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<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.0//EN"
"http://www.oasis-open.org/docbook/xml/4.0/docbookx.dtd">
<!-- File: $Id: Bv9ARM-book.xml,v 1.16 2000/10/02 22:21:44 bwelling Exp $ -->
<book>
<chapter id="ch01">
<title>Introduction </title>
<para>The Internet Domain Name System (<acronym>DNS</acronym>) consists of the syntax
to specify the names of entities in the Internet in a hierarchical
manner, the rules used for delegating authority over names, and the
system implementation that actually maps names to Internet
addresses. <acronym>DNS</acronym> data is maintained in a group of distributed
hierarchical databases.</para>
<sect1>
<title>Scope of Document</title>
<para>The Berkeley Internet Name Domain (<acronym>BIND</acronym>) implements an
Internet nameserver for a number of operating systems. This
document provides basic information about the installation and
care of the Internet Software Consortium (<acronym>ISC</acronym>) <acronym>BIND</acronym> version 9
software package for system administrators.</para>
</sect1>
<sect1><title>Organization of This Document</title>
<para>In this document, <emphasis>Section 1</emphasis> introduces
the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Section 2</emphasis>
describes resource requirements for running <acronym>BIND</acronym> in various
environments. Information in <emphