref linkend="diagnostic_tools"/>).
</para>
<section xml:id="primary_master"><info><title>The Primary Master</title></info>
<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>. Typically it loads the zone
contents from some local file edited by humans or perhaps
generated mechanically from some other local file which is
edited by humans. This file is called the
<emphasis>zone file</emphasis> or
<emphasis>master file</emphasis>.
</para>
<para>
In some cases, however, the master file may not be edited
by humans at all, but may instead be the result of
<emphasis>dynamic update</emphasis> operations.
</para>
</section>
<section xml:id="slave_server"><info><title>Slave Servers</title></info>
<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>
<para>
Periodically, the slave server must send a refresh query to
determine whether the zone contents have been updated. This
is done by sending a query for the zone's SOA record and
checking whether the SERIAL field has been updated; if so,
a new transfer request is initiated. The timing of these
refresh queries is controlled by the SOA REFRESH and RETRY
fields, but can be overrridden with the
<command>max-refresh-time</command>,
<command>min-refresh-time</command>,
<command>max-retry-time</command>, and
<command>min-retry-time</command> options.
</para>
<para>
If the zone data cannot be updated within the time specified
by the SOA EXPIRE option (up to a hard-coded maximum of
24 weeks) then the slave zone expires and will no longer
respond to queries.
</para>
</section>
<section xml:id="stealth_server"><info><title>Stealth Servers</title></info>
<para>
Usually all of the zone's authoritative servers are listed in
NS records in the parent zone. These NS records constitute
a <emphasis>delegation</emphasis> of the zone from the parent.
The authoritative servers are also listed in the zone file itself,
at the <emphasis>top level</emphasis> or <emphasis>apex</emphasis>
of the zone. 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>
</section>
</section>
<section xml:id="cache_servers"><info><title>Caching Name Servers</title></info>
<!--
- Terminology here is inconsistent. Probably ought to
- convert to using "recursive name server" everywhere
- with just a note about "caching" terminology.
-->
<para>
The resolver libraries provided by most operating systems are
<emphasis>stub resolvers</emphasis>, meaning that they are not
capable of
performing the full DNS resolution process by themselves by talking
directly to the authoritative servers. Instead, they rely on a
local
name server to perform the resolution on their behalf. Such a
server
is called a <emphasis>recursive</emphasis> name server; it performs
<emphasis>recursive lookups</emphasis> for local clients.
</para>
<para>
To improve performance, recursive servers cache the results of
the lookups they perform. Since the processes of recursion and
caching are intimately connected, the terms
<emphasis>recursive server</emphasis> and
<emphasis>caching server</emphasis> are often used synonymously.
</para>
<para>
The length of time for which a record may be retained in
the cache of a caching name server is controlled by the
Time To Live (TTL) field associated with each resource record.
</para>
<section xml:id="forwarder"><info><title>Forwarding</title></info>
<para>
Even a caching name server does not necessarily perform
the complete recursive lookup itself. Instead, it can
<emphasis>forward</emphasis> some or all of the queries
that it cannot satisfy from its cache to another caching name
server,
commonly referred to as a <emphasis>forwarder</emphasis>.
</para>
<para>
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.
</para>
</section>
</section>
<section xml:id="multi_role"><info><title>Name Servers in Multiple Roles</title></info>
<para>
The <acronym>BIND</acronym> name server can
simultaneously act as
a 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>
</section>
</section>
</chapter>
<chapter xml:id="Bv9ARM.ch02"><info><title><acronym>BIND</acronym> Resource Requirements</title></info>
<section xml:id="hw_req"><info><title>Hardware requirements</title></info>
<para>
<acronym>DNS</acronym> hardware requirements have
traditionally been quite modest.
For many installations, servers that have been pensioned off from
active duty have performed admirably as <acronym>DNS</acronym> servers.
</para>
<para>
The DNSSEC 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 fully multithreaded, allowing
full utilization of
multiprocessor systems for installations that need it.
</para>
</section>
<section xml:id="cpu_req"><info><title>CPU Requirements</title></info>
<para>
CPU requirements for <acronym>BIND</acronym> 9 range from
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>
</section>
<section xml:id="mem_req"><info><title>Memory Requirements</title></info>
<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 — unfortunately, the best
way
to determine this for a given installation is to watch the name server
in operation. After a few weeks the server process should reach
a relatively stable size where entries are expiring from the cache as
fast as they are being inserted.
</para>
<!--
- Add something here about leaving overhead for attacks?
- How much overhead? Percentage?
-->
</section>
<section xml:id="intensive_env"><info><title>Name Server Intensive Environment Issues</title></info>
<para>
For name server intensive environments, there are two alternative
configurations that may be used. The first is where clients and
any second-level internal name servers query a main name server, which
has enough memory to build a large cache. This approach minimizes
the bandwidth used by external name lookups. The second alternative
is to set up second-level internal name servers to make queries
independently.
In this configuration, none of the individual machines 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 name servers share their cached data.
</para>
</section>
<section xml:id="supported_os"><info><title>Supported Operating Systems</title></info>
<para>
ISC <acronym>BIND</acronym> 9 compiles and runs on a large
number
of Unix-like operating systems and on
Microsoft Windows Server 2003 and 2008, and Windows XP and Vista.
For an up-to-date
list of supported systems, see the README file in the top level
directory
of the BIND 9 source distribution.
</para>
</section>
</chapter>
<chapter xml:id="Bv9ARM.ch03"><info><title>Name Server Configuration</title></info>
<para>
In this chapter we provide some suggested configurations along
with guidelines for their use. We suggest reasonable values for
certain option settings.
</para>
<section xml:id="sample_configuration"><info><title>Sample Configurations</title></info>
<section xml:id="cache_only_sample"><info><title>A Caching-only Name Server</title></info>
<para>
The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation. All
queries
from outside clients are refused using the <command>allow-query</command>
option. Alternatively, the same effect could be achieved using
suitable
firewall rules.
</para>
<programlisting>
// Two corporate subnets we wish to allow queries from.
acl corpnets { 192.168.4.0/24; 192.168.7.0/24; };
options {
// Working directory
directory "/etc/namedb";
allow-query { corpnets; };
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
</programlisting>
</section>
<section xml:id="auth_only_sample"><info><title>An Authoritative-only Name Server</title></info>
<para>
This sample configuration is for an authoritative-only server
that is the master server for "<filename>example.com</filename>"
and a slave for the subdomain "<filename>eng.example.com</filename>".
</para>
<programlisting>
options {
// Working directory
directory "/etc/namedb";
// Do not allow access to cache
allow-query-cache { none; };
// This is the default
allow-query { any; };
// Do not provide recursive service
recursion no;
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the 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>
</section>
</section>
<section xml:id="load_balancing"><info><title>Load Balancing</title></info>
<!--
- Add explanation of why load balancing is fragile at best
- and completely pointless in the general case.
-->
<para>
A primitive form of load balancing can be achieved in
the <acronym>DNS</acronym> by using multiple records
(such as multiple A records) for one name.
</para>
<para>
For example, 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/>
</entry>
<entry colname="2">
<para>
<literal>600</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>10.0.0.2</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>600</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>10.0.0.3</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
When a resolver queries for these records, <acronym>BIND</acronym> 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> sub-statement in the
<command>options</command> statement, see
<xref endterm="rrset_ordering_title" linkend="rrset_ordering"/>.
</para>
</section>
<section xml:id="ns_operations"><info><title>Name Server Operations</title></info>
<section xml:id="tools"><info><title>Tools for Use With the Name Server Daemon</title></info>
<para>
This section describes several indispensable diagnostic,
administrative and monitoring tools available to the system
administrator for controlling and debugging the name server
daemon.
</para>
<section xml:id="diagnostic_tools"><info><title>Diagnostic Tools</title></info>
<para>
The <command>dig</command>, <command>host</command>, and
<command>nslookup</command> programs are all command
line tools
for manually querying name servers. They differ in style and
output format.
</para>
<variablelist>
<varlistentry>
<term xml:id="dig"><command>dig</command></term>
<listitem>
<para>
<command>dig</command>
is the most versatile and complete of these lookup tools.
It has two modes: simple interactive
mode for a single query, and batch mode which executes a
query for
each in a list of several query lines. All query options are
accessible
from the command line.
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>dig</command>
<arg choice="opt" rep="norepeat">@<replaceable>server</replaceable></arg>
<arg choice="plain" rep="norepeat"><replaceable>domain</replaceable></arg>
<arg choice="opt" rep="norepeat"><replaceable>query-type</replaceable></arg>
<arg choice="opt" rep="norepeat"><replaceable>query-class</replaceable></arg>
<arg choice="opt" rep="norepeat">+<replaceable>query-option</replaceable></arg>
<arg choice="opt" rep="norepeat">-<replaceable>dig-option</replaceable></arg>
<arg choice="opt" rep="norepeat">%<replaceable>comment</replaceable></arg>
</cmdsynopsis>
<para>
The usual simple use of <command>dig</command> 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 emphasizes
simplicity
and ease of use. By default, it converts
between host names and Internet addresses, but its
functionality
can be extended with the use of options.
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>host</command>
<arg choice="opt" rep="norepeat">-aCdlnrsTwv</arg>
<arg choice="opt" rep="norepeat">-c <replaceable>class</replaceable></arg>
<arg choice="opt" rep="norepeat">-N <replaceable>ndots</replaceable></arg>
<arg choice="opt" rep="norepeat">-t <replaceable>type</replaceable></arg>
<arg choice="opt" rep="norepeat">-W <replaceable>timeout</replaceable></arg>
<arg choice="opt" rep="norepeat">-R <replaceable>retries</replaceable></arg>
<arg choice="opt" rep="norepeat">-m <replaceable>flag</replaceable></arg>
<arg choice="opt" rep="norepeat">-4</arg>
<arg choice="opt" rep="norepeat">-6</arg>
<arg choice="plain" rep="norepeat"><replaceable>hostname</replaceable></arg>
<arg choice="opt" rep="norepeat"><replaceable>server</replaceable></arg>
</cmdsynopsis>
<para>
For more information and a list of available commands and
options, see the <command>host</command> man
page.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nslookup</command></term>
<listitem>
<para><command>nslookup</command>
has two modes: interactive and
non-interactive. Interactive mode allows the user to
query name servers for information about various
hosts and domains or to print a list of hosts in a
domain. Non-interactive mode is used to print just
the name and requested information for a host or
domain.
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>nslookup</command>
<arg rep="repeat" choice="opt">-option</arg>
<group choice="opt" rep="norepeat">
<arg choice="opt" rep="norepeat"><replaceable>host-to-find</replaceable></arg>
<arg choice="opt" rep="norepeat">- <arg choice="opt" rep="norepeat">server</arg></arg>
</group>
</cmdsynopsis>
<para>
Interactive mode is entered when no arguments are given (the
default name server will be used) or when the first argument
is a
hyphen (`-') and the second argument is the host name or
Internet address
of a name server.
</para>
<para>
Non-interactive mode is used when the name or Internet
address
of the host to be looked up is given as the first argument.
The
optional second argument specifies the host name or address
of a name server.
</para>
<para>
Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of <command>nslookup</command>.
Use <command>dig</command> instead.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="admin_tools"><info><title>Administrative Tools</title></info>
<para>
Administrative tools play an integral part in the management
of a server.
</para>
<variablelist>
<varlistentry xml:id="named-checkconf" xreflabel="Named Configuration Checking application">
<term><command>named-checkconf</command></term>
<listitem>
<para>
The <command>named-checkconf</command> program
checks the syntax of a <filename>named.conf</filename> file.
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>named-checkconf</command>
<arg choice="opt" rep="norepeat">-jvz</arg>
<arg choice="opt" rep="norepeat">-t <replaceable>directory</replaceable></arg>
<arg choice="opt" rep="norepeat"><replaceable>filename</replaceable></arg>
</cmdsynopsis>
</listitem>
</varlistentry>
<varlistentry xml:id="named-checkzone" xreflabel="Zone Checking application">
<term><command>named-checkzone</command></term>
<listitem>
<para>
The <command>named-checkzone</command> program
checks a master file for
syntax and consistency.
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>named-checkzone</command>
<arg choice="opt" rep="norepeat">-djqvD</arg>
<arg choice="opt" rep="norepeat">-c <replaceable>class</replaceable></arg>
<arg choice="opt" rep="norepeat">-o <replaceable>output</replaceable></arg>
<arg choice="opt" rep="norepeat">-t <replaceable>directory</replaceable></arg>
<arg choice="opt" rep="norepeat">-w <replaceable>directory</replaceable></arg>
<arg choice="opt" rep="norepeat">-k <replaceable>(ignore|warn|fail)</replaceable></arg>
<arg choice="opt" rep="norepeat">-n <replaceable>(ignore|warn|fail)</replaceable></arg>
<arg choice="opt" rep="norepeat">-W <replaceable>(ignore|warn)</replaceable></arg>
<arg choice="plain" rep="norepeat"><replaceable>zone</replaceable></arg>
<arg choice="opt" rep="norepeat"><replaceable>filename</replaceable></arg>
</cmdsynopsis>
</listitem>
</varlistentry>
<varlistentry xml:id="named-compilezone" xreflabel="Zone Compilation application">
<term><command>named-compilezone</command></term>
<listitem>
<para>
Similar to <command>named-checkzone,</command> but
it always dumps the zone content to a specified file
(typically in a different format).
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="rndc" xreflabel="Remote Name Daemon Control application">
<term><command>rndc</command></term>
<listitem>
<para>
The remote name daemon control
(<command>rndc</command>) program allows the
system
administrator to control the operation of a name server.
If you run <command>rndc</command> without any
options, it will display a usage message as follows:
</para>
<cmdsynopsis label="Usage" sepchar=" ">
<command>rndc</command>
<arg choice="opt" rep="norepeat">-c <replaceable>config</replaceable></arg>
<arg choice="opt" rep="norepeat">-s <replaceable>server</replaceable></arg>
<arg choice="opt" rep="norepeat">-p <replaceable>port</replaceable></arg>
<arg choice="opt" rep="norepeat">-y <replaceable>key</replaceable></arg>
<arg choice="plain" rep="norepeat"><replaceable>command</replaceable></arg>
<arg rep="repeat" choice="opt"><replaceable>command</replaceable></arg>
</cmdsynopsis>
<para>See <xref linkend="man.rndc"/> for details of
the available <command>rndc</command> commands.
</para>
<para>
<command>rndc</command> requires a configuration file,
since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
<command>rndc</command> configuration file is
<filename>/etc/rndc.conf</filename>, but an
alternate
location can be specified with the <option>-c</option>
option. If the configuration file is not found,
<command>rndc</command> 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 a key as its argument, as defined by a <command>key</command> statement.
<command>default-port</command> specifies the
port to which
<command>rndc</command> should connect if no
port is given on the command line or in a
<command>server</command> statement.
</para>
<para>
The <command>key</command> statement defines a
key to be used
by <command>rndc</command> when authenticating
with
<command>named</command>. Its syntax is
identical to the
<command>key</command> statement in <filename>named.conf</filename>.
The keyword <userinput>key</userinput> is
followed by a key name, which must be a valid
domain name, though it need not actually be hierarchical;
thus,
a string like "<userinput>rndc_key</userinput>" is a valid
name.
The <command>key</command> statement has two
clauses:
<command>algorithm</command> and <command>secret</command>.
While the configuration parser will accept any string as the
argument
to algorithm, currently only the strings
"<userinput>hmac-md5</userinput>",
"<userinput>hmac-sha1</userinput>",
"<userinput>hmac-sha224</userinput>",
"<userinput>hmac-sha256</userinput>",
"<userinput>hmac-sha384</userinput>"
and "<userinput>hmac-sha512</userinput>"
have any meaning. The secret is a Base64 encoded string
as specified in RFC 3548.
</para>
<para>
The <command>server</command> statement
associates a key
defined using the <command>key</command>
statement with a server.
The keyword <userinput>server</userinput> is followed by a
host name or address. The <command>server</command> statement
has two clauses: <command>key</command> and <command>port</command>.
The <command>key</command> clause specifies the
name of the key
to be used when communicating with this server, and the
<command>port</command> clause can be used to
specify the port <command>rndc</command> should
connect
to on the server.
</para>
<para>
A sample minimal configuration file is as follows:
</para>
<programlisting>
key rndc_key {
algorithm "hmac-sha256";
secret
"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
default-server 127.0.0.1;
default-key rndc_key;
};
</programlisting>
<para>
This file, if installed as <filename>/etc/rndc.conf</filename>,
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 name server
to reload, if a name server 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>
</section>
</section>
<section xml:id="signals"><info><title>Signals</title></info>
<para>
Certain UNIX signals cause the name server to take specific
actions, as described in the following table. These signals can
be sent using the <command>kill</command> command.
</para>
<informaltable frame="all">
<tgroup cols="2">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>SIGHUP</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to read <filename>named.conf</filename> and
reload the database.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SIGTERM</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to clean up and exit.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SIGINT</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to clean up and exit.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
</section>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="plugins.xml"/>
</chapter>
<chapter xml:id="Bv9ARM.ch04"><info><title>Advanced DNS Features</title></info>
<section xml:id="notify"><info><title>Notify</title></info>
<para>
<acronym>DNS</acronym> NOTIFY is a mechanism that allows master
servers 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 zone transfer.
</para>
<para>
For more information about <acronym>DNS</acronym>
<command>NOTIFY</command>, see the description of the
<command>notify</command> option in <xref linkend="boolean_options"/> and
the description of the zone option <command>also-notify</command> in
<xref linkend="zone_transfers"/>. The <command>NOTIFY</command>
protocol is specified in RFC 1996.
</para>
<note><simpara>
As a slave zone can also be a master to other slaves, <command>named</command>,
by default, sends <command>NOTIFY</command> messages for every zone
it loads. Specifying <command>notify master-only;</command> will
cause <command>named</command> to only send <command>NOTIFY</command> for master
zones that it loads.
</simpara></note>
</section>
<section xml:id="dynamic_update"><info><title>Dynamic Update</title></info>
<para>
Dynamic Update is a method for adding, replacing or deleting
records in a master server by sending it a special form of DNS
messages. The format and meaning of these messages is specified
in RFC 2136.
</para>
<para>
Dynamic update is enabled by including an
<command>allow-update</command> or an <command>update-policy</command>
clause in the <command>zone</command> statement.
</para>
<para>
If the zone's <command>update-policy</command> is set to
<userinput>local</userinput>, updates to the zone
will be permitted for the key <varname>local-ddns</varname>,
which will be generated by <command>named</command> at startup.
See <xref linkend="dynamic_update_policies"/> for more details.
</para>
<para>
Dynamic updates using Kerberos signed requests can be made
using the TKEY/GSS protocol by setting either the
<command>tkey-gssapi-keytab</command> option, or alternatively
by setting both the <command>tkey-gssapi-credential</command>
and <command>tkey-domain</command> options. Once enabled,
Kerberos signed requests will be matched against the update
policies for the zone, using the Kerberos principal as the
signer for the request.
</para>
<para>
Updating of secure zones (zones using DNSSEC) follows RFC
3007: RRSIG, NSEC and NSEC3 records affected by updates are
automatically regenerated by the server using an online
zone key. Update authorization is based on transaction
signatures and an explicit server policy.
</para>
<section xml:id="journal"><info><title>The journal file</title></info>
<para>
All changes made to a zone using dynamic update are stored
in the zone's journal file. This file is automatically created
by the server when the first dynamic update takes place.
The name of the journal file is formed by appending the extension
<filename>.jnl</filename> to the name of the
corresponding zone
file unless specifically overridden. The journal file is in a
binary format and should not be edited manually.
</para>
<para>
The server 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
up to 15 minutes, allowing additional updates to take place.
During the dump process, transient files will be created
with the extensions <filename>.jnw</filename> and
<filename>.jbk</filename>; under ordinary circumstances, these
will be removed when the dump is complete, and can be safely
ignored.
</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
journaled in a similar way.
</para>
<para>
The zone files of dynamic zones cannot normally be edited by
hand because they are not guaranteed to contain the most recent
dynamic changes — those are only in the journal file.
The only way to ensure that the zone file of a dynamic zone
is up to date is to run <command>rndc stop</command>.
</para>
<para>
If you have to make changes to a dynamic zone
manually, the following procedure will work:
Disable dynamic updates to the zone using
<command>rndc freeze <replaceable>zone</replaceable></command>.
This will update the zone's master file with the changes
stored in its <filename>.jnl</filename> file.
Edit the zone file. Run
<command>rndc thaw <replaceable>zone</replaceable></command>
to reload the changed zone and re-enable dynamic updates.
</para>
<para>
<command>rndc sync <replaceable>zone</replaceable></command>
will update the zone file with changes from the journal file
without stopping dynamic updates; this may be useful for viewing
the current zone state. To remove the <filename>.jnl</filename>
file after updating the zone file, use
<command>rndc sync -clean</command>.
</para>
</section>
</section>
<section xml:id="incremental_zone_transfers"><info><title>Incremental Zone Transfers (IXFR)</title></info>
<para>
The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is specified 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>
</section>
<section xml:id="split_dns"><info><title>Split DNS</title></info>
<para>
Setting up different views, or visibility, of the DNS space to
internal and external resolvers is usually referred to as a
<emphasis>Split DNS</emphasis> setup. There are several
reasons an organization 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.
However, since listing addresses of internal servers that
external clients cannot possibly reach can result in
connection delays and other annoyances, an organization may
choose to use a Split DNS to present a consistent view of itself
to the outside world.
</para>
<para>
Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.
</para>
<section xml:id="split_dns_sample"><info><title>Example split DNS setup</title></info>
<para>
Let's say a company named <emphasis>Example, Inc.</emphasis>
(<literal>example.com</literal>)
has several corporate sites that have an internal network with
reserved
Internet Protocol (IP) space and an external demilitarized zone (DMZ),
or "outside" section of a network, that is available to the public.
</para>
<para>
<emphasis>Example, Inc.</emphasis> wants its internal clients
to be able to resolve external hostnames and to exchange mail with
people on the outside. The company also wants its internal resolvers
to have access to certain internal-only zones that are not available
at all outside of the internal network.
</para>
<para>
In order to accomplish this, the company will set up two sets
of name servers. 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>, <filename>site1.internal</filename>,
and <filename>site2.internal</filename>.
</para>
<para>
To protect the <filename>site1.internal</filename> and <filename>site2.internal</filename> domains,
the internal name servers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.
</para>
<para>
The external servers, which are on the bastion hosts, 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>* IN MX 10 external1.example.com.</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
name servers 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
name servers for DNS queries. This could also be enforced via
selective
filtering on the network.
</para>
<para>
If everything has been set properly, <emphasis>Example, Inc.</emphasis>'s
internal clients 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 both 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;
// forward to external servers
forwarders {
<varname>bastion-ips-go-here</varname>;
};
// sample allow-transfer (no one)
allow-transfer { none; };
// restrict query access
allow-query { internals; externals; };
// restrict recursion
allow-recursion { internals; };
...
...
};
// sample master zone
zone "site1.example.com" {
type master;
file "m/site1.example.com";
// do normal iterative resolution (do not forward)
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
// sample slave zone
zone "site2.example.com" {
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</programlisting>
<para>
External (bastion host) DNS server config:
</para>
<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
// sample allow-transfer (no one)
allow-transfer { none; };
// default query access
allow-query { any; };
// restrict cache access
allow-query-cache { internals; externals; };
// restrict recursion
allow-recursion { internals; externals; };
...
...
};
// sample slave zone
zone "site1.example.com" {
type master;
file "m/site1.foo.com";
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-transfer { internals; externals; }
};
</programlisting>
<para>
In the <filename>resolv.conf</filename> (or equivalent) on
the bastion host(s):
</para>
<programlisting>
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</programlisting>
</section>
</section>
<section xml:id="tsig"><info><title>TSIG</title></info>
<para>
TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS
messages, originally specified in RFC 2845. It allows DNS messages
to be cryptographically signed using a shared secret. TSIG can
be used in any DNS transaction, as a way to restrict access to
certain server functions (e.g., recursive queries) to authorized
clients when IP-based access control is insufficient or needs to
be overridden, or as a way to ensure message authenticity when it
is critical to the integrity of the server, such as with dynamic
UPDATE messages or zone transfers from a master to a slave server.
</para>
<para>
This is a guide to setting up TSIG in <acronym>BIND</acronym>.
It describes the configuration syntax and the process of creating
TSIG keys.
</para>
<para>
<command>named</command> supports TSIG for server-to-server
communication, and some of the tools included with
<acronym>BIND</acronym> support it for sending messages to
<command>named</command>:
<itemizedlist>
<listitem>
<xref linkend="man.nsupdate"/> supports TSIG via the
<option>-k</option>, <option>-l</option> and
<option>-y</option> command line options, or via
the <command>key</command> command when running
interactively.
</listitem>
<listitem>
<xref linkend="man.dig"/> supports TSIG via the
<option>-k</option> and <option>-y</option> command
line options.
</listitem>
</itemizedlist>
</para>
<section><info><title>Generating a Shared Key</title></info>
<para>
TSIG keys can be generated using the <command>tsig-keygen</command>
command; the output of the command is a <command>key</command> directive
suitable for inclusion in <filename>named.conf</filename>. The
key name, algorithm and size can be specified by command line parameters;
the defaults are "tsig-key", HMAC-SHA256, and 256 bits, respectively.
</para>
<para>
Any string which is a valid DNS name can be used as a key name.
For example, a key to be shared between servers called
<emphasis>host1</emphasis> and <emphasis>host2</emphasis> could
be called "host1-host2.", and this key could be generated using:
</para>
<programlisting>
$ tsig-keygen host1-host2. > host1-host2.key
</programlisting>
<para>
This key may then be copied to both hosts. The key name and secret
must be identical on both hosts.
(Note: copying a shared secret from one server to another is beyond
the scope of the DNS. A secure transport mechanism should be used:
secure FTP, SSL, ssh, telephone, encrypted email, etc.)
</para>
<para>
<command>tsig-keygen</command> can also be run as
<command>ddns-confgen</command>, in which case its output includes
additional configuration text for setting up dynamic DNS in
<command>named</command>. See <xref linkend="man.ddns-confgen"/>
for details.
</para>
</section>
<section><info><title>Loading A New Key</title></info>
<para>
For a key shared between servers called
<emphasis>host1</emphasis> and <emphasis>host2</emphasis>,
the following could be added to each server's
<filename>named.conf</filename> file:
</para>
<programlisting>
key "host1-host2." {
algorithm hmac-sha256;
secret "DAopyf1mhCbFVZw7pgmNPBoLUq8wEUT7UuPoLENP2HY=";
};
</programlisting>
<para>
(This is the same key generated above using
<command>tsig-keygen</command>.)
</para>
<para>
Since this text contains a secret, it
is recommended that either <filename>named.conf</filename> not be
world-readable, or that the <command>key</command> directive
be stored in a file which is not world-readable, and which is
included in <filename>named.conf</filename> via the
<command>include</command> directive.
</para>
<para>
Once a key has been added to <filename>named.conf</filename> and the
server has been restarted or reconfigured, the server can recognize
the key. If the server receives a message signed by the
key, it will be able to verify the signature. If the signature
is valid, the response will be signed using the same key.
</para>
<para>
TSIG keys that are known to a server can be listed using the
command <command>rndc tsig-list</command>.
</para>
</section>
<section><info><title>Instructing the Server to Use a Key</title></info>
<para>
A server sending a request to another server must be told whether
to use a key, and if so, which key to use.
</para>
<para>
For example, a key may be specified for each server in the
<command>masters</command> statement in the definition of a
slave zone; in this case, all SOA QUERY messages, NOTIFY
messages, and zone transfer requests (AXFR or IXFR) will be
signed using the specified key. Keys may also be specified
in the <command>also-notify</command> statement of a master
or slave zone, causing NOTIFY messages to be signed using
the specified key.
</para>
<para>
Keys can also be specified in a <command>server</command>
directive. Adding the following on <emphasis>host1</emphasis>,
if the IP address of <emphasis>host2</emphasis> is 10.1.2.3, would
cause <emphasis>all</emphasis> requests from <emphasis>host1</emphasis>
to <emphasis>host2</emphasis>, including normal DNS queries, to be
signed using the <command>host1-host2.</command> key:
</para>
<programlisting>
server 10.1.2.3 {
keys { host1-host2. ;};
};
</programlisting>
<para>
Multiple keys may be present in the <command>keys</command>
statement, but only the first one is used. As this directive does
not contain secrets, it can be used in a world-readable file.
</para>
<para>
Requests sent by <emphasis>host2</emphasis> to <emphasis>host1</emphasis>
would <emphasis>not</emphasis> be signed, unless a similar
<command>server</command> directive were in <emphasis>host2</emphasis>'s
configuration file.
</para>
<para>
Whenever any server sends a TSIG-signed DNS request, it will expect
the response to be signed with the same key. If a response is not
signed, or if the signature is not valid, the response will be
rejected.
</para>
</section>
<section><info><title>TSIG-Based Access Control</title></info>
<para>
TSIG keys may be specified in ACL definitions and ACL directives
such as <command>allow-query</command>, <command>allow-transfer</command>
and <command>allow-update</command>.
The above key would be denoted in an ACL element as
<command>key host1-host2.</command>
</para>
<para>
An example of an <command>allow-update</command> directive using
a TSIG key:
</para>
<programlisting>
allow-update { !{ !localnets; any; }; key host1-host2. ;};
</programlisting>
<para>
This allows dynamic updates to succeed only if the UPDATE
request comes from an address in <command>localnets</command>,
<emphasis>and</emphasis> if it is signed using the
<command>host1-host2.</command> key.
</para>
<para>
See <xref linkend="dynamic_update_policies"/> for a discussion of
the more flexible <command>update-policy</command> statement.
</para>
</section>
<section><info><title>Errors</title></info>
<para>
Processing of TSIG-signed messages can result in several errors:
<itemizedlist>
<listitem>
If a TSIG-aware server receives a message signed by an
unknown key, the response will be unsigned, with the TSIG
extended error code set to BADKEY.
</listitem>
<listitem>
If a TSIG-aware server receives a message from a known key
but with an invalid signature, the response will be unsigned,
with the TSIG extended error code set to BADSIG.
</listitem>
<listitem>
If a TSIG-aware server receives a message with a time
outside of the allowed range, the response will be signed, with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified.
</listitem>
</itemizedlist>
In all of the above cases, the server will return a response code
of NOTAUTH (not authenticated).
</para>
</section>
</section>
<section xml:id="tkey"><info><title>TKEY</title></info>
<para>
TKEY (Transaction KEY) is a mechanism for automatically negotiating
a shared secret between two hosts, originally specified in RFC 2930.
</para>
<para>
There are several TKEY "modes" that specify how a key is to be
generated or assigned. <acronym>BIND</acronym> 9 implements only
one of these modes: Diffie-Hellman key exchange. Both hosts are
required to have a KEY record with algorithm DH (though this
record is not required to be present in a zone).
</para>
<para>
The TKEY process is initiated by a client or server by sending
a query of type TKEY to a TKEY-aware server. The query must include
an appropriate KEY record in the additional section, and
must be signed using either TSIG or SIG(0) with a previously
established key. The server's response, if successful, will
contain a TKEY record in its answer section. After this transaction,
both participants will have enough information to calculate a
shared secret using Diffie-Hellman key exchange. The shared secret
can then be used by to sign subsequent transactions between the
two servers.
</para>
<para>
TSIG keys known by the server, including TKEY-negotiated keys, can
be listed using <command>rndc tsig-list</command>.
</para>
<para>
TKEY-negotiated keys can be deleted from a server using
<command>rndc tsig-delete</command>. This can also be done via
the TKEY protocol itself, by sending an authenticated TKEY query
specifying the "key deletion" mode.
</para>
</section>
<section xml:id="sig0"><info><title>SIG(0)</title></info>
<para>
<acronym>BIND</acronym> partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC 2931.
SIG(0) uses public/private keys to authenticate messages. Access control
is performed in the same manner as TSIG keys; privileges can be
granted or denied in ACL directives based on the key name.
</para>
<para>
When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server. The
server will not attempt to recursively fetch or validate the
key.
</para>
<para>
SIG(0) signing of multiple-message TCP streams is not supported.
</para>
<para>
The only tool shipped with <acronym>BIND</acronym> 9 that
generates SIG(0) signed messages is <command>nsupdate</command>.
</para>
</section>
<section xml:id="DNSSEC"><info><title>DNSSEC</title></info>
<para>
Cryptographic authentication of DNS information is possible
through the DNS Security (<emphasis>DNSSEC-bis</emphasis>) extensions,
defined in RFC 4033, RFC 4034, and RFC 4035.
This section describes the creation and use of DNSSEC signed zones.
</para>
<para>
In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <acronym>BIND</acronym>
9 ships
with several tools
that are used in this process, which are explained in more detail
below. In all cases, the <option>-h</option> option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset files to be in the working directory or the
directory specified by the <option>-d</option> option, and
that the tools shipped with BIND 9.2.x and earlier are not 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. A zone's security
status must be indicated by the parent zone for a DNSSEC capable
resolver to trust its data. This is done through the presence
or absence of a <literal>DS</literal> record at the
delegation
point.
</para>
<para>
For other servers to trust data in this zone, they must
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>
<section xml:id="generating_dnssec_keys"><info><title>Generating Keys</title></info>
<para>
The <command>dnssec-keygen</command> program is used to
generate keys.
</para>
<para>
A secure zone must contain one or more zone keys. The zone keys will
sign all other records in the zone, as well as the zone keys of any
secure delegated zones. Zone keys must have the same name as the
zone, a name type of <command>ZONE</command>, and must be usable for
authentication. It is recommended that zone keys use a cryptographic
algorithm designated as "mandatory to implement" by the IETF;
currently the are two algorithms: RSASHA256 and ECDSAP256SHA256.
ECDSAP256SHA256 is recommended for current and future deployments.
</para>
<para>
The following command will generate a ECDSAP256SHA256 key for
the <filename>child.example</filename> zone:
</para>
<para>
<userinput>dnssec-keygen -a ECDSAP256SHA256 -n ZONE child.example.</userinput>
</para>
<para>
Two output files will be produced:
<filename>Kchild.example.+013+12345.key</filename> and
<filename>Kchild.example.+013+12345.private</filename> (where 12345 is
an example of a key tag). The key filenames contain the key name
(<filename>child.example.</filename>), algorithm (5 is RSASHA1, 8 is
RSASHA256, 13 is ECDSAP256SHA256, 15 is ED25519 etc.), and the key tag
(12345 in this case). The private key (in the
<filename>.private</filename> file) is used to generate signatures,
and the public key (in the <filename>.key</filename> file) is used for
signature verification.
</para>
<para>
To generate another key with the same properties (but with
a different key tag), repeat the above command.
</para>
<para>
The <command>dnssec-keyfromlabel</command> program is used
to get a key pair from a crypto hardware and build the key
files. Its usage is similar to <command>dnssec-keygen</command>.
</para>
<para>
The public keys should be inserted into the zone file by
including the <filename>.key</filename> files using
<command>$INCLUDE</command> statements.
</para>
</section>
<section xml:id="dnssec_signing"><info><title>Signing the Zone</title></info>
<para>
The <command>dnssec-signzone</command> program is used
to sign a zone.
</para>
<para>
Any <filename>keyset</filename> files corresponding to
secure sub-zones should be present. The zone signer will
generate <literal>NSEC</literal>, <literal>NSEC3</literal>
and <literal>RRSIG</literal> records for the zone, as
well as <literal>DS</literal> for the child zones if
<literal>'-g'</literal> is specified. If <literal>'-g'</literal>
is not specified, then DS RRsets for the secure child
zones need to be added manually.
</para>
<para>
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>
<para><command>dnssec-signzone</command>
will also produce a keyset and dsset files. These are used
to provide the parent zone administrators with the
<literal>DNSKEYs</literal> (or their corresponding
<literal>DS</literal> records) that are the secure entry
point to the zone.
</para>
</section>
<section xml:id="dnssec_config"><info><title>Configuring Servers for DNSSEC</title></info>
<para>
To enable <command>named</command> to validate answers
received from other servers, the
<command>dnssec-validation</command> option must be set to
either <userinput>yes</userinput> or <userinput>auto</userinput>.
</para>
<para>
When <command>dnssec-validation</command> is set to
<userinput>auto</userinput>, a trust anchor for the DNS
root zone will automatically be used. This trust anchor is
provided as part of BIND and is kept up to date using RFC 5011
key management.
</para>
<para>
When <command>dnssec-validation</command> is set to
<userinput>yes</userinput>, DNSSEC validation will only occur
if at least one trust anchor has been explicitly configured
in <filename>named.conf</filename>
using a <command>dnssec-keys</command> statement (or the
<command>managed-keys</command> and <command>trusted-keys</command>
statements, both deprecated).
</para>
<para>
When <command>dnssec-validation</command> is set to
<userinput>no</userinput>, DNSSEC validation will not occur.
</para>
<para>
The default is <userinput>auto</userinput> unless BIND is
built with <command>configure --disable-auto-validation</command>,
in which case the default is <userinput>yes</userinput>.
</para>
<para>
The keys specified in <command>dnssec-keys</command>
copies of DNSKEY RRs for zones that are used to form the
first link in the cryptographic chain of trust. Keys configured
with the keyword <command>static-key</command> are loaded directly
into the table of trust anchors, and can only be changed by
altering the configuration. Keys configured with
<command>initial-key</command> are used to initialize
RFC 5011 trust anchor maintenance, and will be kept up to
date automatically after the first time <command>named</command>
runs.
</para>
<para>
<command>dnssec-keys</command> is described in more detail
later in this document.
</para>
<para>
Unlike <acronym>BIND</acronym> 8, <acronym>BIND</acronym>
9 does not verify signatures on load, so zone keys for
authoritative zones do not need to be specified in the
configuration file.
</para>
<para>
After DNSSEC gets established, a typical DNSSEC configuration
will look something like the following. It has one or
more public keys for the root. This allows answers from
outside the organization to be validated. It will also
have several keys for parts of the namespace the organization
controls. These are here to ensure that <command>named</command>
is immune to compromises in the DNSSEC components of the security
of parent zones.
</para>
<programlisting>
dnssec-keys {
/* Root Key */
"." initial-key 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
JxrGkxJWoZu6I7PzJu/E9gx4UC1zGAHlXKdE4zYIpRh
aBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3zy2Xy
4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYg
hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M/lUUVRbke
g1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq
66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
97S+LKUTpQcq27R7AT3/V5hRQxScINqwcz4jYqZD2fQ
dgxbcDTClU0CRBdiieyLMNzXG3";
/* Key for our organization's forward zone */
example.com. static-key 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
kBOUKUf/mC7HvfwYH/Be22GnClrinKJp1O
g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
FxmAVZP20igTixin/1LcrgX/KMEGd/biuv
F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
/oyWR8BW/hWdzOvnSCThlHf3xiYleDbt/o
1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. static-key 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc
xOdNax071L18QqZnQQQAVVr+i
LhGTnNGp3HoWQLUIzKrJVZ3zg
gy3WwNT6kZo6c0tszYqbtvchm
gQC8CzKojM/W16i6MG/eafGU3
siaOdS0yOI6BgPsw+YZdzlYMa
IJGf4M4dyoKIhzdZyQ2bYQrjy
Q4LB0lC7aOnsMyYKHHYeRvPxj
IQXmdqgOJGq+vsevG06zW+1xg
YJh9rCIfnm1GX/KMgxLPG2vXT
D/RnLX+D3T3UL7HJYHJhAZD5L
59VvjSPsZJHeDCUyWYrvPZesZ
DIRvhDD52SKvbheeTJUm6Ehkz
ytNN2SN96QRk8j/iI8ib";
};
options {
...
dnssec-validation yes;
};
</programlisting>
<note><simpara>
None of the keys listed in this example are valid. In particular,
the root key is not valid.
</simpara></note>
<para>
When DNSSEC validation is enabled and properly configured,
the resolver will reject any answers from signed, secure zones
which fail to validate, and will return SERVFAIL to the client.
</para>
<para>
Responses may fail to validate for any of several reasons,
including missing, expired, or invalid signatures, a key which
does not match the DS RRset in the parent zone, or an insecure
response from a zone which, according to its parent, should have
been secure.
</para>
<note>
<para>
When the validator receives a response from an unsigned zone
that has a signed parent, it must confirm with the parent
that the zone was intentionally left unsigned. It does
this by verifying, via signed and validated NSEC/NSEC3 records,
that the parent zone contains no DS records for the child.
</para>
<para>
If the validator <emphasis>can</emphasis> prove that the zone
is insecure, then the response is accepted. However, if it
cannot, then it must assume an insecure response to be a
forgery; it rejects the response and logs an error.
</para>
<para>
The logged error reads "insecurity proof failed" and
"got insecure response; parent indicates it should be secure".
</para>
</note>
</section>
</section>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dnssec.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="managed-keys.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="pkcs11.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dlz.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dyndb.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="catz.xml"/>
<section xml:id="ipv6"><info><title>IPv6 Support in <acronym>BIND</acronym> 9</title></info>
<para>
<acronym>BIND</acronym> 9 fully supports all currently
defined forms of IPv6 name to address and address to name
lookups. It 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
only AAAA records. RFC 3363 deprecated the use of A6 records,
and client-side support for A6 records was accordingly removed
from <acronym>BIND</acronym> 9.
However, authoritative <acronym>BIND</acronym> 9 name servers still
load zone files containing A6 records correctly, answer queries
for A6 records, and accept zone transfer for a zone containing A6
records.
</para>
<para>
For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports
the traditional "nibble" format used in the
<emphasis>ip6.arpa</emphasis> domain, as well as the older, deprecated
<emphasis>ip6.int</emphasis> domain.
Older versions of <acronym>BIND</acronym> 9
supported the "binary label" (also known as "bitstring") format,
but support of binary labels has been completely removed per
RFC 3363.
Many applications in <acronym>BIND</acronym> 9 do not understand
the binary label format at all any more, and will return an
error if given.
In particular, an authoritative <acronym>BIND</acronym> 9
name server will not load a zone file containing binary labels.
</para>
<para>
For an overview of the format and structure of IPv6 addresses,
see <xref linkend="ipv6addresses"/>.
</para>
<section><info><title>Address Lookups Using AAAA Records</title></info>
<para>
The IPv6 AAAA record is a parallel to the IPv4 A record,
and, unlike the deprecated A6 record, specifies the entire
IPv6 address in a single record. For example,
</para>
<programlisting>
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
</programlisting>
<para>
Use of IPv4-in-IPv6 mapped addresses is not recommended.
If a host has an IPv4 address, use an A record, not
a AAAA, with <literal>::ffff:192.168.42.1</literal> as
the address.
</para>
</section>
<section><info><title>Address to Name Lookups Using Nibble Format</title></info>
<para>
When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<literal>ip6.arpa.</literal> is appended to the
resulting name.
For example, the following would provide reverse name lookup for
a host with address
<literal>2001:db8::1</literal>.
</para>
<programlisting>
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
host.example.com. )
</programlisting>
</section>
</section>
</chapter>
<chapter xml:id="Bv9ARM.ch05"><info><title><acronym>BIND</acronym> 9 Configuration Reference</title></info>
<para>
<acronym>BIND</acronym> 9 configuration is broadly similar
to <acronym>BIND</acronym> 8; however, there are a few new
areas
of configuration, such as views. <acronym>BIND</acronym>
8 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>
<section xml:id="configuration_file_elements"><info><title>Configuration File Elements</title></info>
<para>
Following is a list of elements used throughout the <acronym>BIND</acronym> configuration
file documentation:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.855in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.770in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<varname>acl_name</varname>
</para>
</entry>
<entry colname="2">
<para>
The name of an <varname>address_match_list</varname> as
defined by the <command>acl</command> statement.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>address_match_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more
<varname>ip_addr</varname>,
<varname>ip_prefix</varname>, <varname>key_id</varname>,
or <varname>acl_name</varname> elements, see
<xref linkend="address_match_lists"/>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>masters_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A named list of one or more <varname>ip_addr</varname>
with optional <varname>key_id</varname> and/or
<varname>ip_port</varname>.
A <varname>masters_list</varname> may include other
<varname>masters_lists</varname>.
</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>namelist</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more <varname>domain_name</varname>
elements.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>dotted_decimal</varname>
</para>
</entry>
<entry colname="2">
<para>
One to four integers valued 0 through
255 separated by dots (`.'), such as <command>123</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>2001:db8::1234</command>.
IPv6 scoped addresses that have ambiguity on their
scope zones must be disambiguated by an appropriate
zone ID with the percent character (`%') as
delimiter. It is strongly recommended to use
string zone names rather than numeric identifiers,
in order to be robust against system configuration
changes. However, since there is no standard
mapping for such names and identifier values,
currently only interface names as link identifiers
are supported, assuming one-to-one mapping between
interfaces and links. For example, a link-local
address <command>fe80::1</command> on the link
attached to the interface <command>ne0</command>
can be specified as <command>fe80::1%ne0</command>.
Note that on most systems link-local addresses
always have the ambiguity, and need to be
disambiguated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_addr</varname>
</para>
</entry>
<entry colname="2">
<para>
An <varname>ip4_addr</varname> or <varname>ip6_addr</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_dscp</varname>
</para>
</entry>
<entry colname="2">
<para>
A <varname>number</varname> between 0 and 63, used
to select a differentiated services code point (DSCP)
value for use with outgoing traffic on operating systems
that support DSCP.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_port</varname>
</para>
</entry>
<entry colname="2">
<para>
An IP port <varname>number</varname>.
The <varname>number</varname> is limited to 0
through 65535, with values
below 1024 typically restricted to use by processes running
as root.
In some cases, an asterisk (`*') character can be used as a
placeholder to
select a random high-numbered port.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_prefix</varname>
</para>
</entry>
<entry colname="2">
<para>
An IP network specified as an <varname>ip_addr</varname>,
followed by a slash (`/') and then the number of bits in the
netmask.
Trailing zeros in 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>
<para>
When specifying a prefix involving a IPv6 scoped address
the scope may be omitted. In that case the prefix will
match packets from any scope.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>key_id</varname>
</para>
</entry>
<entry colname="2">
<para>
A <varname>domain_name</varname> representing
the name of a shared key, to be used for transaction
security.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>key_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more
<varname>key_id</varname>s,
separated by semicolons and ending with a semicolon.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>number</varname>
</para>
</entry>
<entry colname="2">
<para>
A non-negative 32-bit integer
(i.e., a number between 0 and 4294967295, inclusive).
Its acceptable value might be further
limited by the context in which it is used.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>fixedpoint</varname>
</para>
</entry>
<entry colname="2">
<para>
A non-negative real number that can be specified to
the nearest one hundredth. Up to five digits can be
specified before a decimal point, and up to two
digits after, so the maximum value is 99999.99.
Acceptable values might be further limited by the
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>port_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of an <varname>ip_port</varname> or a port
range.
A port range is specified in the form of
<userinput>range</userinput> followed by
two <varname>ip_port</varname>s,
<varname>port_low</varname> and
<varname>port_high</varname>, which represents
port numbers from <varname>port_low</varname> through
<varname>port_high</varname>, inclusive.
<varname>port_low</varname> must not be larger than
<varname>port_high</varname>.
For example,
<userinput>range 1024 65535</userinput> represents
ports from 1024 through 65535.
In either case an asterisk (`*') character is not
allowed as a valid <varname>ip_port</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>size_spec</varname>
</para>
</entry>
<entry colname="2">
<para>
A 64-bit unsigned integer, or the keywords
<userinput>unlimited</userinput> or
<userinput>default</userinput>.
</para>
<para>
Integers may take values
0 &lt;= value &lt;= 18446744073709551615, though
certain parameters
(such as <command>max-journal-size</command>) may
use a more limited range within these extremes.
In most cases, setting a value to 0 does not
literally mean zero; it means "undefined" or
"as big as possible", depending on the context.
See the explanations of particular parameters
that use <varname>size_spec</varname>
for details on how they interpret its use.
</para>
<para>
Numeric values can optionally be followed by a
scaling factor:
<userinput>K</userinput> or <userinput>k</userinput>
for kilobytes,
<userinput>M</userinput> or <userinput>m</userinput>
for megabytes, and
<userinput>G</userinput> or <userinput>g</userinput>
for gigabytes, which scale by 1024, 1024*1024, and
1024*1024*1024 respectively.
</para>
<para>
<varname>unlimited</varname> generally means
"as big as possible", and is usually the best
way to safely set a very large number.
</para>
<para>
<varname>default</varname>
uses the limit that was in force when the server was started.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>size_or_percent</varname>
</para>
</entry>
<entry colname="2">
<para>
<varname>size_spec</varname> or integer value
followed by '%' to represent percents.
</para>
<para>
The behavior is exactly the same as
<varname>size_spec</varname>, but
<varname>size_or_percent</varname> allows also
to specify a positive integer value followed by
'%' sign to represent percents.
</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>
<section xml:id="address_match_lists"><info><title>Address Match Lists</title></info>
<section><info><title>Syntax</title></info>
<programlisting><replaceable>address_match_list</replaceable> = <replaceable>address_match_list_element</replaceable> <command>;</command> ...
<replaceable>address_match_list_element</replaceable> = [ <command>!</command> ] ( <replaceable>ip_address</replaceable> | <replaceable>ip_prefix</replaceable> |
<command>key</command> <replaceable>key_id</replaceable> | <replaceable>acl_name</replaceable> | <command>{</command> <replaceable>address_match_list</replaceable> <command>}</command> )
</programlisting>
</section>
<section><info><title>Definition and Usage</title></info>
<para>
Address match lists are primarily used to determine access
control for various server operations. They are also used in
the <command>listen-on</command> and <command>sortlist</command>
statements. The elements which constitute an address match
list can be any of the following:
</para>
<itemizedlist>
<listitem>
<simpara>an IP address (IPv4 or IPv6)</simpara>
</listitem>
<listitem>
<simpara>an IP prefix (in `/' notation)</simpara>
</listitem>
<listitem>
<simpara>
a key ID, as defined by the <command>key</command>
statement
</simpara>
</listitem>
<listitem>
<simpara>the name of an address match list defined with
the <command>acl</command> statement
</simpara>
</listitem>
<listitem>
<simpara>a nested address match list enclosed in braces</simpara>
</listitem>
</itemizedlist>
<para>
Elements can be negated with a leading exclamation mark (`!'),
and the match list names "any", "none", "localhost", and
"localnets" are predefined. More information on those names
can be found in the description of the 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 comparison takes place in approximately O(1)
time. However, key comparisons require that the list of keys
be traversed until a matching key is found, and therefore may
be somewhat slower.
</para>
<para>
The interpretation of a match depends on whether the list is being
used for access control, defining <command>listen-on</command> ports, or in a
<command>sortlist</command>, and whether the element was negated.
</para>
<para>
When used as an access control list, a non-negated match
allows access and a negated match denies access. If
there is no match, access is denied. The clauses
<command>allow-notify</command>,
<command>allow-recursion</command>,
<command>allow-recursion-on</command>,
<command>allow-query</command>,
<command>allow-query-on</command>,
<command>allow-query-cache</command>,
<command>allow-query-cache-on</command>,
<command>allow-transfer</command>,
<command>allow-update</command>,
<command>allow-update-forwarding</command>,
<command>blackhole</command>, and
<command>keep-response-order</command> all use address match
lists. Similarly, the <command>listen-on</command> option will cause the
server to refuse queries on any of the machine's
addresses which do not match the list.
</para>
<para>
Order of insertion is significant. If more than one element
in an ACL is found to match a given IP address or prefix,
preference will be given to the one that came
<emphasis>first</emphasis> in the ACL definition.
Because of this first-match behavior, an element that
defines a subset of another element in the list should
come before the broader element, regardless of whether
either is negated. For example, in
<command>1.2.3/24; ! 1.2.3.13;</command>
the 1.2.3.13 element is completely useless because the
algorithm 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>
</section>
</section>
<section xml:id="comment_syntax"><info><title>Comment Syntax</title></info>
<para>
The <acronym>BIND</acronym> 9 comment syntax allows for
comments to appear
anywhere that whitespace may appear in a <acronym>BIND</acronym> configuration
file. To appeal to programmers of all kinds, they can be written
in the C, C++, or shell/perl style.
</para>
<section><info><title>Syntax</title></info>
<para>
<programlisting>/* This is a <acronym>BIND</acronym> comment as in C */</programlisting>
<programlisting>// This is a <acronym>BIND</acronym> comment as in C++</programlisting>
<programlisting># This is a <acronym>BIND</acronym> comment as in common UNIX shells
# and perl</programlisting>
</para>
</section>
<section><info><title>Definition and Usage</title></info>
<para>
Comments may appear anywhere that whitespace may appear in
a <acronym>BIND</acronym> configuration file.
</para>
<para>
C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.
</para>
<para>
C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:
</para>
<para>
<programlisting>/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */
</programlisting>
</para>
<para>
C++-style comments start with the two characters // (slash,
slash) and continue to the end of the physical line. They cannot
be continued across multiple physical lines; to have one logical
comment span multiple lines, each line must use the // pair.
For example:
</para>
<para>
<programlisting>// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
</programlisting>
</para>
<para>
Shell-style (or perl-style, 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.
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>
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>
</section>
</section>
</section>
<section xml:id="Configuration_File_Grammar"><info><title>Configuration File Grammar</title></info>
<para>
A <acronym>BIND</acronym> 9 configuration consists of
statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of sub-statements, which are also
terminated with a semicolon.
</para>
<para>
The following statements are supported:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.336in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.778in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>acl</command></para>
</entry>
<entry colname="2">
<para>
defines a named IP address
matching list, for access control and other uses.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>controls</command></para>
</entry>
<entry colname="2">
<para>
declares control channels to be used
by the <command>rndc</command> utility.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>include</command></para>
</entry>
<entry colname="2">
<para>
includes a file.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>key</command></para>
</entry>
<entry colname="2">
<para>
specifies key information for use in
authentication and authorization using TSIG.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>logging</command></para>
</entry>
<entry colname="2">
<para>
specifies what the server logs, and where
the log messages are sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>masters</command></para>
</entry>
<entry colname="2">
<para>
defines a named masters list for
inclusion in stub and slave zones'
<command>masters</command> or
<command>also-notify</command> lists.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>options</command></para>
</entry>
<entry colname="2">
<para>
controls global server configuration
options and sets defaults for other statements.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>server</command></para>
</entry>
<entry colname="2">
<para>
sets certain configuration options on
a per-server basis.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>statistics-channels</command></para>
</entry>
<entry colname="2">
<para>
declares communication channels to get access to
<command>named</command> statistics.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>dnssec-keys</command></para>
</entry>
<entry colname="2">
<para>
defines DNSSEC keys: if used with the
<command>initial-key</command> keyword,
keys are kept up to date using RFC 5011
trust anchor maintenance, and if used with
<command>static-key</command>, keys are permanent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>managed-keys</command></para>
</entry>
<entry colname="2">
<para>
is identical to <command>dnssec-keys</command>;
this option is deprecated in favor
of <command>dnssec-keys</command> with
the <command>initial-key</command> keyword,
and may be removed in a future release.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>trusted-keys</command></para>
</entry>
<entry colname="2">
<para>
defines permanent trusted DNSSEC keys;
this option is deprecated in favor
of <command>dnssec-keys</command> with
the <command>static-key</command> keyword,
and may be removed in a future release.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>view</command></para>
</entry>
<entry colname="2">
<para>
defines a view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>zone</command></para>
</entry>
<entry colname="2">
<para>
defines a zone.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The <command>logging</command> and
<command>options</command> statements may only occur once
per
configuration.
</para>
<section xml:id="acl_grammar"><info><title><command>acl</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="acl.grammar.xml"/>
</section>
<section xml:id="acl"><info><title><command>acl</command> Statement Definition and
Usage</title></info>
<para>
The <command>acl</command> statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).
</para>
<para>
The following ACLs are built-in:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.130in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>any</command></para>
</entry>
<entry colname="2">
<para>
Matches all hosts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>none</command></para>
</entry>
<entry colname="2">
<para>
Matches no hosts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>localhost</command></para>
</entry>
<entry colname="2">
<para>
Matches the IPv4 and IPv6 addresses of all network
interfaces on the system. When addresses are
added or removed, the <command>localhost</command>
ACL element is updated to reflect the changes.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>localnets</command></para>
</entry>
<entry colname="2">
<para>
Matches any host on an IPv4 or IPv6 network
for which the system has an interface.
When addresses are added or removed,
the <command>localnets</command>
ACL element is updated to reflect the changes.
Some systems do not provide a way to determine the prefix
lengths of
local IPv6 addresses.
In such a case, <command>localnets</command>
only matches the local
IPv6 addresses, just like <command>localhost</command>.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="controls_grammar"><info><title><command>controls</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="controls.grammar.xml"/>
</section>
<section xml:id="controls_statement_definition_and_usage"><info><title><command>controls</command> Statement Definition and
Usage</title></info>
<para>
The <command>controls</command> statement declares control
channels to be used by system administrators to control the
operation of the name server. These control channels are
used by the <command>rndc</command> utility to send
commands to and retrieve non-DNS results from a name server.
</para>
<para>
An <command>inet</command> control channel is a TCP socket
listening at the specified <command>ip_port</command> on the
specified <command>ip_addr</command>, which can be an IPv4 or IPv6
address. An <command>ip_addr</command> of <literal>*</literal> (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <command>ip_addr</command> of <literal>::</literal>.
If you will only use <command>rndc</command> on the local host,
using the loopback address (<literal>127.0.0.1</literal>
or <literal>::1</literal>) is recommended for maximum security.
</para>
<para>
If no port is specified, port 953 is used. The asterisk
"<literal>*</literal>" cannot be used for <command>ip_port</command>.
</para>
<para>
The ability to issue commands over the control channel is
restricted by the <command>allow</command> and
<command>keys</command> clauses.
Connections to the control channel are permitted based on the
<command>address_match_list</command>. This is for simple
IP address based filtering only; any <command>key_id</command>
elements of the <command>address_match_list</command>
are ignored.
</para>
<para>
A <command>unix</command> control channel is a UNIX domain
socket listening at the specified path in the file system.
Access to the socket is specified by the <command>perm</command>,
<command>owner</command> and <command>group</command> clauses.
Note on some platforms (SunOS and Solaris) the permissions
(<command>perm</command>) are applied to the parent directory
as the permissions on the socket itself are ignored.
</para>
<para>
The primary authorization mechanism of the command
channel is the <command>key_list</command>, which
contains a list of <command>key_id</command>s.
Each <command>key_id</command> in the <command>key_list</command>
is authorized to execute commands over the control channel.
See <xref linkend="rndc"/> in <xref linkend="admin_tools"/>)
for information about configuring keys in <command>rndc</command>.
</para>
<para>
If the <command>read-only</command> clause is enabled, the
control channel is limited to the following set of read-only
commands: <command>nta -dump</command>,
<command>null</command>, <command>status</command>,
<command>showzone</command>, <command>testgen</command>, and
<command>zonestatus</command>. By default,
<command>read-only</command> is not enabled and the control
channel allows read-write access.
</para>
<para>
If no <command>controls</command> statement is present,
<command>named</command> 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-confgen -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
a
<filename>rndc.conf</filename> file and make it group
readable by a group
that contains the users who should have access.
</para>
<para>
To disable the command channel, use an empty
<command>controls</command> statement:
<command>controls { };</command>.
</para>
</section>
<section xml:id="include_grammar"><info><title><command>include</command> Statement Grammar</title></info>
<programlisting><command>include</command> <replaceable>filename</replaceable><command>;</command></programlisting>
</section>
<section xml:id="include_statement"><info><title><command>include</command> Statement Definition and Usage</title></info>
<para>
The <command>include</command> statement inserts the
specified file at the point where the <command>include</command>
statement is encountered. The <command>include</command>
statement facilitates the administration of configuration
files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by the name server.
</para>
</section>
<section xml:id="key_grammar"><info><title><command>key</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="key.grammar.xml"/>
</section>
<section xml:id="key_statement"><info><title><command>key</command> Statement Definition and Usage</title></info>
<para>
The <command>key</command> statement defines a shared
secret key for use with TSIG (see <xref linkend="tsig"/>)
or the command channel
(see <xref linkend="controls_statement_definition_and_usage"/>).
</para>
<para>
The <command>key</command> statement can occur at the
top level
of the configuration file or inside a <command>view</command>
statement. Keys defined in top-level <command>key</command>
statements can be used in all views. Keys intended for use in
a <command>controls</command> statement
(see <xref linkend="controls_statement_definition_and_usage"/>)
must be defined at the top level.
</para>
<para>
The <replaceable>key_id</replaceable>, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a <command>server</command>
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
</para>
<para>
The <replaceable>algorithm_id</replaceable> is a string
that specifies a security/authentication algorithm. The
<command>named</command> server supports <literal>hmac-md5</literal>,
<literal>hmac-sha1</literal>, <literal>hmac-sha224</literal>,
<literal>hmac-sha256</literal>, <literal>hmac-sha384</literal>
and <literal>hmac-sha512</literal> TSIG authentication.
Truncated hashes are supported by appending the minimum
number of required bits preceded by a dash, e.g.
<literal>hmac-sha1-80</literal>. The
<replaceable>secret_string</replaceable> is the secret
to be used by the algorithm, and is treated as a Base64
encoded string.
</para>
</section>
<section xml:id="logging_grammar"><info><title><command>logging</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="logging.grammar.xml"/>
</section>
<section xml:id="logging_statement"><info><title><command>logging</command> Statement Definition and Usage</title></info>
<para>
The <command>logging</command> statement configures a
wide
variety of logging options for the name server. Its <command>channel</command> phrase
associates output methods, format options and severity levels with
a name that can then be used with the <command>category</command> phrase
to select how various classes of messages are logged.
</para>
<para>
Only one <command>logging</command> statement is used to
define
as many channels and categories as are wanted. If there is no <command>logging</command> statement,
the logging configuration will be:
</para>
<programlisting>logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
</programlisting>
<para>
If <command>named</command> is started with the
<option>-L</option> option, it logs to the specified file
at startup, instead of using syslog. In this case the logging
configuration will be:
</para>
<programlisting>logging {
category default { default_logfile; default_debug; };
category unmatched { null; };
};
</programlisting>
<para>
The logging configuration is only established when
the entire configuration file has been parsed.
When the server 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>
<section xml:id="channel"><info><title>The <command>channel</command> Phrase</title></info>
<para>
All log output goes to one or more <emphasis>channels</emphasis>;
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 additional
arguments to specify how large the file is allowed to
become before it is rolled to a backup file
(<command>size</command>), how many backup versions of
the file will be saved each time this happens
(<command>versions</command>), and the format to use
for naming backup versions (<command>suffix</command>).
</para>
<para>
The <command>size</command> option is used to limit
log file growth. If the file ever exceeds the specified
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 below. 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>
File rolling only occurs when the file exceeds the size
specified with the <command>size</command> option. No
backup versions are kept by default; any existing
log file is simply appended. The
<command>versions</command> option specifies
how many backup versions of the file should be kept.
If set to <literal>unlimited</literal>, there is no limit.
</para>
<para>
The <command>suffix</command> option can be set to
either <literal>increment</literal> or
<literal>timestamp</literal>. If set to
<literal>timestamp</literal>, then when a log file is
rolled, it is saved with the current timestamp as a
file suffix. If set to <literal>increment</literal>,
then backup files are saved with incrementing numbers
as suffixes; older files are renamed when rolling.
For example, if <command>versions</command>
is set to 3 and <command>suffix</command> to
<literal>increment</literal>, then when
<filename>filename.log</filename> reaches the size
specified by <command>size</command>,
<filename>filename.log.1</filename> is renamed to
<filename>filename.log.2</filename>,
<filename>filename.log.0</filename> is renamed
to <filename>filename.log.1</filename>,
and <filename>filename.log</filename> is
renamed to <filename>filename.log.0</filename>,
whereupon a new <filename>filename.log</filename> is
opened.
</para>
<para>
Example usage of the <command>size</command>,
<command>versions</command>, and <command>suffix</command>
options:
</para>
<programlisting>channel an_example_channel {
file "example.log" versions 3 size 20m suffix increment;
print-time yes;
print-category yes;
};
</programlisting>
<para>
The <command>syslog</command> destination clause
directs the
channel to the system log. Its argument is a
syslog facility as described in the <command>syslog</command> man
page. Known facilities are <command>kern</command>, <command>user</command>,
<command>mail</command>, <command>daemon</command>, <command>auth</command>,
<command>syslog</command>, <command>lpr</command>, <command>news</command>,
<command>uucp</command>, <command>cron</command>, <command>authpriv</command>,
<command>ftp</command>, <command>local0</command>, <command>local1</command>,
<command>local2</command>, <command>local3</command>, <command>local4</command>,
<command>local5</command>, <command>local6</command> and
<command>local7</command>, however not all facilities
are supported on
all operating systems.
How <command>syslog</command> 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>
On Windows machines syslog messages are directed to the EventViewer.
</para>
<para>
The <command>severity</command> clause works like <command>syslog</command>'s
"priorities", except that they can also be used 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>rndc
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 debug level to determine what messages to print.
</para>
<para>
<command>print-time</command> can be set to
<userinput>yes</userinput>, <userinput>no</userinput>,
or a time format specifier, which may be one of
<userinput>local</userinput>, <userinput>iso8601</userinput> or
<userinput>iso8601-utc</userinput>. If set to
<userinput>no</userinput>, then the date and time will
not be logged. If set to <userinput>yes</userinput>
or <userinput>local</userinput>, the date and time are logged
in a human readable format, using the local time zone.
If set to <userinput>iso8601</userinput> the local time is
logged in ISO8601 format. If set to
<userinput>iso8601-utc</userinput>, then the date and time
are logged in ISO8601 format, with time zone set to
UTC. The default is <userinput>no</userinput>.
</para>
<para>
<command>print-time</command> may
be specified for a <command>syslog</command> channel,
but it is usually
pointless since <command>syslog</command> also logs
the date and time.
</para>
<para>
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>
If <command>buffered</command> has been turned on the output
to files will not be flushed after each log entry. By default
all log messages are flushed.
</para>
<para>
There are four predefined channels that are used for
<command>named</command>'s default logging as follows.
If <command>named</command> is started with the
<option>-L</option> then a
fifth channel <command>default_logfile</command> is added.
How they are
used is described in <xref linkend="the_category_phrase"/>.
</para>
<programlisting>channel default_syslog {
// send to syslog's daemon facility
syslog daemon;
// only send priority info and higher
severity info;
};
channel default_debug {
// write to named.run in the working directory
// Note: stderr is used instead of "named.run" if
// the server is started with the '-g' option.
file "named.run";
// log at the server's current debug level
severity dynamic;
};
channel default_stderr {
// writes to stderr
stderr;
// only send priority info and higher
severity info;
};
channel null {
// toss anything sent to this channel
null;
};
channel default_logfile {
// this channel is only present if named is
// started with the -L option, whose argument
// provides the file name
file "...";
// log at the server's current debug level
severity dynamic;
};
</programlisting>
<para>
The <command>default_debug</command> channel has the
special
property that it only produces output when the server's debug
level is
nonzero. It normally writes to a file called <filename>named.run</filename>
in the server's working directory.
</para>
<para>
For security reasons, when the <option>-u</option>
command line option is used, the <filename>named.run</filename> file
is created only after <command>named</command> has
changed to the
new UID, and any debug output generated while <command>named</command> is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the <option>-L</option>
option to specify a default logfile, or the <option>-g</option>
option to log to standard error which you can redirect 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>
</section>
<section xml:id="the_category_phrase"><info><title>The <command>category</command> Phrase</title></info>
<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>
If you start <command>named</command> with the
<option>-L</option> option then the default category is:
</para>
<programlisting>category default { default_logfile; 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>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="logging-categories.xml"/>
</section>
<section xml:id="query_errors"><info><title>The <command>query-errors</command> Category</title></info>
<para>
The <command>query-errors</command> category is
specifically intended for debugging purposes: To identify
why and how specific queries result in responses which
indicate an error.
Messages of this category are therefore only logged
with <command>debug</command> levels.
</para>
<para>
At the debug levels of 1 or higher, each response with the
rcode of SERVFAIL is logged as follows:
</para>
<para>
<computeroutput>client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</computeroutput>
</para>
<para>
This means an error resulting in SERVFAIL was
detected at line 3880 of source file
<filename>query.c</filename>.
Log messages of this level will particularly
help identify the cause of SERVFAIL for an
authoritative server.
</para>
<para>
At the debug levels of 2 or higher, detailed context
information of recursive resolutions that resulted in
SERVFAIL is logged.
The log message will look like as follows:
</para>
<para>
<!-- NOTE: newlines and some spaces added so this would fit on page -->
<programlisting>
fetch completed at resolver.c:2970 for www.example.com/A
in 30.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
</programlisting>
</para>
<para>
The first part before the colon shows that a recursive
resolution for AAAA records of www.example.com completed
in 30.000183 seconds and the final result that led to the
SERVFAIL was determined at line 2970 of source file
<filename>resolver.c</filename>.
</para>
<para>
The following part shows the detected final result and the
latest result of DNSSEC validation.
The latter is always success when no validation attempt
is made.
In this example, this query resulted in SERVFAIL probably
because all name servers are down or unreachable, leading
to a timeout in 30 seconds.
DNSSEC validation was probably not attempted.
</para>
<para>
The last part enclosed in square brackets shows statistics
information collected for this particular resolution
attempt.
The <varname>domain</varname> field shows the deepest zone
that the resolver reached;
it is the zone where the error was finally detected.
The meaning of the other fields is summarized in the
following table.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><varname>referral</varname></para>
</entry>
<entry colname="2">
<para>
The number of referrals the resolver received
throughout the resolution process.
In the above example this is 2, which are most
likely com and example.com.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>restart</varname></para>
</entry>
<entry colname="2">
<para>
The number of cycles that the resolver tried
remote servers at the <varname>domain</varname>
zone.
In each cycle the resolver sends one query
(possibly resending it, depending on the response)
to each known name server of
the <varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>qrysent</varname></para>
</entry>
<entry colname="2">
<para>
The number of queries the resolver sent at the
<varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>timeout</varname></para>
</entry>
<entry colname="2">
<para>
The number of timeouts since the resolver
received the last response.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>lame</varname></para>
</entry>
<entry colname="2">
<para>
The number of lame servers the resolver detected
at the <varname>domain</varname> zone.
A server is detected to be lame either by an
invalid response or as a result of lookup in
BIND9's address database (ADB), where lame
servers are cached.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>neterr</varname></para>
</entry>
<entry colname="2">
<para>
The number of erroneous results that the
resolver encountered in sending queries
at the <varname>domain</varname> zone.
One common case is the remote server is
unreachable and the resolver receives an ICMP
unreachable error message.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>badresp</varname></para>
</entry>
<entry colname="2">
<para>
The number of unexpected responses (other than
<varname>lame</varname>) to queries sent by the
resolver at the <varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>adberr</varname></para>
</entry>
<entry colname="2">
<para>
Failures in finding remote server addresses
of the <varname>domain</varname> zone in the ADB.
One common case of this is that the remote
server's name does not have any address records.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>findfail</varname></para>
</entry>
<entry colname="2">
<para>
Failures of resolving remote server addresses.
This is a total number of failures throughout
the resolution process.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>valfail</varname></para>
</entry>
<entry colname="2">
<para>
Failures of DNSSEC validation.
Validation failures are counted throughout
the resolution process (not limited to
the <varname>domain</varname> zone), but should
only happen in <varname>domain</varname>.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
At the debug levels of 3 or higher, the same messages
as those at the debug 1 level are logged for other errors
than SERVFAIL.
Note that negative responses such as NXDOMAIN are not
regarded as errors here.
</para>
<para>
At the debug levels of 4 or higher, the same messages
as those at the debug 2 level are logged for other errors
than SERVFAIL.
Unlike the above case of level 3, messages are logged for
negative responses.
This is because any unexpected results can be difficult to
debug in the recursion case.
</para>
</section>
</section>
<section xml:id="masters_grammar"><info><title><command>masters</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="masters.grammar.xml"/>
</section>
<section xml:id="masters_statement"><info><title><command>masters</command> Statement Definition and
Usage</title></info>
<para><command>masters</command>
lists allow for a common set of masters to be easily used by
multiple stub and slave zones in their <command>masters</command>
or <command>also-notify</command> lists.
</para>
</section>
<section xml:id="options_grammar"><info><title><command>options</command> Statement Grammar</title></info>
<para>
This is the grammar of the <command>options</command>
statement in the <filename>named.conf</filename> file:
</para>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="options.grammar.xml"/>
</section>
<section xml:id="options"><info><title><command>options</command> Statement Definition and
Usage</title></info>
<para>
The <command>options</command> statement sets up global
options
to be used by <acronym>BIND</acronym>. This statement
may appear only
once in a configuration file. If there is no <command>options</command>
statement, an options block with each option set to its default will
be used.
</para>
<variablelist>
<varlistentry>
<term><command>attach-cache</command></term>
<listitem>
<para>
Allows multiple views to share a single cache
database.
Each view has its own cache database by default, but
if multiple views have the same operational policy
for name resolution and caching, those views can
share a single cache to save memory and possibly
improve resolution efficiency by using this option.
</para>
<para>
The <command>attach-cache</command> option
may also be specified in <command>view</command>
statements, in which case it overrides the
global <command>attach-cache</command> option.
</para>
<para>
The <replaceable>cache_name</replaceable> specifies
the cache to be shared.
When the <command>named</command> server configures
views which are supposed to share a cache, it
creates a cache with the specified name for the
first view of these sharing views.
The rest of the views will simply refer to the
already created cache.
</para>
<para>
One common configuration to share a cache would be to
allow all views to share a single cache.
This can be done by specifying
the <command>attach-cache</command> as a global
option with an arbitrary name.
</para>
<para>
Another possible operation is to allow a subset of
all views to share a cache while the others to
retain their own caches.
For example, if there are three views A, B, and C,
and only A and B should share a cache, specify the
<command>attach-cache</command> option as a view A (or
B)'s option, referring to the other view name:
</para>
<programlisting>
view "A" {
// this view has its own cache
...
};
view "B" {
// this view refers to A's cache
attach-cache "A";
};
view "C" {
// this view has its own cache
...
};
</programlisting>
<para>
Views that share a cache must have the same policy
on configurable parameters that may affect caching.
The current implementation requires the following
configurable options be consistent among these
views:
<command>check-names</command>,
<command>dnssec-accept-expired</command>,
<command>dnssec-validation</command>,
<command>max-cache-ttl</command>,
<command>max-ncache-ttl</command>,
<command>max-stale-ttl</command>,
<command>max-cache-size</command>, and
<command>min-cache-ttl</command>,
<command>min-ncache-ttl</command>,
<command>zero-no-soa-ttl</command>.
</para>
<para>
Note that there may be other parameters that may
cause confusion if they are inconsistent for
different views that share a single cache.
For example, if these views define different sets of
forwarders that can return different answers for the
same question, sharing the answer does not make
sense or could even be harmful.
It is administrator's responsibility to ensure
configuration differences in different views do
not cause disruption with a shared cache.
</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, and <emphasis>must</emphasis>
be writable by the effective user ID of the
<command>named</command> process.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnstap</command></term>
<listitem>
<para>
<command>dnstap</command> is a fast, flexible method
for capturing and logging DNS traffic. Developed by
Robert Edmonds at Farsight Security, Inc., and supported
by multiple DNS implementations, <command>dnstap</command>
uses
<command>libfstrm</command> (a lightweight high-speed
framing library, see
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://github.com/farsightsec/fstrm">https://github.com/farsightsec/fstrm</link>) to send
event payloads which are encoded using Protocol Buffers
(<command>libprotobuf-c</command>, a mechanism for
serializing structured data developed
by Google, Inc.; see
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://developers.google.com/protocol-buffers/">https://developers.google.com/protocol-buffers</link>).
</para>
<para>
To enable <command>dnstap</command> at compile time,
the <command>fstrm</command> and <command>protobuf-c</command>
libraries must be available, and BIND must be configured with
<option>--enable-dnstap</option>.
</para>
<para>
The <command>dnstap</command> option is a bracketed list
of message types to be logged. These may be set differently
for each view. Supported types are <literal>client</literal>,
<literal>auth</literal>, <literal>resolver</literal>,
<literal>forwarder</literal>, and <literal>update</literal>.
Specifying type <literal>all</literal> will cause all
<command>dnstap</command> messages to be logged, regardless of
type.
</para>
<para>
Each type may take an additional argument to indicate whether
to log <literal>query</literal> messages or
<literal>response</literal> messages; if not specified,
both queries and responses are logged.
</para>
<para>
Example: To log all authoritative queries and responses,
recursive client responses, and upstream queries sent by
the resolver, use:
<programlisting>dnstap {
auth;
client response;
resolver query;
};
</programlisting>
</para>
<para>
Logged <command>dnstap</command> messages can be parsed
using the <command>dnstap-read</command> utility (see
<xref linkend="man.dnstap-read"/> for details).
</para>
<para>
For more information on <command>dnstap</command>, see
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://dnstap.info">http://dnstap.info</link>.
</para>
<para>
The fstrm library has a number of tunables that are exposed
in <filename>named.conf</filename>, and can be modified
if necessary to improve performance or prevent loss of data.
These are:
</para>
<itemizedlist>
<listitem>
<simpara>
<command>fstrm-set-buffer-hint</command>: The
threshold number of bytes to accumulate in the output
buffer before forcing a buffer flush. The minimum is
1024, the maximum is 65536, and the default is 8192.
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-flush-timeout</command>: The number
of seconds to allow unflushed data to remain in the
output buffer. The minimum is 1 second, the maximum is
600 seconds (10 minutes), and the default is 1 second.
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-output-notify-threshold</command>:
The number of outstanding queue entries to allow on
an input queue before waking the I/O thread.
The minimum is 1 and the default is 32.
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-output-queue-model</command>:
Controls the queuing semantics to use for queue
objects. The default is <literal>mpsc</literal>
(multiple producer, single consumer); the other
option is <literal>spsc</literal> (single producer,
single consumer).
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-input-queue-size</command>: The
number of queue entries to allocate for each
input queue. This value must be a power of 2.
The minimum is 2, the maximum is 16384, and
the default is 512.
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-output-queue-size</command>:
The number of queue entries to allocate for each
output queue. The minimum is 2, the maximum is
system-dependent and based on <option>IOV_MAX</option>,
and the default is 64.
</simpara>
</listitem>
<listitem>
<simpara>
<command>fstrm-set-reopen-interval</command>:
The number of seconds to wait between attempts to
reopen a closed output stream. The minimum is 1 second,
the maximum is 600 seconds (10 minutes), and the default
is 5 seconds.
For convenience, TTL-style time unit suffixes may be
used to specify the value.
</simpara>
</listitem>
</itemizedlist>
<para>
Note that all of the above minimum, maximum, and default
values are set by the <command>libfstrm</command> library,
and may be subject to change in future versions of the
library. See the <command>libfstrm</command> documentation
for more information.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnstap-output</command></term>
<listitem>
<para>
Configures the path to which the <command>dnstap</command>
frame stream will be sent if <command>dnstap</command>
is enabled at compile time and active.
</para>
<para>
The first argument is either <literal>file</literal> or
<literal>unix</literal>, indicating whether the destination
is a file or a UNIX domain socket. The second argument
is the path of the file or socket. (Note: when using a
socket, <command>dnstap</command> messages will
only be sent if another process such as
<command>fstrm_capture</command>
(provided with <command>libfstrm</command>) is listening on
the socket.)
</para>
<para>
If the first argument is <literal>file</literal>, then
up to three additional options can be added:
<command>size</command> indicates the size to which a
<command>dnstap</command> log file can grow before being
rolled to a new file; <command>versions</command>
specifies the number of rolled log files to retain; and
<command>suffix</command> indicates whether to retain
rolled log files with an incrementing counter as the
suffix (<literal>increment</literal>) or with the
current timestamp (<literal>timestamp</literal>).
These are similar to the <command>size</command>,
<command>versions</command>, and <command>suffix</command>
options in a <command>logging</command> channel.
The default is to allow <command>dnstap</command> log
files to grow to any size without rolling.
</para>
<para>
<command>dnstap-output</command> can only be set globally
in <command>options</command>. Currently, it can only be
set once while <command>named</command> is running;
once set, it cannot be changed by
<command>rndc reload</command> or
<command>rndc reconfig</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnstap-identity</command></term>
<listitem>
<para>
Specifies an <command>identity</command> string to send in
<command>dnstap</command> messages. If set to
<literal>hostname</literal>, which is the default, the
server's hostname will be sent. If set to
<literal>none</literal>, no identity string will be sent.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnstap-version</command></term>
<listitem>
<para>
Specifies a <command>version</command> string to send in
<command>dnstap</command> messages. The default is the
version number of the BIND release. If set to
<literal>none</literal>, no version string will be sent.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>geoip-directory</command></term>
<listitem>
<para>
When <command>named</command> is compiled using the
MaxMind GeoIP2 geolocation API,
this specifies the directory containing GeoIP
database files. By default, the option is set based on
the prefix used to build the <command>libmaxminddb</command>
module: for example, if the library is installed in
<filename>/usr/local/lib</filename>, then the default
<command>geoip-directory</command> will be
<filename>/usr/local/share/GeoIP</filename>. On Windows,
the default is the <command>named</command> working
directory. See <xref linkend="acl"/> for details about
<command>geoip</command> ACLs.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>key-directory</command></term>
<listitem>
<para>
When performing dynamic update of secure zones, the
directory where the public and private DNSSEC key files
should be found, if different than the current working
directory. (Note that this option has no effect on the
paths for files containing non-DNSSEC keys such as
<filename>bind.keys</filename>,
<filename>rndc.key</filename> or
<filename>session.key</filename>.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>lmdb-mapsize</command></term>
<listitem>
<para>
When <command>named</command> is built with liblmdb,
this option sets a maximum size for the memory map of
the new-zone database (NZD) in LMDB database format.
This database is used to store configuration information
for zones added using <command>rndc addzone</command>.
Note that this is not the NZD database file size, but
the largest size that the database may grow to.
</para>
<para>
Because the database file is memory mapped, its size is
limited by the address space of the named process. The
default of 32 megabytes was chosen to be usable with
32-bit <command>named</command> builds. The largest
permitted value is 1 terabyte. Given typical zone
configurations without elaborate ACLs, a 32 MB NZD file
ought to be able to hold configurations of about 100,000
zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>managed-keys-directory</command></term>
<listitem>
<para>
Specifies the directory in which to store the files that
track managed DNSSEC keys (i.e., those configured using
the <command>initial-key</command> keyword in a
<command>dnssec-keys</command> statement). By default,
this is the working directory. The directory
<emphasis>must</emphasis> be writable by the effective
user ID of the <command>named</command> process.
</para>
<para>
If <command>named</command> is not configured to use views,
then managed keys for the server will be tracked in a single
file called <filename>managed-keys.bind</filename>.
Otherwise, managed keys will be tracked in separate files,
one file per view; each file name will be the view name
(or, if it contains characters that are incompatible with
use as a file name, the SHA256 hash of the view name),
followed by the extension
<filename>.mkeys</filename>.
</para>
<para>
(Note: in previous releases, file names for views
always used the SHA256 hash of the view name. To ensure
compatibility after upgrade, if a file using the old
name format is found to exist, it will be used instead
of the new format.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>new-zones-directory</command></term>
<listitem>
<para>
Specifies the directory in which to store the configuration
parameters for zones added via <command>rndc addzone</command>.
By default, this is the working directory. If set to a relative
path, it will be relative to the working directory. The
directory <emphasis>must</emphasis> be writable by the
effective user ID of the <command>named</command> process.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>qname-minimization</command></term>
<listitem>
<para>
This option controls QNAME minimization behaviour
in the BIND resolver. When set to <command>strict</command>,
BIND will follow the QNAME minimization algorithm to
the letter, as specified in RFC 7816. Setting this
option to <command>relaxed</command> will cause BIND
to fall back to normal (non-minimized) query mode
when it receives either NXDOMAIN or other unexpected
responses (e.g. SERVFAIL, improper zone cut, REFUSED)
to a minimized query. <command>disabled</command> disables
QNAME minimization completely. The current default is
<command>relaxed</command>, but it might be changed to
<command>strict</command> in a future release.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-gssapi-keytab</command></term>
<listitem>
<para>
The KRB5 keytab file to use for GSS-TSIG updates. If
this option is set and tkey-gssapi-credential is not
set, then updates will be allowed with any key
matching a principal in the specified keytab.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-gssapi-credential</command></term>
<listitem>
<para>
The security credential with which the server should
authenticate keys requested by the GSS-TSIG protocol.
Currently only Kerberos 5 authentication is available
and the credential is a Kerberos principal which the
server can acquire through the default system key
file, normally <filename>/etc/krb5.keytab</filename>.
The location keytab file can be overridden using the
tkey-gssapi-keytab option. Normally this principal is
of the form "<userinput>DNS/</userinput><varname>server.domain</varname>".
To use GSS-TSIG, <command>tkey-domain</command> must
also be set if a specific keytab is not set with
tkey-gssapi-keytab.
</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, or an otherwise
non-existent subdomain like
"_tkey.<varname>domainname</varname>". If you are
using GSS-TSIG, this variable must be defined, unless
you specify a specific keytab using tkey-gssapi-keytab.
</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 <varname>key_name</varname> should be the server's host name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>cache-file</command></term>
<listitem>
<para>
This is for testing only. Do not use.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dump-file</command></term>
<listitem>
<para>
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>
</listitem>
</varlistentry>
<varlistentry>
<term><command>lock-file</command></term>
<listitem>
<para>
The pathname of a file on which <command>named</command> will
attempt to acquire a file lock when starting up for
the first time; if unsuccessful, the server will
will terminate, under the assumption that another
server is already running. If not specified, the default is
<filename>/var/run/named/named.lock</filename>.
</para>
<para>
Specifying <command>lock-file none</command> disables the
use of a lock file. <command>lock-file</command> is
ignored if <command>named</command> was run using the <option>-X</option>
option, which overrides it. Changes to
<command>lock-file</command> are ignored if
<command>named</command> is being reloaded or
reconfigured; it is only effective when the server is
first started up.
</para>
</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/named.pid</filename>.
The PID file is used by programs that want to send signals to
the running
name server. Specifying <command>pid-file none</command> disables the
use of a PID file — no file will be written and any
existing one will be removed. Note that <command>none</command>
is a keyword, not a filename, and therefore is not enclosed
in
double quotes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursing-file</command></term>
<listitem>
<para>
The pathname of the file the server dumps
the queries that are currently recursing when instructed
to do so with <command>rndc recursing</command>.
If not specified, the default is <filename>named.recursing</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>statistics-file</command></term>
<listitem>
<para>
The pathname of the file the server appends statistics
to when instructed to do so using <command>rndc stats</command>.
If not specified, the default is <filename>named.stats</filename> in the
server's current directory. The format of the file is
described
in <xref linkend="statsfile"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>bindkeys-file</command></term>
<listitem>
<para>
The pathname of a file to override the built-in trusted
keys provided by <command>named</command>.
See the discussion of <command>dnssec-validation</command>
for details. If not specified, the default is
<filename>/etc/bind.keys</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>secroots-file</command></term>
<listitem>
<para>
The pathname of the file the server dumps
security roots to when instructed to do so with
<command>rndc secroots</command>.
If not specified, the default is
<filename>named.secroots</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyfile</command></term>
<listitem>
<para>
The pathname of the file into which to write a TSIG
session key generated by <command>named</command> for use by
<command>nsupdate -l</command>. If not specified, the
default is <filename>/var/run/named/session.key</filename>.
(See <xref linkend="dynamic_update_policies"/>, and in
particular the discussion of the
<command>update-policy</command> statement's
<userinput>local</userinput> option for more
information about this feature.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyname</command></term>
<listitem>
<para>
The key name to use for the TSIG session key.
If not specified, the default is "local-ddns".
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyalg</command></term>
<listitem>
<para>
The algorithm to use for the TSIG session key.
Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, hmac-sha512 and hmac-md5. If not
specified, the default is hmac-sha256.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>port</command></term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dscp</command></term>
<listitem>
<para>
The global Differentiated Services Code Point (DSCP)
value to classify outgoing DNS traffic on operating
systems that support DSCP. Valid values are 0 through 63.
It is not configured by default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>random-device</command></term>
<listitem>
<para>
Specifies a source of entropy to be used by the server.
This is a device or file from which to read entropy.
If it is a file, operations requiring entropy
will fail when the file has been exhausted.
</para>
<para>
Entropy is needed for cryptographic operations such as
TKEY transactions, dynamic update of signed zones, and
generation of TSIG session keys. It is also used for
seeding and stirring the pseudo-random number generator,
which is used for less critical functions requiring
randomness such as generation of DNS message transaction
ID's.
</para>
<para>
If <command>random-device</command> is not specified, or
if it is set to <literal>none</literal>, entropy will be
read from the random number generation function supplied
by the cryptographic library with which BIND was linked
(i.e. OpenSSL or a PKCS#11 provider).
</para>
<para>
The <command>random-device</command> option takes
effect during the initial configuration load at server
startup time and is ignored on subsequent reloads.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>preferred-glue</command></term>
<listitem>
<para>
If specified, the listed type (A or AAAA) will be emitted
before other glue
in the additional section of a query response.
The default is to prefer A records when responding
to queries that arrived via IPv4 and AAAA when
responding to queries that arrived via IPv6.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="root_delegation_only">
<term><command>root-delegation-only</command></term>
<listitem>
<para>
Turn on enforcement of delegation-only in TLDs
(top level domains) and root zones with an optional
exclude list.
</para>
<para>
DS queries are expected to be made to and be answered by
delegation only zones. Such queries and responses are
treated as an exception to delegation-only processing
and are not converted to NXDOMAIN responses provided
a CNAME is not discovered at the query name.
</para>
<para>
If a delegation only zone server also serves a child
zone it is not always possible to determine whether
an answer comes from the delegation only zone or the
child zone. SOA NS and DNSKEY records are apex
only records and a matching response that contains
these records or DS is treated as coming from a
child zone. RRSIG records are also examined to see
if they are signed by a child zone or not. The
authority section is also examined to see if there
is evidence that the answer is from the child zone.
Answers that are determined to be from a child zone
are not converted to NXDOMAIN responses. Despite
all these checks there is still a possibility of
false negatives when a child zone is being served.
</para>
<para>
Similarly false positives can arise from empty nodes
(no records at the name) in the delegation only zone
when the query type is not ANY.
</para>
<para>
Note some TLDs are not delegation only (e.g. "DE", "LV",
"US" and "MUSEUM"). This list is not exhaustive.
</para>
<programlisting>
options {
root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term><command>disable-algorithms</command></term>
<listitem>
<para>
Disable the specified DNSSEC algorithms at and below the
specified name.
Multiple <command>disable-algorithms</command>
statements are allowed.
Only the best match <command>disable-algorithms</command>
clause will be used to determine which algorithms are used.
</para>
<para>
If all supported algorithms are disabled, the zones covered
by the <command>disable-algorithms</command> will be treated
as insecure.
</para>
<para>
Configured trust anchors in <command>dnssec-keys</command>
(or <command>managed-keys</command> or
<command>trusted-keys</command>, both deprecated)
that match a disabled algorithm will be ignored and treated
as if they were not configured at all.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>disable-ds-digests</command></term>
<listitem>
<para>
Disable the specified DS digest types at and below the
specified name.
Multiple <command>disable-ds-digests</command>
statements are allowed.
Only the best match <command>disable-ds-digests</command>
clause will be used to determine which digest types are used.
</para>
<para>
If all supported digest types are disabled, the zones covered
by the <command>disable-ds-digests</command> will be treated
as insecure.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-must-be-secure</command></term>
<listitem>
<para>
Specify hierarchies which must be or may not be secure
(signed and validated). If <userinput>yes</userinput>,
then <command>named</command> will only accept answers if
they are secure. If <userinput>no</userinput>, then normal
DNSSEC validation applies allowing for insecure answers to
be accepted. The specified domain must be defined as a
trust anchor, for instance in a <command>dnssec-keys</command>
statement, or <command>dnssec-validation auto</command> must
be active.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dns64</command></term>
<listitem>
<para>
This directive instructs <command>named</command> to
return mapped IPv4 addresses to AAAA queries when
there are no AAAA records. It is intended to be
used in conjunction with a NAT64. Each
<command>dns64</command> defines one DNS64 prefix.
Multiple DNS64 prefixes can be defined.
</para>
<para>
Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
64 and 96 as per RFC 6052. Bits 64..71 inclusive must
be zero with the most significate bit of the prefix in
position 0.
</para>
<para>
Additionally a reverse IP6.ARPA zone will be created for
the prefix to provide a mapping from the IP6.ARPA names
to the corresponding IN-ADDR.ARPA names using synthesized
CNAMEs. <command>dns64-server</command> and
<command>dns64-contact</command> can be used to specify
the name of the server and contact for the zones. These
are settable at the view / options level. These are
not settable on a per-prefix basis.
</para>
<para>
Each <command>dns64</command> supports an optional
<command>clients</command> ACL that determines which
clients are affected by this directive. If not defined,
it defaults to <userinput>any;</userinput>.
</para>
<para>
Each <command>dns64</command> supports an optional
<command>mapped</command> ACL that selects which
IPv4 addresses are to be mapped in the corresponding
A RRset. If not defined it defaults to
<userinput>any;</userinput>.
</para>
<para>
Normally, DNS64 won't apply to a domain name that
owns one or more AAAA records; these records will
simply be returned. The optional
<command>exclude</command> ACL allows specification
of a list of IPv6 addresses that will be ignored
if they appear in a domain name's AAAA records, and
DNS64 will be applied to any A records the domain
name owns. If not defined, <command>exclude</command>
defaults to ::ffff:0.0.0.0/96.
</para>
<para>
A optional <command>suffix</command> can also
be defined to set the bits trailing the mapped
IPv4 address bits. By default these bits are
set to <userinput>::</userinput>. The bits
matching the prefix and mapped IPv4 address
must be zero.
</para>
<para>
If <command>recursive-only</command> is set to
<command>yes</command> the DNS64 synthesis will
only happen for recursive queries. The default
is <command>no</command>.
</para>
<para>
If <command>break-dnssec</command> is set to
<command>yes</command> the DNS64 synthesis will
happen even if the result, if validated, would
cause a DNSSEC validation failure. If this option
is set to <command>no</command> (the default), the DO
is set on the incoming query, and there are RRSIGs on
the applicable records, then synthesis will not happen.
</para>
<programlisting>
acl rfc1918 { 10/8; 192.168/16; 172.16/12; };
dns64 64:FF9B::/96 {
clients { any; };
mapped { !rfc1918; any; };
exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
suffix ::;
};
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-loadkeys-interval</command></term>
<listitem>
<para>
When a zone is configured with <command>auto-dnssec
maintain;</command> its key repository must be checked
periodically to see if any new keys have been added
or any existing keys' timing metadata has been updated
(see <xref linkend="man.dnssec-keygen"/> and
<xref linkend="man.dnssec-settime"/>). The
<command>dnssec-loadkeys-interval</command> option
sets the frequency of automatic repository checks, in
minutes. The default is <literal>60</literal> (1 hour),
the minimum is <literal>1</literal> (1 minute), and the
maximum is <literal>1440</literal> (24 hours); any higher
value is silently reduced.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-update-mode</command></term>
<listitem>
<para>
If this option is set to its default value of
<literal>maintain</literal> in a zone of type
<literal>master</literal> which is DNSSEC-signed
and configured to allow dynamic updates (see
<xref linkend="dynamic_update_policies"/>), and
if <command>named</command> has access to the
private signing key(s) for the zone, then
<command>named</command> will automatically sign all new
or changed records and maintain signatures for the zone
by regenerating RRSIG records whenever they approach
their expiration date.
</para>
<para>
If the option is changed to <literal>no-resign</literal>,
then <command>named</command> will sign all new or
changed records, but scheduled maintenance of
signatures is disabled.
</para>
<para>
With either of these settings, <command>named</command>
will reject updates to a DNSSEC-signed zone when the
signing keys are inactive or unavailable to
<command>named</command>. (A planned third option,
<literal>external</literal>, will disable all automatic
signing and allow DNSSEC data to be submitted into a zone
via dynamic update; this is not yet implemented.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nta-lifetime</command></term>
<listitem>
<para>
Species the default lifetime, in seconds,
that will be used for negative trust anchors added
via <command>rndc nta</command>.
</para>
<para>
A negative trust anchor selectively disables
DNSSEC validation for zones that are known to be
failing because of misconfiguration rather than
an attack. When data to be validated is
at or below an active NTA (and above any other
configured trust anchors), <command>named</command> will
abort the DNSSEC validation process and treat the data as
insecure rather than bogus. This continues until the
NTA's lifetime is elapsed. NTAs persist
across <command>named</command> restarts.
</para>
<para>
For convenience, TTL-style time unit suffixes can be
used to specify the NTA lifetime in seconds, minutes
or hours. <option>nta-lifetime</option> defaults to
one hour. It cannot exceed one week.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nta-recheck</command></term>
<listitem>
<para>
Species how often to check whether negative
trust anchors added via <command>rndc nta</command>
are still necessary.
</para>
<para>
A negative trust anchor is normally used when a
domain has stopped validating due to operator error;
it temporarily disables DNSSEC validation for that
domain. In the interest of ensuring that DNSSEC
validation is turned back on as soon as possible,
<command>named</command> will periodically send a
query to the domain, ignoring negative trust anchors,
to find out whether it can now be validated. If so,
the negative trust anchor is allowed to expire early.
</para>
<para>
Validity checks can be disabled for an individual
NTA by using <command>rndc nta -f</command>, or
for all NTAs by setting <option>nta-recheck</option>
to zero.
</para>
<para>
For convenience, TTL-style time unit suffixes can be
used to specify the NTA recheck interval in seconds,
minutes or hours. The default is five minutes. It
cannot be longer than <option>nta-lifetime</option>
(which cannot be longer than a week).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-zone-ttl</command></term>
<listitem>
<para>
Specifies a maximum permissible TTL value in seconds.
For convenience, TTL-style time unit suffixes may be
used to specify the maximum value.
When loading a zone file using a
<option>masterfile-format</option> of
<constant>text</constant> or <constant>raw</constant>,
any record encountered with a TTL higher than
<option>max-zone-ttl</option> will cause the zone to
be rejected.
</para>
<para>
This is useful in DNSSEC-signed zones because when
rolling to a new DNSKEY, the old key needs to remain
available until RRSIG records have expired from
caches. The <option>max-zone-ttl</option> option guarantees
that the largest TTL in the zone will be no higher
than the set value.
</para>
<para>
(NOTE: Because <constant>map</constant>-format files
load directly into memory, this option cannot be
used with them.)
</para>
<para>
The default value is <constant>unlimited</constant>.
A <option>max-zone-ttl</option> of zero is treated as
<constant>unlimited</constant>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>stale-answer-ttl</command></term>
<listitem>
<para>
Specifies the TTL to be returned on stale answers.
The default is 1 second. The minimum allowed is
also 1 second; a value of 0 will be updated silently
to 1 second.
</para>
<para>
For stale answers to be returned, they must be enabled,
either in the configuration file using
<command>stale-answer-enable</command> or via
<command>rndc serve-stale on</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>serial-update-method</command></term>
<listitem>
<para>
Zones configured for dynamic DNS may use this
option to set the update method that will be used for
the zone serial number in the SOA record.
</para>
<para>
With the default setting of
<command>serial-update-method increment;</command>, the
SOA serial number will be incremented by one each time
the zone is updated.
</para>
<para>
When set to
<command>serial-update-method unixtime;</command>, the
SOA serial number will be set to the number of seconds
since the UNIX epoch, unless the serial number is
already greater than or equal to that value, in which
case it is simply incremented by one.
</para>
<para>
When set to
<command>serial-update-method date;</command>, the
new SOA serial number will be the current date
in the form "YYYYMMDD", followed by two zeroes,
unless the existing serial number is already greater
than or equal to that value, in which case it is
incremented by one.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zone-statistics</command></term>
<listitem>
<para>
If <userinput>full</userinput>, the server will collect
statistical data on all zones (unless specifically
turned off on a per-zone basis by specifying
<command>zone-statistics terse</command> or
<command>zone-statistics none</command>
in the <command>zone</command> statement).
These include, for example, DNSSEC signing operations
and the number of authoritative answers per query type.
The default is <userinput>terse</userinput>, providing
minimal statistics on zones (including name and
current serial number, but not query type
counters).
</para>
<para>
These statistics may be accessed via the
<command>statistics-channel</command> or
using <command>rndc stats</command>, which
will dump them to the file listed
in the <command>statistics-file</command>. See
also <xref linkend="statsfile"/>.
</para>
<para>
For backward compatibility with earlier versions
of BIND 9, the <command>zone-statistics</command>
option can also accept <userinput>yes</userinput>
or <userinput>no</userinput>; <userinput>yes</userinput>
has the same meaning as <userinput>full</userinput>.
As of <acronym>BIND</acronym> 9.10,
<userinput>no</userinput> has the same meaning
as <userinput>none</userinput>; previously, it
was the same as <userinput>terse</userinput>.
</para>
</listitem>
</varlistentry>
</variablelist>
<section xml:id="boolean_options"><info><title>Boolean Options</title></info>
<variablelist>
<varlistentry>
<term><command>automatic-interface-scan</command></term>
<listitem>
<para>
If <userinput>yes</userinput> and supported by the OS,
automatically rescan network interfaces when the interface
addresses are added or removed. The default is
<userinput>yes</userinput>.
</para>
<para>
Currently the OS needs to support routing sockets for
<command>automatic-interface-scan</command> to be
supported.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-new-zones</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then zones can be
added at runtime via <command>rndc addzone</command>.
The default is <userinput>no</userinput>.
</para>
<para>
Newly added zones' configuration parameters
are stored so that they can persist after the
server is restarted. The configuration information
is saved in a file called
<filename><replaceable>viewname</replaceable>.nzf</filename>
(or, if <command>named</command> is compiled with
liblmdb, in an LMDB database file called
<filename><replaceable>viewname</replaceable>.nzd</filename>).
<replaceable>viewname</replaceable> is the name of the
view, unless the view name contains characters that are
incompatible with use as a file name, in which case a
cryptographic hash of the view name is used instead.
</para>
<para>
Zones added at runtime will have their configuration
stored either in a new-zone file (NZF) or a new-zone
database (NZD) depending on whether
<command>named</command> was linked with
liblmdb at compile time.
See <xref linkend="man.rndc"/> for further details
about <command>rndc addzone</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>auth-nxdomain</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then the
<command>AA</command> bit is always set on NXDOMAIN
responses, even if the server is not actually
authoritative. The default is <userinput>no</userinput>.
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>memstatistics</command></term>
<listitem>
<para>
Write memory statistics to the file specified by
<command>memstatistics-file</command> at exit.
The default is <userinput>no</userinput> unless
'-m record' is specified on the command line in
which case it is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dialup</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then the
server treats all zones as if they are doing zone transfers
across
a dial-on-demand dialup link, which can be brought up by
traffic
originating from this server. 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 (default). This should 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.
The set of servers to which NOTIFY is sent can be controlled
by
<command>notify</command> and <command>also-notify</command>.
</para>
<para>
If the
zone is a 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 sends refresh
queries
when the <command>heartbeat-interval</command>
expires, and
<userinput>passive</userinput> which just disables normal
refresh
processing.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="4" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="1.150in"/>
<colspec colname="4" colnum="4" colsep="0" colwidth="1.150in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
dialup mode
</para>
</entry>
<entry colname="2">
<para>
normal refresh
</para>
</entry>
<entry colname="3">
<para>
heart-beat refresh
</para>
</entry>
<entry colname="4">
<para>
heart-beat notify
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>no</command> (default)</para>
</entry>
<entry colname="2">
<para>
yes
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>yes</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
yes
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>notify</command></para>
</entry>
<entry colname="2">
<para>
yes
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>refresh</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
yes
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>passive</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>notify-passive</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
Note that normal NOTIFY processing is not affected by
<command>dialup</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>flush-zones-on-shutdown</command></term>
<listitem>
<para>
When the nameserver exits due receiving SIGTERM,
flush or do not flush any pending zone writes. The default
is
<command>flush-zones-on-shutdown</command> <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>geoip-use-ecs</command></term>
<listitem>
<para>
This option was part of an experimental implementation
of the EDNS CLIENT-SUBNET for authoritative servers,
but is now obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>root-key-sentinel</command></term>
<listitem>
<para>
Respond to root key sentinel probes as described in
draft-ietf-dnsop-kskroll-sentinel-08. The default is
<userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>message-compression</command></term> <listitem>
<para>
If <userinput>yes</userinput>, DNS name compression is
used in responses to regular queries (not including
AXFR or IXFR, which always uses compression). Setting
this option to <userinput>no</userinput> reduces CPU
usage on servers and may improve throughput. However,
it increases response size, which may cause more queries
to be processed using TCP; a server with compression
disabled is out of compliance with RFC 1123 Section
6.1.3.2. The default is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>minimal-responses</command></term>
<listitem>
<para>
This option controls the addition of records to the
authority and additional sections of responses. Such
records may be included in responses to be helpful
to clients; for example, NS or MX records may
have associated address records included in the additional
section, obviating the need for a separate address lookup.
However, adding these records to responses is not mandatory
and requires additional database lookups, causing extra
latency when marshalling responses.
<command>minimal-responses</command> takes one of
four values:
</para>
<itemizedlist>
<listitem>
<userinput>no</userinput>: the server will be
as complete as possible when generating responses.
</listitem>
<listitem>
<userinput>yes</userinput>: the server will only add
records to the authority and additional sections when
such records are required by the DNS protocol (for
example, when returning delegations or negative
responses). This provides the best server performance
but may result in more client queries.
</listitem>
<listitem>
<userinput>no-auth</userinput>: the server
will omit records from the authority section except
when they are required, but it may still add records
to the additional section.
</listitem>
<listitem>
<userinput>no-auth-recursive</userinput>: the same
as <userinput>no-auth</userinput> when recursion is
requested in the query (RD=1), or the same as
<userinput>no</userinput> if recursion is not
requested.
</listitem>
</itemizedlist>
<para>
<userinput>no-auth</userinput> and
<userinput>no-auth-recursive</userinput> are useful when
answering stub clients, which usually ignore the
authority section. <userinput>no-auth-recursive</userinput>
is meant for use in mixed-mode servers that handle both
authoritative and recursive queries.
</para>
<para>
The default is <userinput>no-auth-recursive</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>glue-cache</command></term>
<listitem>
<para>
When set to <userinput>yes</userinput>, a cache is
used to improve query performance when adding
address-type (A and AAAA) glue records to the
additional section of DNS response messages that
delegate to a child zone.
</para>
<para>
The glue cache uses memory proportional to the number
of delegations in the zone. The default setting is
<userinput>yes</userinput>, which improves performance
at the cost of increased memory usage for the zone. If
you don't want this, set it to <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>minimal-any</command></term>
<listitem>
<para>
If set to <userinput>yes</userinput>, then when
generating a positive response to a query of type
ANY over UDP, the server will reply with only one
of the RRsets for the query name, and its covering
RRSIGs if any, instead of replying with all known
RRsets for the name. Similarly, a query for type
RRSIG will be answered with the RRSIG records covering
only one type. This can reduce the impact of some kinds
of attack traffic, without harming legitimate
clients. (Note, however, that the RRset returned is the
first one found in the database; it is not necessarily
the smallest available RRset.)
Additionally, <option>minimal-responses</option> is
turned on for these queries, so no unnecessary records
will be added to the authority or additional sections.
The default is <userinput>no</userinput>.
</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>master-only</userinput>, notifies are only
sent
for master zones.
If <userinput>explicit</userinput>, notifies are sent only
to
servers explicitly listed using <command>also-notify</command>.
If <userinput>no</userinput>, no notifies are sent.
</para>
<para>
The <command>notify</command> option may also be
specified in the <command>zone</command>
statement,
in which case it overrides the <command>options notify</command> statement.
It would only be necessary to turn off this option if it
caused slaves
to crash.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-to-soa</command></term>
<listitem>
<para>
If <userinput>yes</userinput> do not check the nameservers
in the NS RRset against the SOA MNAME. Normally a NOTIFY
message is not sent to the SOA MNAME (SOA ORIGIN) as it is
supposed to contain the name of the ultimate master.
Sometimes, however, a slave is listed as the SOA MNAME in
hidden master configurations and in that case you would
want the ultimate master to still send NOTIFY messages to
all the nameservers listed in the NS RRset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursion</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, and a
DNS query requests recursion, then the server 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>request-nsid</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then an empty EDNS(0)
NSID (Name Server Identifier) option is sent with all
queries to authoritative name servers during iterative
resolution. If the authoritative server returns an NSID
option in its response, then its contents are logged in
the <command>nsid</command> category at level
<command>info</command>.
The default is <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>request-sit</command></term>
<listitem>
<para>
This experimental option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>require-server-cookie</command></term>
<listitem>
<para>
Require a valid server cookie before sending a full
response to a UDP request from a cookie aware client.
BADCOOKIE is sent if there is a bad or no existent
server cookie.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>answer-cookie</command></term>
<listitem>
<para>
When set to the default value of <userinput>yes</userinput>,
COOKIE EDNS options will be sent when applicable in
replies to client queries. If set to
<userinput>no</userinput>, COOKIE EDNS options will not
be sent in replies. This can only be set at the global
options level, not per-view.
</para>
<para>
<command>answer-cookie no</command> is intended as a
temporary measure, for use when <command>named</command>
shares an IP address with other servers that do not yet
support DNS COOKIE. A mismatch between servers on the same
address is not expected to cause operational problems, but
the option to disable COOKIE responses so that all servers
have the same behavior is provided out of an abundance of
caution. DNS COOKIE is an important security mechanism,
and should not be disabled unless absolutely necessary.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>send-cookie</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then a COOKIE EDNS
option is sent along with the query. If the
resolver has previously talked to the server, the
COOKIE returned in the previous transaction is sent.
This is used by the server to determine whether
the resolver has talked to it before. A resolver
sending the correct COOKIE is assumed not to be an
off-path attacker sending a spoofed-source query;
the query is therefore unlikely to be part of a
reflection/amplification attack, so resolvers
sending a correct COOKIE option are not subject to
response rate limiting (RRL). Resolvers which
do not send a correct COOKIE option may be limited
to receiving smaller responses via the
<command>nocookie-udp-size</command> option.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>stale-answer-enable</command></term>
<listitem>
<para>
Enable the returning of "stale" cached answers when
the nameservers for a zone are not answering. The
default is not to return stale answers.
</para>
<para>
Stale answers can also be enabled or disabled at
runtime via <command>rndc serve-stale on</command> or
<command>rndc serve-stale off</command>; these
override the configured setting.
<command>rndc serve-stale reset</command>
restores the setting to the one specified in
<filename>named.conf</filename>. Note that if
stale answers have been disabled by <command>rndc</command>,
then they cannot be re-enabled by reloading or
reconfiguring <command>named</command>;
they must be re-enabled with
<command>rndc serve-stale on</command>,
or the server must be restarted.
</para>
<para>
Information about stale answers is logged under
the <command>serve-stale</command> log category.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nocookie-udp-size</command></term>
<listitem>
<para>
Sets the maximum size of UDP responses that will be
sent to queries without a valid server COOKIE. A value
below 128 will be silently raised to 128. The default
value is 4096, but the <command>max-udp-size</command>
option may further limit the response size.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sit-secret</command></term>
<listitem>
<para>
This experimental option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>cookie-algorithm</command></term>
<listitem>
<para>
Set the algorithm to be used when generating the
server cookie. One of "aes", "sha1" or "sha256".
The default is "aes" if supported by the cryptographic
library or otherwise "sha256".
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>cookie-secret</command></term>
<listitem>
<para>
If set, this is a shared secret used for generating
and verifying EDNS COOKIE options
within an anycast cluster. If not set, the system
will generate a random secret at startup. The
shared secret is encoded as a hex string and needs
to be 128 bits for AES128, 160 bits for SHA1 and
256 bits for SHA256.
</para>
<para>
If there are multiple secrets specified, the first
one listed in <filename>named.conf</filename> is
used to generate new server cookies. The others
will only be used to verify returned cookies.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>response-padding</command></term>
<listitem>
<para>
The EDNS Padding option is intended to improve
confidentiality when DNS queries are sent over an
encrypted channel by reducing the variability in
packet sizes. If a query:
<orderedlist inheritnum="ignore" continuation="restarts">
<listitem>
contains an EDNS Padding option,
</listitem>
<listitem>
includes a valid server cookie or uses TCP,
</listitem>
<listitem>
is <emphasis>not</emphasis> signed using TSIG or
SIG(0), and
</listitem>
<listitem>
is from a client whose address matches the specified ACL,
</listitem>
</orderedlist>
then the response is padded with an EDNS Padding option
to a multiple of <varname>block-size</varname> bytes.
If these conditions are not met, the response is not
padded.
</para>
<para>
If <varname>block-size</varname> is 0 or the ACL is
<command>none;</command>, then this feature is
disabled and no padding will occur; this is the
default. If <varname>block-size</varname> is greater
than 512, a warning is logged and the value is truncated
to 512. Block sizes are ordinarily expected to be powers
of two (for instance, 128), but this is not mandatory.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>trust-anchor-telemetry</command></term>
<listitem>
<para>
Causes <command>named</command> to send specially-formed
queries once per day to domains for which trust anchors
have been configured via, e.g.,
<command>dnssec-keys</command> or
<command>dnssec-validation auto</command>.
</para>
<para>
The query name used for these queries has the
form "_ta-xxxx(-xxxx)(...)".&lt;domain&gt;, where
each "xxxx" is a group of four hexadecimal digits
representing the key ID of a trusted DNSSEC key.
The key IDs for each domain are sorted smallest
to largest prior to encoding. The query type is NULL.
</para>
<para>
By monitoring these queries, zone operators will
be able to see which resolvers have been updated to
trust a new key; this may help them decide when it
is safe to remove an old one.
</para>
<para>
The default is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-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>provide-ixfr</command></term>
<listitem>
<para>
See the description of
<command>provide-ixfr</command> in
<xref linkend="server_statement_definition_and_usage"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>request-ixfr</command></term>
<listitem>
<para>
See the description of
<command>request-ixfr</command> in
<xref linkend="server_statement_definition_and_usage"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>request-expire</command></term>
<listitem>
<para>
See the description of
<command>request-expire</command> in
<xref linkend="server_statement_definition_and_usage"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>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.
</para>
<para>
This option was introduced to work around a kernel quirk
in some operating systems that causes IPv4 TCP
connections, such as zone transfers, to be accepted on an
IPv6 socket using mapped addresses. This caused address
match lists designed for IPv4 to fail to match. However,
<command>named</command> now solves this problem
internally. The use of this option is discouraged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ixfr-from-differences</command></term>
<listitem>
<para>
When <userinput>yes</userinput> and the server loads a new
version of a master zone from its zone file or receives a
new version of a slave file via 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>
<para><command>ixfr-from-differences</command>
also accepts <command>master</command> (or
<command>primary</command>) and
<command>slave</command> (or <command>secondary</command>)
at the view and options levels, which causes
<command>ixfr-from-differences</command> to be enabled for
all primary or secondary zones, respectively.
It is off for all zones by default.
</para>
<para>
Note: if inline signing is enabled for a zone, the
user-provided <command>ixfr-from-differences</command>
setting is ignored for that zone.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>multi-master</command></term>
<listitem>
<para>
This should be set when you have multiple masters for a zone
and the
addresses refer to different machines. If <userinput>yes</userinput>, <command>named</command> will
not log
when the serial number on the master is less than what <command>named</command>
currently
has. The default is <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>auto-dnssec</command></term>
<listitem>
<para>
Zones configured for dynamic DNS may use this
option to allow varying levels of automatic DNSSEC key
management. There are three possible settings:
</para>
<para>
<command>auto-dnssec allow;</command> permits
keys to be updated and the zone fully re-signed
whenever the user issues the command <command>rndc sign
<replaceable>zonename</replaceable></command>.
</para>
<para>
<command>auto-dnssec maintain;</command> includes the
above, but also automatically adjusts the zone's DNSSEC
keys on schedule, according to the keys' timing metadata
(see <xref linkend="man.dnssec-keygen"/> and
<xref linkend="man.dnssec-settime"/>). The command
<command>rndc sign
<replaceable>zonename</replaceable></command> causes
<command>named</command> to load keys from the key
repository and sign the zone with all keys that are
active.
<command>rndc loadkeys
<replaceable>zonename</replaceable></command> causes
<command>named</command> to load keys from the key
repository and schedule key maintenance events to occur
in the future, but it does not sign the full zone
immediately. Note: once keys have been loaded for a
zone the first time, the repository will be searched
for changes periodically, regardless of whether
<command>rndc loadkeys</command> is used. The recheck
interval is defined by
<command>dnssec-loadkeys-interval</command>.)
</para>
<para>
The default setting is <command>auto-dnssec off</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-enable</command></term>
<listitem>
<para>
This option is obsolete and has no effect.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="dnssec_validation">
<term xml:id="dnssec_validation_term"><command>dnssec-validation</command></term>
<listitem>
<para>
This option enables DNSSEC validation in
<command>named</command>.
</para>
<para>
If set to <userinput>auto</userinput>,
DNSSEC validation is enabled, and a default trust anchor
for the DNS root zone is used.
</para>
<para>
If set to <userinput>yes</userinput>, DNSSEC validation is
enabled, but a trust anchor must be manually configured
using a <command>dnssec-keys</command> statement (or
the <command>managed-keys</command> or the
<command>trusted-keys</command> statements, both deprecated).
If there is no configured trust anchor, validation will
not take place.
</para>
<para>
If set to <userinput>no</userinput>, DNSSEC validation
is disabled.
</para>
<para>
The default is <userinput>auto</userinput>, unless
BIND is built with
<command>configure --disable-auto-validation</command>,
in which case the default is <userinput>yes</userinput>.
</para>
<para>
The default root trust anchor is stored in the file
<filename>bind.keys</filename>.
<command>named</command> will load that key at
startup if <command>dnssec-validation</command> is
set to <userinput>auto</userinput>. A copy of the file is
installed along with BIND 9, and is current as of the
release date. If the root key expires, a new copy of
<filename>bind.keys</filename> can be downloaded
from <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.isc.org/bind-keys">https://www.isc.org/bind-keys</link>.
</para>
<para>
(To prevent problems if <filename>bind.keys</filename> is
not found, the current trust anchor is also compiled in
to <command>named</command>. Relying on this is not
recommended, however, as it requires <command>named</command>
to be recompiled with a new key when the root key expires.)
</para>
<note>
<para>
<command>named</command> loads <emphasis>only</emphasis>
the root key from <filename>bind.keys</filename>.
The file cannot be used to store keys for other zones.
The root key in <filename>bind.keys</filename> is ignored
if <command>dnssec-validation auto</command> is not in
use.
</para>
<para>
Whenever the resolver sends out queries to an
EDNS-compliant server, it always sets the DO bit
indicating it can support DNSSEC responses even if
<command>dnssec-validation</command> is off.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>validate-except</command></term>
<listitem>
<para>
Specifies a list of domain names at and beneath which DNSSEC
validation should <emphasis>not</emphasis> be performed,
regardless of the presence of a trust anchor at or above
those names. This may be used, for example, when configuring
a top-level domain intended only for local use, so that the
lack of a secure delegation for that domain in the root zone
will not cause validation failures. (This is similar
to setting a negative trust anchor, except that it is a
permanent configuration, whereas negative trust anchors
expire and are removed after a set period of time.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-accept-expired</command></term>
<listitem>
<para>
Accept expired signatures when verifying DNSSEC signatures.
The default is <userinput>no</userinput>.
Setting this option to <userinput>yes</userinput>
leaves <command>named</command> vulnerable to
replay attacks.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>querylog</command></term>
<listitem>
<para>
Specify whether query logging should be started when <command>named</command>
starts.
If <command>querylog</command> is not specified,
then the query logging
is determined by the presence of the logging category <command>queries</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-names</command></term>
<listitem>
<para>
This option is used to restrict the character set and syntax
of
certain domain names in master files and/or DNS responses
received
from the network. The default varies according to usage
area. For
<command>master</command> zones the default is <command>fail</command>.
For <command>slave</command> zones the default
is <command>warn</command>.
For answers received from the network (<command>response</command>)
the default is <command>ignore</command>.
</para>
<para>
The rules for legal hostnames and mail domains are derived
from RFC 952 and RFC 821 as modified by RFC 1123.
</para>
<para><command>check-names</command>
applies to the owner names of A, AAAA and MX records.
It also applies to the domain names in the RDATA of NS, SOA,
MX, and SRV records.
It also applies to the RDATA of PTR records where the owner
name indicated that it is a reverse lookup of a hostname
(the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-dup-records</command></term>
<listitem>
<para>
Check master zones for records that are treated as different
by DNSSEC but are semantically equal in plain DNS. The
default is to <command>warn</command>. Other possible
values are <command>fail</command> and
<command>ignore</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx</command></term>
<listitem>
<para>
Check whether the MX record appears to refer to a IP address.
The default is to <command>warn</command>. Other possible
values are <command>fail</command> and
<command>ignore</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-wildcard</command></term>
<listitem>
<para>
This option is used to check for non-terminal wildcards.
The use of non-terminal wildcards is almost always as a
result of a failure
to understand the wildcard matching algorithm (RFC 1034).
This option
affects master zones. The default (<command>yes</command>) is to check
for non-terminal wildcards and issue a warning.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-integrity</command></term>
<listitem>
<para>
Perform post load zone integrity checks on master
zones. This checks that MX and SRV records refer
to address (A or AAAA) records and that glue
address records exist for delegated zones. For
MX and SRV records only in-zone hostnames are
checked (for out-of-zone hostnames use
<command>named-checkzone</command>).
For NS records only names below top of zone are
checked (for out-of-zone names and glue consistency
checks use <command>named-checkzone</command>).
The default is <command>yes</command>.
</para>
<para>
The use of the SPF record for publishing Sender
Policy Framework is deprecated as the migration
from using TXT records to SPF records was abandoned.
Enabling this option also checks that a TXT Sender
Policy Framework record exists (starts with "v=spf1")
if there is an SPF record. Warnings are emitted if the
TXT record does not exist and can be suppressed with
<command>check-spf</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx-cname</command></term>
<listitem>
<para>
If <command>check-integrity</command> is set then
fail, warn or ignore MX records that refer
to CNAMES. The default is to <command>warn</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-srv-cname</command></term>
<listitem>
<para>
If <command>check-integrity</command> is set then
fail, warn or ignore SRV records that refer
to CNAMES. The default is to <command>warn</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-sibling</command></term>
<listitem>
<para>
When performing integrity checks, also check that
sibling glue exists. The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-spf</command></term>
<listitem>
<para>
If <command>check-integrity</command> is set then
check that there is a TXT Sender Policy Framework
record present (starts with "v=spf1") if there is an
SPF record present. The default is
<command>warn</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl</command></term>
<listitem>
<para>
When returning authoritative negative responses to
SOA queries set the TTL of the SOA record returned in
the authority section to zero.
The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl-cache</command></term>
<listitem>
<para>
When caching a negative response to a SOA query
set the TTL to zero.
The default is <command>no</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-check-ksk</command></term>
<listitem>
<para>
When set to the default value of <literal>yes</literal>,
check the KSK bit in each key to determine how the key
should be used when generating RRSIGs for a secure zone.
</para>
<para>
Ordinarily, zone-signing keys (that is, keys without the
KSK bit set) are used to sign the entire zone, while
key-signing keys (keys with the KSK bit set) are only
used to sign the DNSKEY RRset at the zone apex.
However, if this option is set to <literal>no</literal>,
then the KSK bit is ignored; KSKs are treated as if they
were ZSKs and are used to sign the entire zone. This is
similar to the <command>dnssec-signzone -z</command>
command line option.
</para>
<para>
When this option is set to <literal>yes</literal>, there
must be at least two active keys for every algorithm
represented in the DNSKEY RRset: at least one KSK and one
ZSK per algorithm. If there is any algorithm for which
this requirement is not met, this option will be ignored
for that algorithm.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-dnskey-kskonly</command></term>
<listitem>
<para>
When this option and <command>update-check-ksk</command>
are both set to <literal>yes</literal>, only key-signing
keys (that is, keys with the KSK bit set) will be used
to sign the DNSKEY, CDNSKEY, and CDS RRsets at the zone apex.
Zone-signing keys (keys without the KSK bit set) will be used
to sign the remainder of the zone, but not the DNSKEY RRset.
This is similar to the
<command>dnssec-signzone -x</command> command line option.
</para>
<para>
The default is <command>no</command>. If
<command>update-check-ksk</command> is set to
<literal>no</literal>, this option is ignored.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>try-tcp-refresh</command></term>
<listitem>
<para>
Try to refresh the zone using TCP if UDP queries fail.
The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-secure-to-insecure</command></term>
<listitem>
<para>
Allow a dynamic zone to transition from secure to
insecure (i.e., signed to unsigned) by deleting all
of the DNSKEY records. The default is <command>no</command>.
If set to <command>yes</command>, and if the DNSKEY RRset
at the zone apex is deleted, all RRSIG and NSEC records
will be removed from the zone as well.
</para>
<para>
If the zone uses NSEC3, then it is also necessary to
delete the NSEC3PARAM RRset from the zone apex; this will
cause the removal of all corresponding NSEC3 records.
(It is expected that this requirement will be eliminated
in a future release.)
</para>
<para>
Note that if a zone has been configured with
<command>auto-dnssec maintain</command> and the
private keys remain accessible in the key repository,
then the zone will be automatically signed again the
next time <command>named</command> is started.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>synth-from-dnssec</command></term>
<listitem>
<para>
Synthesize answers from cached NSEC, NSEC3 and
other RRsets that have been proved to be correct
using DNSSEC. The default is <command>yes</command>.
</para>
<para>
Note:
<itemizedlist>
<listitem>
<para>
DNSSEC validation must be enabled for this
option to be effective.
</para>
<para>
This initial implementation only covers synthesis
of answers from NSEC records. Synthesis from NSEC3
is planned for the future. This will also be
controlled by <command>synth-from-dnssec</command>.
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="forwarding"><info><title>Forwarding</title></info>
<para>
The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
name servers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up
exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.
</para>
<variablelist>
<varlistentry>
<term><command>forward</command></term>
<listitem>
<para>
This option is only meaningful if the
forwarders list is not empty. A value of <varname>first</varname>,
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>
</section>
<section xml:id="dual_stack"><info><title>Dual-stack Servers</title></info>
<para>
Dual-stack servers are used as servers of last resort to work
around
problems in reachability due the lack of support for either IPv4
or IPv6
on the host machine.
</para>
<variablelist>
<varlistentry>
<term><command>dual-stack-servers</command></term>
<listitem>
<para>
Specifies host names or addresses of machines with access to
both IPv4 and IPv6 transports. If a hostname is used, the
server must be able
to resolve the name using only the transport it has. If the
machine is dual
stacked, then the <command>dual-stack-servers</command> have no effect unless
access to a transport has been disabled on the command line
(e.g. <command>named -4</command>).
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="access_control"><info><title>Access Control</title></info>
<para>
Access to the server can be restricted based on the IP address
of the requesting system. See <xref linkend="address_match_lists"/> for
details on how to specify IP address lists.
</para>
<variablelist>
<varlistentry>
<term><command>allow-notify</command></term>
<listitem>
<para>
This ACL specifies which hosts may send NOTIFY messages
to inform this server of changes to zones for which it
is acting as a secondary server. This is only
applicable for secondary zones (i.e., type
<literal>secondary</literal> or <literal>slave</literal>).
</para>
<para>
If this option is set in <command>view</command> or
<command>options</command>, it is globally applied to
all secondary zones. If set in the <command>zone</command>
statement, the global value is overridden.
</para>
<para>
If not specified, the default is to process NOTIFY
messages only from the configured
<command>masters</command> for the zone.
<command>allow-notify</command> can be used to expand the
list of permitted hosts, not to reduce it.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query</command></term>
<listitem>
<para>
Specifies which hosts are allowed to ask ordinary
DNS questions. <command>allow-query</command> may
also be specified in the <command>zone</command>
statement, in which case it overrides the
<command>options allow-query</command> statement.
If not specified, the default is to allow queries
from all hosts.
</para>
<note>
<para>
<command>allow-query-cache</command> is now
used to specify access to the cache.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-on</command></term>
<listitem>
<para>
Specifies which local addresses can accept ordinary
DNS questions. This makes it possible, for instance,
to allow queries on internal-facing interfaces but
disallow them on external-facing ones, without
necessarily knowing the internal network's addresses.
</para>
<para>
Note that <command>allow-query-on</command> is only
checked for queries that are permitted by
<command>allow-query</command>. A query must be
allowed by both ACLs, or it will be refused.
</para>
<para>
<command>allow-query-on</command> may
also be specified in the <command>zone</command>
statement, in which case it overrides the
<command>options allow-query-on</command> statement.
</para>
<para>
If not specified, the default is to allow queries
on all addresses.
</para>
<note>
<para>
<command>allow-query-cache</command> is
used to specify access to the cache.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-cache</command></term>
<listitem>
<para>
Specifies which hosts are allowed to get answers
from the cache. If <command>allow-query-cache</command>
is not set then <command>allow-recursion</command>
is used if set, otherwise <command>allow-query</command>
is used if set unless <command>recursion no;</command> is
set in which case <command>none;</command> is used,
otherwise the default (<command>localnets;</command>
<command>localhost;</command>) is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-cache-on</command></term>
<listitem>
<para>
Specifies which local addresses can send answers
from the cache. If <command>allow-query-cache-on</command>
is not set, then <command>allow-recursion-on</command> is
used if set. Otherwise, the default is
to allow cache responses to be sent from any address.
Note: Both <command>allow-query-cache</command> and
<command>allow-query-cache-on</command> must be
satisfied before a cache response can be sent;
a client that is blocked by one cannot be allowed
by the other.
</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
<command>allow-recursion</command> is not set
then <command>allow-query-cache</command> is
used if set, otherwise <command>allow-query</command>
is used if set, otherwise the default
(<command>localnets;</command>
<command>localhost;</command>) is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-recursion-on</command></term>
<listitem>
<para>
Specifies which local addresses can accept recursive
queries. If <command>allow-recursion-on</command>
is not set, then <command>allow-query-cache-on</command>
is used if set; otherwise, the default is to allow
recursive queries on all addresses: Any client permitted
to send recursive queries can send them to any address
on which <command>named</command> is listening.
Note: Both <command>allow-recursion</command> and
<command>allow-recursion-on</command> must be
satisfied before recursion is allowed;
a client that is blocked by one cannot be allowed
by the other.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update</command></term>
<listitem>
<para>
When set in the <command>zone</command> statement for
a master zone, specifies which hosts are allowed to
submit Dynamic DNS updates to that zone. The default
is to deny updates from all hosts.
</para>
<para>
Note that allowing updates based on the
requestor's IP address is insecure; see
<xref linkend="dynamic_update_security"/> for details.
</para>
<para>
In general this option should only be set at the
<command>zone</command> level. While a default
value can be set at the <command>options</command> or
<command>view</command> level and inherited by zones,
this could lead to some zones unintentionally allowing
updates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update-forwarding</command></term>
<listitem>
<para>
When set in the <command>zone</command> statement for
a slave zone, specifies which hosts are allowed to
submit Dynamic DNS updates and have them be forwarded
to the master. The default is
<userinput>{ none; }</userinput>, which means that no
update forwarding will be performed.
</para>
<para>
To enable update forwarding, specify
<userinput>allow-update-forwarding { any; };</userinput>.
in the <command>zone</command> statement.
Specifying values other than <userinput>{ none; }</userinput>
or <userinput>{ any; }</userinput> is usually
counterproductive; the responsibility for update
access control should rest with the master server, not
the slave.
</para>
<para>
Note that enabling the update forwarding feature on a slave
server may expose master servers to attacks if they rely
on insecure IP-address-based access control; see
<xref linkend="dynamic_update_security"/> for more details.
</para>
<para>
In general this option should only be set at the
<command>zone</command> level. While a default
value can be set at the <command>options</command> or
<command>view</command> level and inherited by zones,
this can lead to some zones unintentionally forwarding
updates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-v6-synthesis</command></term>
<listitem>
<para>
This option was introduced for the smooth transition from
AAAA
to A6 and from "nibble labels" to binary labels.
However, since both A6 and binary labels were then
deprecated,
this option was also deprecated.
It is now ignored with some warning messages.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="allow_transfer">
<term xml:id="allow_transfer_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>allow-transfer</command> statement set in
<command>options</command> or <command>view</command>.
If not specified, the default is to allow transfers to
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>
<varlistentry>
<term><command>keep-response-order</command></term>
<listitem>
<para>
Specifies a list of addresses to which the server
will send responses to TCP queries in the same order
in which they were received. This disables the
processing of TCP queries in parallel. The default
is <userinput>none</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>no-case-compress</command></term> <listitem>
<para>
Specifies a list of addresses which require responses
to use case-insensitive compression. This ACL can be
used when <command>named</command> needs to work with
clients that do not comply with the requirement in RFC
1034 to use case-insensitive name comparisons when
checking for matching domain names.
</para>
<para>
If left undefined, the ACL defaults to
<command>none</command>: case-insensitive compression
will be used for all clients. If the ACL is defined and
matches a client, then case will be ignored when
compressing domain names in DNS responses sent to that
client.
</para>
<para>
This can result in slightly smaller responses: if
a response contains the names "example.com" and
"example.COM", case-insensitive compression would treat
the second one as a duplicate. It also ensures
that the case of the query name exactly matches the
case of the owner names of returned records, rather
than matching the case of the records entered in
the zone file. This allows responses to exactly
match the query, which is required by some clients
due to incorrect use of case-sensitive comparisons.
</para>
<para>
Case-insensitive compression is <emphasis>always</emphasis>
used in AXFR and IXFR responses, regardless of whether
the client matches this ACL.
</para>
<para>
There are circumstances in which <command>named</command>
will not preserve the case of owner names of records:
if a zone file defines records of different types with
the same name, but the capitalization of the name is
different (e.g., "www.example.com/A" and
"WWW.EXAMPLE.COM/AAAA"), then all responses for that
name will use the <emphasis>first</emphasis> version
of the name that was used in the zone file. This
limitation may be addressed in a future release. However,
domain names specified in the rdata of resource records
(i.e., records of type NS, MX, CNAME, etc) will always
have their case preserved unless the client matches this
ACL.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>resolver-query-timeout</command></term>
<listitem>
<para>
The amount of time in milliseconds that the resolver
will spend attempting to resolve a recursive
query before failing. The default and minimum
is <literal>10000</literal> and the maximum is
<literal>30000</literal>. Setting it to
<literal>0</literal> will result in the default
being used.
</para>
<para>
This value was originally specified in seconds.
Values less than or equal to 300 will be be treated
as seconds and converted to milliseconds before
applying the above limits.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="interfaces"><info><title>Interfaces</title></info>
<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>
of IPv4 addresses. (IPv6 addresses are ignored, with a
logged warning.)
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 name server on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.
</para>
<para>
If no <command>listen-on</command> is specified, the
server will listen on port 53 on all IPv4 interfaces.
</para>
<para>
The <command>listen-on-v6</command> option is used to
specify the interfaces and the ports on which the server will
listen for incoming queries sent using IPv6. If not specified,
the server will listen on port 53 on all IPv6 interfaces.
</para>
<para>
When <programlisting>{ any; }</programlisting> is
specified
as the <varname>address_match_list</varname> for the
<command>listen-on-v6</command> option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC
3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.
</para>
<para>
A list of particular IPv6 addresses can also be specified, in
which case
the server listens on a separate socket for each specified
address,
regardless of whether the desired API is supported by the system.
IPv4 addresses specified in <command>listen-on-v6</command>
will be ignored, with a logged warning.
</para>
<para>
Multiple <command>listen-on-v6</command> options can
be used.
For example,
</para>
<programlisting>listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</programlisting>
<para>
will enable the name server on port 53 for any IPv6 addresses
(with a single wildcard socket),
and on port 1234 of IPv6 addresses that is not in the prefix
2001:db8::/32 (with separate sockets for each matched address.)
</para>
<para>
To make the server not listen on any IPv6 address, use
</para>
<programlisting>listen-on-v6 { none; };
</programlisting>
</section>
<section xml:id="query_address"><info><title>Query Address</title></info>
<para>
If the server doesn't know the answer to a question, it will
query other name servers. <command>query-source</command> specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate <command>query-source-v6</command> option.
If <command>address</command> is <command>*</command> (asterisk) or is omitted,
a wildcard IP address (<command>INADDR_ANY</command>)
will be used.
</para>
<para>
If <command>port</command> is <command>*</command> or is omitted,
a random port number from a pre-configured
range is picked up and will be used for each query.
The port range(s) is that specified in
the <command>use-v4-udp-ports</command> (for IPv4)
and <command>use-v6-udp-ports</command> (for IPv6)
options, excluding the ranges specified in
the <command>avoid-v4-udp-ports</command>
and <command>avoid-v6-udp-ports</command> options, respectively.
</para>
<para>
The defaults of the <command>query-source</command> and
<command>query-source-v6</command> options
are:
</para>
<programlisting>query-source address * port *;
query-source-v6 address * port *;
</programlisting>
<para>
If <command>use-v4-udp-ports</command> or
<command>use-v6-udp-ports</command> is unspecified,
<command>named</command> will check if the operating
system provides a programming interface to retrieve the
system's default range for ephemeral ports.
If such an interface is available,
<command>named</command> will use the corresponding system
default range; otherwise, it will use its own defaults:
</para>
<programlisting>use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</programlisting>
<para>
Note: make sure the ranges be sufficiently large for
security. A desirable size depends on various parameters,
but we generally recommend it contain at least 16384 ports
(14 bits of entropy).
Note also that the system's default range when used may be
too small for this purpose, and that the range may even be
changed while <command>named</command> is running; the new
range will automatically be applied when <command>named</command>
is reloaded.
It is encouraged to
configure <command>use-v4-udp-ports</command> and
<command>use-v6-udp-ports</command> explicitly so that the
ranges are sufficiently large and are reasonably
independent from the ranges used by other applications.
</para>
<para>
Note: the operational configuration
where <command>named</command> runs may prohibit the use
of some ports. For example, UNIX systems will not allow
<command>named</command> running without a root privilege
to use ports less than 1024.
If such ports are included in the specified (or detected)
set of query ports, the corresponding query attempts will
fail, resulting in resolution failures or delay.
It is therefore important to configure the set of ports
that can be safely used in the expected operational environment.
</para>
<para>
The defaults of the <command>avoid-v4-udp-ports</command> and
<command>avoid-v6-udp-ports</command> options
are:
</para>
<programlisting>avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</programlisting>
<para>
Note: BIND 9.5.0 introduced
the <command>use-queryport-pool</command>
option to support a pool of such random ports, but this
option is now obsolete because reusing the same ports in
the pool may not be sufficiently secure.
For the same reason, it is generally strongly discouraged to
specify a particular port for the
<command>query-source</command> or
<command>query-source-v6</command> options;
it implicitly disables the use of randomized port numbers.
</para>
<variablelist>
<varlistentry>
<term><command>use-queryport-pool</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>queryport-pool-ports</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>queryport-pool-updateinterval</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
</variablelist>
<note>
<para>
The address specified in the <command>query-source</command> option
is used for both UDP and TCP queries, but the port applies only
to UDP queries. TCP queries always use a random
unprivileged port.
</para>
</note>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the source
address for TCP sockets.
</para>
</note>
<note>
<para>
See also <command>transfer-source</command> and
<command>notify-source</command>.
</para>
</note>
</section>
<section xml:id="zone_transfers"><info><title>Zone Transfers</title></info>
<para>
<acronym>BIND</acronym> has mechanisms in place to
facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.
</para>
<variablelist>
<varlistentry>
<term><command>also-notify</command></term>
<listitem>
<para>
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.
Optionally, a port may be specified with each
<command>also-notify</command> address to send
the notify messages to a port other than the
default of 53.
An optional TSIG key can also be specified with each
address to cause the notify messages to be signed; this
can be useful when sending notifies to multiple views.
In place of explicit addresses, one or more named
<command>masters</command> lists can be used.
</para>
<para>
If an <command>also-notify</command> list
is given in a <command>zone</command> statement,
it 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). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-in</command></term>
<listitem>
<para>
Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes
(1 hour). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-out</command></term>
<listitem>
<para>
Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-out</command></term>
<listitem>
<para>
Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes (1
hour). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-rate</command></term>
<listitem>
<para>
The rate at which NOTIFY requests will be sent
during normal zone maintenance operations. (NOTIFY
requests due to initial zone loading are subject
to a separate rate limit; see below.) The default is
20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>startup-notify-rate</command></term>
<listitem>
<para>
The rate at which NOTIFY requests will be sent
when the name server is first starting up, or when
zones have been newly added to the nameserver.
The default is 20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</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 bandwidth used, BIND 9 limits the
rate at which queries are sent. The value of the
<command>serial-query-rate</command> option, an
integer, is the maximum number of queries sent
per second. The default is 20 per second.
The lowest possible rate is one per second; when set
to zero, it will be silently raised to one.
</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 <acronym>BIND</acronym> 4.9.5 onwards.
The <command>many-answers</command> format is also supported by
recent Microsoft Windows nameservers.
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>transfer-message-size</command></term>
<listitem>
<para>
This is an upper bound on the uncompressed size of DNS
messages used in zone transfers over TCP. If a message
grows larger than this size, additional messages will be
used to complete the zone transfer. (Note, however,
that this is a hint, not a hard limit; if a message
contains a single resource record whose RDATA does not
fit within the size limit, a larger message will be
permitted so the record can be transferred.)
</para>
<para>
Valid values are between 512 and 65535 octets, and any
values outside that range will be adjusted to the nearest
value within it. The default is <literal>20480</literal>,
which was selected to improve message compression:
most DNS messages of this size will compress to less
than 16536 bytes. Larger messages cannot be compressed
as effectively, because 16536 is the largest permissible
compression offset pointer in a DNS message.
</para>
<para>
This option is mainly intended for server testing;
there is rarely any benefit in setting a value other
than the default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfers-in</command></term>
<listitem>
<para>
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
name server.
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 name server. <command>transfers-per-ns</command> may
be overridden on a per-server basis by using the <command>transfers</command> phrase
of the <command>server</command> statement.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source</command></term>
<listitem>
<para><command>transfer-source</command>
determines which local address 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>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source-v6</command></term>
<listitem>
<para>
The same as <command>transfer-source</command>,
except zone transfers are performed using IPv6.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source</command></term>
<listitem>
<para>
An alternate transfer source if the one listed in
<command>transfer-source</command> fails and
<command>use-alt-transfer-source</command> is
set.
</para>
<note><simpara>
If you do not wish the alternate transfer source
to be used, you should set
<command>use-alt-transfer-source</command>
appropriately and you should not depend upon
getting an answer back to the first refresh
query.
</simpara></note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source-v6</command></term>
<listitem>
<para>
An alternate transfer source if the one listed in
<command>transfer-source-v6</command> fails and
<command>use-alt-transfer-source</command> is
set.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-alt-transfer-source</command></term>
<listitem>
<para>
Use the alternate transfer sources or not. If views are
specified this defaults to <command>no</command>,
otherwise it defaults to
<command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source</command></term>
<listitem>
<para><command>notify-source</command>
determines which local source address, and
optionally UDP port, 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 or
per-view basis by including a
<command>notify-source</command> statement within
the <command>zone</command> or
<command>view</command> block in the configuration
file.
</para>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source-v6</command></term>
<listitem>
<para>
Like <command>notify-source</command>,
but applies to notify messages sent to IPv6 addresses.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="port_lists"><info><title>UDP Port Lists</title></info>
<para>
<command>use-v4-udp-ports</command>,
<command>avoid-v4-udp-ports</command>,
<command>use-v6-udp-ports</command>, and
<command>avoid-v6-udp-ports</command>
specify a list of IPv4 and IPv6 UDP ports that will be
used or not used as source ports for UDP messages.
See <xref linkend="query_address"/> about how the
available ports are determined.
For example, with the following configuration
</para>
<programlisting>
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</programlisting>
<para>
UDP ports of IPv6 messages sent
from <command>named</command> will be in one
of the following ranges: 32768 to 39999, 40001 to 49999,
and 60001 to 65535.
</para>
<para>
<command>avoid-v4-udp-ports</command> and
<command>avoid-v6-udp-ports</command> can be used
to prevent <command>named</command> from choosing as its random source port a
port that is blocked by your firewall or a port that is
used by other applications;
if a query went out with a source port blocked by a
firewall, the
answer would not get by the firewall and the name server would
have to query again.
Note: the desired range can also be represented only with
<command>use-v4-udp-ports</command> and
<command>use-v6-udp-ports</command>, and the
<command>avoid-</command> options are redundant in that
sense; they are provided for backward compatibility and
to possibly simplify the port specification.
</para>
</section>
<section xml:id="resource_limits"><info><title>Operating System Resource Limits</title></info>
<para>
The server's usage of many system resources can be limited.
Scaled values are allowed when specifying resource limits. For
example, <command>1G</command> can be used instead of
<command>1073741824</command> to specify a limit of
one
gigabyte. <command>unlimited</command> requests
unlimited use, or the
maximum available amount. <command>default</command>
uses the limit
that was in force when the server was started. See the description
of <command>size_spec</command> in <xref linkend="configuration_file_elements"/>.
</para>
<para>
The following options set operating system resource limits for
the name server process. Some operating systems 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>
</section>
<section xml:id="server_resource_limits"><info><title>Server Resource Limits</title></info>
<para>
The following options set limits on the server's
resource consumption that are enforced internally by the
server rather than the operating system.
</para>
<variablelist>
<varlistentry>
<term><command>max-journal-size</command></term>
<listitem>
<para>
Sets a maximum size for each journal file (see
<xref linkend="journal"/>), expressed in bytes
or, if followed by an optional unit suffix ('k',
'm', or 'g'), in kilobytes, megabytes, or gigabytes.
When the journal file approaches the specified size,
some of the oldest transactions in the journal
will be automatically removed. The largest
permitted value is 2 gigabytes. Very small
values are rounded up to 4096 bytes. You
can specify <literal>unlimited</literal>, which
also means 2 gigabytes. If you set the limit to
<literal>default</literal> or leave it unset, the
journal is allowed to grow up to twice as large as
the zone. (There is little benefit in storing
larger journals.)
</para>
<para>
This option may also be set on a per-zone basis.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-records</command></term>
<listitem>
<para>
The maximum number of records permitted in a zone.
The default is zero which means unlimited.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursive-clients</command></term>
<listitem>
<para>
The maximum number ("hard quota") of simultaneous
recursive lookups the server will perform on behalf
of clients. The default is
<literal>1000</literal>. Because each recursing
client uses a fair
bit of memory (on the order of 20 kilobytes), the
value of the
<command>recursive-clients</command> option may
have to be decreased on hosts with limited memory.
</para>
<para>
<option>recursive-clients</option> defines a "hard
quota" limit for pending recursive clients: when more
clients than this are pending, new incoming requests
will not be accepted, and for each incoming request
a previous pending request will also be dropped.
</para>
<para>
A "soft quota" is also set. When this lower
quota is exceeded, incoming requests are accepted, but
for each one, a pending request will be dropped.
If <option>recursive-clients</option> is greater than
1000, the soft quota is set to
<option>recursive-clients</option> minus 100;
otherwise it is set to 90% of
<option>recursive-clients</option>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-clients</command></term>
<listitem>
<para>
The maximum number of simultaneous client TCP
connections that the server will accept.
The default is <literal>150</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="clients-per-query">
<term xml:id="cpq_term"><command>clients-per-query</command></term>
<term><command>max-clients-per-query</command></term>
<listitem>
<para>These set the
initial value (minimum) and maximum number of recursive
simultaneous clients for any given query
(&lt;qname,qtype,qclass&gt;) that the server will accept
before dropping additional clients. <command>named</command> will attempt to
self tune this value and changes will be logged. The
default values are 10 and 100.
</para>
<para>
This value should reflect how many queries come in for
a given name in the time it takes to resolve that name.
If the number of queries exceed this value, <command>named</command> will
assume that it is dealing with a non-responsive zone
and will drop additional queries. If it gets a response
after dropping queries, it will raise the estimate. The
estimate will then be lowered in 20 minutes if it has
remained unchanged.
</para>
<para>
If <command>clients-per-query</command> is set to zero,
then there is no limit on the number of clients per query
and no queries will be dropped.
</para>
<para>
If <command>max-clients-per-query</command> is set to zero,
then there is no upper bound other than imposed by
<command>recursive-clients</command>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="fetches-per-zone">
<term><command>fetches-per-zone</command></term>
<listitem>
<para>
The maximum number of simultaneous iterative
queries to any one domain that the server will
permit before blocking new queries for data
in or beneath that zone.
This value should reflect how many fetches would
normally be sent to any one zone in the time it
would take to resolve them. It should be smaller
than <option>recursive-clients</option>.
</para>
<para>
When many clients simultaneously query for the
same name and type, the clients will all be attached
to the same fetch, up to the
<option>max-clients-per-query</option> limit,
and only one iterative query will be sent.
However, when clients are simultaneously
querying for <emphasis>different</emphasis> names
or types, multiple queries will be sent and
<option>max-clients-per-query</option> is not
effective as a limit.
</para>
<para>
Optionally, this value may be followed by the keyword
<literal>drop</literal> or <literal>fail</literal>,
indicating whether queries which exceed the fetch
quota for a zone will be dropped with no response,
or answered with SERVFAIL. The default is
<literal>drop</literal>.
</para>
<para>
If <command>fetches-per-zone</command> is set to zero,
then there is no limit on the number of fetches per query
and no queries will be dropped. The default is zero.
</para>
<para>
The current list of active fetches can be dumped by
running <command>rndc recursing</command>. The list
includes the number of active fetches for each
domain and the number of queries that have been
passed or dropped as a result of the
<option>fetches-per-zone</option> limit. (Note:
these counters are not cumulative over time; whenever
the number of active fetches for a domain drops to
zero, the counter for that domain is deleted, and the
next time a fetch is sent to that domain, it is
recreated with the counters set to zero.)
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="fetches-per-server">
<term><command>fetches-per-server</command></term>
<listitem>
<para>
The maximum number of simultaneous iterative
queries that the server will allow to be sent to
a single upstream name server before blocking
additional queries.
This value should reflect how many fetches would
normally be sent to any one server in the time it
would take to resolve them. It should be smaller
than <option>recursive-clients</option>.
</para>
<para>
Optionally, this value may be followed by the keyword
<literal>drop</literal> or <literal>fail</literal>,
indicating whether queries will be dropped with no
response, or answered with SERVFAIL, when all of the
servers authoritative for a zone are found to have
exceeded the per-server quota. The default is
<literal>fail</literal>.
</para>
<para>
If <command>fetches-per-server</command> is set to zero,
then there is no limit on the number of fetches per query
and no queries will be dropped. The default is zero.
</para>
<para>
The <command>fetches-per-server</command> quota is
dynamically adjusted in response to detected
congestion. As queries are sent to a server
and are either answered or time out, an
exponentially weighted moving average is calculated
of the ratio of timeouts to responses. If the
current average timeout ratio rises above a "high"
threshold, then <command>fetches-per-server</command>
is reduced for that server. If the timeout ratio
drops below a "low" threshold, then
<command>fetches-per-server</command> is increased.
The <command>fetch-quota-params</command> options
can be used to adjust the parameters for this
calculation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>fetch-quota-params</command></term>
<listitem>
<para>
Sets the parameters to use for dynamic resizing of
the <option>fetches-per-server</option> quota in
response to detected congestion.
</para>
<para>
The first argument is an integer value indicating
how frequently to recalculate the moving average
of the ratio of timeouts to responses for each
server. The default is 100, meaning we recalculate
the average ratio after every 100 queries have either
been answered or timed out.
</para>
<para>
The remaining three arguments represent the "low"
threshold (defaulting to a timeout ratio of 0.1),
the "high" threshold (defaulting to a timeout
ratio of 0.3), and the discount rate for
the moving average (defaulting to 0.7).
A higher discount rate causes recent events to
weigh more heavily when calculating the moving
average; a lower discount rate causes past
events to weigh more heavily, smoothing out
short-term blips in the timeout ratio.
These arguments are all fixed-point numbers with
precision of 1/100: at most two places after
the decimal point are significant.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>reserved-sockets</command></term>
<listitem>
<para>
The number of file descriptors reserved for TCP, stdio,
etc. This needs to be big enough to cover the number of
interfaces <command>named</command> listens on plus
<command>tcp-clients</command>, as well as
to provide room for outgoing TCP queries and incoming zone
transfers. The default is <literal>512</literal>.
The minimum value is <literal>128</literal> and the
maximum value is <literal>128</literal> less than
maxsockets (-S). This option may be removed in the future.
</para>
<para>
This option has little effect on Windows.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-cache-size</command></term>
<listitem>
<para>
The maximum amount of memory to use for the
server's cache, in bytes or % of total physical memory.
When the amount of data in the cache
reaches this limit, the server will cause records to
expire prematurely based on an LRU based strategy so
that the limit is not exceeded.
The keyword <userinput>unlimited</userinput>,
or the value 0, will place no limit on cache size;
records will be purged from the cache only when their
TTLs expire.
Any positive values less than 2MB will be ignored
and reset to 2MB.
In a server with multiple views, the limit applies
separately to the cache of each view.
The default is <userinput>90%</userinput>.
On systems where detection of amount of physical
memory is not supported values represented as %
fall back to unlimited.
Note that the detection of physical memory is done only
once at startup, so <command>named</command> will not
adjust the cache size if the amount of physical memory
is changed during runtime.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-listen-queue</command></term>
<listitem>
<para>
The listen queue depth. The default and minimum is 10.
If the kernel supports the accept filter "dataready" this
also controls how
many TCP connections that will be queued in kernel space
waiting for
some data before being passed to accept. Nonzero values
less than 10 will be silently raised. A value of 0 may also
be used; on most platforms this sets the listen queue
length to a system-defined default value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-initial-timeout</command></term>
<listitem>
<para>
The amount of time (in units of 100 milliseconds) the
server waits on a new TCP connection for the first message
from the client. The default is 300 (30 seconds),
the minimum is 25 (2.5 seconds), and the maximum is
1200 (two minutes). Values above the maximum or below
the minimum will be adjusted with a logged warning.
(Note: This value must be greater than the expected
round trip delay time; otherwise no client will ever
have enough time to submit a message.)
This value can be updated at runtime by using
<command>rndc tcp-timeouts</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-idle-timeout</command></term>
<listitem>
<para>
The amount of time (in units of 100 milliseconds) the
server waits on an idle TCP connection before closing
it when the client is not using the EDNS TCP keepalive
option. The default is 300 (30 seconds), the maximum
is 1200 (two minutes), and the minimum is 1 (one tenth
of a second). Values above the maximum or below the minimum
will be adjusted with a logged warning.
See <command>tcp-keepalive-timeout</command>
for clients using the EDNS TCP keepalive option.
This value can be updated at runtime by using
<command>rndc tcp-timeouts</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-keepalive-timeout</command></term>
<listitem>
<para>
The amount of time (in units of 100 milliseconds) the
server waits on an idle TCP connection before closing
it when the client is using the EDNS TCP keepalive
option. The default is 300 (30 seconds), the maximum
is 65535 (about 1.8 hours), and the minimum is 1 (one tenth
of a second). Values above the maximum or below the minimum
will be adjusted with a logged warning.
This value may be greater than
<command>tcp-idle-timeout</command>, because
clients using the EDNS TCP keepalive option are expected
to use TCP connections for more than one message.
This value can be updated at runtime by using
<command>rndc tcp-timeouts</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-advertised-timeout</command></term>
<listitem>
<para>
The timeout value (in units of 100 milliseconds) the
server will send in respones containing the EDNS TCP
keepalive option. This informs a client of the
amount of time it may keep the session open.
The default is 300 (30 seconds), the maximum is
65535 (about 1.8 hours), and the minimum is 0, which
signals that the clients must close TCP connections
immediately. Ordinarily this should be set to the
same value as <command>tcp-keepalive-timeout</command>.
This value can be updated at runtime by using
<command>rndc tcp-timeouts</command>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="intervals"><info><title>Periodic Task Intervals</title></info>
<variablelist>
<varlistentry>
<term><command>cleaning-interval</command></term>
<listitem>
<para>
This option is obsolete.
</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). The maximum value is 28 days
(40320 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. The maximum value is 28 days (40320 minutes).
If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, the
server will
begin listening for queries on any newly discovered
interfaces (provided they are allowed by the
<command>listen-on</command> configuration), and
will stop listening on interfaces that have gone away.
For convenience, TTL-style time unit suffixes may be
used to specify the value.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="the_sortlist_statement"><info><title>The <command>sortlist</command> Statement</title></info>
<para>
The response to a DNS query may consist of multiple resource
records (RRs) forming a resource record set (RRset). The name
server 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 name
servers, not all the clients.
</para>
<para>
The <command>sortlist</command> statement (see below) takes an
<command>address_match_list</command> and interprets it in a
special way. Each top level statement in the
<command>sortlist</command> must itself be an explicit
<command>address_match_list</command> with one or two elements.
The first element (which may be an IP address, an IP prefix, an
ACL name or a nested <command>address_match_list</command>) of
each top level list is checked against the source address of
the query until a match is found.
</para>
<para>
Once the source address of the query has been matched, if the
top level statement contains only one element, the actual
primitive element that matched the source address is used to
select the address in the response to move to the beginning of
the response. If the statement is a list of two elements, then
the second element is interpreted as a topology preference
list. Each top level element is assigned a distance and the
address in the response with the minimum distance is moved to
the beginning of the response.
</para>
<para>
In the following example, any queries received from any of the
addresses of the host itself 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 {
// IF the local host
// THEN first fit on the following nets
{ localhost;
{ localnets;
192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.1 THEN use .1, or .2 or .3
{ 192.168.1/24;
{ 192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.2 THEN use .2, or .1 or .3
{ 192.168.2/24;
{ 192.168.2/24;
{ 192.168.1/24; 192.168.3/24; }; }; };
// IF on class C 192.168.3 THEN use .3, or .1 or .2
{ 192.168.3/24;
{ 192.168.3/24;
{ 192.168.1/24; 192.168.2/24; }; }; };
// IF .4 or .5 THEN prefer that net
{ { 192.168.4/24; 192.168.5/24; };
};
};</programlisting>
<para>
The following example 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>
</section>
<section xml:id="rrset_ordering"><info><title xml:id="rrset_ordering_title">RRset Ordering</title></info>
<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>
<para>
<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>
</para>
<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>" (asterisk).
</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. This option
is only available if <acronym>BIND</acronym>
is configured with "--enable-fixed-rrset" at
compile time.
</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 cyclic round-robin order,
rotating by one record per query.
</para>
<para>
If <acronym>BIND</acronym> is configured with
"--enable-fixed-rrset" at compile time, then
the initial ordering of the RRset will match the
one specified in the zone file; otherwise the
initial ordering is indeterminate.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>none</command></para>
</entry>
<entry colname="2">
<para>
Records are returned in whatever order they were
retrieved from the database. This order is
indeterminate, but will be consistent as long as the
database is not modified. When no ordering is
specified, this is the default.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
</para>
<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 — the last one applies.
</para>
<para>
By default, records are returned in <command>random</command> order.
</para>
<note>
<simpara>
In this release of <acronym>BIND</acronym> 9, the
<command>rrset-order</command> statement does not support
"fixed" ordering by default. Fixed ordering can be enabled
at compile time by specifying "--enable-fixed-rrset" on
the "configure" command line.
</simpara>
</note>
</section>
<section xml:id="tuning"><info><title>Tuning</title></info>
<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.)
The default is <literal>600</literal> (10 minutes) and the
maximum value is
<literal>1800</literal> (30 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>servfail-ttl</command></term>
<listitem>
<para>
Sets the number of seconds to cache a
SERVFAIL response due to DNSSEC validation failure or
other general server failure. If set to
<literal>0</literal>, SERVFAIL caching is disabled.
The SERVFAIL cache is not consulted if a query has
the CD (Checking Disabled) bit set; this allows a
query that failed due to DNSSEC validation to be retried
without waiting for the SERVFAIL TTL to expire.
</para>
<para>
The maximum value is <literal>30</literal>
seconds; any higher value will be silently
reduced. The default is <literal>1</literal>
second.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-ncache-ttl</command></term>
<listitem>
<para>
To reduce network traffic and increase performance, the server
stores negative answers. <command>min-ncache-ttl</command> is
used to set a minimum retention time for these answers in the
server in seconds. For convenience, TTL-style time unit
suffixes may be used to specify the value. The default
<command>min-ncache-ttl</command> is <literal>0</literal>
seconds. <command>min-ncache-ttl</command> cannot exceed 90
seconds and will be truncated to 90 seconds if set to a
greater value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-cache-ttl</command></term>
<listitem>
<para>
Sets the minimum time for which the server will cache ordinary
(positive) answers in seconds. For convenience, TTL-style time
unit suffixes may be used to specify the value. The default
<command>min-cache-ttl</command> is <literal>0</literal>
seconds. <command>min-cache-ttl</command> cannot exceed 90
seconds and will be truncated to 90 seconds if set to a
greater value.
</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.
For convenience, TTL-style time unit suffixes may be
used to specify the value. 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>
Sets the maximum time for which the server will
cache ordinary (positive) answers in seconds.
For convenience, TTL-style time unit suffixes may be
used to specify the value.
The default is 604800 (one week).
A value of zero may cause all queries to return
SERVFAIL, because of lost caches of intermediate
RRsets (such as NS and glue AAAA/A records) in the
resolution process.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-stale-ttl</command></term>
<listitem>
<para>
If stale answers are enabled,
<command>max-stale-ttl</command>
sets the maximum time for which the server will
retain records past their normal expiry to
return them as stale records when the servers
for those records are not reachable.
The default is 1 week. The minimum allowed is
1 second; a value of 0 will be updated silently
to 1 second.
</para>
<para>
For stale answers to be returned, they must be enabled,
either in the configuration file using
<command>stale-answer-enable</command> or via
<command>rndc serve-stale on</command>.
</para>
</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. There
is an optional second field which specifies how
long before expiry that the signatures will be
regenerated. If not specified, the signatures will
be regenerated at 1/4 of base interval. The second
field is specified in days if the base interval is
greater than 7 days otherwise it is specified in hours.
The default base interval is <literal>30</literal> days
giving a re-signing interval of 7 1/2 days. The maximum
values are 10 years (3660 days).
</para>
<para>
The signature inception time is unconditionally
set to one hour before the current time to allow
for a limited amount of clock skew.
</para>
<para>
The <command>sig-validity-interval</command> can be
overridden for DNSKEY records by setting
<command>dnskey-sig-validity</command>.
</para>
<para>
The <command>sig-validity-interval</command>
should be, at least, several multiples of the SOA
expire interval to allow for reasonable interaction
between the various timer and expiry dates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnskey-sig-validity</command></term>
<listitem>
<para>
Specifies the number of days into the future when
DNSSEC signatures that are automatically generated
for DNSKEY RRsets as a result of dynamic updates
(<xref linkend="dynamic_update"/>) will expire.
If set to a non-zero value, this overrides the
value set by <command>sig-validity-interval</command>.
The default is zero, meaning
<command>sig-validity-interval</command> is used.
The maximum value is 3660 days (10 years), and
higher values will be rejected.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-nodes</command></term>
<listitem>
<para>
Specify the maximum number of nodes to be
examined in each quantum when signing a zone with
a new DNSKEY. The default is
<literal>100</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-signatures</command></term>
<listitem>
<para>
Specify a threshold number of signatures that
will terminate processing a quantum when signing
a zone with a new DNSKEY. The default is
<literal>10</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-type</command></term>
<listitem>
<para>
Specify a private RDATA type to be used when generating
signing state records. The default is
<literal>65534</literal>.
</para>
<para>
It is expected that this parameter may be removed
in a future version once there is a standard type.
</para>
<para>
Signing state records are used to internally by
<command>named</command> to track the current state of
a zone-signing process, i.e., whether it is still active
or has been completed. The records can be inspected
using the command
<command>rndc signing -list <replaceable>zone</replaceable></command>.
Once <command>named</command> has finished signing
a zone with a particular key, the signing state
record associated with that key can be removed from
the zone by running
<command>rndc signing -clear <replaceable>keyid/algorithm</replaceable> <replaceable>zone</replaceable></command>.
To clear all of the completed signing state
records for a zone, use
<command>rndc signing -clear all <replaceable>zone</replaceable></command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-refresh-time</command></term>
<term><command>max-refresh-time</command></term>
<term><command>min-retry-time</command></term>
<term><command>max-retry-time</command></term>
<listitem>
<para>
These options control the server's behavior on refreshing a
zone (querying for SOA changes) or retrying failed
transfers. Usually the SOA values for the zone are used,
up to a hard-coded maximum expiry of 24 weeks. However,
these values are set by the 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 in seconds per-zone,
per-view, or globally. These options are valid for
slave and stub zones, and clamp the SOA refresh and
retry times to the specified values.
</para>
<para>
The following defaults apply.
<command>min-refresh-time</command> 300 seconds,
<command>max-refresh-time</command> 2419200 seconds
(4 weeks), <command>min-retry-time</command> 500 seconds,
and <command>max-retry-time</command> 1209600 seconds
(2 weeks).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>edns-udp-size</command></term>
<listitem>
<para>
Sets the maximum advertised EDNS UDP buffer size in
bytes, to control the size of packets received from
authoritative servers in response to recursive queries.
Valid values are 512 to 4096 (values outside this range
will be silently adjusted to the nearest value within
it). The default value is 4096.
</para>
<para>
The usual reason for setting
<command>edns-udp-size</command> to a non-default value
is to get UDP answers to pass through broken firewalls
that block fragmented packets and/or block UDP DNS
packets that are greater than 512 bytes.
</para>
<para>
When <command>named</command> first queries a remote
server, it will advertise a UDP buffer size of 512, as
this has the greatest chance of success on the first try.
</para>
<para>
If the initial response times out, <command>named</command>
will try again with plain DNS, and if that is successful,
it will be taken as evidence that the server does not
support EDNS. After enough failures using EDNS and
successes using plain DNS, <command>named</command>
will default to plain DNS for future communications
with that server. (Periodically, <command>named</command>
will send an EDNS query to see if the situation has
improved.)
</para>
<para>
However, if the initial query is successful with
EDNS advertising a buffer size of 512, then
<command>named</command> will advertise progressively
larger buffer sizes on successive queries, until
responses begin timing out or
<command>edns-udp-size</command> is reached.
</para>
<para>
The default buffer sizes used by <command>named</command>
are 512, 1232, 1432, and 4096, but never exceeding
<command>edns-udp-size</command>. (The values 1232 and
1432 are chosen to allow for an IPv4/IPv6 encapsulated
UDP message to be sent without fragmentation at the
minimum MTU sizes for Ethernet and IPv6 networks.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-udp-size</command></term>
<listitem>
<para>
Sets the maximum EDNS UDP message size
<command>named</command> will send in bytes.
Valid values are 512 to 4096 (values outside this
range will be silently adjusted to the nearest
value within it). The default value is 4096.
</para>
<para>
This value applies to responses sent by a server; to
set the advertised buffer size in queries, see
<command>edns-udp-size</command>.
</para>
<para>
The usual reason for setting
<command>max-udp-size</command> to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
This is independent of the advertised receive
buffer (<command>edns-udp-size</command>).
</para>
<para>
Setting this to a low value will encourage additional
TCP traffic to the nameserver.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>masterfile-format</command></term>
<listitem>
<para>Specifies
the file format of zone files (see
<xref linkend="zonefile_format"/>).
The default value is <constant>text</constant>, which is the
standard textual representation, except for slave zones,
in which the default value is <constant>raw</constant>.
Files in other formats than <constant>text</constant> are
typically expected to be generated by the
<command>named-compilezone</command> tool, or dumped by
<command>named</command>.
</para>
<para>
Note that when a zone file in a different format than
<constant>text</constant> is loaded, <command>named</command>
may omit some of the checks which would be performed for a
file in the <constant>text</constant> format. In particular,
<command>check-names</command> checks do not apply
for the <constant>raw</constant> format. This means
a zone file in the <constant>raw</constant> format
must be generated with the same check level as that
specified in the <command>named</command> configuration
file. Also, <constant>map</constant> format files are
loaded directly into memory via memory mapping, with only
minimal checking.
</para>
<para>
This statement sets the
<command>masterfile-format</command> for all zones,
but can be overridden on a per-zone or per-view basis
by including a <command>masterfile-format</command>
statement within the <command>zone</command> or
<command>view</command> block in the configuration
file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>masterfile-style</command></term>
<listitem>
<para>
Specifies the formatting of zone files during dump
when the <option>masterfile-format</option> is
<constant>text</constant>. (This option is ignored
with any other <option>masterfile-format</option>.)
</para>
<para>
When set to <constant>relative</constant>,
records are printed in a multi-line format with owner
names expressed relative to a shared origin. When set
to <constant>full</constant>, records are printed in
a single-line format with absolute owner names.
The <constant>full</constant> format is most suitable
when a zone file needs to be processed automatically
by a script. The <constant>relative</constant> format
is more human-readable, and is thus suitable when a
zone is to be edited by hand. The default is
<constant>relative</constant>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="max-recursion-depth">
<term><command>max-recursion-depth</command></term>
<listitem>
<para>
Sets the maximum number of levels of recursion
that are permitted at any one time while servicing
a recursive query. Resolving a name may require
looking up a name server address, which in turn
requires resolving another name, etc; if the number
of indirections exceeds this value, the recursive
query is terminated and returns SERVFAIL. The
default is 7.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="max-recursion-queries">
<term><command>max-recursion-queries</command></term>
<listitem>
<para>
Sets the maximum number of iterative queries that
may be sent while servicing a recursive query.
If more queries are sent, the recursive query
is terminated and returns SERVFAIL. Queries to
look up top level domains such as "com" and "net"
and the DNS root zone are exempt from this limitation.
The default is 75.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-delay</command></term>
<listitem>
<para>
The delay, in seconds, between sending sets of notify
messages for a zone. The default is five (5) seconds.
</para>
<para>
The overall rate that NOTIFY messages are sent for all
zones is controlled by <command>serial-query-rate</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-rsa-exponent-size</command></term>
<listitem>
<para>
The maximum RSA exponent size, in bits, that will
be accepted when validating. Valid values are 35
to 4096 bits. The default zero (0) is also accepted
and is equivalent to 4096.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>prefetch</command></term>
<listitem>
<para>
When a query is received for cached data which
is to expire shortly, <command>named</command> can
refresh the data from the authoritative server
immediately, ensuring that the cache always has an
answer available.
</para>
<para>
The <option>prefetch</option> specifies the
"trigger" TTL value at which prefetch of the current
query will take place: when a cache record with a
lower TTL value is encountered during query processing,
it will be refreshed. Valid trigger TTL values are 1 to
10 seconds. Values larger than 10 seconds will be silently
reduced to 10.
Setting a trigger TTL to zero (0) causes
prefetch to be disabled.
The default trigger TTL is <literal>2</literal>.
</para>
<para>
An optional second argument specifies the "eligibility"
TTL: the smallest <emphasis>original</emphasis>
TTL value that will be accepted for a record to be
eligible for prefetching. The eligibility TTL must
be at least six seconds longer than the trigger TTL;
if it isn't, <command>named</command> will silently
adjust it upward.
The default eligibility TTL is <literal>9</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>v6-bias</command></term>
<listitem>
<para>
When determining the next nameserver to try
preference IPv6 nameservers by this many milliseconds.
The default is <literal>50</literal> milliseconds.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="builtin"><info><title>Built-in server information zones</title></info>
<para>
The server provides some helpful diagnostic information
through a number of built-in zones under the
pseudo-top-level-domain <literal>bind</literal> in the
<command>CHAOS</command> class. These zones are part
of a
built-in view (see <xref linkend="view_statement_grammar"/>) of
class
<command>CHAOS</command> which is separate from the
default view of class <command>IN</command>. Most global
configuration options (<command>allow-query</command>,
etc) will apply to this view, but some are locally
overridden: <command>notify</command>,
<command>recursion</command> and
<command>allow-new-zones</command> are
always set to <userinput>no</userinput>, and
<command>rate-limit</command> is set to allow
three responses per second.
</para>
<para>
If you need to disable these zones, use the options
below, or hide the built-in <command>CHAOS</command>
view by
defining an explicit view of class <command>CHAOS</command>
that matches all clients.
</para>
<variablelist>
<varlistentry>
<term><command>version</command></term>
<listitem>
<para>
The version the server should report
via a query of the name <literal>version.bind</literal>
with type <command>TXT</command>, class <command>CHAOS</command>.
The default is the real version number of this server.
Specifying <command>version none</command>
disables processing of the queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>hostname</command></term>
<listitem>
<para>
The hostname the server should report via a query of
the name <filename>hostname.bind</filename>
with type <command>TXT</command>, class <command>CHAOS</command>.
This defaults to the hostname of the machine hosting the
name server as
found by the gethostname() function. The primary purpose of such queries
is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <command>hostname none;</command>
disables processing of the queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-id</command></term>
<listitem>
<para>
The ID the server should report when receiving a Name
Server Identifier (NSID) query, or a query of the name
<filename>ID.SERVER</filename> with type
<command>TXT</command>, class <command>CHAOS</command>.
The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <command>server-id none;</command>
disables processing of the queries.
Specifying <command>server-id hostname;</command> will cause <command>named</command> to
use the hostname as found by the gethostname() function.
The default <command>server-id</command> is <command>none</command>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="empty"><info><title>Built-in Empty Zones</title></info>
<para>
The <command>named</command> server has some built-in
empty zones (SOA and NS records only).
These are for zones that should normally be answered locally
and which queries should not be sent to the Internet's root
servers. The official servers which cover these namespaces
return NXDOMAIN responses to these queries. In particular,
these cover the reverse namespaces for addresses from
RFC 1918, RFC 4193, RFC 5737 and RFC 6598. They also include the
reverse namespace for IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address and the
IPv6 unknown address.
</para>
<para>
The server will attempt to determine if a built-in zone
already exists or is active (covered by a forward-only
forwarding declaration) and will not create an empty
zone in that case.
</para>
<para>
The current list of empty zones is:
<itemizedlist>
<listitem>10.IN-ADDR.ARPA</listitem>
<listitem>16.172.IN-ADDR.ARPA</listitem>
<listitem>17.172.IN-ADDR.ARPA</listitem>
<listitem>18.172.IN-ADDR.ARPA</listitem>
<listitem>19.172.IN-ADDR.ARPA</listitem>
<listitem>20.172.IN-ADDR.ARPA</listitem>
<listitem>21.172.IN-ADDR.ARPA</listitem>
<listitem>22.172.IN-ADDR.ARPA</listitem>
<listitem>23.172.IN-ADDR.ARPA</listitem>
<listitem>24.172.IN-ADDR.ARPA</listitem>
<listitem>25.172.IN-ADDR.ARPA</listitem>
<listitem>26.172.IN-ADDR.ARPA</listitem>
<listitem>27.172.IN-ADDR.ARPA</listitem>
<listitem>28.172.IN-ADDR.ARPA</listitem>
<listitem>29.172.IN-ADDR.ARPA</listitem>
<listitem>30.172.IN-ADDR.ARPA</listitem>
<listitem>31.172.IN-ADDR.ARPA</listitem>
<listitem>168.192.IN-ADDR.ARPA</listitem>
<listitem>64.100.IN-ADDR.ARPA</listitem>
<listitem>65.100.IN-ADDR.ARPA</listitem>
<listitem>66.100.IN-ADDR.ARPA</listitem>
<listitem>67.100.IN-ADDR.ARPA</listitem>
<listitem>68.100.IN-ADDR.ARPA</listitem>
<listitem>69.100.IN-ADDR.ARPA</listitem>
<listitem>70.100.IN-ADDR.ARPA</listitem>
<listitem>71.100.IN-ADDR.ARPA</listitem>
<listitem>72.100.IN-ADDR.ARPA</listitem>
<listitem>73.100.IN-ADDR.ARPA</listitem>
<listitem>74.100.IN-ADDR.ARPA</listitem>
<listitem>75.100.IN-ADDR.ARPA</listitem>
<listitem>76.100.IN-ADDR.ARPA</listitem>
<listitem>77.100.IN-ADDR.ARPA</listitem>
<listitem>78.100.IN-ADDR.ARPA</listitem>
<listitem>79.100.IN-ADDR.ARPA</listitem>
<listitem>80.100.IN-ADDR.ARPA</listitem>
<listitem>81.100.IN-ADDR.ARPA</listitem>
<listitem>82.100.IN-ADDR.ARPA</listitem>
<listitem>83.100.IN-ADDR.ARPA</listitem>
<listitem>84.100.IN-ADDR.ARPA</listitem>
<listitem>85.100.IN-ADDR.ARPA</listitem>
<listitem>86.100.IN-ADDR.ARPA</listitem>
<listitem>87.100.IN-ADDR.ARPA</listitem>
<listitem>88.100.IN-ADDR.ARPA</listitem>
<listitem>89.100.IN-ADDR.ARPA</listitem>
<listitem>90.100.IN-ADDR.ARPA</listitem>
<listitem>91.100.IN-ADDR.ARPA</listitem>
<listitem>92.100.IN-ADDR.ARPA</listitem>
<listitem>93.100.IN-ADDR.ARPA</listitem>
<listitem>94.100.IN-ADDR.ARPA</listitem>
<listitem>95.100.IN-ADDR.ARPA</listitem>
<listitem>96.100.IN-ADDR.ARPA</listitem>
<listitem>97.100.IN-ADDR.ARPA</listitem>
<listitem>98.100.IN-ADDR.ARPA</listitem>
<listitem>99.100.IN-ADDR.ARPA</listitem>
<listitem>100.100.IN-ADDR.ARPA</listitem>
<listitem>101.100.IN-ADDR.ARPA</listitem>
<listitem>102.100.IN-ADDR.ARPA</listitem>
<listitem>103.100.IN-ADDR.ARPA</listitem>
<listitem>104.100.IN-ADDR.ARPA</listitem>
<listitem>105.100.IN-ADDR.ARPA</listitem>
<listitem>106.100.IN-ADDR.ARPA</listitem>
<listitem>107.100.IN-ADDR.ARPA</listitem>
<listitem>108.100.IN-ADDR.ARPA</listitem>
<listitem>109.100.IN-ADDR.ARPA</listitem>
<listitem>110.100.IN-ADDR.ARPA</listitem>
<listitem>111.100.IN-ADDR.ARPA</listitem>
<listitem>112.100.IN-ADDR.ARPA</listitem>
<listitem>113.100.IN-ADDR.ARPA</listitem>
<listitem>114.100.IN-ADDR.ARPA</listitem>
<listitem>115.100.IN-ADDR.ARPA</listitem>
<listitem>116.100.IN-ADDR.ARPA</listitem>
<listitem>117.100.IN-ADDR.ARPA</listitem>
<listitem>118.100.IN-ADDR.ARPA</listitem>
<listitem>119.100.IN-ADDR.ARPA</listitem>
<listitem>120.100.IN-ADDR.ARPA</listitem>
<listitem>121.100.IN-ADDR.ARPA</listitem>
<listitem>122.100.IN-ADDR.ARPA</listitem>
<listitem>123.100.IN-ADDR.ARPA</listitem>
<listitem>124.100.IN-ADDR.ARPA</listitem>
<listitem>125.100.IN-ADDR.ARPA</listitem>
<listitem>126.100.IN-ADDR.ARPA</listitem>
<listitem>127.100.IN-ADDR.ARPA</listitem>
<listitem>0.IN-ADDR.ARPA</listitem>
<listitem>127.IN-ADDR.ARPA</listitem>
<listitem>254.169.IN-ADDR.ARPA</listitem>
<listitem>2.0.192.IN-ADDR.ARPA</listitem>
<listitem>100.51.198.IN-ADDR.ARPA</listitem>
<listitem>113.0.203.IN-ADDR.ARPA</listitem>
<listitem>255.255.255.255.IN-ADDR.ARPA</listitem>
<listitem>0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
<listitem>1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
<listitem>8.B.D.0.1.0.0.2.IP6.ARPA</listitem>
<listitem>D.F.IP6.ARPA</listitem>
<listitem>8.E.F.IP6.ARPA</listitem>
<listitem>9.E.F.IP6.ARPA</listitem>
<listitem>A.E.F.IP6.ARPA</listitem>
<listitem>B.E.F.IP6.ARPA</listitem>
<listitem>EMPTY.AS112.ARPA</listitem>
<listitem>HOME.ARPA</listitem>
</itemizedlist>
</para>
<para>
Empty zones are settable at the view level and only apply to
views of class IN. Disabled empty zones are only inherited
from options if there are no disabled empty zones specified
at the view level. To override the options list of disabled
zones, you can disable the root zone at the view level, for example:
<programlisting>
disable-empty-zone ".";
</programlisting>
</para>
<para>
If you are using the address ranges covered here, you should
already have reverse zones covering the addresses you use.
In practice this appears to not be the case with many queries
being made to the infrastructure servers for names in these
spaces. So many in fact that sacrificial servers were needed
to be deployed to channel the query load away from the
infrastructure servers.
</para>
<note><simpara>
The real parent servers for these zones should disable all
empty zone under the parent zone they serve. For the real
root servers, this is all built-in empty zones. This will
enable them to return referrals to deeper in the tree.
</simpara></note>
<variablelist>
<varlistentry>
<term><command>empty-server</command></term>
<listitem>
<para>
Specify what server name will appear in the returned
SOA record for empty zones. If none is specified, then
the zone's name will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>empty-contact</command></term>
<listitem>
<para>
Specify what contact name will appear in the returned
SOA record for empty zones. If none is specified, then
"." will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>empty-zones-enable</command></term>
<listitem>
<para>
Enable or disable all empty zones. By default, they
are enabled.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>disable-empty-zone</command></term>
<listitem>
<para>
Disable individual empty zones. By default, none are
disabled. This option can be specified multiple times.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="content_filtering"><info><title>Content Filtering</title></info>
<para>
<acronym>BIND</acronym> 9 provides the ability to filter
out DNS responses from external DNS servers containing
certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if
the corresponding IPv4 or IPv6 addresses match the given
<varname>address_match_list</varname> of the
<command>deny-answer-addresses</command> option.
It can also reject CNAME or DNAME records if the "alias"
name (i.e., the CNAME alias or the substituted query name
due to DNAME) matches the
given <varname>namelist</varname> of the
<command>deny-answer-aliases</command> option, where
"match" means the alias name is a subdomain of one of
the <varname>name_list</varname> elements.
If the optional <varname>namelist</varname> is specified
with <command>except-from</command>, records whose query name
matches the list will be accepted regardless of the filter
setting.
Likewise, if the alias name is a subdomain of the
corresponding zone, the <command>deny-answer-aliases</command>
filter will not apply;
for example, even if "example.com" is specified for
<command>deny-answer-aliases</command>,
</para>
<programlisting>www.example.com. CNAME xxx.example.com.</programlisting>
<para>
returned by an "example.com" server will be accepted.
</para>
<para>
In the <varname>address_match_list</varname> of the
<command>deny-answer-addresses</command> option, only
<varname>ip_addr</varname>
and <varname>ip_prefix</varname>
are meaningful;
any <varname>key_id</varname> will be silently ignored.
</para>
<para>
If a response message is rejected due to the filtering,
the entire message is discarded without being cached, and
a SERVFAIL error will be returned to the client.
</para>
<para>
This filtering is intended to prevent "DNS rebinding attacks," in
which an attacker, in response to a query for a domain name the
attacker controls, returns an IP address within your own network or
an alias name within your own domain.
A naive web browser or script could then serve as an
unintended proxy, allowing the attacker
to get access to an internal node of your local network
that couldn't be externally accessed otherwise.
See the paper available at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://portal.acm.org/citation.cfm?id=1315245.1315298">
http://portal.acm.org/citation.cfm?id=1315245.1315298
</link>
for more details about the attacks.
</para>
<para>
For example, if you own a domain named "example.net" and
your internal network uses an IPv4 prefix 192.0.2.0/24,
you might specify the following rules:
</para>
<programlisting>deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</programlisting>
<para>
If an external attacker lets a web browser in your local
network look up an IPv4 address of "attacker.example.com",
the attacker's DNS server would return a response like this:
</para>
<programlisting>attacker.example.com. A 192.0.2.1</programlisting>
<para>
in the answer section.
Since the rdata of this record (the IPv4 address) matches
the specified prefix 192.0.2.0/24, this response will be
ignored.
</para>
<para>
On the other hand, if the browser looks up a legitimate
internal web server "www.example.net" and the
following response is returned to
the <acronym>BIND</acronym> 9 server
</para>
<programlisting>www.example.net. A 192.0.2.2</programlisting>
<para>
it will be accepted since the owner name "www.example.net"
matches the <command>except-from</command> element,
"example.net".
</para>
<para>
Note that this is not really an attack on the DNS per se.
In fact, there is nothing wrong for an "external" name to
be mapped to your "internal" IP address or domain name
from the DNS point of view.
It might actually be provided for a legitimate purpose,
such as for debugging.
As long as the mapping is provided by the correct owner,
it is not possible or does not make sense to detect
whether the intent of the mapping is legitimate or not
within the DNS.
The "rebinding" attack must primarily be protected at the
application that uses the DNS.
For a large site, however, it may be difficult to protect
all possible applications at once.
This filtering feature is provided only to help such an
operational environment;
it is generally discouraged to turn it on unless you are
very sure you have no other choice and the attack is a
real threat for your applications.
</para>
<para>
Care should be particularly taken if you want to use this
option for addresses within 127.0.0.0/8.
These addresses are obviously "internal", but many
applications conventionally rely on a DNS mapping from
some name to such an address.
Filtering out DNS records containing this address
spuriously can break such applications.
</para>
</section>
<section xml:id="rpz"><info><title>Response Policy Zone (RPZ) Rewriting</title></info>
<para>
<acronym>BIND</acronym> 9 includes a limited
mechanism to modify DNS responses for requests
analogous to email anti-spam DNS blacklists.
Responses can be changed to deny the existence of domains (NXDOMAIN),
deny the existence of IP addresses for domains (NODATA),
or contain other IP addresses or data.
</para>
<para>
Response policy zones are named in the
<command>response-policy</command> option for the view or among the
global options if there is no response-policy option for the view.
Response policy zones are ordinary DNS zones containing RRsets
that can be queried normally if allowed.
It is usually best to restrict those queries with something like
<command>allow-query { localhost; };</command>.
Note that zones using <command>masterfile-format map</command>
cannot be used as policy zones.
</para>
<para>
A <command>response-policy</command> option can support
multiple policy zones. To maximize performance, a radix
tree is used to quickly identify response policy zones
containing triggers that match the current query. This
imposes an upper limit of 64 on the number of policy zones
in a single <command>response-policy</command> option; more
than that is a configuration error.
</para>
<para>
Rules encoded in response policy zones are processed after
<link linkend="access_control">Access Control Lists
(ACLs)</link>. All queries from clients which are not
permitted access to the resolver will be answered with a
status code of REFUSED, regardless of configured RPZ rules.
</para>
<para>
Five policy triggers can be encoded in RPZ records.
<variablelist>
<varlistentry>
<term><command>RPZ-CLIENT-IP</command></term>
<listitem>
<para>
IP records are triggered by the IP address of the
DNS client.
Client IP address triggers are encoded in records that have
owner names that are subdomains of
<command>rpz-client-ip</command> relativized to the
policy zone origin name
and encode an address or address block.
IPv4 addresses are represented as
<userinput>prefixlength.B4.B3.B2.B1.rpz-client-ip</userinput>.
The IPv4 prefix length must be between 1 and 32.
All four bytes, B4, B3, B2, and B1, must be present.
B4 is the decimal value of the least significant byte of the
IPv4 address as in IN-ADDR.ARPA.
</para>
<para>
IPv6 addresses are encoded in a format similar
to the standard IPv6 text representation,
<userinput>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-client-ip</userinput>.
Each of W8,...,W1 is a one to four digit hexadecimal number
representing 16 bits of the IPv6 address as in the standard
text representation of IPv6 addresses, but reversed as in
IP6.ARPA. (Note that this representation of IPv6
address is different from IP6.ARPA where each hex
digit occupies a label.)
All 8 words must be present except when one set of consecutive
zero words is replaced with <userinput>.zz.</userinput>
analogous to double colons (::) in standard IPv6 text
encodings.
The IPv6 prefix length must be between 1 and 128.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>QNAME</command></term>
<listitem>
<para>
QNAME policy records are triggered by query names of
requests and targets of CNAME records resolved to generate
the response.
The owner name of a QNAME policy record is
the query name relativized to the policy zone.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RPZ-IP</command></term>
<listitem>
<para>
IP triggers are IP addresses in an
A or AAAA record in the ANSWER section of a response.
They are encoded like client-IP triggers except as
subdomains of <command>rpz-ip</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RPZ-NSDNAME</command></term>
<listitem>
<para>
NSDNAME triggers match names of authoritative servers
for the query name, a parent of the query name, a CNAME for
query name, or a parent of a CNAME.
They are encoded as subdomains of
<command>rpz-nsdname</command> relativized
to the RPZ origin name.
NSIP triggers match IP addresses in A and
AAAA RRsets for domains that can be checked against NSDNAME
policy records.
The <command>nsdname-enable</command> phrase turns NSDNAME
triggers off or on for a single policy zone or all
zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RPZ-NSIP</command></term>
<listitem>
<para>
NSIP triggers match the IP addresses of authoritative
servers. They are enncoded like IP triggers, except as
subdomains of <command>rpz-nsip</command>.
NSDNAME and NSIP triggers are checked only for names with at
least <command>min-ns-dots</command> dots.
The default value of <command>min-ns-dots</command> is
1, to exclude top level domains.
The <command>nsip-enable</command> phrase turns NSIP
triggers off or on for a single policy zone or all
zones.
</para>
<para>
If a name server's IP address is not yet known,
<command>named</command> will recursively look up
the IP address before applying an RPZ-NSIP rule.
This can cause a processing delay. To speed up
processing at the cost of precision, the
<command>nsip-wait-recurse</command> option
can be used: when set to <userinput>no</userinput>,
RPZ-NSIP rules will only be applied when a name
servers's IP address has already been looked up and
cached. If a server's IP address is not in the
cache, then the RPZ-NSIP rule will be ignored,
but the address will be looked up in the
background, and the rule will be applied
to subsequent queries. The default is
<userinput>yes</userinput>, meaning RPZ-NSIP
rules should always be applied even if an
address needs to be looked up first.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
The query response is checked against all response policy zones,
so two or more policy records can be triggered by a response.
Because DNS responses are rewritten according to at most one
policy record, a single record encoding an action (other than
<command>DISABLED</command> actions) must be chosen.
Triggers or the records that encode them are chosen for the
rewriting in the following order:
<orderedlist inheritnum="ignore" continuation="restarts">
<listitem>Choose the triggered record in the zone that appears
first in the <command>response-policy</command> option.
</listitem>
<listitem>Prefer CLIENT-IP to QNAME to IP to NSDNAME to NSIP
triggers in a single zone.
</listitem>
<listitem>Among NSDNAME triggers, prefer the
trigger that matches the smallest name under the DNSSEC ordering.
</listitem>
<listitem>Among IP or NSIP triggers, prefer the trigger
with the longest prefix.
</listitem>
<listitem>Among triggers with the same prefix length,
prefer the IP or NSIP trigger that matches
the smallest IP address.
</listitem>
</orderedlist>
</para>
<para>
When the processing of a response is restarted to resolve
DNAME or CNAME records and a policy record set has
not been triggered,
all response policy zones are again consulted for the
DNAME or CNAME names and addresses.
</para>
<para>
RPZ record sets are any types of DNS record except
DNAME or DNSSEC that encode actions or responses to
individual queries.
Any of the policies can be used with any of the triggers.
For example, while the <command>TCP-only</command> policy is
commonly used with <command>client-IP</command> triggers,
it can be used with any type of trigger to force the use of
TCP for responses with owner names in a zone.
<variablelist>
<varlistentry>
<term><command>PASSTHRU</command></term>
<listitem>
<para>
The whitelist policy is specified
by a CNAME whose target is <command>rpz-passthru</command>.
It causes the response to not be rewritten
and is most often used to "poke holes" in policies for
CIDR blocks.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>DROP</command></term>
<listitem>
<para>
The blacklist policy is specified
by a CNAME whose target is <command>rpz-drop</command>.
It causes the response to be discarded.
Nothing is sent to the DNS client.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>TCP-Only</command></term>
<listitem>
<para>
The "slip" policy is specified
by a CNAME whose target is <command>rpz-tcp-only</command>.
It changes UDP responses to short, truncated DNS responses
that require the DNS client to try again with TCP.
It is used to mitigate distributed DNS reflection attacks.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>NXDOMAIN</command></term>
<listitem>
<para>
The domain undefined response is encoded
by a CNAME whose target is the root domain (.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>NODATA</command></term>
<listitem>
<para>
The empty set of resource records is specified by
CNAME whose target is the wildcard top-level
domain (*.).
It rewrites the response to NODATA or ANCOUNT=0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>Local Data</command></term>
<listitem>
<para>
A set of ordinary DNS records can be used to answer queries.
Queries for record types not the set are answered with
NODATA.
</para>
<para>
A special form of local data is a CNAME whose target is a
wildcard such as *.example.com.
It is used as if were an ordinary CNAME after the asterisk (*)
has been replaced with the query name.
The purpose for this special form is query logging in the
walled garden's authority DNS server.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
All of the actions specified in all of the individual records
in a policy zone
can be overridden with a <command>policy</command> clause in the
<command>response-policy</command> option.
An organization using a policy zone provided by another
organization might use this mechanism to redirect domains
to its own walled garden.
<variablelist>
<varlistentry>
<term><command>GIVEN</command></term>
<listitem>
<para>The placeholder policy says "do not override but
perform the action specified in the zone."
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>DISABLED</command></term>
<listitem>
<para>
The testing override policy causes policy zone records to do
nothing but log what they would have done if the
policy zone were not disabled.
The response to the DNS query will be written (or not)
according to any triggered policy records that are not
disabled.
Disabled policy zones should appear first,
because they will often not be logged
if a higher precedence trigger is found first.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>PASSTHRU</command></term>,
<term><command>DROP</command></term>,
<term><command>TCP-Only</command></term>,
<term><command>NXDOMAIN</command></term>,
and
<term><command>NODATA</command></term>
<listitem>
<para>
override with the corresponding per-record policy.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>CNAME domain</command></term>
<listitem>
<para>
causes all RPZ policy records to act as if they were
"cname domain" records.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
By default, the actions encoded in a response policy zone
are applied only to queries that ask for recursion (RD=1).
That default can be changed for a single policy zone or
all response policy zones in a view
with a <command>recursive-only no</command> clause.
This feature is useful for serving the same zone files
both inside and outside an RFC 1918 cloud and using RPZ to
delete answers that would otherwise contain RFC 1918 values
on the externally visible name server or view.
</para>
<para>
Also by default, RPZ actions are applied only to DNS requests
that either do not request DNSSEC metadata (DO=0) or when no
DNSSEC records are available for request name in the original
zone (not the response policy zone). This default can be
changed for all response policy zones in a view with a
<command>break-dnssec yes</command> clause. In that case, RPZ
actions are applied regardless of DNSSEC. The name of the
clause option reflects the fact that results rewritten by RPZ
actions cannot verify.
</para>
<para>
No DNS records are needed for a QNAME or Client-IP trigger.
The name or IP address itself is sufficient,
so in principle the query name need not be recursively resolved.
However, not resolving the requested
name can leak the fact that response policy rewriting is in use
and that the name is listed in a policy zone to operators of
servers for listed names. To prevent that information leak, by
default any recursion needed for a request is done before any
policy triggers are considered. Because listed domains often
have slow authoritative servers, this behavior can cost
significant time.
The <command>qname-wait-recurse yes</command> option
overrides the default and enables that behavior
when recursion cannot change a non-error response.
The option does not affect QNAME or client-IP triggers
in policy zones listed
after other zones containing IP, NSIP and NSDNAME triggers, because
those may depend on the A, AAAA, and NS records that would be
found during recursive resolution. It also does not affect
DNSSEC requests (DO=1) unless <command>break-dnssec yes</command>
is in use, because the response would depend on whether or not
RRSIG records were found during resolution.
Using this option can cause error responses such as SERVFAIL to
appear to be rewritten, since no recursion is being done to
discover problems at the authoritative server.
</para>
<para>
The <command>dnsrps-enable yes</command> option turns on
the DNS Rsponse Policy Service (DNSRPS) interface, if it has been
compiled in to <command>named</command> using
<command>configure --enable-dnsrps</command>.
</para>
<para>
The <command>dnsrps-options</command> block provides additional
RPZ configuration settings, which are passed through to the
DNSRPS provider library.
Multiple DNSRPS settings in an <command>dnsrps-options</command>
string should be separated with semi-colons.
The DNSRPS provider, librpz, is passed a configuration string
consisting of the <command>dnsrps-options</command> text,
concatenated with settings derived from the
<command>response-policy</command> statement.
</para>
<para>
Note: The <command>dnsrps-options</command> text should only include
configuration settings that are specific to the DNSRPS
provider. For example, the DNSRPS provider from
Farsight Security takes options such as
<command>dnsrpzd-conf</command>,
<command>dnsrpzd-sock</command>, and
<command>dnzrpzd-args</command> (for details of these options,
see the <command>librpz</command> documentation).
Other RPZ configuration settings could be included in
<command>dnsrps-options</command>
as well, but if <command>named</command> were switched
back to traditional RPZ by setting
<command>dnsrps-enable</command> to "no", those options would
be ignored.
</para>
<para>
The TTL of a record modified by RPZ policies is set from the
TTL of the relevant record in policy zone. It is then limited
to a maximum value.
The <command>max-policy-ttl</command> clause changes the
maximum seconds from its default of 5.
For convenience, TTL-style time unit suffixes may be
used to specify the value.
</para>
<para>
For example, you might use this option statement
</para>
<programlisting> response-policy { zone "badlist"; };</programlisting>
<para>
and this zone statement
</para>
<programlisting> zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</programlisting>
<para>
with this zone file
</para>
<programlisting>$TTL 1H
@ SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
NS LOCALHOST.
; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com CNAME . ; NXDOMAIN policy
*.nxdomain.domain.com CNAME . ; NXDOMAIN policy
nodata.domain.com CNAME *. ; NODATA policy
*.nodata.domain.com CNAME *. ; NODATA policy
bad.domain.com A 10.0.0.1 ; redirect to a walled garden
AAAA 2001:2::1
bzone.domain.com CNAME garden.example.com.
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com CNAME rpz-passthru.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com CNAME *.garden.example.com.
; IP policy records that rewrite all responses containing A records in 127/8
; except 127.0.0.1
8.0.0.0.127.rpz-ip CNAME .
32.1.0.0.127.rpz-ip CNAME rpz-passthru.
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname CNAME .
48.zz.2.2001.rpz-nsip CNAME .
; blacklist and whitelist some DNS clients
112.zz.2001.rpz-client-ip CNAME rpz-drop.
8.0.0.0.127.rpz-client-ip CNAME rpz-drop.
; force some DNS clients and responses in the example.com zone to TCP
16.0.0.1.10.rpz-client-ip CNAME rpz-tcp-only.
example.com CNAME rpz-tcp-only.
*.example.com CNAME rpz-tcp-only.
</programlisting>
<para>
RPZ can affect server performance.
Each configured response policy zone requires the server to
perform one to four additional database lookups before a
query can be answered.
For example, a DNS server with four policy zones, each with all
four kinds of response triggers, QNAME, IP, NSIP, and
NSDNAME, requires a total of 17 times as many database
lookups as a similar DNS server with no response policy zones.
A <acronym>BIND9</acronym> server with adequate memory and one
response policy zone with QNAME and IP triggers might achieve a
maximum queries-per-second rate about 20% lower.
A server with four response policy zones with QNAME and IP
triggers might have a maximum QPS rate about 50% lower.
</para>
<para>
Responses rewritten by RPZ are counted in the
<command>RPZRewrites</command> statistics.
</para>
<para>
The <command>log</command> clause can be used to optionally
turn off rewrite logging for a particular response policy
zone. By default, all rewrites are logged.
</para>
<para>
The <command>add-soa</command> option controls whether the RPZ's
SOA record is added to the additional section for traceback
of changes from this zone or not. This can be set at the
individual policy zone level or at the response-policy level.
The default is <literal>yes</literal>.
</para>
<para>
Updates to RPZ zones are processed asynchronously; if there
is more than one update pending they are bundled together.
If an update to a RPZ zone (for example, via IXFR) happens less
than <option>min-update-interval</option> seconds after the most
recent update, then the changes will not be carried out until this
interval has elapsed. The default is <literal>60</literal> seconds.
For convenience, TTL-style time unit suffixes may be
used to specify the value.
</para>
</section>
<section xml:id="rrl"><info><title>Response Rate Limiting</title></info>
<para>
Excessive almost identical UDP <emphasis>responses</emphasis>
can be controlled by configuring a
<command>rate-limit</command> clause in an
<command>options</command> or <command>view</command> statement.
This mechanism keeps authoritative BIND 9 from being used
in amplifying reflection denial of service (DoS) attacks.
Short truncated (TC=1) responses can be sent to provide
rate-limited responses to legitimate clients within
a range of forged, attacked IP addresses.
Legitimate clients react to dropped or truncated response
by retrying with UDP or with TCP respectively.
</para>
<para>
This mechanism is intended for authoritative DNS servers.
It can be used on recursive servers but can slow
applications such as SMTP servers (mail receivers) and
HTTP clients (web browsers) that repeatedly request the
same domains.
When possible, closing "open" recursive servers is better.
</para>
<para>
Response rate limiting uses a "credit" or "token bucket" scheme.
Each combination of identical response and client
has a conceptual account that earns a specified number
of credits every second.
A prospective response debits its account by one.
Responses are dropped or truncated
while the account is negative.
Responses are tracked within a rolling window of time
which defaults to 15 seconds, but can be configured with
the <command>window</command> option to any value from
1 to 3600 seconds (1 hour).
The account cannot become more positive than
the per-second limit
or more negative than <command>window</command>
times the per-second limit.
When the specified number of credits for a class of
responses is set to 0, those responses are not rate limited.
</para>
<para>
The notions of "identical response" and "DNS client"
for rate limiting are not simplistic.
All responses to an address block are counted as if to a
single client.
The prefix lengths of addresses blocks are
specified with <command>ipv4-prefix-length</command> (default 24)
and <command>ipv6-prefix-length</command> (default 56).
</para>
<para>
All non-empty responses for a valid domain name (qname)
and record type (qtype) are identical and have a limit specified
with <command>responses-per-second</command>
(default 0 or no limit).
All empty (NODATA) responses for a valid domain,
regardless of query type, are identical.
Responses in the NODATA class are limited by
<command>nodata-per-second</command>
(default <command>responses-per-second</command>).
Requests for any and all undefined subdomains of a given
valid domain result in NXDOMAIN errors, and are identical
regardless of query type.
They are limited by <command>nxdomains-per-second</command>
(default <command>responses-per-second</command>).
This controls some attacks using random names, but
can be relaxed or turned off (set to 0)
on servers that expect many legitimate
NXDOMAIN responses, such as from anti-spam blacklists.
Referrals or delegations to the server of a given
domain are identical and are limited by
<command>referrals-per-second</command>
(default <command>responses-per-second</command>).
</para>
<para>
Responses generated from local wildcards are counted and limited
as if they were for the parent domain name.
This controls flooding using random.wild.example.com.
</para>
<para>
All requests that result in DNS errors other
than NXDOMAIN, such as SERVFAIL and FORMERR, are identical
regardless of requested name (qname) or record type (qtype).
This controls attacks using invalid requests or distant,
broken authoritative servers.
By default the limit on errors is the same as the
<command>responses-per-second</command> value,
but it can be set separately with
<command>errors-per-second</command>.
</para>
<para>
Many attacks using DNS involve UDP requests with forged source
addresses.
Rate limiting prevents the use of BIND 9 to flood a network
with responses to requests with forged source addresses,
but could let a third party block responses to legitimate requests.
There is a mechanism that can answer some legitimate
requests from a client whose address is being forged in a flood.
Setting <command>slip</command> to 2 (its default) causes every
other UDP request to be answered with a small truncated (TC=1)
response.
The small size and reduced frequency, and so lack of
amplification, of "slipped" responses make them unattractive
for reflection DoS attacks.
<command>slip</command> must be between 0 and 10.
A value of 0 does not "slip":
no truncated responses are sent due to rate limiting,
all responses are dropped.
A value of 1 causes every response to slip;
values between 2 and 10 cause every n'th response to slip.
Some error responses including REFUSED and SERVFAIL
cannot be replaced with truncated responses and are instead
leaked at the <command>slip</command> rate.
</para>
<para>
(NOTE: Dropped responses from an authoritative server may
reduce the difficulty of a third party successfully forging
a response to a recursive resolver. The best security
against forged responses is for authoritative operators
to sign their zones using DNSSEC and for resolver operators
to validate the responses. When this is not an option,
operators who are more concerned with response integrity
than with flood mitigation may consider setting
<command>slip</command> to 1, causing all rate-limited
responses to be truncated rather than dropped. This reduces
the effectiveness of rate-limiting against reflection attacks.)
</para>
<para>
When the approximate query per second rate exceeds
the <command>qps-scale</command> value,
then the <command>responses-per-second</command>,
<command>errors-per-second</command>,
<command>nxdomains-per-second</command> and
<command>all-per-second</command> values are reduced by the
ratio of the current rate to the <command>qps-scale</command> value.
This feature can tighten defenses during attacks.
For example, with
<command>qps-scale 250; responses-per-second 20;</command> and
a total query rate of 1000 queries/second for all queries from
all DNS clients including via TCP,
then the effective responses/second limit changes to
(250/1000)*20 or 5.
Responses sent via TCP are not limited
but are counted to compute the query per second rate.
</para>
<para>
Rate limiters for different name spaces maintain
separate counters: If, for example, there is a
<command>rate-limit</command> statement for "com" and
another for "example.com", queries matching "example.com"
will not be debited against the rate limiter for "com".
</para>
<para>
If a <command>rate-limit</command> statement does not specify a
<command>domain</command>, then it applies to the root domain
(".") and thus affects the entire DNS namespace, except those
portions covered by other <command>rate-limit</command>
statements.
</para>
<para>
Communities of DNS clients can be given their own parameters or no
rate limiting by putting
<command>rate-limit</command> statements in <command>view</command>
statements instead of the global <command>option</command>
statement.
A <command>rate-limit</command> statement in a view replaces,
rather than supplementing, a <command>rate-limit</command>
statement among the main options.
DNS clients within a view can be exempted from rate limits
with the <command>exempt-clients</command> clause.
</para>
<para>
UDP responses of all kinds can be limited with the
<command>all-per-second</command> phrase. This rate
limiting is unlike the rate limiting provided by
<command>responses-per-second</command>,
<command>errors-per-second</command>, and
<command>nxdomains-per-second</command> on a DNS server
which are often invisible to the victim of a DNS
reflection attack. Unless the forged requests of the
attack are the same as the legitimate requests of the
victim, the victim's requests are not affected. Responses
affected by an <command>all-per-second</command> limit
are always dropped; the <command>slip</command> value
has no effect. An <command>all-per-second</command>
limit should be at least 4 times as large as the other
limits, because single DNS clients often send bursts
of legitimate requests. For example, the receipt of a
single mail message can prompt requests from an SMTP
server for NS, PTR, A, and AAAA records as the incoming
SMTP/TCP/IP connection is considered. The SMTP server
can need additional NS, A, AAAA, MX, TXT, and SPF records
as it considers the STMP <command>Mail From</command>
command. Web browsers often repeatedly resolve the
same names that are repeated in HTML &lt;IMG&gt; tags
in a page. <command>all-per-second</command> is similar
to the rate limiting offered by firewalls but often
inferior. Attacks that justify ignoring the contents
of DNS responses are likely to be attacks on the DNS
server itself. They usually should be discarded before
the DNS server spends resources make TCP connections
or parsing DNS requests, but that rate limiting must
be done before the DNS server sees the requests.
</para>
<para>
The maximum size of the table used to track requests and
rate limit responses is set with <command>max-table-size</command>.
Each entry in the table is between 40 and 80 bytes.
The table needs approximately as many entries as the number
of requests received per second.
The default is 20,000.
To reduce the cold start of growing the table,
<command>min-table-size</command> (default 500)
can set the minimum table size.
Enable <command>rate-limit</command> category logging to monitor
expansions of the table and inform
choices for the initial and maximum table size.
</para>
<para>
Use <command>log-only yes</command> to test rate limiting parameters
without actually dropping any requests.
</para>
<para>
Responses dropped by rate limits are included in the
<command>RateDropped</command> and <command>QryDropped</command>
statistics.
Responses that truncated by rate limits are included in
<command>RateSlipped</command> and <command>RespTruncated</command>.
</para>
</section>
<section title="NXDOMAIN Redirection"><info/>
<para>
Named supports NXDOMAIN redirection via two methods:
<itemizedlist>
<listitem>Redirect zone <xref linkend="zone_statement_grammar"/></listitem>
<listitem>Redirect namespace</listitem>
</itemizedlist>
</para>
<para>
With both methods when named gets a NXDOMAIN response
it examines a separate namespace to see if the NXDOMAIN
response should be replaced with an alternative response.
</para>
<para>
With a redirect zone (<command>zone "." { type redirect; };</command>), the
data used to replace the NXDOMAIN is held in a single
zone which is not part of the normal namespace. All the
redirect information is contained in the zone; there are
no delegations.
</para>
<para>
With a redirect namespace (<command>option { nxdomain-redirect
&lt;suffix&gt; };</command>) the data used to replace the
NXDOMAIN is part of the normal namespace and is looked up by
appending the specified suffix to the original query name.
This roughly doubles the cache required to process NXDOMAIN
responses as you have the original NXDOMAIN response and
the replacement data or a NXDOMAIN indicating that there
is no replacement.
</para>
<para>
If both a redirect zone and a redirect namespace are configured,
the redirect zone is tried first.
</para>
</section>
</section>
<section xml:id="server_statement_grammar"><info><title><command>server</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="server.grammar.xml"/>
</section>
<section xml:id="server_statement_definition_and_usage"><info><title><command>server</command> Statement Definition and
Usage</title></info>
<para>
The <command>server</command> statement defines
characteristics
to be associated with a remote name server. If a prefix length is
specified, then a range of servers is covered. Only the most
specific
server clause applies regardless of the order in
<filename>named.conf</filename>.
</para>
<para>
The <command>server</command> statement can occur at
the top level of the
configuration file or inside a <command>view</command>
statement.
If a <command>view</command> statement contains
one or more <command>server</command> statements, only
those
apply to the view and any top-level ones are ignored.
If a view contains no <command>server</command>
statements,
any top-level <command>server</command> statements are
used as
defaults.
</para>
<para>
If 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 non-incremental. If not set, the
value
of the <command>provide-ixfr</command> option in the
view or
global options block is used as a default.
</para>
<para>
The <command>request-ixfr</command> clause determines
whether
the local server, acting as a 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 view or global options block is used as a default. It may
also be set in the zone block and, if set there, it will
override the global or view setting for that zone.
</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>request-expire</command> clause determines
whether the local server, when acting as a slave, will
request the EDNS EXPIRE value. The EDNS EXPIRE value
indicates the remaining time before the zone data will
expire and need to be be refreshed. This is used
when a secondary server transfers a zone from another
secondary server; when transferring from the primary, the
expiration timer is set from the EXPIRE field of the SOA
record instead.
The default is <command>yes</command>.
</para>
<para>
The <command>edns</command> clause determines whether
the local server will attempt to use EDNS when communicating
with the remote server. The default is <command>yes</command>.
</para>
<para>
The <command>edns-udp-size</command> option sets the
EDNS UDP size that is advertised by <command>named</command>
when querying the remote server. Valid values are 512
to 4096 bytes (values outside this range will be silently
adjusted to the nearest value within it). This option
is useful when you wish to advertise a different value
to this server than the value you advertise globally,
for example, when there is a firewall at the remote
site that is blocking large replies. (Note: Currently,
this sets a single UDP size for all packets sent to the
server; <command>named</command> will not deviate from
this value. This differs from the behavior of
<command>edns-udp-size</command> in <command>options</command>
or <command>view</command> statements, where it specifies
a maximum value. The <command>server</command> statement
behavior may be brought into conformance with the
<command>options/view</command> behavior in future releases.)
</para>
<para>
The <command>edns-version</command> option sets the
maximum EDNS VERSION that will be sent to the server(s)
by the resolver. The actual EDNS version sent is still
subject to normal EDNS version negotiation rules (see
RFC 6891), the maximum EDNS version supported by the
server, and any other heuristics that indicate that a
lower version should be sent. This option is intended
to be used when a remote server reacts badly to a given
EDNS version or higher; it should be set to the highest
version the remote server is known to support. Valid
values are 0 to 255; higher values will be silently
adjusted. This option will not be needed until higher
EDNS versions than 0 are in use.
</para>
<para>
The <command>max-udp-size</command> option sets the
maximum EDNS UDP message size <command>named</command>
will send. Valid values are 512 to 4096 bytes (values
outside this range will be silently adjusted). This
option is useful when you know that there is a firewall
that is blocking large replies from <command>named</command>.
</para>
<para>
The <command>padding</command> option adds EDNS Padding
options to outgoing messages, increasing the packet size to
a multiple of the specified block size. Valid block sizes
range from 0 (the default, which disables the use of
EDNS Padding) to 512 bytes. Larger values will be reduced
to 512, with a logged warning.
Note: This option is not currently compatible with no TSIG
or SIG(0), as the EDNS OPT record containing the padding
would have to be added to the packet after it had already
been signed.
</para>
<para>
The <command>tcp-only</command> option sets the transport
protocol to TCP. The default is to use the UDP transport
and to fallback on TCP only when a truncated response
is received.
</para>
<para>
The <command>tcp-keepalive</command> option adds EDNS
TCP keepalive to messages sent over TCP. Note currently
idle timeouts in responses are ignored.
</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 identifies a
<command>key_id</command> defined by the <command>key</command> statement,
to be used for transaction security (TSIG, <xref linkend="tsig"/>)
when talking to the remote server.
When a request is sent to the remote server, a request signature
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>
Only a single key per server is currently supported.
</para>
<para>
The <command>transfer-source</command> and
<command>transfer-source-v6</command> clauses specify
the IPv4 and IPv6 source
address to be used for zone transfer with the remote server,
respectively.
For an IPv4 remote server, only <command>transfer-source</command> can
be specified.
Similarly, for an IPv6 remote server, only
<command>transfer-source-v6</command> can be
specified.
For more details, see the description of
<command>transfer-source</command> and
<command>transfer-source-v6</command> in
<xref linkend="zone_transfers"/>.
</para>
<para>
The <command>notify-source</command> and
<command>notify-source-v6</command> clauses specify the
IPv4 and IPv6 source address to be used for notify
messages sent to remote servers, respectively. For an
IPv4 remote server, only <command>notify-source</command>
can be specified. Similarly, for an IPv6 remote server,
only <command>notify-source-v6</command> can be specified.
</para>
<para>
The <command>query-source</command> and
<command>query-source-v6</command> clauses specify the
IPv4 and IPv6 source address to be used for queries
sent to remote servers, respectively. For an IPv4
remote server, only <command>query-source</command> can
be specified. Similarly, for an IPv6 remote server,
only <command>query-source-v6</command> can be specified.
</para>
<para>
The <command>request-nsid</command> clause determines
whether the local server will add a NSID EDNS option
to requests sent to the server. This overrides
<command>request-nsid</command> set at the view or
option level.
</para>
<para>
The <command>send-cookie</command> clause determines
whether the local server will add a COOKIE EDNS option
to requests sent to the server. This overrides
<command>send-cookie</command> set at the view or
option level. The <command>named</command> server may
determine that COOKIE is not supported by the remote server
and not add a COOKIE EDNS option to requests.
</para>
</section>
<section xml:id="statschannels"><info><title><command>statistics-channels</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="statistics-channels.grammar.xml"/>
</section>
<section xml:id="statistics_channels"><info><title><command>statistics-channels</command> Statement Definition and
Usage</title></info>
<para>
The <command>statistics-channels</command> statement
declares communication channels to be used by system
administrators to get access to statistics information of
the name server.
</para>
<para>
This statement intends to be flexible to support multiple
communication protocols in the future, but currently only
HTTP access is supported.
It requires that BIND 9 be compiled with libxml2 and/or
json-c (also known as libjson0); the
<command>statistics-channels</command> statement is
still accepted even if it is built without the library,
but any HTTP access will fail with an error.
</para>
<para>
An <command>inet</command> control channel is a TCP socket
listening at the specified <command>ip_port</command> on the
specified <command>ip_addr</command>, which can be an IPv4 or IPv6
address. An <command>ip_addr</command> of <literal>*</literal>
(asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <command>ip_addr</command> of <literal>::</literal>.
</para>
<para>
If no port is specified, port 80 is used for HTTP channels.
The asterisk "<literal>*</literal>" cannot be used for
<command>ip_port</command>.
</para>
<para>
The attempt of opening a statistics channel is
restricted by the optional <command>allow</command> clause.
Connections to the statistics channel are permitted based on the
<command>address_match_list</command>.
If no <command>allow</command> clause is present,
<command>named</command> accepts connection
attempts from any address; since the statistics may
contain sensitive internal information, it is highly
recommended to restrict the source of connection requests
appropriately.
</para>
<para>
If no <command>statistics-channels</command> statement is present,
<command>named</command> will not open any communication channels.
</para>
<para>
The statistics are available in various formats and views
depending on the URI used to access them. For example, if
the statistics channel is configured to listen on 127.0.0.1
port 8888, then the statistics are accessible in XML format at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/">http://127.0.0.1:8888/</link> or
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml">http://127.0.0.1:8888/xml</link>. A CSS file is
included which can format the XML statistics into tables
when viewed with a stylesheet-capable browser, and into
charts and graphs using the Google Charts API when using a
javascript-capable browser.
</para>
<para>
Broken-out subsets of the statistics can be viewed at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/status">http://127.0.0.1:8888/xml/v3/status</link>
(server uptime and last reconfiguration time),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/server">http://127.0.0.1:8888/xml/v3/server</link>
(server and resolver statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/zones">http://127.0.0.1:8888/xml/v3/zones</link>
(zone statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/net">http://127.0.0.1:8888/xml/v3/net</link>
(network status and socket statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/mem">http://127.0.0.1:8888/xml/v3/mem</link>
(memory manager statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/tasks">http://127.0.0.1:8888/xml/v3/tasks</link>
(task manager statistics), and
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/xml/v3/traffic">http://127.0.0.1:8888/xml/v3/traffic</link>
(traffic sizes).
</para>
<para>
The full set of statistics can also be read in JSON format at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json">http://127.0.0.1:8888/json</link>,
with the broken-out subsets at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/status">http://127.0.0.1:8888/json/v1/status</link>
(server uptime and last reconfiguration time),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/server">http://127.0.0.1:8888/json/v1/server</link>
(server and resolver statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/zones">http://127.0.0.1:8888/json/v1/zones</link>
(zone statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/net">http://127.0.0.1:8888/json/v1/net</link>
(network status and socket statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/mem">http://127.0.0.1:8888/json/v1/mem</link>
(memory manager statistics),
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/tasks">http://127.0.0.1:8888/json/v1/tasks</link>
(task manager statistics), and
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://127.0.0.1:8888/json/v1/traffic">http://127.0.0.1:8888/json/v1/traffic</link>
(traffic sizes).
</para>
</section>
<section xml:id="dnssec_keys"><info><title><command>dnssec-keys</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="dnssec-keys.grammar.xml"/>
</section>
<section xml:id="dnssec-keys"><info><title><command>dnssec-keys</command> Statement Definition
and Usage</title></info>
<para>
The <command>dnssec-keys</command> statement defines DNSSEC
trust anchors. DNSSEC is described in <xref linkend="DNSSEC"/>.
</para>
<para>
A trust anchor is defined when the public key for
a non-authoritative zone is known, but cannot be securely
obtained through DNS, either because it is the DNS root zone
or because its parent zone is unsigned. Once a key has been
configured as a trust anchor, it is treated as if it had
been validated and proven secure.
</para>
<para>
The resolver attempts DNSSEC validation on all DNS data
in subdomains of configured trust anchors. (Validation below
specified names can be temporarily disabled by using
<command>rndc nta</command>, or permanently disabled with
the <command>validate-except</command> option).
</para>
<para>
All keys listed in <command>dnssec-keys</command>, and
their corresponding zones, are deemed to exist regardless
of what parent zones say. Only keys configured as trust anchors
are used to validate the DNSKEY RRset for the corresponding
name. The parent's DS RRset will not be used.
</para>
<para>
The <command>dnssec-keys</command> statement can contain
multiple key entries, each consisting of the key's
domain name, followed by the <command>static-key</command> or
<command>initial-key</command> keyword, then the key's flags,
protocol, algorithm, and the Base64 representation of the key
data. Spaces, tabs, newlines and carriage returns are ignored
in the key data, so the configuration may be split up into
multiple lines.
</para>
<para>
<command>dnssec-keys</command> may be set at the top level
of <filename>named.conf</filename> or within a view. If it is
set in both places, the configurations are additive: keys
defined at the top level are inherited by all views, but keys
defined in a view are only used within that view.
</para>
<para>
<command>dnssec-keys</command> entries can be configured with
two keywords: <command>static-key</command> or
<command>initial-key</command>. Keys configured with
<command>static-key</command> are immutable,
while keys configured with <command>initial-key</command>
can be kept up to date automatically, without intervention
from the resolver operator. (<command>static-key</command>
keys are identical to keys configured using the deprecated
<command>trusted-keys</command> statement.)
</para>
<para>
Suppose, for example, that a zone's key-signing
key was compromised, and the zone owner had to revoke and
replace the key. A resolver which had the original key
configured as a <command>static-key</command> would be
unable to validate this zone any longer; it would
reply with a SERVFAIL response code. This would
continue until the resolver operator had updated the
<command>dnssec-keys</command> statement with the new key.
</para>
<para>
If, however, the trust anchor had been configured with
<command>initial-key</command> instead, then the
zone owner could add a "stand-by" key to their zone in advance.
<command>named</command> would store the stand-by key, and
when the original key was revoked, <command>named</command>
would be able to transition smoothly to the new key. It would
also recognize that the old key had been revoked, and cease
using that key to validate answers, minimizing the damage that
the compromised key could do. This is the process used to
keep the ICANN root DNSSEC key up to date.
</para>
<para>
Whereas <command>static-key</command>
keys continue to be trusted until they are removed from
<filename>named.conf</filename>, an
<command>initial-key</command> is only trusted
<emphasis>once</emphasis>: for as long as it
takes to load the managed key database and start the RFC 5011
key maintenance process.
</para>
<para>
The first time <command>named</command> runs with an
<command>initial-key</command> configured in
<filename>named.conf</filename>, it fetches the
DNSKEY RRset directly from the zone apex, and validates it
using the key specified in <command>dnssec-keys</command>.
If the DNSKEY RRset is validly signed, then it is
used as the basis for a new managed keys database.
</para>
<para>
From that point on, whenever <command>named</command> runs, it
sees the <command>initial-key</command> listed in
<command>dnssec-keys</command>, checks to
make sure RFC 5011 key maintenance has already been initialized
for the specified domain, and if so, it simply moves on. The
key specified in the <command>dnssec-keys</command>
statement is not used to validate answers; it is
superseded by the key or keys stored in the managed keys
database.
</para>
<para>
The next time <command>named</command> runs after an
<command>initial-key</command> has been
<emphasis>removed</emphasis> from the
<command>dnssec-keys</command> statement (or changed to
a <command>static-key</command>), the corresponding
zone will be removed from the managed keys database,
and RFC 5011 key maintenance will no longer be used for that
domain.
</para>
<para>
In the current implementation, the managed keys database
is stored as a master-format zone file.
</para>
<para>
On servers which do not use views, this file is named
<filename>managed-keys.bind</filename>. When views are in
use, there will be a separate managed keys database for each
view; the filename will be the view name (or, if a view name
contains characters which would make it illegal as a filename,
a hash of the view name), followed by
the suffix <filename>.mkeys</filename>.
</para>
<para>
When the key database is changed, the zone is updated.
As with any other dynamic zone, changes will be written
into a journal file, e.g.,
<filename>managed-keys.bind.jnl</filename> or
<filename>internal.mkeys.jnl</filename>.
Changes are committed to the master file as soon as
possible afterward; this will usually occur within 30
seconds. So, whenever <command>named</command> is using
automatic key maintenance, the zone file and journal file
can be expected to exist in the working directory.
(For this reason among others, the working directory
should be always be writable by <command>named</command>.)
</para>
<para>
If the <command>dnssec-validation</command> option is
set to <userinput>auto</userinput>, <command>named</command>
will automatically initialize an <command>initial-key</command>
for the root zone. The key that is used to initialize the key
maintenance process is stored in <filename>bind.keys</filename>;
the location of this file can be overridden with the
<command>bindkeys-file</command> option. As a fallback
in the event no <filename>bind.keys</filename> can be
found, the initializing key is also compiled directly
into <command>named</command>.
</para>
</section>
<section xml:id="managed-keys"><info><title><command>managed-keys</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="managed-keys.grammar.xml"/>
</section>
<section xml:id="managed_keys"><info><title><command>managed-keys</command> Statement Definition
and Usage</title></info>
<para>
The <command>managed-keys</command> statement has been
deprecated in favor of <xref linkend="dnssec_keys"/>
with the <command>initial-key</command> keyword.
</para>
</section>
<section xml:id="trusted-keys"><info><title><command>trusted-keys</command> Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="trusted-keys.grammar.xml"/>
</section>
<section xml:id="trusted_keys"><info><title><command>trusted-keys</command> Statement Definition
and Usage</title></info>
<para>
The <command>trusted-keys</command> statement has been
deprecated in favor of <xref linkend="dnssec_keys"/>
with the <command>static-key</command> keyword.
</para>
</section>
<section xml:id="view_statement_grammar"><info><title><command>view</command> Statement Grammar</title></info>
<programlisting><command>view</command> <replaceable>view_name</replaceable> [ <replaceable>class</replaceable> ] <command>{</command>
<command>match-clients {</command> <replaceable>address_match_list</replaceable> <command>}</command> ;
<command>match-destinations {</command> <replaceable>address_match_list</replaceable> <command>}</command> ;
<command>match-recursive-only</command> <replaceable>yes_or_no</replaceable> ;
[ <replaceable>view_option</replaceable> ; ... ]
[ <replaceable>zone_statement</replaceable> ; ... ]
<command>} </command>;
</programlisting>
</section>
<section xml:id="view_statement"><info><title><command>view</command> Statement Definition and Usage</title></info>
<para>
The <command>view</command> statement is a powerful
feature
of <acronym>BIND</acronym> 9 that lets a name server
answer a DNS query differently
depending on who is asking. It is particularly useful for
implementing
split DNS setups without having to run multiple servers.
</para>
<para>
Each <command>view</command> statement defines a view
of the
DNS namespace that 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. In addition to checking IP
addresses
<command>match-clients</command> and <command>match-destinations</command>
can also take <command>keys</command> which provide an
mechanism for the
client to select the view. A view can also be specified
as <command>match-recursive-only</command>, which
means that only recursive
requests from matching clients will match that view.
The order of the <command>view</command> statements is
significant —
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
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. Any <command>zone</command> statements
specified on
the top level of the configuration file are considered to be part
of
this default view, and the <command>options</command>
statement will
apply to the default view. If any explicit <command>view</command>
statements are present, all <command>zone</command>
statements must
occur inside <command>view</command> statements.
</para>
<para>
Here is an example of a typical split DNS setup implemented
using <command>view</command> statements:
</para>
<programlisting>view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal
// clients only.
recursion yes;
// Provide a complete view of the example.com
// zone including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
// Match all clients not matched by the
// previous view.
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com
// zone containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
</programlisting>
</section>
<section xml:id="zone_statement_grammar"><info><title><command>zone</command>
Statement Grammar</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="master.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="slave.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="mirror.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="hint.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="stub.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="static-stub.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="forward.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="redirect.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="delegation-only.zoneopt.xml"/>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="in-view.zoneopt.xml"/>
</section>
<section xml:id="zone_statement"><info><title><command>zone</command> Statement Definition and Usage</title></info>
<section xml:id="zone_types"><info><title>Zone Types</title></info>
<para>
The <command>type</command> keyword is required
for the <command>zone</command> configuration unless
it is an <command>in-view</command> configuration. Its
acceptable values include:
<varname>master</varname> (or <varname>primary</varname>),
<varname>slave</varname> (or <varname>secondary</varname>),
<varname>mirror</varname>,
<varname>delegation-only</varname>,
<varname>forward</varname>,
<varname>hint</varname>,
<varname>redirect</varname>,
<varname>static-stub</varname>,
and <varname>stub</varname>.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<!--colspec colname="1" colnum="1" colsep="0" colwidth="1.108in"/-->
<!--colspec colname="2" colnum="2" colsep="0" colwidth="4.017in"/-->
<colspec colname="1" colnum="1" colsep="0"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.017in"/>
<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. Type <varname>primary</varname> is
a synonym for <varname>master</varname>.
</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. Type <varname>secondary</varname> is a
synonym for <varname>slave</varname>.
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.
Masters list elements can also be names of other
masters lists.
By default, transfers are made from port 53 on the
servers; this can
be changed for all servers by specifying a port number
before the
list of IP addresses, or on a per-server basis after
the IP address.
Authentication to the 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 startup and
eliminates
a needless waste of bandwidth. Note that for large
numbers (in the
tens or hundreds of thousands) of zones per server, it
is best to
use a two-level naming scheme for zone filenames. For
example,
a 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 100000 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
RFC1918 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>mirror</varname>
</para>
</entry>
<entry colname="2">
<para>
<emphasis role="bold">Note:</emphasis> using
this zone type with any zone other than the root
zone should be considered
<emphasis>experimental</emphasis> and may cause
performance issues, especially for zones which
are large and/or frequently updated.
</para>
<para>
A mirror zone acts like a zone of type
<userinput>secondary</userinput> whose data is
subject to DNSSEC validation before being used
in answers. Validation is performed during the
zone transfer process (for both AXFR and IXFR),
and again when the zone file is loaded from disk
when <command>named</command> is restarted. If
validation of a new version of a mirror zone
fails, a retransfer is scheduled and the most
recent correctly validated version of that zone
is used until it expires; if a newer version of
that zone is later correctly validated, it
replaces the previously used version. If no
usable zone data is available for a mirror zone
(either because it was never loaded from disk
and has not yet been transferred from a primary
server or because its most recent correctly
validated version expired), traditional DNS
recursion will be used to look up the answers
instead.
</para>
<para>
While any zone may be configured with this type,
it is intended to be used to set up a fast local
copy of the root zone, similar to the one
described in RFC 7706. Note, however, that
mirror zones are not supposed to augment the
example configuration provided by RFC 7706 but
rather to replace it altogether.
</para>
<para>
A default list of primary servers for the IANA
root zone is built into <command>named</command>
and thus its mirroring can be enabled using the
following configuration:
</para>
<programlisting>zone "." {
type mirror;
};</programlisting>
<para>
In order to set up mirroring of any other zone,
an explicit list of primary servers needs to be
provided using the <command>masters</command>
option (see <xref linkend="masters_grammar"/>
for details).
</para>
<para>
To make mirror zone contents persist between
<command>named</command> restarts, use the
<xref endterm="file_option_term" linkend="file_option"/>
option.
</para>
<para>
Mirror zone validation always happens for the
entire zone contents, i.e. no "incremental
validation" takes place, even for IXFRs. This
is required to ensure that each version of the
zone used by the resolver is fully
self-consistent with respect to DNSSEC. Other,
more efficient zone verification methods may be
added in the future.
</para>
<para>
For validation to succeed, a key-signing key
(KSK) for the zone must be configured as a trust
anchor in <filename>named.conf</filename>: that
is, a key for the zone must be specified in
<command>dnssec-keys</command>. In the case
of the root zone, you may also rely on the
built-in root trust anchor, which is enabled
when <xref endterm="dnssec_validation_term"
linkend="dnssec_validation"/> is set to the
default value <userinput>auto</userinput>.
</para>
<para>
Answers coming from a mirror zone look almost
exactly like answers from a zone of type
<userinput>secondary</userinput>, with the
notable exceptions that the AA bit
("authoritative answer") is not set, and the AD
bit ("authenticated data") is.
</para>
<para>
Since mirror zones are intended to be used by
recursive resolvers, adding one to a view with
recursion disabled is considered to be a
configuration error.
</para>
<para>
When configuring NOTIFY for a mirror zone, only
<userinput>notify no;</userinput> and
<userinput>notify explicit;</userinput> can be
used. Using any other <command>notify</command>
setting at the zone level is a configuration
error. Using any other
<command>notify</command> setting at the
<command>options</command> or
<command>view</command> level will cause
that setting to be overridden with
<userinput>notify explicit;</userinput> for the
mirror zone in question. Since the global
default for the <command>notify</command> option
is <userinput>yes</userinput>, mirror zones are
by default configured with
<userinput>notify explicit;</userinput>.
</para>
<para>
Outgoing transfers of mirror zones are disabled
by default but may be enabled using
<xref endterm="allow_transfer_term" linkend="allow_transfer"/>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>static-stub</varname>
</para>
</entry>
<entry colname="2">
<para>
A static-stub zone is similar to a stub zone
with the following exceptions:
the zone data is statically configured, rather
than transferred from a master server;
when recursion is necessary for a query that
matches a static-stub zone, the locally
configured data (nameserver names and glue addresses)
is always used even if different authoritative
information is cached.
</para>
<para>
Zone data is configured via the
<command>server-addresses</command> and
<command>server-names</command> zone options.
</para>
<para>
The zone data is maintained in the form of NS
and (if necessary) glue A or AAAA RRs
internally, which can be seen by dumping zone
databases by <command>rndc dumpdb -all</command>.
The configured RRs are considered local configuration
parameters rather than public data.
Non recursive queries (i.e., those with the RD
bit off) to a static-stub zone are therefore
prohibited and will be responded with REFUSED.
</para>
<para>
Since the data is statically configured, no
zone maintenance action takes place for a static-stub
zone.
For example, there is no periodic refresh
attempt, and an incoming notify message
will be rejected with an rcode of NOTAUTH.
</para>
<para>
Each static-stub zone is configured with
internally generated NS and (if necessary)
glue A or AAAA RRs
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>forward</varname>
</para>
</entry>
<entry colname="2">
<para>
A "forward zone" is a way to configure
forwarding on a per-domain basis. A <command>zone</command> statement
of type <command>forward</command> can
contain a <command>forward</command>
and/or <command>forwarders</command>
statement,
which 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, canceling 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 re-specify 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 name servers is
specified using a "hint zone". When the server starts
up, it uses
the root hints to find a root name server and get the
most recent
list of root name servers. If no hint zone is
specified for class
IN, the server uses a compiled-in default set of root
servers hints.
Classes other than IN have no built-in defaults hints.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>redirect</varname>
</para>
</entry>
<entry colname="2">
<para>
Redirect zones are used to provide answers to
queries when normal resolution would result in
NXDOMAIN being returned.
Only one redirect zone is supported
per view. <command>allow-query</command> can be
used to restrict which clients see these answers.
</para>
<para>
If the client has requested DNSSEC records (DO=1) and
the NXDOMAIN response is signed then no substitution
will occur.
</para>
<para>
To redirect all NXDOMAIN responses to
100.100.100.2 and
2001:ffff:ffff::100.100.100.2, one would
configure a type redirect zone named ".",
with the zone file containing wildcard records
that point to the desired addresses:
<literal>"*. IN A 100.100.100.2"</literal>
and
<literal>"*. IN AAAA 2001:ffff:ffff::100.100.100.2"</literal>.
</para>
<para>
To redirect all Spanish names (under .ES) one
would use similar entries but with the names
"*.ES." instead of "*.". To redirect all
commercial Spanish names (under COM.ES) one
would use wildcard entries called "*.COM.ES.".
</para>
<para>
Note that the redirect zone supports all
possible types; it is not limited to A and
AAAA records.
</para>
<para>
If a redirect zone is configured with a
<option>masters</option> option, then it is
transfered in as if it were a slave zone.
Otherwise, it is loaded from a file as if it
were a master zone.
</para>
<para>
Because redirect zones are not referenced
directly by name, they are not kept in the
zone lookup table with normal master and slave
zones. To reload a redirect zone, use
<command>rndc reload -redirect</command>,
and to retransfer a redirect zone configured
as slave, use
<command>rndc retransfer -redirect</command>.
When using <command>rndc reload</command>
without specifying a zone name, redirect zones
will be reloaded along with other zones.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>delegation-only</varname>
</para>
</entry>
<entry colname="2">
<para>
This is used to enforce the delegation-only
status of infrastructure zones (e.g. COM,
NET, ORG). Any answer that is received
without an explicit or implicit delegation
in the authority section will be treated
as NXDOMAIN. This does not apply to the
zone apex. This should not be applied to
leaf zones.
</para>
<para>
<varname>delegation-only</varname> has no
effect on answers received from forwarders.
</para>
<para>
See caveats in <xref linkend="root_delegation_only"/>.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="class"><info><title>Class</title></info>
<para>
The zone's name may optionally be followed by a class. If
a class is not specified, class <literal>IN</literal> (for <varname>Internet</varname>),
is assumed. This is correct for the vast majority of cases.
</para>
<para>
The <literal>hesiod</literal> class is
named for an information service from MIT's Project Athena. It
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>
</section>
<section xml:id="zone_options"><info><title>Zone Options</title></info>
<variablelist>
<varlistentry>
<term><command>allow-notify</command></term>
<listitem>
<para>
See the description of
<command>allow-notify</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query</command></term>
<listitem>
<para>
See the description of
<command>allow-query</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-on</command></term>
<listitem>
<para>
See the description of
<command>allow-query-on</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-transfer</command></term>
<listitem>
<para>
See the description of <command>allow-transfer</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update</command></term>
<listitem>
<para>
See the description of <command>allow-update</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-policy</command></term>
<listitem>
<para>
Specifies a "Simple Secure Update" policy. See
<xref linkend="dynamic_update_policies"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update-forwarding</command></term>
<listitem>
<para>
See the description of <command>allow-update-forwarding</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>also-notify</command></term>
<listitem>
<para>
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 name servers
(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.
A TSIG key may also be specified to cause the
<literal>NOTIFY</literal> to be signed by the
given key.
<command>also-notify</command> is not
meaningful for stub zones.
The default is the empty list.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-names</command></term>
<listitem>
<para>
This option is used to restrict the character set and
syntax of
certain domain names in master files and/or DNS responses
received from the
network. The default varies according to zone type. For <command>master</command> zones the default is <command>fail</command>. For <command>slave</command>
zones the default is <command>warn</command>.
It is not implemented for <command>hint</command> zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx</command></term>
<listitem>
<para>
See the description of
<command>check-mx</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-spf</command></term>
<listitem>
<para>
See the description of
<command>check-spf</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-wildcard</command></term>
<listitem>
<para>
See the description of
<command>check-wildcard</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-integrity</command></term>
<listitem>
<para>
See the description of
<command>check-integrity</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-sibling</command></term>
<listitem>
<para>
See the description of
<command>check-sibling</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl</command></term>
<listitem>
<para>
See the description of
<command>zero-no-soa-ttl</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-check-ksk</command></term>
<listitem>
<para>
See the description of
<command>update-check-ksk</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-loadkeys-interval</command></term>
<listitem>
<para>
See the description of
<command>dnssec-loadkeys-interval</command> in <xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-update-mode</command></term>
<listitem>
<para>
See the description of
<command>dnssec-update-mode</command> in <xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-dnskey-kskonly</command></term>
<listitem>
<para>
See the description of
<command>dnssec-dnskey-kskonly</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>try-tcp-refresh</command></term>
<listitem>
<para>
See the description of
<command>try-tcp-refresh</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>database</command></term>
<listitem>
<para>
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>delegation-only</command></term>
<listitem>
<para>
The flag only applies to forward, hint and stub
zones. If set to <userinput>yes</userinput>,
then the zone will also be treated as if it is
also a delegation-only type zone.
</para>
<para>
See caveats in <xref linkend="root_delegation_only"/>.
</para>
</listitem>
</varlistentry>
<varlistentry xml:id="file_option">
<term xml:id="file_option_term"><command>file</command></term>
<listitem>
<para>
Set the zone's filename. In <command>master</command>,
<command>hint</command>, and <command>redirect</command>
zones which do not have <command>masters</command>
defined, zone data is loaded from this file. In
<command>slave</command>, <command>mirror</command>,
<command>stub</command>, and <command>redirect</command>
zones which do have <command>masters</command>
defined, zone data is retrieved from another server
and saved in this file. This option is not
applicable to other zone types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>forward</command></term>
<listitem>
<para>
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 and the global options are
not used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>journal</command></term>
<listitem>
<para>
Allow the default journal's filename to be overridden.
The default is the zone's filename with "<filename>.jnl</filename>" appended.
This is applicable to <command>master</command> and <command>slave</command> zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-journal-size</command></term>
<listitem>
<para>
See the description of
<command>max-journal-size</command> in <xref linkend="server_resource_limits"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-records</command></term>
<listitem>
<para>
See the description of
<command>max-records</command> in <xref linkend="server_resource_limits"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-in</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-time-in</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-in</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-idle-in</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-out</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-time-out</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-out</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-idle-out</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify</command></term>
<listitem>
<para>
See the description of
<command>notify</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-delay</command></term>
<listitem>
<para>
See the description of
<command>notify-delay</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-to-soa</command></term>
<listitem>
<para>
See the description of
<command>notify-to-soa</command> in
<xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zone-statistics</command></term>
<listitem>
<para>
See the description of
<command>zone-statistics</command> in
<xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-addresses</command></term>
<listitem>
<para>
Only meaningful for static-stub zones.
This is a list of IP addresses to which queries
should be sent in recursive resolution for the
zone.
A non empty list for this option will internally
configure the apex NS RR with associated glue A or
AAAA RRs.
</para>
<para>
For example, if "example.com" is configured as a
static-stub zone with 192.0.2.1 and 2001:db8::1234
in a <command>server-addresses</command> option,
the following RRs will be internally configured.
</para>
<programlisting>example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</programlisting>
<para>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
will initiate recursive resolution and send
queries to 192.0.2.1 and/or 2001:db8::1234.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-names</command></term>
<listitem>
<para>
Only meaningful for static-stub zones.
This is a list of domain names of nameservers that
act as authoritative servers of the static-stub
zone.
These names will be resolved to IP addresses when
<command>named</command> needs to send queries to
these servers.
To make this supplemental resolution successful,
these names must not be a subdomain of the origin
name of static-stub zone.
That is, when "example.net" is the origin of a
static-stub zone, "ns.example" and
"master.example.com" can be specified in the
<command>server-names</command> option, but
"ns.example.net" cannot, and will be rejected by
the configuration parser.
</para>
<para>
A non empty list for this option will internally
configure the apex NS RR with the specified names.
For example, if "example.com" is configured as a
static-stub zone with "ns1.example.net" and
"ns2.example.net"
in a <command>server-names</command> option,
the following RRs will be internally configured.
</para>
<programlisting>example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</programlisting>
<para>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
initiate recursive resolution,
resolve "ns1.example.net" and/or
"ns2.example.net" to IP addresses, and then send
queries to (one or more of) these addresses.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-validity-interval</command></term>
<listitem>
<para>
See the description of
<command>sig-validity-interval</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-nodes</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-nodes</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-signatures</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-signatures</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-type</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-type</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source</command></term>
<listitem>
<para>
See the description of
<command>transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source-v6</command></term>
<listitem>
<para>
See the description of
<command>transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source</command></term>
<listitem>
<para>
See the description of
<command>alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source-v6</command></term>
<listitem>
<para>
See the description of
<command>alt-transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-alt-transfer-source</command></term>
<listitem>
<para>
See the description of
<command>use-alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source</command></term>
<listitem>
<para>
See the description of
<command>notify-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source-v6</command></term>
<listitem>
<para>
See the description of
<command>notify-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-refresh-time</command></term>
<term><command>max-refresh-time</command></term>
<term><command>min-retry-time</command></term>
<term><command>max-retry-time</command></term>
<listitem>
<para>
See the 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"/>.
(Note that the <command>ixfr-from-differences</command>
<userinput>master</userinput> and
<userinput>slave</userinput> choices are not
available at the zone level.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>key-directory</command></term>
<listitem>
<para>
See the description of
<command>key-directory</command> in <xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>auto-dnssec</command></term>
<listitem>
<para>
See the description of
<command>auto-dnssec</command> in
<xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>serial-update-method</command></term>
<listitem>
<para>
See the description of
<command>serial-update-method</command> in
<xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>inline-signing</command></term>
<listitem>
<para>
If <literal>yes</literal>, this enables
"bump in the wire" signing of a zone, where a
unsigned zone is transferred in or loaded from
disk and a signed version of the zone is served,
with possibly, a different serial number. This
behavior is disabled by default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>multi-master</command></term>
<listitem>
<para>
See the description of <command>multi-master</command> in
<xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>masterfile-format</command></term>
<listitem>
<para>
See the description of <command>masterfile-format</command>
in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-zone-ttl</command></term>
<listitem>
<para>
See the description of <command>max-zone-ttl</command>
in <xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-secure-to-insecure</command></term>
<listitem>
<para>
See the description of
<command>dnssec-secure-to-insecure</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="dynamic_update_policies"><info><title>Dynamic Update Policies</title></info>
<para><acronym>BIND</acronym> 9 supports two 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 is a simple
access control list. Any client that matches
the ACL is granted permission to update any record
in the zone.
</para>
<para>
The <command>update-policy</command> clause
allows more fine-grained control over what updates are
allowed. It specifies a set of rules, in which each rule
either grants or denies permission for one or more
names in the zone to be updated by one or more
identities. Identity is determined by the key that
signed the update request using either TSIG or SIG(0).
In most cases, <command>update-policy</command> rules
only apply to key-based identities. There is no way
to specify update permissions based on client source
address.
</para>
<para>
<command>update-policy</command> rules are only meaningful
for zones of type <command>master</command>, and are
not allowed in any other zone type.
It is a configuration error to specify both
<command>allow-update</command> and
<command>update-policy</command> at the same time.
</para>
<para>
A pre-defined <command>update-policy</command> rule can be
switched on with the command
<command>update-policy local;</command>.
Using this in a zone causes
<command>named</command> to generate a TSIG session key
when starting up and store it in a file; this key can then
be used by local clients to update the zone while
<command>named</command> is running.
By default, the session key is stored in the file
<filename>/var/run/named/session.key</filename>, the key name
is "local-ddns", and the key algorithm is HMAC-SHA256.
These values are configurable with the
<command>session-keyfile</command>,
<command>session-keyname</command> and
<command>session-keyalg</command> options, respectively.
A client running on the local system, if run with appropriate
permissions, may read the session key from the key file and
use it to sign update requests. The zone's update
policy will be set to allow that key to change any record
within the zone. Assuming the key name is "local-ddns",
this policy is equivalent to:
</para>
<programlisting>update-policy { grant local-ddns zonesub any; };
</programlisting>
<para>
...with the additional restriction that only clients
connecting from the local system will be permitted to send
updates.
</para>
<para>
Note that only one session key is generated by
<command>named</command>; all zones configured to use
<command>update-policy local</command> will accept the same key.
</para>
<para>
The command <command>nsupdate -l</command> implements this
feature, sending requests to localhost and signing them using
the key retrieved from the session key file.
</para>
<para>
Other rule definitions look like this:
</para>
<programlisting>
( <command>grant</command> | <command>deny</command> ) <replaceable>identity</replaceable> <replaceable>ruletype</replaceable> <optional> <replaceable>name</replaceable> </optional> <optional> <replaceable>types</replaceable> </optional>
</programlisting>
<para>
Each rule grants or denies privileges. Rules are checked
in the order in which they are specified in the
<command>update-policy</command> statement. Once a message
has successfully matched a rule, the operation is immediately
granted or denied, and no further rules are examined. There
are 13 types of rules; the rule type is specified by the
<command>ruletype</command> field, and the interpretation
of other fields varies depending on the rule type.
</para>
<para>
In general, a rule is matched when the
key that signed an update request matches the
<command>identity</command> field, the name of the record
to be updated matches the <command>name</command> field
(in the manner specified by the <command>ruletype</command>
field), and the type of the record to be updated matches the
<command>types</command> field. Details for each rule type
are described below.
</para>
<para>
The <command>identity</command> field must be set to
a fully-qualified domain name. In most cases, this
represensts the name of the TSIG or SIG(0) key that must be
used to sign the update request. If the specified name is a
wildcard, it is subject to DNS wildcard expansion, and the
rule may apply to multiple identities. When a TKEY exchange
has been used to create a shared secret, the identity of
the key used to authenticate the TKEY exchange will be
used as the identity of the shared secret. Some rule types
use identities matching the client's Kerberos principal
(e.g, <userinput>"host/machine@REALM"</userinput>) or
Windows realm (<userinput>machine$@REALM</userinput>).
</para>
<para>
The <replaceable>name</replaceable> field also specifies
a fully-qualified domain name. This often
represents the name of the record to be updated.
Interpretation of this field is dependent on rule type.
</para>
<para>
If no <command>types</command> are explicitly specified,
then a rule matches all types except RRSIG, NS, SOA, NSEC
and NSEC3. Types may be specified by name, including
"ANY" (ANY matches all types except NSEC and NSEC3,
which can never be updated). Note that when an attempt
is made to delete all records associated with a name,
the rules are checked for each existing record type.
</para>
<para>
The <replaceable>ruletype</replaceable> field has 16
values:
<varname>name</varname>, <varname>subdomain</varname>,
<varname>wildcard</varname>, <varname>self</varname>,
<varname>selfsub</varname>, <varname>selfwild</varname>,
<varname>krb5-self</varname>, <varname>ms-self</varname>,
<varname>krb5-selfsub</varname>, <varname>ms-selfsub</varname>,
<varname>krb5-subdomain</varname>,
<varname>ms-subdomain</varname>,
<varname>tcp-self</varname>, <varname>6to4-self</varname>,
<varname>zonesub</varname>, and <varname>external</varname>.
</para>
<informaltable>
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.819in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.681in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<varname>name</varname>
</para>
</entry> <entry colname="2">
<para>
Exact-match semantics. This rule matches
when the name being updated is identical
to the contents of the
<replaceable>name</replaceable> field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
This rule matches when the name being updated
is a subdomain of, or identical to, the
contents of the <replaceable>name</replaceable>
field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>zonesub</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to subdomain, except that
it matches when the name being updated is a
subdomain of the zone in which the
<command>update-policy</command> statement
appears. This obviates the need to type the zone
name twice, and enables the use of a standard
<command>update-policy</command> statement in
multiple zones without modification.
</para>
<para>
When this rule is used, the
<replaceable>name</replaceable> field is omitted.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>wildcard</varname>
</para>
</entry> <entry colname="2">
<para>
The <replaceable>name</replaceable> field
is subject to DNS wildcard expansion, and
this rule matches when the name being updated
is a valid expansion of the wildcard.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>self</varname>
</para>
</entry>
<entry colname="2">
<para>
This rule matches when the name of the record
being updated matches the contents of the
<replaceable>identity</replaceable> field.
The <replaceable>name</replaceable> field
is ignored. To avoid confusion, it is recommended
that this field be set to the same value as the
<replaceable>identity</replaceable> field or to
"."
</para>
<para>
The <varname>self</varname> rule type is
most useful when allowing one key per
name to update, where the key has the same
name as the record to be updated. In this case,
the <replaceable>identity</replaceable> field
can be specified as <constant>*</constant>
(an asterisk).
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>selfsub</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to <varname>self</varname>
except that subdomains of <varname>self</varname>
can also be updated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>selfwild</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to <varname>self</varname>
except that only subdomains of
<varname>self</varname> can be updated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ms-self</varname>
</para>
</entry> <entry colname="2">
<para>
When a client sends an UPDATE using a Windows
machine principal (for example, 'machine$@REALM'),
this rule allows records with the absolute name
of 'machine.REALM' to be updated.
</para>
<para>
The realm to be matched is specified in the
<replaceable>identity</replaceable> field.
</para>
<para>
The <replaceable>name</replaceable> field has
no effect on this rule; it should be set to "."
as a placeholder.
</para>
<para>
For example,
<userinput>grant EXAMPLE.COM ms-self . A AAAA</userinput>
allows any machine with a valid principal in
the realm <userinput>EXAMPLE.COM</userinput> to update
its own address records.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ms-selfsub</varname>
</para>
</entry> <entry colname="2">
<para>
This is similar to <command>ms-self</command>
except it also allows updates to any subdomain of
the name specified in the Windows machine
principal, not just to the name itself.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ms-subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
When a client sends an UPDATE using a Windows
machine principal (for example, 'machine$@REALM'),
this rule allows any machine in the specified
realm to update any record in the zone or in a
specified subdomain of the zone.
</para>
<para>
The realm to be matched is specified in the
<replaceable>identity</replaceable> field.
</para>
<para>
The <replaceable>name</replaceable> field
specifies the subdomain that may be updated.
If set to "." (or any other name at or above
the zone apex), any name in the zone can be
updated.
</para>
<para>
For example, if <command>update-policy</command>
for the zone "example.com" includes
<userinput>grant EXAMPLE.COM ms-subdomain hosts.example.com. A AAAA</userinput>,
any machine with a valid principal in
the realm <userinput>EXAMPLE.COM</userinput> will
be able to update address records at or below
"hosts.example.com".
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>krb5-self</varname>
</para>
</entry> <entry colname="2">
<para>
When a client sends an UPDATE using a
Kerberos machine principal (for example,
'host/machine@REALM'), this rule allows
records with the absolute name of 'machine'
to be updated provided it has been authenticated
by REALM. This is similar but not identical
to <command>ms-self</command> due to the
'machine' part of the Kerberos principal
being an absolute name instead of a unqualified
name.
</para>
<para>
The realm to be matched is specified in the
<replaceable>identity</replaceable> field.
</para>
<para>
The <replaceable>name</replaceable> field has
no effect on this rule; it should be set to "."
as a placeholder.
</para>
<para>
For example,
<userinput>grant EXAMPLE.COM krb5-self . A AAAA</userinput>
allows any machine with a valid principal in
the realm <userinput>EXAMPLE.COM</userinput> to update
its own address records.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>krb5-selfsub</varname>
</para>
</entry> <entry colname="2">
<para>
This is similar to <command>krb5-self</command>
except it also allows updates to any subdomain of
the name specified in the 'machine' part of the
Kerberos principal, not just to the name itself.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>krb5-subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is identical to
<command>ms-subdomain</command>, except that it works
with Kerberos machine principals (i.e.,
'host/machine@REALM') rather than Windows machine
principals.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>tcp-self</varname>
</para>
</entry> <entry colname="2">
<para>
This rule allows updates that have been sent via
TCP and for which the standard mapping from the
client's IP address into the
<literal>in-addr.arpa</literal> and
<literal>ip6.arpa</literal>
namespaces match the name to be updated.
The <command>identity</command> field must match
that name. The <command>name</command> field
should be set to ".".
Note that, since identity is based on the client's
IP address, it is not necessary for update request
messages to be signed.
</para>
<note>
It is theoretically possible to spoof these TCP
sessions.
</note>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>6to4-self</varname>
</para>
</entry> <entry colname="2">
<para>
This allows the name matching a 6to4 IPv6 prefix,
as specified in RFC 3056, to be updated by any
TCP connection from either the 6to4 network or
from the corresponding IPv4 address. This is
intended to allow NS or DNAME RRsets to be added
to the <literal>ip6.arpa</literal> reverse tree.
</para>
<para>
The <command>identity</command> field must match
the 6to4 prefix in <literal>ip6.arpa</literal>.
The <command>name</command> field should
be set to ".".
Note that, since identity is based on the client's
IP address, it is not necessary for update request
messages to be signed.
</para>
<para>
In addition, if specified for an
<literal>ip6.arpa</literal> name outside of the
<literal>2.0.0.2.ip6.arpa</literal> namespace,
the corresponding /48 reverse name can be updated.
For example, TCP/IPv6 connections
from 2001:DB8:ED0C::/48 can update records at
<literal>C.0.D.E.8.B.D.0.1.0.0.2.ip6.arpa</literal>.
</para>
<note>
It is theoretically possible to spoof these TCP
sessions.
</note>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>external</varname>
</para>
</entry> <entry colname="2">
<para>
This rule allows <command>named</command>
to defer the decision of whether to allow a
given update to an external daemon.
</para>
<para>
The method of communicating with the daemon is
specified in the <replaceable>identity</replaceable>
field, the format of which is
"<constant>local:</constant><replaceable>path</replaceable>",
where <replaceable>path</replaceable> is the location
of a UNIX-domain socket. (Currently, "local" is the
only supported mechanism.)
</para>
<para>
Requests to the external daemon are sent over the
UNIX-domain socket as datagrams with the following
format:
</para>
<programlisting>
Protocol version number (4 bytes, network byte order, currently 1)
Request length (4 bytes, network byte order)
Signer (null-terminated string)
Name (null-terminated string)
TCP source address (null-terminated string)
Rdata type (null-terminated string)
Key (null-terminated string)
TKEY token length (4 bytes, network byte order)
TKEY token (remainder of packet)</programlisting>
<para>
The daemon replies with a four-byte value in
network byte order, containing either 0 or 1; 0
indicates that the specified update is not
permitted, and 1 indicates that it is.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="multiple_views"><info><title>Multiple views</title></info>
<para>
When multiple views are in use, a zone may be
referenced by more than one of them. Often, the views
will contain different zones with the same name, allowing
different clients to receive different answers for the same
queries. At times, however, it is desirable for multiple
views to contain identical zones. The
<command>in-view</command> zone option provides an efficient
way to do this: it allows a view to reference a zone that
was defined in a previously configured view. Example:
</para>
<programlisting>
view internal {
match-clients { 10/8; };
zone example.com {
type master;
file "example-external.db";
};
};
view external {
match-clients { any; };
zone example.com {
in-view internal;
};
};
</programlisting>
<para>
An <command>in-view</command> option cannot refer to a view
that is configured later in the configuration file.
</para>
<para>
A <command>zone</command> statement which uses the
<command>in-view</command> option may not use any other
options with the exception of <command>forward</command>
and <command>forwarders</command>. (These options control
the behavior of the containing view, rather than changing
the zone object itself.)
</para>
<para>
Zone level acls (e.g. allow-query, allow-transfer) and
other configuration details of the zone are all set
in the view the referenced zone is defined in. Care
need to be taken to ensure that acls are wide enough
for all views referencing the zone.
</para>
<para>
An <command>in-view</command> zone cannot be used as a
response policy zone.
</para>
<para>
An <command>in-view</command> zone is not intended to reference
a <command>forward</command> zone.
</para>
</section>
</section>
</section>
<section xml:id="zone_file"><info><title>Zone File</title></info>
<section xml:id="types_of_resource_records_and_when_to_use_them"><info><title>Types of Resource Records and When to Use Them</title></info>
<para>
This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been
identified
and implemented in the DNS. These are also included.
</para>
<section><info><title>Resource Records</title></info>
<para>
A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by name servers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See <xref linkend="the_sortlist_statement"/> and <xref linkend="rrset_ordering"/>.
</para>
<para>
The components of a Resource Record are:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.000in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.500in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
owner name
</para>
</entry>
<entry colname="2">
<para>
The domain name where the RR is found.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
type
</para>
</entry>
<entry colname="2">
<para>
An encoded 16-bit value that specifies
the type of the resource record.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TTL
</para>
</entry>
<entry colname="2">
<para>
The time-to-live of the RR. This field
is a 32-bit integer in units of seconds, and is
primarily used by
resolvers when they cache RRs. The TTL describes how
long a RR can
be cached before it should be discarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
class
</para>
</entry>
<entry colname="2">
<para>
An encoded 16-bit value that identifies
a protocol family or instance of a protocol.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RDATA
</para>
</entry>
<entry colname="2">
<para>
The resource data. The format of the
data is type (and sometimes class) specific.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The following are <emphasis>types</emphasis> of valid RRs:
</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. In the IN class, this is a
32-bit IP address. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AAAA
</para>
</entry>
<entry colname="2">
<para>
IPv6 address. Described in RFC 1886.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
A6
</para>
</entry>
<entry colname="2">
<para>
IPv6 address. This can be a partial
address (a suffix) and an indirection to the name
where the rest of the
address (the prefix) can be found. Experimental.
Described in RFC 2874.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AFSDB
</para>
</entry>
<entry colname="2">
<para>
Location of AFS database servers.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AMTRELAY
</para>
</entry>
<entry colname="2">
<para>
Automatic Multicast Tunneling Relay
discovery record.
Work in progress draft-ietf-mboned-driad-amt-discovery.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
APL
</para>
</entry>
<entry colname="2">
<para>
Address prefix list. Experimental.
Described in RFC 3123.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
ATMA
</para>
</entry>
<entry colname="2">
<para>
ATM Address.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AVC
</para>
</entry>
<entry colname="2">
<para>
Application Visibility and Control record.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CAA
</para>
</entry>
<entry colname="2">
<para>
Identifies which Certificate Authorities can issue
certificates for this domain and what rules they
need to follow when doing so. Defined in RFC 6844.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CDNSKEY
</para>
</entry>
<entry colname="2">
<para>
Identifies which DNSKEY records should be published
as DS records in the parent zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CDS
</para>
</entry>
<entry colname="2">
<para>
Contains the set of DS records that should be published
by the parent zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CERT
</para>
</entry>
<entry colname="2">
<para>
Holds a digital certificate.
Described in RFC 2538.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CNAME
</para>
</entry>
<entry colname="2">
<para>
Identifies the canonical name of an alias.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CSYNC
</para>
</entry>
<entry colname="2">
<para>
Child-to-Parent Synchronization in DNS as described
in RFC 7477.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DHCID
</para>
</entry>
<entry colname="2">
<para>
Is used for identifying which DHCP client is
associated with this name. Described in RFC 4701.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DLV
</para>
</entry>
<entry colname="2">
<para>
A DNS Lookaside Validation record which contains
the records that are used as trust anchors for
zones in a DLV namespace. Described in RFC 4431.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DNAME
</para>
</entry>
<entry colname="2">
<para>
Replaces the domain name specified with
another name to be looked up, effectively aliasing an
entire
subtree of the domain name space rather than a single
record
as in the case of the CNAME RR.
Described in RFC 2672.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DNSKEY
</para>
</entry>
<entry colname="2">
<para>
Stores a public key associated with a signed
DNS zone. Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DOA
</para>
</entry>
<entry colname="2">
<para>
Implements the Digital Object Architecture over
DNS. Experimental.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DS
</para>
</entry>
<entry colname="2">
<para>
Stores the hash of a public key associated with a
signed DNS zone. Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
EID
</para>
</entry>
<entry colname="2">
<para>
End Point Identifier.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
EUI48
</para>
</entry>
<entry colname="2">
<para>
A 48-bit EUI address. Described in RFC 7043.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
EUI64
</para>
</entry>
<entry colname="2">
<para>
A 64-bit EUI address. Described in RFC 7043.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
GID
</para>
</entry>
<entry colname="2">
<para>
Reserved.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
GPOS
</para>
</entry>
<entry colname="2">
<para>
Specifies the global position. Superseded by LOC.
</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.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
HIP
</para>
</entry>
<entry colname="2">
<para>
Host Identity Protocol Address.
Described in RFC 5205.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
IPSECKEY
</para>
</entry>
<entry colname="2">
<para>
Provides a method for storing IPsec keying material in
DNS. Described in RFC 4025.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
ISDN
</para>
</entry>
<entry colname="2">
<para>
Representation of ISDN addresses.
Experimental. Described in RFC 1183.
</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. Used in original DNSSEC; replaced
by DNSKEY in DNSSECbis, but still used with
SIG(0). Described in RFCs 2535 and 2931.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
KX
</para>
</entry>
<entry colname="2">
<para>
Identifies a key exchanger for this
DNS name. Described in RFC 2230.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
L32
</para>
</entry>
<entry colname="2">
<para>
Holds 32-bit Locator values for
Identifier-Locator Network Protocol. Described
in RFC 6742.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
L64
</para>
</entry>
<entry colname="2">
<para>
Holds 64-bit Locator values for
Identifier-Locator Network Protocol. Described
in RFC 6742.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
LOC
</para>
</entry>
<entry colname="2">
<para>
For storing GPS info. Described in RFC 1876.
Experimental.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
LP
</para>
</entry>
<entry colname="2">
<para>
Identifier-Locator Network Protocol.
Described in RFC 6742.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MB
</para>
</entry>
<entry colname="2">
<para>
Mail Box. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MD
</para>
</entry>
<entry colname="2">
<para>
Mail Destination. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MF
</para>
</entry>
<entry colname="2">
<para>
Mail Forwarder. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MG
</para>
</entry>
<entry colname="2">
<para>
Mail Group. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MINFO
</para>
</entry>
<entry colname="2">
<para>
Mail Information.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MR
</para>
</entry>
<entry colname="2">
<para>
Mail Rename. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MX
</para>
</entry>
<entry colname="2">
<para>
Identifies a mail exchange for the domain with
a 16-bit preference value (lower is better)
followed by the host name of the mail exchange.
Described in RFC 974, RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NAPTR
</para>
</entry>
<entry colname="2">
<para>
Name authority pointer. Described in RFC 2915.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NID
</para>
</entry>
<entry colname="2">
<para>
Holds values for Node Identifiers in
Identifier-Locator Network Protocol. Described
in RFC 6742.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NINFO
</para>
</entry>
<entry colname="2">
<para>
Contains zone status information.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NIMLOC
</para>
</entry>
<entry colname="2">
<para>
Nimrod Locator.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSAP
</para>
</entry>
<entry colname="2">
<para>
A network service access point.
Described in RFC 1706.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSAP-PTR
</para>
</entry>
<entry colname="2">
<para>
Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NS
</para>
</entry>
<entry colname="2">
<para>
The authoritative name server for the
domain. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis 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.
Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC3
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis 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. NSEC3 differs from NSEC in that it
prevents zone enumeration but is more
computationally expensive on both the server
and the client than NSEC. Described in RFC
5155.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC3PARAM
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis to tell the authoritative
server which NSEC3 chains are available to use.
Described in RFC 5155.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NULL
</para>
</entry>
<entry colname="2">
<para>
This is an opaque container.
</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.
Used in original DNSSEC; replaced by NSEC in
DNSSECbis.
Described in RFC 2535.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
OPENPGPKEY
</para>
</entry>
<entry colname="2">
<para>
Used to hold an OPENPGPKEY.
</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. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
PX
</para>
</entry>
<entry colname="2">
<para>
Provides mappings between RFC 822 and X.400
addresses. Described in RFC 2163.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RKEY
</para>
</entry>
<entry colname="2">
<para>
Resource key.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RP
</para>
</entry>
<entry colname="2">
<para>
Information on persons responsible
for the domain. Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RRSIG
</para>
</entry>
<entry colname="2">
<para>
Contains DNSSECbis signature data. Described
in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RT
</para>
</entry>
<entry colname="2">
<para>
Route-through binding for hosts that
do not have their own direct wide area network
addresses.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SIG
</para>
</entry>
<entry colname="2">
<para>
Contains DNSSEC signature data. Used in
original DNSSEC; replaced by RRSIG in
DNSSECbis, but still used for SIG(0).
Described in RFCs 2535 and 2931.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SINK
</para>
</entry>
<entry colname="2">
<para>
The kitchen sink record.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SMIMEA
</para>
</entry>
<entry colname="2">
<para>
The S/MIME Security Certificate Association.
</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.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SPF
</para>
</entry>
<entry colname="2">
<para>
Contains the Sender Policy Framework information
for a given email domain. Described in RFC 4408.
</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). Described in RFC 2782.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SSHFP
</para>
</entry>
<entry colname="2">
<para>
Provides a way to securely publish a secure shell key's
fingerprint. Described in RFC 4255.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TA
</para>
</entry>
<entry colname="2">
<para>
Trust Anchor. Experimental.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TALINK
</para>
</entry>
<entry colname="2">
<para>
Trust Anchor Link. Experimental.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TLSA
</para>
</entry>
<entry colname="2">
<para>
Transport Layer Security Certificate Association.
Described in RFC 6698.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TXT
</para>
</entry>
<entry colname="2">
<para>
Text records. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
UID
</para>
</entry>
<entry colname="2">
<para>
Reserved.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
UINFO
</para>
</entry>
<entry colname="2">
<para>
Reserved.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
UNSPEC
</para>
</entry>
<entry colname="2">
<para>
Reserved. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
URI
</para>
</entry>
<entry colname="2">
<para>
Holds a URI. Described in RFC 7553.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
WKS
</para>
</entry>
<entry colname="2">
<para>
Information about which well known
network services, such as SMTP, that a domain
supports. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
X25
</para>
</entry>
<entry colname="2">
<para>
Representation of X.25 network addresses.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
ZONEMD
</para>
</entry>
<entry colname="2">
<para>
Zone Message Digest.
Work in progress draft-wessels-dns-zone-digest.
</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.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CH
</para>
</entry>
<entry colname="2">
<para>
Chaosnet, a LAN protocol created at MIT in the
mid-1970s.
Rarely used for its historical purpose, but reused for
BIND's
built-in server information zones, e.g.,
<literal>version.bind</literal>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
HS
</para>
</entry>
<entry colname="2">
<para>
Hesiod, an information service
developed by MIT's Project Athena. It is used to share
information
about various systems databases, such as users,
groups, printers
and so on.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The owner name is often implicit, rather than forming an
integral
part of the RR. For example, many name servers internally form
tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA)
that
fits the needs of the resource being described.
</para>
<para>
The 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>
</section>
<section xml:id="rr_text"><info><title>Textual expression of RRs</title></info>
<para>
RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form
when
stored in a name server or resolver. In the examples provided
in
RFC 1034, a style similar to that used in 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/>
</entry>
<entry colname="2">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10 VAXA.ISI.EDU</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>VENERA.ISI.EDU</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>128.9.0.32</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.1.0.52</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>VAXA.ISI.EDU</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.2.0.27</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>128.9.0.33</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The MX RRs have an RDATA section which consists of a 16-bit
number followed by a domain name. The address RRs use a
standard
IP address format to contain a 32-bit internet address.
</para>
<para>
The above example shows six RRs, with two RRs at each of three
domain names.
</para>
<para>
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.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.0.0.44</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1"/>
<entry colname="2">
<para>
<literal>CH A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MIT.EDU. 2420</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
This example shows two addresses for
<literal>XX.LCS.MIT.EDU</literal>, each of a different class.
</para>
</section>
</section>
<section xml:id="mx_records"><info><title>Discussion of MX Records</title></info>
<para>
As described above, domain servers store information as a
series of resource records, each of which contains a particular
piece of information about a given domain name (which is usually,
but not always, a host). The simplest way to think of a RR is as
a typed pair of data, a domain name matched with a relevant datum,
and stored with some additional type information to help systems
determine when the RR is relevant.
</para>
<para>
MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The
priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest
priority.
Priority numbers do not have any absolute meaning — they are
relevant
only respective to other MX records for that domain name. The
domain
name given is the machine to which the mail will be delivered.
It <emphasis>must</emphasis> have an associated address record
(A or AAAA) — CNAME is not sufficient.
</para>
<para>
For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored.
Instead,
the mail will be delivered to the server specified in the MX
record
pointed to by the CNAME.
For example:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="5" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.708in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="0.444in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="0.444in"/>
<colspec colname="4" colnum="4" colsep="0" colwidth="0.976in"/>
<colspec colname="5" colnum="5" colsep="0" colwidth="1.553in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail.example.com.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail2.example.com.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>20</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail.backup.org.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>mail.example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10.0.0.1</literal>
</para>
</entry>
<entry colname="5">
<para/>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>mail2.example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10.0.0.2</literal>
</para>
</entry>
<entry colname="5">
<para/>
</entry>
</row>
</tbody>
</tgroup>
</informaltable><para>
Mail delivery 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>
</section>
<section xml:id="Setting_TTLs"><info><title>Setting TTLs</title></info>
<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 $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every
RR without
a specific TTL set.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RR TTLs
</para>
</entry>
<entry colname="2">
<para>
Each RR can have a TTL as the second
field in the RR, which will control how long other
servers can cache it.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, <literal>1h30m</literal>.
</para>
</section>
<section xml:id="ipv4_reverse"><info><title>Inverse Mapping in IPv4</title></info>
<para>
Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the <emphasis>in-addr.arpa</emphasis> domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a
corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally,
multiple
PTR records if the machine has more than one name. For example,
in the <optional>example.com</optional> domain:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>$ORIGIN</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>2.1.10.in-addr.arpa</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>3</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN PTR foo.example.com.</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<note>
<para>
The <command>$ORIGIN</command> lines in the examples
are for providing context to the examples only — they do not
necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.
</para>
</note>
</section>
<section xml:id="zone_directives"><info><title>Other Zone File Directives</title></info>
<para>
The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format
itself
is class independent all records in a Master File must be of the
same
class.
</para>
<para>
Master File Directives include <command>$ORIGIN</command>, <command>$INCLUDE</command>,
and <command>$TTL.</command>
</para>
<section xml:id="atsign"><info><title>The <command>@</command> (at-sign)</title></info>
<para>
When used in the label (or name) field, the asperand or
at-sign (@) symbol represents the current origin.
At the start of the zone file, it is the
&lt;<varname>zone_name</varname>&gt; (followed by
trailing dot).
</para>
</section>
<section xml:id="origin_directive"><info><title>The <command>$ORIGIN</command> Directive</title></info>
<para>
Syntax: <command>$ORIGIN</command>
<replaceable>domain-name</replaceable>
<optional><replaceable>comment</replaceable></optional>
</para>
<para><command>$ORIGIN</command>
sets the domain name that will be appended to any
unqualified records. When a zone is first read in there
is an implicit <command>$ORIGIN</command>
&lt;<varname>zone_name</varname>&gt;<command>.</command>
(followed by trailing dot).
The current <command>$ORIGIN</command> is appended to
the domain specified in the <command>$ORIGIN</command>
argument if it is not absolute.
</para>
<programlisting>
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
</programlisting>
<para>
is equivalent to
</para>
<programlisting>
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
</programlisting>
</section>
<section xml:id="include_directive"><info><title>The <command>$INCLUDE</command> Directive</title></info>
<para>
Syntax: <command>$INCLUDE</command>
<replaceable>filename</replaceable>
<optional>
<replaceable>origin</replaceable> </optional>
<optional> <replaceable>comment</replaceable> </optional>
</para>
<para>
Read and process the file <filename>filename</filename> as
if it were included into the file at this point. If <command>origin</command> is
specified the file is processed with <command>$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>$INCLUDE</command>, but it is silent
on whether the current
domain name should also be restored. BIND 9 restores both of
them.
This could be construed as a deviation from RFC 1035, a
feature, or both.
</para>
</note>
</section>
<section xml:id="ttl_directive"><info><title>The <command>$TTL</command> Directive</title></info>
<para>
Syntax: <command>$TTL</command>
<replaceable>default-ttl</replaceable>
<optional>
<replaceable>comment</replaceable> </optional>
</para>
<para>
Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647
seconds.
</para>
<para><command>$TTL</command>
is defined in RFC 2308.
</para>
</section>
</section>
<section xml:id="generate_directive"><info><title><acronym>BIND</acronym> Master File Extension: the <command>$GENERATE</command> Directive</title></info>
<para>
Syntax: <command>$GENERATE</command>
<replaceable>range</replaceable>
<replaceable>lhs</replaceable>
<optional><replaceable>ttl</replaceable></optional>
<optional><replaceable>class</replaceable></optional>
<replaceable>type</replaceable>
<replaceable>rhs</replaceable>
<optional><replaceable>comment</replaceable></optional>
</para>
<para><command>$GENERATE</command>
is used to create a series of resource records that only
differ from each other by an
iterator. <command>$GENERATE</command> can be used to
easily generate the sets of records required to support
sub /24 reverse delegations described in RFC 2317:
Classless IN-ADDR.ARPA delegation.
</para>
<programlisting>$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</programlisting>
<para>
is equivalent to
</para>
<programlisting>0.0.0.192.IN-ADDR.ARPA. NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.
</programlisting>
<para>
Generate a set of A and MX records. Note the MX's right hand
side is a quoted string. The quotes will be stripped when the
right hand side is processed.
</para>
<programlisting>
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."</programlisting>
<para>
is equivalent to
</para>
<programlisting>HOST-1.EXAMPLE. A 1.2.3.1
HOST-1.EXAMPLE. MX 0 .
HOST-2.EXAMPLE. A 1.2.3.2
HOST-2.EXAMPLE. MX 0 .
HOST-3.EXAMPLE. A 1.2.3.3
HOST-3.EXAMPLE. MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .
</programlisting>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.250in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>range</command></para>
</entry>
<entry colname="2">
<para>
This can be one of two forms: start-stop
or start-stop/step. If the first form is used, then step
is set to 1. start, stop and step must be positive
integers between 0 and (2^31)-1. start must not be
larger than stop.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>lhs</command></para>
</entry>
<entry colname="2">
<para>This
describes the owner name of the resource records
to be created. Any single <command>$</command>
(dollar sign)
symbols within the <command>lhs</command> string
are replaced by the iterator value.
To get a $ in the output, 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
iterator, field width and base.
Modifiers are introduced by a
<command>{</command> (left brace) immediately following the
<command>$</command> as
<command>${offset[,width[,base]]}</command>.
For example, <command>${-20,3,d}</command>
subtracts 20 from the current value, prints the
result as a decimal in a zero-padded field of
width 3.
Available output forms are decimal
(<command>d</command>), octal
(<command>o</command>), hexadecimal
(<command>x</command> or <command>X</command>
for uppercase) and nibble
(<command>n</command> or <command>N</command>\
for uppercase). The default modifier is
<command>${0,0,d}</command>. If the
<command>lhs</command> is not absolute, the
current <command>$ORIGIN</command> is appended
to the name.
</para>
<para>
In nibble mode the value will be treated as
if it was a reversed hexadecimal string
with each hexadecimal digit as a separate
label. The width field includes the label
separator.
</para>
<para>
For compatibility with earlier versions,
<command>$$</command> is still recognized as
indicating a literal $ in the output.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ttl</command></para>
</entry>
<entry colname="2">
<para>
Specifies the time-to-live of the generated records. If
not specified this will be inherited using the
normal TTL inheritance rules.
</para>
<para><command>class</command>
and <command>ttl</command> can be
entered in either order.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>class</command></para>
</entry>
<entry colname="2">
<para>
Specifies the class of the generated records.
This must match the zone class if it is
specified.
</para>
<para><command>class</command>
and <command>ttl</command> can be
entered in either order.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>type</command></para>
</entry>
<entry colname="2">
<para>
Any valid type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>rhs</command></para>
</entry>
<entry colname="2">
<para>
<command>rhs</command>, optionally, quoted string.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The <command>$GENERATE</command> directive is a <acronym>BIND</acronym> extension
and not part of the standard zone file format.
</para>
</section>
<section xml:id="zonefile_format"><info><title>Additional File Formats</title></info>
<para>
In addition to the standard textual format, BIND 9
supports the ability to read or dump to zone files in
other formats.
</para>
<para>
The <constant>raw</constant> format is
a binary representation of zone data in a manner similar
to that used in zone transfers. Since it does not require
parsing text, load time is significantly reduced.
</para>
<para>
An even faster alternative is the <constant>map</constant>
format, which is an image of a <acronym>BIND</acronym> 9
in-memory zone database; it is capable of being loaded
directly into memory via the <command>mmap()</command>
function; the zone can begin serving queries almost
immediately.
</para>
<para>
For a primary server, a zone file in
<constant>raw</constant> or <constant>map</constant>
format is expected to be generated from a textual zone
file by the <command>named-compilezone</command> command.
For a secondary server or for a dynamic zone, it is automatically
generated (if this format is specified by the
<command>masterfile-format</command> option) when
<command>named</command> dumps the zone contents after
zone transfer or when applying prior updates.
</para>
<para>
If a zone file in a binary format needs manual modification,
it first must be converted to a textual form by the
<command>named-compilezone</command> command. All
necessary modification should go to the text file, which
should then be converted to the binary form by the
<command>named-compilezone</command> command again.
</para>
<para>
Note that <command>map</command> format is extremely
architecture-specific. A <constant>map</constant>
file <emphasis>cannot</emphasis> be used on a system
with different pointer size, endianness or data alignment
than the system on which it was generated, and should in
general be used only inside a single system.
While <constant>raw</constant> format uses
network byte order and avoids architecture-dependent
data alignment so that it is as portable as
possible, it is also primarily expected to be used
inside the same single system. To export a
zone file in either <constant>raw</constant> or
<constant>map</constant> format, or make a
portable backup of such a file, conversion to
<constant>text</constant> format is recommended.
</para>
</section>
</section>
<section xml:id="statistics"><info><title>BIND9 Statistics</title></info>
<para>
<acronym>BIND</acronym> 9 maintains lots of statistics
information and provides several interfaces for users to
get access to the statistics.
The available statistics include all statistics counters
that were available in <acronym>BIND</acronym> 8 and
are meaningful in <acronym>BIND</acronym> 9,
and other information that is considered useful.
</para>
<para>
The statistics information is categorized into the following
sections.
</para>
<informaltable frame="all">
<tgroup cols="2">
<colspec colname="1" colnum="1" colsep="0" colwidth="3.300in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>Incoming Requests</para>
</entry>
<entry colname="2">
<para>
The number of incoming DNS requests for each OPCODE.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Incoming Queries</para>
</entry>
<entry colname="2">
<para>
The number of incoming queries for each RR type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Outgoing Queries</para>
</entry>
<entry colname="2">
<para>
The number of outgoing queries for each RR
type sent from the internal resolver.
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Name Server Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about incoming request processing.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Zone Maintenance Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters regarding zone maintenance
operations such as zone transfers.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Resolver Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about name resolution
performed in the internal resolver.
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Cache DB RRsets</para>
</entry>
<entry colname="2">
<para>
The number of RRsets per RR type and nonexistent
names stored in the cache database.
If the exclamation mark (!) is printed for a RR
type, it means that particular type of RRset is
known to be nonexistent (this is also known as
"NXRRSET"). If a hash mark (#) is present then
the RRset is marked for garbage collection.
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Socket I/O Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about network related events.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
A subset of Name Server Statistics is collected and shown
per zone for which the server has the authority when
<command>zone-statistics</command> is set to
<userinput>full</userinput> (or <userinput>yes</userinput>
for backward compatibility. See the description of
<command>zone-statistics</command> in <xref linkend="options"/>
for further details.
</para>
<para>
These statistics counters are shown with their zone and
view names. The view name is omitted when the server is
not configured with explicit views.</para>
<para>
There are currently two user interfaces to get access to the
statistics.
One is in the plain text format dumped to the file specified
by the <command>statistics-file</command> configuration option.
The other is remotely accessible via a statistics channel
when the <command>statistics-channels</command> statement
is specified in the configuration file
(see <xref linkend="statschannels"/>.)
</para>
<section xml:id="statsfile"><info><title>The Statistics File</title></info>
<para>
The text format statistics dump begins with a line, like:
</para>
<para>
<command>+++ Statistics Dump +++ (973798949)</command>
</para>
<para>
The number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970.
Following
that line is a set of statistics information, which is categorized
as described above.
Each section begins with a line, like:
</para>
<para>
<command>++ Name Server Statistics ++</command>
</para>
<para>
Each section consists of lines, each containing the statistics
counter value followed by its textual description.
See below for available counters.
For brevity, counters that have a value of 0 are not shown
in the statistics file.
</para>
<para>
The statistics dump ends with the line where the
number is identical to the number in the beginning line; for example:
</para>
<para>
<command>--- Statistics Dump --- (973798949)</command>
</para>
</section>
<section xml:id="statistics_counters"><info><title>Statistics Counters</title></info>
<para>
The following tables summarize statistics counters that
<acronym>BIND</acronym> 9 provides.
For each row of the tables, the leftmost column is the
abbreviated symbol name of that counter.
These symbols are shown in the statistics information
accessed via an HTTP statistics channel.
The rightmost column gives the description of the counter,
which is also shown in the statistics file
(but, in this document, possibly with slight modification
for better readability).
Additional notes may also be provided in this column.
When a middle column exists between these two columns,
it gives the corresponding counter name of the
<acronym>BIND</acronym> 8 statistics, if applicable.
</para>
<para>
Note: BIND statistics counters are signed 64-bit values on
all platforms except one: 32-bit Windows, where they are
signed 32-bit values. Given that 32-bit values have a
vastly smaller range than 64-bit values, BIND statistics
counters in 32-bit Windows builds overflow significantly
more quickly than on all other platforms.
</para>
<section xml:id="stats_counters"><info><title>Name Server Statistics Counters</title></info>
<informaltable colsep="0" rowsep="0">
<tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>BIND8 Symbol</emphasis>
</para>
</entry>
<entry colname="3">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Requestv4</command></para>
</entry>
<entry colname="2">
<para><command>RQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 requests received.
Note: this also counts non query requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Requestv6</command></para>
</entry>
<entry colname="2">
<para><command>RQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 requests received.
Note: this also counts non query requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqEdns0</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requests with EDNS(0) received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqBadEDNSVer</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requests with unsupported EDNS version received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqTSIG</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requests with TSIG received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqSIG0</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requests with SIG(0) received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqBadSIG</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requests with invalid (TSIG or SIG(0)) signature.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqTCP</command></para>
</entry>
<entry colname="2">
<para><command>RTCP</command></para>
</entry>
<entry colname="3">
<para>
TCP requests received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AuthQryRej</command></para>
</entry>
<entry colname="2">
<para><command>RUQ</command></para>
</entry>
<entry colname="3">
<para>
Authoritative (non recursive) queries rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RecQryRej</command></para>
</entry>
<entry colname="2">
<para><command>RURQ</command></para>
</entry>
<entry colname="3">
<para>
Recursive queries rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrRej</command></para>
</entry>
<entry colname="2">
<para><command>RUXFR</command></para>
</entry>
<entry colname="3">
<para>
Zone transfer requests rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateRej</command></para>
</entry>
<entry colname="2">
<para><command>RUUpd</command></para>
</entry>
<entry colname="3">
<para>
Dynamic update requests rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Response</command></para>
</entry>
<entry colname="2">
<para><command>SAns</command></para>
</entry>
<entry colname="3">
<para>
Responses sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespTruncated</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Truncated responses sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespEDNS0</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Responses with EDNS(0) sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespTSIG</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Responses with TSIG sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespSIG0</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Responses with SIG(0) sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QrySuccess</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in a successful answer.
This means the query which returns a NOERROR response
with at least one answer RR.
This corresponds to the
<command>success</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryAuthAns</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in authoritative answer.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNoauthAns</command></para>
</entry>
<entry colname="2">
<para><command>SNaAns</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in non authoritative answer.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryReferral</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in referral answer.
This corresponds to the
<command>referral</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNxrrset</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NOERROR responses with no data.
This corresponds to the
<command>nxrrset</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QrySERVFAIL</command></para>
</entry>
<entry colname="2">
<para><command>SFail</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in SERVFAIL.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryFORMERR</command></para>
</entry>
<entry colname="2">
<para><command>SFErr</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in FORMERR.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNXDOMAIN</command></para>
</entry>
<entry colname="2">
<para><command>SNXD</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NXDOMAIN.
This corresponds to the
<command>nxdomain</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryRecursion</command></para>
</entry>
<entry colname="2">
<para><command>RFwdQ</command></para>
</entry>
<entry colname="3">
<para>
Queries which caused the server
to perform recursion in order to find the final answer.
This corresponds to the
<command>recursion</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryDuplicate</command></para>
</entry>
<entry colname="2">
<para><command>RDupQ</command></para>
</entry>
<entry colname="3">
<para>
Queries which the server attempted to
recurse but discovered an existing query with the same
IP address, port, query ID, name, type and class
already being processed.
This corresponds to the
<command>duplicate</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryDropped</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Recursive queries for which the server
discovered an excessive number of existing
recursive queries for the same name, type and
class and were subsequently dropped.
This is the number of dropped queries due to
the reason explained with the
<command>clients-per-query</command>
and
<command>max-clients-per-query</command>
options
(see the description about
<xref endterm="cpq_term" linkend="clients-per-query"/>.)
This corresponds to the
<command>dropped</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryFailure</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Other query failures.
This corresponds to the
<command>failure</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
Note: this counter is provided mainly for
backward compatibility with the previous versions.
Normally a more fine-grained counters such as
<command>AuthQryRej</command> and
<command>RecQryRej</command>
that would also fall into this counter are provided,
and so this counter would not be of much
interest in practice.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNXRedir</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NXDOMAIN that were redirected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNXRedirRLookup</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NXDOMAIN that were redirected
and resulted in a successful remote lookup.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrReqDone</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Requested zone transfers completed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateReqFwd</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Update requests forwarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateRespFwd</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Update responses forwarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateFwdFail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Dynamic update forward failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateDone</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Dynamic updates completed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateFail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Dynamic updates failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateBadPrereq</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Dynamic updates rejected due to prerequisite failure.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RateDropped</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Responses dropped by rate limits.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RateSlipped</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Responses truncated by rate limits.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RPZRewrites</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Response policy zone rewrites.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="zone_stats"><info><title>Zone Maintenance Statistics Counters</title></info>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyOutv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 notifies sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyOutv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 notifies sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyInv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 notifies received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyInv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 notifies received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyRej</command></para>
</entry>
<entry colname="2">
<para>
Incoming notifies rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SOAOutv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 SOA queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SOAOutv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 SOA queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AXFRReqv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 AXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AXFRReqv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 AXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>IXFRReqv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 IXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>IXFRReqv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 IXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrSuccess</command></para>
</entry>
<entry colname="2">
<para>
Zone transfer requests succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrFail</command></para>
</entry>
<entry colname="2">
<para>
Zone transfer requests failed.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="resolver_stats"><info><title>Resolver Statistics Counters</title></info>
<informaltable colsep="0" rowsep="0">
<tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>BIND8 Symbol</emphasis>
</para>
</entry>
<entry colname="3">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Queryv4</command></para>
</entry>
<entry colname="2">
<para><command>SFwdQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Queryv6</command></para>
</entry>
<entry colname="2">
<para><command>SFwdQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Responsev4</command></para>
</entry>
<entry colname="2">
<para><command>RR</command></para>
</entry>
<entry colname="3">
<para>
IPv4 responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Responsev6</command></para>
</entry>
<entry colname="2">
<para><command>RR</command></para>
</entry>
<entry colname="3">
<para>
IPv6 responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NXDOMAIN</command></para>
</entry>
<entry colname="2">
<para><command>RNXD</command></para>
</entry>
<entry colname="3">
<para>
NXDOMAIN received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SERVFAIL</command></para>
</entry>
<entry colname="2">
<para><command>RFail</command></para>
</entry>
<entry colname="3">
<para>
SERVFAIL received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>FORMERR</command></para>
</entry>
<entry colname="2">
<para><command>RFErr</command></para>
</entry>
<entry colname="3">
<para>
FORMERR received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>OtherError</command></para>
</entry>
<entry colname="2">
<para><command>RErr</command></para>
</entry>
<entry colname="3">
<para>
Other errors received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>EDNS0Fail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
EDNS(0) query failures.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Mismatch</command></para>
</entry>
<entry colname="2">
<para><command>RDupR</command></para>
</entry>
<entry colname="3">
<para>
Mismatch responses received.
The DNS ID, response's source address,
and/or the response's source port does not
match what was expected.
(The port must be 53 or as defined by
the <command>port</command> option.)
This may be an indication of a cache
poisoning attempt.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Truncated</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Truncated responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Lame</command></para>
</entry>
<entry colname="2">
<para><command>RLame</command></para>
</entry>
<entry colname="3">
<para>
Lame delegations received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Retry</command></para>
</entry>
<entry colname="2">
<para><command>SDupQ</command></para>
</entry>
<entry colname="3">
<para>
Query retries performed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QueryAbort</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Queries aborted due to quota control.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QuerySockFail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Failures in opening query sockets.
One common reason for such failures is a
failure of opening a new socket due to a
limitation on file descriptors.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QueryTimeout</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Query timeouts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv4</command></para>
</entry>
<entry colname="2">
<para><command>SSysQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 NS address fetches invoked.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv6</command></para>
</entry>
<entry colname="2">
<para><command>SSysQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 NS address fetches invoked.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv4Fail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
IPv4 NS address fetch failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv6Fail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
IPv6 NS address fetch failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValAttempt</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation attempted.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValOk</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValNegOk</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation on negative information succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValFail</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryRTTnn</command></para>
</entry>
<entry colname="2">
<para><command/></para>
</entry>
<entry colname="3">
<para>
Frequency table on round trip times (RTTs) of
queries.
Each <command>nn</command> specifies the corresponding
frequency.
In the sequence of
<command>nn_1</command>,
<command>nn_2</command>,
...,
<command>nn_m</command>,
the value of <command>nn_i</command> is the
number of queries whose RTTs are between
<command>nn_(i-1)</command> (inclusive) and
<command>nn_i</command> (exclusive) milliseconds.
For the sake of convenience we define
<command>nn_0</command> to be 0.
The last entry should be represented as
<command>nn_m+</command>, which means the
number of queries whose RTTs are equal to or over
<command>nn_m</command> milliseconds.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="socket_stats"><info><title>Socket I/O Statistics Counters</title></info>
<para>
Socket I/O statistics counters are defined per socket
types, which are
<command>UDP4</command> (UDP/IPv4),
<command>UDP6</command> (UDP/IPv6),
<command>TCP4</command> (TCP/IPv4),
<command>TCP6</command> (TCP/IPv6),
<command>Unix</command> (Unix Domain), and
<command>FDwatch</command> (sockets opened outside the
socket module).
In the following table <command>&lt;TYPE&gt;</command>
represents a socket type.
Not all counters are available for all socket types;
exceptions are noted in the description field.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;Open</command></para>
</entry>
<entry colname="2">
<para>
Sockets opened successfully.
This counter is not applicable to the
<command>FDwatch</command> type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;OpenFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of opening sockets.
This counter is not applicable to the
<command>FDwatch</command> type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;Close</command></para>
</entry>
<entry colname="2">
<para>
Sockets closed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;BindFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of binding sockets.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;ConnFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of connecting sockets.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;Conn</command></para>
</entry>
<entry colname="2">
<para>
Connections established successfully.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;AcceptFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of accepting incoming connection requests.
This counter is not applicable to the
<command>UDP</command> and
<command>FDwatch</command> types.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;Accept</command></para>
</entry>
<entry colname="2">
<para>
Incoming connections successfully accepted.
This counter is not applicable to the
<command>UDP</command> and
<command>FDwatch</command> types.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;SendErr</command></para>
</entry>
<entry colname="2">
<para>
Errors in socket send operations.
This counter corresponds
to <command>SErr</command> counter of
<command>BIND</command> 8.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>&lt;TYPE&gt;RecvErr</command></para>
</entry>
<entry colname="2">
<para>
Errors in socket receive operations.
This includes errors of send operations on a
connected UDP socket notified by an ICMP error
message.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section xml:id="bind8_compatibility"><info><title>Compatibility with <emphasis>BIND</emphasis> 8 Counters</title></info>
<para>
Most statistics counters that were available
in <command>BIND</command> 8 are also supported in
<command>BIND</command> 9 as shown in the above tables.
Here are notes about other counters that do not appear
in these tables.
</para>
<variablelist>
<varlistentry>
<term><command>RFwdR,SFwdR</command></term>
<listitem>
<para>
These counters are not supported
because <command>BIND</command> 9 does not adopt
the notion of <emphasis>forwarding</emphasis>
as <command>BIND</command> 8 did.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RAXFR</command></term>
<listitem>
<para>
This counter is accessible in the Incoming Queries section.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RIQ</command></term>
<listitem>
<para>
This counter is accessible in the Incoming Requests section.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ROpts</command></term>
<listitem>
<para>
This counter is not supported
because <command>BIND</command> 9 does not care
about IP options in the first place.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>
</section>
</chapter>
<chapter xml:id="Bv9ARM.ch06"><info><title><acronym>BIND</acronym> 9 Security Considerations</title></info>
<section xml:id="Access_Control_Lists"><info><title>Access Control Lists</title></info>
<para>
Access Control Lists (ACLs) are address match lists that
you can set up and nickname for future use in
<command>allow-notify</command>, <command>allow-query</command>,
<command>allow-query-on</command>, <command>allow-recursion</command>,
<command>blackhole</command>, <command>allow-transfer</command>,
<command>match-clients</command>, etc.
</para>
<para>
Using ACLs allows you to have finer control over who can access
your name server, 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 denial of service
(DoS) attacks against your server.
</para>
<para>
ACLs match clients on the basis of up to three characteristics:
1) The client's IP address; 2) the TSIG or SIG(0) key that was
used to sign the request, if any; and 3) an address prefix
encoded in an EDNS Client Subnet option, if any.
</para>
<para>
Here is an example of ACLs based on client addresses:
</para>
<programlisting>
// Set up an ACL named "bogusnets" that will block
// RFC1918 space and some reserved space, which is
// commonly used in spoofing attacks.
acl bogusnets {
0.0.0.0/8; 192.0.2.0/24; 224.0.0.0/3;
10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
};
// Set up an ACL called our-nets. Replace this with the
// real IP numbers.
acl our-nets { x.x.x.x/24; x.x.x.x/21; };
options {
...
...
allow-query { our-nets; };
allow-recursion { our-nets; };
...
blackhole { bogusnets; };
...
};
zone "example.com" {
type master;
file "m/example.com";
allow-query { any; };
};
</programlisting>
<para>
This allows authoritative queries for "example.com" from any
address, but recursive queries only from the networks specified
in "our-nets", and no queries at all from the networks
specified in "bogusnets".
</para>
<para>
In addition to network addresses and prefixes, which are
matched against the source address of the DNS request, ACLs
may include <option>key</option> elements, which specify the
name of a TSIG or SIG(0) key.
</para>
<para>
When <acronym>BIND</acronym> 9 is built with GeoIP support,
ACLs can also be used for geographic access restrictions.
This is done by specifying an ACL element of the form:
<command>geoip <optional>db <replaceable>database</replaceable></optional> <replaceable>field</replaceable> <replaceable>value</replaceable></command>
</para>
<para>
The <replaceable>field</replaceable> indicates which field
to search for a match. Available fields are "country",
"region", "city", "continent", "postal" (postal code),
"metro" (metro code), "area" (area code), "tz" (timezone),
"isp", "asnum", and "domain".
</para>
<para>
<replaceable>value</replaceable> is the value to search
for within the database. A string may be quoted if it
contains spaces or other special characters. An "asnum"
search for autonomous system number can be specified using
the string "ASNNNN" or the integer NNNN.
When "country" search is specified with a string is two
characters long, then it must be a standard ISO-3166-1
two-letter country code; otherwise it is interpreted as
the full name of the country. Similarly, if this is a
"region" search and the string is two characters long,
then it treated as a standard two-letter state or province
abbreviation; otherwise it treated as the full name of the
state or province.
</para>
<para>
The <replaceable>database</replaceable> field indicates which
GeoIP database to search for a match. In most cases this is
unnecessary, because most search fields can only be found in
a single database. However, searches for "continent" or "country"
can be answered from either the "city" or "country" databases,
so for these search types, specifying a
<replaceable>database</replaceable>
will force the query to be answered from that database and no
other. If <replaceable>database</replaceable> is not
specified, then these queries will be answered from the "city",
database if it is installed, or the "country" database if it
is installed, in that order. Valid database names are
"country", "city", "asnum", "isp", and "domain".
</para>
<para>
Some example GeoIP ACLs:
</para>
<programlisting>geoip country US;
geoip country JP;
geoip db country country Canada;
geoip region WA;
geoip city "San Francisco";
geoip region Oklahoma;
geoip postal 95062;
geoip tz "America/Los_Angeles";
geoip org "Internet Systems Consortium";
</programlisting>
<para>
ACLs use a "first-match" logic rather than "best-match":
if an address prefix matches an ACL element, then that ACL
is considered to have matched even if a later element would
have matched more specifically. For example, the ACL
<command> { 10/8; !10.0.0.1; }</command> would actually
match a query from 10.0.0.1, because the first element
indicated that the query should be accepted, and the second
element is ignored.
</para>
<para>
When using "nested" ACLs (that is, ACLs included or referenced
within other ACLs), a negative match of a nested ACL will
the containing ACL to continue looking for matches. This
enables complex ACLs to be constructed, in which multiple
client characteristics can be checked at the same time. For
example, to construct an ACL which allows queries only when
it originates from a particular network <emphasis>and</emphasis>
only when it is signed with a particular key, use:
</para>
<programlisting>
allow-query { !{ !10/8; any; }; key example; };
</programlisting>
<para>
Within the nested ACL, any address that is
<emphasis>not</emphasis> in the 10/8 network prefix will
be rejected, and this will terminate processing of the
ACL. Any address that <emphasis>is</emphasis> in the 10/8
network prefix will be accepted, but this causes a negative
match of the nested ACL, so the containing ACL continues
processing. The query will then be accepted if it is signed
by the key "example", and rejected otherwise. The ACL, then,
will only matches when <emphasis>both</emphasis> conditions
are true.
</para>
</section>
<section xml:id="chroot_and_setuid"><info><title><command>Chroot</command> and <command>Setuid</command></title></info>
<para>
On UNIX servers, it is possible to run <acronym>BIND</acronym>
in a <emphasis>chrooted</emphasis> environment (using
the <command>chroot()</command> function) by specifying
the <option>-t</option> option for <command>named</command>.
This can help improve system security by placing
<acronym>BIND</acronym> in a "sandbox", which 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 an unprivileged user ( <option>-u</option> <replaceable>user</replaceable> ).
We suggest running as an unprivileged user when using the <command>chroot</command> feature.
</para>
<para>
Here is an example command line to load <acronym>BIND</acronym> in a <command>chroot</command> sandbox,
<command>/var/named</command>, and to run <command>named</command> <command>setuid</command> to
user 202:
</para>
<para>
<userinput>/usr/local/sbin/named -u 202 -t /var/named</userinput>
</para>
<section xml:id="chroot"><info><title>The <command>chroot</command> Environment</title></info>
<para>
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 <command>directory</command> and
<command>pid-file</command> to account for this.
</para>
<para>
Unlike with earlier versions of BIND, you typically will
<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
<filename>/etc/localtime</filename>.
</para>
</section>
<section xml:id="setuid"><info><title>Using the <command>setuid</command> Function</title></info>
<para>
Prior to running the <command>named</command> daemon,
use
the <command>touch</command> utility (to change file
access and
modification times) or the <command>chown</command>
utility (to
set the user id and/or group id) on files
to which you want <acronym>BIND</acronym>
to write.
</para>
<note><simpara>
If the <command>named</command> daemon is running as an
unprivileged user, it will not be able to bind to new restricted
ports if the server is reloaded.
</simpara></note>
</section>
</section>
<section xml:id="dynamic_update_security"><info><title>Dynamic Update Security</title></info>
<para>
Access to the dynamic
update facility should be strictly limited. In earlier versions of
<acronym>BIND</acronym>, the only way to do this was
based on the IP
address of the host requesting the update, by listing an IP address
or
network prefix in the <command>allow-update</command>
zone option.
This method is insecure since the source address of the update UDP
packet
is easily forged. Also note that if the IP addresses allowed by the
<command>allow-update</command> option include the
address of a 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>
</section>
</chapter>
<chapter xml:id="Bv9ARM.ch07"><info><title>Troubleshooting</title></info>
<section xml:id="common_problems"><info><title>Common Problems</title></info>
<section><info><title>It's not working; how can I figure out what's wrong?</title></info>
<para>
The best solution to 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>
</section>
<section><info><title>EDNS compliance issues</title></info>
<para>
EDNS (Extended DNS) is a standard that was first specified
in 1999. It is required for DNSSEC validation, DNS COOKIE
options, and other features. There are broken and outdated
DNS servers and firewalls still in use which misbehave when
queried with EDNS; for example, they may drop EDNS queries
rather than replying with FORMERR. BIND and other recursive
name servers have traditionally employed workarounds in this
situation, retrying queries in different ways and eventually
falling back to plain DNS queries without EDNS.
</para>
<para>
Such workarounds cause unnecessary resolution delays,
increase code complexity, and prevent deployment of new DNS
features. As of February 2019, all major DNS software vendors
have agreed to remove these workarounds; see
<link xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:href="https://dnsflagday.net">https://dnsflagday.net</link>
for further details. This change was implemented in BIND
as of release 9.14.0.
</para>
<para>
As a result, some domains may be non-resolvable without manual
intervention. In these cases, resolution can be restored by
adding <command>server</command> clauses for the offending
servers, specifying <command>edns no</command> or
<command>send-cookie no</command>, depending on the specific
noncompliance.
</para>
<para>
To determine which <command>server</command> clause to use,
run the following commands to send queries to the authoritative
servers for the broken domain:
</para>
<literallayout>
dig soa &lt;zone&gt; @&lt;server&gt; +dnssec
dig soa &lt;zone&gt; @&lt;server&gt; +dnssec +nocookie
dig soa &lt;zone&gt; @&lt;server&gt; +noedns
</literallayout>
<para>
If the first command fails but the second succeeds, the
server most likely needs <command>send-cookie no</command>.
If the first two fail but the third succeeds, then the server
needs EDNS to be fully disabled with <command>edns no</command>.
</para>
<para>
Please contact the administrators of noncompliant domains
and encourage them to upgrade their broken DNS servers.
</para>
</section>
</section>
<section><info><title>Incrementing and Changing the Serial Number</title></info>
<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.
Occasionally they will make a mistake and set them to a
"date in the future" then try to correct them by setting
them to the "current date". This causes problems because
serial numbers are used to indicate that a zone has been
updated. If the serial number on the 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>
</section>
<section xml:id="more_help"><info><title>Where Can I Get Help?</title></info>
<para>
The Internet Systems 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
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="mailto:info@isc.org">info@isc.org</link> or visit the
<acronym>ISC</acronym> web page at
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.isc.org/services/support/">http://www.isc.org/services/support/</link>
to read more.
</para>
</section>
</chapter>
<appendix xml:id="Bv9ARM.ch08"><info><title>Release Notes</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="notes.xml"/>
</appendix>
<appendix xml:id="Bv9ARM.ch09"><info><title>A Brief History of the <acronym>DNS</acronym> and <acronym>BIND</acronym></title></info>
<para xml:id="historical_dns_information">
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 a rapidly expanding,
operational network environment. New RFCs were written and
published in 1987 that modified the original documents to
incorporate improvements based on the working model. RFC 1034,
"Domain Names-Concepts and Facilities", and RFC 1035, "Domain
Names-Implementation and Specification" were published and
became the standards upon which all <acronym>DNS</acronym> implementations are
built.
</para>
<para>
The first working domain name server, called "Jeeves", was
written in 1983-84 by Paul Mockapetris for operation on DEC
Tops-20
machines located at the University of Southern California's
Information
Sciences Institute (USC-ISI) and SRI International's Network
Information
Center (SRI-NIC). A <acronym>DNS</acronym> server for
Unix machines, the Berkeley Internet
Name Domain (<acronym>BIND</acronym>) package, was
written soon after by a group of
graduate students at the University of California at Berkeley
under
a grant from the US Defense Advanced Research Projects
Administration
(DARPA).
</para>
<para>
Versions of <acronym>BIND</acronym> through
4.8.3 were maintained by the Computer
Systems Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark
Painter, David Riggle and Songnian Zhou made up the initial <acronym>BIND</acronym>
project team. After that, additional work on the software package
was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment
Corporation
employee on loan to the CSRG, worked on <acronym>BIND</acronym> for 2 years, from 1985
to 1987. Many other people also contributed to <acronym>BIND</acronym> development
during that time: Doug Kingston, Craig Partridge, Smoot
Carl-Mitchell,
Mike Muuss, Jim Bloom and Mike Schwartz. <acronym>BIND</acronym> maintenance was subsequently
handled by Mike Karels and Øivind Kure.
</para>
<para>
<acronym>BIND</acronym> versions 4.9 and 4.9.1 were
released by Digital Equipment
Corporation (now Compaq Computer Corporation). Paul Vixie, then
a DEC employee, became <acronym>BIND</acronym>'s
primary caretaker. He was assisted
by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan
Beecher, Andrew
Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat
Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe
Wolfhugel, and others.
</para>
<para>
In 1994, <acronym>BIND</acronym> version 4.9.2 was sponsored by
Vixie Enterprises. Paul
Vixie became <acronym>BIND</acronym>'s principal
architect/programmer.
</para>
<para>
<acronym>BIND</acronym> versions from 4.9.3 onward
have been developed and maintained
by the Internet Systems Consortium and its predecessor,
the Internet Software Consortium, with support being provided
by ISC's sponsors.
</para>
<para>
As co-architects/programmers, Bob Halley and
Paul Vixie released the first production-ready version of
<acronym>BIND</acronym> version 8 in May 1997.
</para>
<para>
BIND version 9 was released in September 2000 and is a
major rewrite of nearly all aspects of the underlying
BIND architecture.
</para>
<para>
BIND versions 4 and 8 are officially deprecated.
No additional development is done
on BIND version 4 or BIND version 8.
</para>
<para>
<acronym>BIND</acronym> development work is made
possible today by the sponsorship
of several corporations, and by the tireless work efforts of
numerous individuals.
</para>
</appendix>
<appendix xml:id="Bv9ARM.ch10"><info><title>General <acronym>DNS</acronym> Reference Information</title></info>
<section xml:id="ipv6addresses"><info><title>IPv6 addresses (AAAA)</title></info>
<para>
IPv6 addresses are 128-bit identifiers for interfaces and
sets of interfaces which were introduced in the <acronym>DNS</acronym> to facilitate
scalable Internet routing. There are three types of addresses: <emphasis>Unicast</emphasis>,
an identifier for a single interface;
<emphasis>Anycast</emphasis>,
an identifier for a set of interfaces; and <emphasis>Multicast</emphasis>,
an identifier for a set of interfaces. Here we describe the global
Unicast address scheme. For more information, see RFC 3587,
"Global Unicast Address Format."
</para>
<para>
IPv6 unicast addresses consist of a
<emphasis>global routing prefix</emphasis>, a
<emphasis>subnet identifier</emphasis>, and an
<emphasis>interface identifier</emphasis>.
</para>
<para>
The global routing prefix is provided by the
upstream provider or ISP, and (roughly) corresponds to the
IPv4 <emphasis>network</emphasis> section
of the address range.
The subnet identifier is for local subnetting, much the
same as subnetting an
IPv4 /16 network into /24 subnets.
The interface identifier is the address of an individual
interface on a given network; in IPv6, addresses belong to
interfaces rather than to machines.
</para>
<para>
The subnetting capability of IPv6 is much more flexible than
that of IPv4: subnetting can be carried out on bit boundaries,
in much the same way as Classless InterDomain Routing
(CIDR), and the DNS PTR representation ("nibble" format)
makes setting up reverse zones easier.
</para>
<para>
The Interface Identifier must be unique on the local link,
and is usually generated automatically by the IPv6
implementation, although it is usually possible to
override the default setting if necessary. A typical IPv6
address might look like:
<command>2001:db8:201:9:a00:20ff:fe81:2b32</command>
</para>
<para>
IPv6 address specifications often contain long strings
of zeros, so the architects have included a shorthand for
specifying
them. The double colon (`::') indicates the longest possible
string
of zeros that can fit, and can be used only once in an address.
</para>
</section>
<section xml:id="bibliography"><info><title>Bibliography (and Suggested Reading)</title></info>
<section xml:id="rfcs"><info><title>Request for Comments (RFCs)</title></info>
<para>
Specification documents for the Internet protocol suite, including
the <acronym>DNS</acronym>, are published as part of
the Request for Comments (RFCs)
series of technical notes. The standards themselves are defined
by the Internet Engineering Task Force (IETF) and the Internet
Engineering Steering Group (IESG). RFCs can be obtained online via FTP at:
</para>
<para>
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ftp://www.isi.edu/in-notes/">
ftp://www.isi.edu/in-notes/RFC<replaceable>xxxx</replaceable>.txt
</link>
</para>
<para>
(where <replaceable>xxxx</replaceable> is
the number of the RFC). RFCs are also available via the Web at:
</para>
<para>
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.ietf.org/rfc/">http://www.ietf.org/rfc/</link>.
</para>
<bibliography>
<bibliodiv><info><title>Standards</title></info>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<biblioentry>
<abbrev>RFC974</abbrev>
<author><personname><surname>Partridge</surname><firstname>C.</firstname></personname></author>
<citetitle>Mail Routing and the Domain System</citetitle>
<pubdate>January 1986</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1034</abbrev>
<author><personname><surname>Mockapetris</surname><firstname>P.V.</firstname></personname></author>
<citetitle>Domain Names — Concepts and Facilities</citetitle>
<pubdate>November 1987</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1035</abbrev>
<author><personname><surname>Mockapetris</surname><firstname>P. V.</firstname></personname></author> <citetitle>Domain Names — Implementation and
Specification</citetitle>
<pubdate>November 1987</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv xml:id="proposed_standards" xreflabel="Proposed Standards"><info><title>Proposed Standards</title></info>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<biblioentry>
<abbrev>RFC2181</abbrev>
<author><personname><surname>Elz</surname><firstname>R., R. Bush</firstname></personname></author>
<citetitle>Clarifications to the <acronym>DNS</acronym>
Specification</citetitle>
<pubdate>July 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2308</abbrev>
<author><personname><surname>Andrews</surname><firstname>M.</firstname></personname></author>
<citetitle>Negative Caching of <acronym>DNS</acronym>
Queries</citetitle>
<pubdate>March 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1995</abbrev>
<author><personname><surname>Ohta</surname><firstname>M.</firstname></personname></author>
<citetitle>Incremental Zone Transfer in <acronym>DNS</acronym></citetitle>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1996</abbrev>
<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
<citetitle>A Mechanism for Prompt Notification of Zone Changes</citetitle>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2136</abbrev>
<authorgroup>
<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
<author><personname><firstname>S.</firstname><surname>Thomson</surname></personname></author>
<author><personname><firstname>Y.</firstname><surname>Rekhter</surname></personname></author>
<author><personname><firstname>J.</firstname><surname>Bound</surname></personname></author>
</authorgroup>
<citetitle>Dynamic Updates in the Domain Name System</citetitle>
<pubdate>April 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2671</abbrev>
<authorgroup>
<author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
</authorgroup>
<citetitle>Extension Mechanisms for DNS (EDNS0)</citetitle>
<pubdate>August 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2672</abbrev>
<authorgroup>
<author><personname><firstname>M.</firstname><surname>Crawford</surname></personname></author>
</authorgroup>
<citetitle>Non-Terminal DNS Name Redirection</citetitle>
<pubdate>August 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2845</abbrev>
<authorgroup>
<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
<author><personname><firstname>O.</firstname><surname>Gudmundsson</surname></personname></author>
<author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
<author><personname><firstname>B.</firstname><surname>Wellington</surname></personname></author>
</authorgroup>
<citetitle>Secret Key Transaction Authentication for <acronym>DNS</acronym> (TSIG)</citetitle>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2930</abbrev>
<authorgroup>
<author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
</authorgroup>
<citetitle>Secret Key Establishment for DNS (TKEY RR)</citetitle>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2931</abbrev>
<authorgroup>
<author><personname><firstname>D.</firstname><surname>Eastlake</surname><lineage>3rd</lineage></personname></author>
</authorgroup>
<citetitle>DNS Request and Transaction Signatures (SIG(0)s)</citetitle>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3007</abbrev>
<authorgroup>
<author><personname><firstname>B.</firstname><surname>Wellington</surname></personname></author>
</authorgroup>
<citetitle>Secure Domain Name System (DNS) Dynamic Update</citetitle>
<pubdate>November 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3645</abbrev>
<authorgroup>
<author><personname><firstname>S.</firstname><surname>Kwan</surname></personname></author>
<author><personname><firstname>P.</firstname><surname>Garg</surname></personname></author>
<author><personname><firstname>J.</firstname><surname>Gilroy</surname></personname></author>
<author><personname><firstname>L.</firstname><surname>Esibov</surname></personname></author>
<author><personname><firstname>J.</firstname><surname>Westhead</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Hall</surname></personname></author>
</authorgroup>
<citetitle>Generic Security Service Algorithm for Secret
Key Transaction Authentication for DNS
(GSS-TSIG)</citetitle>
<pubdate>October 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title><acronym>DNS</acronym> Security Proposed Standards</title></info>
<biblioentry>
<abbrev>RFC3225</abbrev>
<authorgroup>
<author><personname><firstname>D.</firstname><surname>Conrad</surname></personname></author>
</authorgroup>
<citetitle>Indicating Resolver Support of DNSSEC</citetitle>
<pubdate>December 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3833</abbrev>
<authorgroup>
<author><personname><firstname>D.</firstname><surname>Atkins</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
</authorgroup>
<citetitle>Threat Analysis of the Domain Name System (DNS)</citetitle>
<pubdate>August 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4033</abbrev>
<authorgroup>
<author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
<author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
<author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
<author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
</authorgroup>
<citetitle>DNS Security Introduction and Requirements</citetitle>
<pubdate>March 2005</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4034</abbrev>
<authorgroup>
<author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
<author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
<author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
<author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
</authorgroup>
<citetitle>Resource Records for the DNS Security Extensions</citetitle>
<pubdate>March 2005</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4035</abbrev>
<authorgroup>
<author><personname><firstname>R.</firstname><surname>Arends</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Austein</surname></personname></author>
<author><personname><firstname>M.</firstname><surname>Larson</surname></personname></author>
<author><personname><firstname>D.</firstname><surname>Massey</surname></personname></author>
<author><personname><firstname>S.</firstname><surname>Rose</surname></personname></author>
</authorgroup>
<citetitle>Protocol Modifications for the DNS
Security Extensions</citetitle>
<pubdate>March 2005</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Other Important RFCs About <acronym>DNS</acronym>
Implementation</title></info>
<biblioentry>
<abbrev>RFC1535</abbrev>
<author><personname><surname>Gavron</surname><firstname>E.</firstname></personname></author>
<citetitle>A Security Problem and Proposed Correction With Widely
Deployed <acronym>DNS</acronym> Software</citetitle>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1536</abbrev>
<authorgroup>
<author><personname><surname>Kumar</surname><firstname>A.</firstname></personname></author>
<author><personname><firstname>J.</firstname><surname>Postel</surname></personname></author>
<author><personname><firstname>C.</firstname><surname>Neuman</surname></personname></author>
<author><personname><firstname>P.</firstname><surname>Danzig</surname></personname></author>
<author><personname><firstname>S.</firstname><surname>Miller</surname></personname></author>
</authorgroup>
<citetitle>Common <acronym>DNS</acronym> Implementation
Errors and Suggested Fixes</citetitle>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1982</abbrev>
<authorgroup>
<author><personname><surname>Elz</surname><firstname>R.</firstname></personname></author>
<author><personname><firstname>R.</firstname><surname>Bush</surname></personname></author>
</authorgroup>
<citetitle>Serial Number Arithmetic</citetitle>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4074</abbrev>
<authorgroup>
<author><personname><surname>Morishita</surname><firstname>Y.</firstname></personname></author>
<author><personname><firstname>T.</firstname><surname>Jinmei</surname></personname></author>
</authorgroup>
<citetitle>Common Misbehaviour Against <acronym>DNS</acronym>
Queries for IPv6 Addresses</citetitle>
<pubdate>May 2005</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Resource Record Types</title></info>
<biblioentry>
<abbrev>RFC1183</abbrev>
<authorgroup>
<author><personname><surname>Everhart</surname><firstname>C.F.</firstname></personname></author>
<author><personname><firstname>L. A.</firstname><surname>Mamakos</surname></personname></author>
<author><personname><firstname>R.</firstname><surname>Ullmann</surname></personname></author>
<author><personname><firstname>P.</firstname><surname>Mockapetris</surname></personname></author>
</authorgroup>
<citetitle>New <acronym>DNS</acronym> RR Definitions</citetitle>
<pubdate>October 1990</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1706</abbrev>
<authorgroup>
<author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
<author><personname><firstname>R.</firstname><surname>Colella</surname></personname></author>
</authorgroup>
<citetitle><acronym>DNS</acronym> NSAP Resource Records</citetitle>
<pubdate>October 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2168</abbrev>
<authorgroup>
<author><personname><surname>Daniel</surname><firstname>R.</firstname></personname></author>
<author><personname><firstname>M.</firstname><surname>Mealling</surname></personname></author>
</authorgroup>
<citetitle>Resolution of Uniform Resource Identifiers using
the Domain Name System</citetitle>
<pubdate>June 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1876</abbrev>
<authorgroup>
<author><personname><surname>Davis</surname><firstname>C.</firstname></personname></author>
<author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
<author><personname><firstname>T.</firstname><firstname>Goodwin</firstname></personname></author>
<author><personname><firstname>I.</firstname><surname>Dickinson</surname></personname></author>
</authorgroup>
<citetitle>A Means for Expressing Location Information in the
Domain
Name System</citetitle>
<pubdate>January 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2052</abbrev>
<authorgroup>
<author><personname><surname>Gulbrandsen</surname><firstname>A.</firstname></personname></author>
<author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
</authorgroup>
<citetitle>A <acronym>DNS</acronym> RR for Specifying the
Location of
Services</citetitle>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2163</abbrev>
<author><personname><surname>Allocchio</surname><firstname>A.</firstname></personname></author>
<citetitle>Using the Internet <acronym>DNS</acronym> to
Distribute MIXER
Conformant Global Address Mapping</citetitle>
<pubdate>January 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2230</abbrev>
<author><personname><surname>Atkinson</surname><firstname>R.</firstname></personname></author>
<citetitle>Key Exchange Delegation Record for the <acronym>DNS</acronym></citetitle>
<pubdate>October 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2536</abbrev>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
<citetitle>DSA KEYs and SIGs in the Domain Name System (DNS)</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2537</abbrev>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
<citetitle>RSA/MD5 KEYs and SIGs in the Domain Name System (DNS)</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2538</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
<author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
</authorgroup>
<citetitle>Storing Certificates in the Domain Name System (DNS)</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2539</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
</authorgroup>
<citetitle>Storage of Diffie-Hellman Keys in the Domain Name System (DNS)</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2540</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
</authorgroup>
<citetitle>Detached Domain Name System (DNS) Information</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2782</abbrev>
<author><personname><surname>Gulbrandsen</surname><firstname>A.</firstname></personname></author>
<author><personname><surname>Vixie</surname><firstname>P.</firstname></personname></author>
<author><personname><surname>Esibov</surname><firstname>L.</firstname></personname></author>
<citetitle>A DNS RR for specifying the location of services (DNS SRV)</citetitle>
<pubdate>February 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2915</abbrev>
<author><personname><surname>Mealling</surname><firstname>M.</firstname></personname></author>
<author><personname><surname>Daniel</surname><firstname>R.</firstname></personname></author>
<citetitle>The Naming Authority Pointer (NAPTR) DNS Resource Record</citetitle>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3110</abbrev>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
<citetitle>RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)</citetitle>
<pubdate>May 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3123</abbrev>
<author><personname><surname>Koch</surname><firstname>P.</firstname></personname></author>
<citetitle>A DNS RR Type for Lists of Address Prefixes (APL RR)</citetitle>
<pubdate>June 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3596</abbrev>
<authorgroup>
<author><personname><surname>Thomson</surname><firstname>S.</firstname></personname></author>
<author><personname><firstname>C.</firstname><surname>Huitema</surname></personname></author>
<author><personname><firstname>V.</firstname><surname>Ksinant</surname></personname></author>
<author><personname><firstname>M.</firstname><surname>Souissi</surname></personname></author>
</authorgroup>
<citetitle><acronym>DNS</acronym> Extensions to support IP
version 6</citetitle>
<pubdate>October 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3597</abbrev>
<author><personname><surname>Gustafsson</surname><firstname>A.</firstname></personname></author>
<citetitle>Handling of Unknown DNS Resource Record (RR) Types</citetitle>
<pubdate>September 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title><acronym>DNS</acronym> and the Internet</title></info>
<biblioentry>
<abbrev>RFC1101</abbrev>
<author><personname><surname>Mockapetris</surname><firstname>P. V.</firstname></personname></author>
<citetitle><acronym>DNS</acronym> Encoding of Network Names
and Other Types</citetitle>
<pubdate>April 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1123</abbrev>
<author><personname><surname>Braden</surname><surname>R.</surname></personname></author>
<citetitle>Requirements for Internet Hosts - Application and
Support</citetitle>
<pubdate>October 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1591</abbrev>
<author><personname><surname>Postel</surname><firstname>J.</firstname></personname></author>
<citetitle>Domain Name System Structure and Delegation</citetitle>
<pubdate>March 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2317</abbrev>
<authorgroup>
<author><personname><surname>Eidnes</surname><firstname>H.</firstname></personname></author>
<author><personname><firstname>G.</firstname><surname>de Groot</surname></personname></author>
<author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
</authorgroup>
<citetitle>Classless IN-ADDR.ARPA Delegation</citetitle>
<pubdate>March 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2826</abbrev>
<authorgroup>
<author><personname><surname>Internet Architecture Board</surname></personname></author>
</authorgroup>
<citetitle>IAB Technical Comment on the Unique DNS Root</citetitle>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2929</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><firstname>D.</firstname><lineage>3rd</lineage></personname></author>
<author><personname><surname>Brunner-Williams</surname><firstname>E.</firstname></personname></author>
<author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
</authorgroup>
<citetitle>Domain Name System (DNS) IANA Considerations</citetitle>
<pubdate>September 2000</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title><acronym>DNS</acronym> Operations</title></info>
<biblioentry>
<abbrev>RFC1033</abbrev>
<author><personname><surname>Lottor</surname><firstname>M.</firstname></personname></author>
<citetitle>Domain administrators operations guide</citetitle>
<pubdate>November 1987</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1537</abbrev>
<author><personname><surname>Beertema</surname><firstname>P.</firstname></personname></author>
<citetitle>Common <acronym>DNS</acronym> Data File
Configuration Errors</citetitle>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1912</abbrev>
<author><personname><surname>Barr</surname><firstname>D.</firstname></personname></author>
<citetitle>Common <acronym>DNS</acronym> Operational and
Configuration Errors</citetitle>
<pubdate>February 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2010</abbrev>
<authorgroup>
<author><personname><surname>Manning</surname><firstname>B.</firstname></personname></author>
<author><personname><firstname>P.</firstname><surname>Vixie</surname></personname></author>
</authorgroup>
<citetitle>Operational Criteria for Root Name Servers</citetitle>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2219</abbrev>
<authorgroup>
<author><personname><surname>Hamilton</surname><firstname>M.</firstname></personname></author>
<author><personname><firstname>R.</firstname><surname>Wright</surname></personname></author>
</authorgroup>
<citetitle>Use of <acronym>DNS</acronym> Aliases for
Network Services</citetitle>
<pubdate>October 1997</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Internationalized Domain Names</title></info>
<biblioentry>
<abbrev>RFC2825</abbrev>
<authorgroup>
<author><personname><surname>IAB</surname></personname></author>
<author><personname><surname>Daigle</surname><firstname>R.</firstname></personname></author>
</authorgroup>
<citetitle>A Tangled Web: Issues of I18N, Domain Names,
and the Other Internet protocols</citetitle>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3490</abbrev>
<authorgroup>
<author><personname><surname>Faltstrom</surname><firstname>P.</firstname></personname></author>
<author><personname><surname>Hoffman</surname><firstname>P.</firstname></personname></author>
<author><personname><surname>Costello</surname><firstname>A.</firstname></personname></author>
</authorgroup>
<citetitle>Internationalizing Domain Names in Applications (IDNA)</citetitle>
<pubdate>March 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3491</abbrev>
<authorgroup>
<author><personname><surname>Hoffman</surname><firstname>P.</firstname></personname></author>
<author><personname><surname>Blanchet</surname><firstname>M.</firstname></personname></author>
</authorgroup>
<citetitle>Nameprep: A Stringprep Profile for Internationalized Domain Names</citetitle>
<pubdate>March 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3492</abbrev>
<authorgroup>
<author><personname><surname>Costello</surname><firstname>A.</firstname></personname></author>
</authorgroup>
<citetitle>Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in
Applications (IDNA)</citetitle>
<pubdate>March 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Other <acronym>DNS</acronym>-related RFCs</title></info>
<note>
<para>
Note: the following list of RFCs, although
<acronym>DNS</acronym>-related, are not
concerned with implementing software.
</para>
</note>
<biblioentry>
<abbrev>RFC1464</abbrev>
<author><personname><surname>Rosenbaum</surname><firstname>R.</firstname></personname></author>
<citetitle>Using the Domain Name System To Store Arbitrary String
Attributes</citetitle>
<pubdate>May 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1713</abbrev>
<author><personname><surname>Romao</surname><firstname>A.</firstname></personname></author>
<citetitle>Tools for <acronym>DNS</acronym> Debugging</citetitle>
<pubdate>November 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1794</abbrev>
<author><personname><surname>Brisco</surname><firstname>T.</firstname></personname></author>
<citetitle><acronym>DNS</acronym> Support for Load
Balancing</citetitle>
<pubdate>April 1995</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2240</abbrev>
<author><personname><surname>Vaughan</surname><firstname>O.</firstname></personname></author>
<citetitle>A Legal Basis for Domain Name Allocation</citetitle>
<pubdate>November 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2345</abbrev>
<authorgroup>
<author><personname><surname>Klensin</surname><firstname>J.</firstname></personname></author>
<author><personname><firstname>T.</firstname><surname>Wolf</surname></personname></author>
<author><personname><firstname>G.</firstname><surname>Oglesby</surname></personname></author>
</authorgroup>
<citetitle>Domain Names and Company Name Retrieval</citetitle>
<pubdate>May 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2352</abbrev>
<author><personname><surname>Vaughan</surname><firstname>O.</firstname></personname></author>
<citetitle>A Convention For Using Legal Names as Domain Names</citetitle>
<pubdate>May 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3071</abbrev>
<authorgroup>
<author><personname><surname>Klensin</surname><firstname>J.</firstname></personname></author>
</authorgroup>
<citetitle>Reflections on the DNS, RFC 1591, and Categories of Domains</citetitle>
<pubdate>February 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3258</abbrev>
<authorgroup>
<author><personname><surname>Hardie</surname><firstname>T.</firstname></personname></author>
</authorgroup>
<citetitle>Distributing Authoritative Name Servers via
Shared Unicast Addresses</citetitle>
<pubdate>April 2002</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3901</abbrev>
<authorgroup>
<author><personname><surname>Durand</surname><firstname>A.</firstname></personname></author>
<author><personname><firstname>J.</firstname><surname>Ihren</surname></personname></author>
</authorgroup>
<citetitle>DNS IPv6 Transport Operational Guidelines</citetitle>
<pubdate>September 2004</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Obsolete and Unimplemented Experimental RFC</title></info>
<biblioentry>
<abbrev>RFC1712</abbrev>
<authorgroup>
<author><personname><surname>Farrell</surname><firstname>C.</firstname></personname></author>
<author><personname><firstname>M.</firstname><surname>Schulze</surname></personname></author>
<author><personname><firstname>S.</firstname><surname>Pleitner</surname></personname></author>
<author><personname><firstname>D.</firstname><surname>Baldoni</surname></personname></author>
</authorgroup>
<citetitle><acronym>DNS</acronym> Encoding of Geographical
Location</citetitle>
<pubdate>November 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2673</abbrev>
<authorgroup>
<author><personname><surname>Crawford</surname><firstname>M.</firstname></personname></author>
</authorgroup>
<citetitle>Binary Labels in the Domain Name System</citetitle>
<pubdate>August 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2874</abbrev>
<authorgroup>
<author><personname><surname>Crawford</surname><firstname>M.</firstname></personname></author>
<author><personname><surname>Huitema</surname><firstname>C.</firstname></personname></author>
</authorgroup>
<citetitle>DNS Extensions to Support IPv6 Address Aggregation
and Renumbering</citetitle>
<pubdate>July 2000</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv><info><title>Obsoleted DNS Security RFCs</title></info>
<note>
<para>
Most of these have been consolidated into RFC4033,
RFC4034 and RFC4035 which collectively describe DNSSECbis.
</para>
</note>
<biblioentry>
<abbrev>RFC2065</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
<author><personname><firstname>C.</firstname><surname>Kaufman</surname></personname></author>
</authorgroup>
<citetitle>Domain Name System Security Extensions</citetitle>
<pubdate>January 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2137</abbrev>
<author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
<citetitle>Secure Domain Name System Dynamic Update</citetitle>
<pubdate>April 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2535</abbrev>
<authorgroup>
<author><personname><surname>Eastlake</surname><lineage>3rd</lineage><firstname>D.</firstname></personname></author>
</authorgroup>
<citetitle>Domain Name System Security Extensions</citetitle>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3008</abbrev>
<authorgroup>
<author><personname><surname>Wellington</surname><firstname>B.</firstname></personname></author>
</authorgroup>
<citetitle>Domain Name System Security (DNSSEC)
Signing Authority</citetitle>
<pubdate>November 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3090</abbrev>
<authorgroup>
<author><personname><surname>Lewis</surname><firstname>E.</firstname></personname></author>
</authorgroup>
<citetitle>DNS Security Extension Clarification on Zone Status</citetitle>
<pubdate>March 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3445</abbrev>
<authorgroup>
<author><personname><surname>Massey</surname><firstname>D.</firstname></personname></author>
<author><personname><surname>Rose</surname><firstname>S.</firstname></personname></author>
</authorgroup>
<citetitle>Limiting the Scope of the KEY Resource Record (RR)</citetitle>
<pubdate>December 2002</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3655</abbrev>
<authorgroup>
<author><personname><surname>Wellington</surname><firstname>B.</firstname></personname></author>
<author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
</authorgroup>
<citetitle>Redefinition of DNS Authenticated Data (AD) bit</citetitle>
<pubdate>November 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3658</abbrev>
<authorgroup>
<author><personname><surname>Gudmundsson</surname><firstname>O.</firstname></personname></author>
</authorgroup>
<citetitle>Delegation Signer (DS) Resource Record (RR)</citetitle>
<pubdate>December 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3755</abbrev>
<authorgroup>
<author><personname><surname>Weiler</surname><firstname>S.</firstname></personname></author>
</authorgroup>
<citetitle>Legacy Resolver Compatibility for Delegation Signer (DS)</citetitle>
<pubdate>May 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3757</abbrev>
<authorgroup>
<author><personname><surname>Kolkman</surname><firstname>O.</firstname></personname></author>
<author><personname><surname>Schlyter</surname><firstname>J.</firstname></personname></author>
<author><personname><surname>Lewis</surname><firstname>E.</firstname></personname></author>
</authorgroup>
<citetitle>Domain Name System KEY (DNSKEY) Resource Record
(RR) Secure Entry Point (SEP) Flag</citetitle>
<pubdate>April 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3845</abbrev>
<authorgroup>
<author><personname><surname>Schlyter</surname><firstname>J.</firstname></personname></author>
</authorgroup>
<citetitle>DNS Security (DNSSEC) NextSECure (NSEC) RDATA Format</citetitle>
<pubdate>August 2004</pubdate>
</biblioentry>
</bibliodiv>
</bibliography>
</section>
<section xml:id="internet_drafts"><info><title>Internet Drafts</title></info>
<para>
Internet Drafts (IDs) are rough-draft working documents of
the Internet Engineering Task Force. They are, in essence, RFCs
in the preliminary stages of development. Implementors are
cautioned not
to regard IDs as archival, and they should not be quoted or cited
in any formal documents unless accompanied by the disclaimer that
they are "works in progress." IDs have a lifespan of six months
after which they are deleted unless updated by their authors.
</para>
</section>
<section xml:id="more_about_bind"><info><title>Other Documents About <acronym>BIND</acronym></title></info>
<para/>
<bibliography>
<biblioentry>
<authorgroup>
<author><personname><surname>Albitz</surname><firstname>Paul</firstname></personname></author>
<author><personname><firstname>Cricket</firstname><surname>Liu</surname></personname></author>
</authorgroup>
<citetitle><acronym>DNS</acronym> and <acronym>BIND</acronym></citetitle>
<copyright>
<year>1998</year>
<holder>Sebastopol, CA: O'Reilly and Associates</holder>
</copyright>
</biblioentry>
</bibliography>
</section>
</section>
</appendix>
<appendix xml:id="Bv9ARM.ch11"><info><title>BIND 9 DNS Library Support</title></info>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="libdns.xml"/>
</appendix>
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</book>
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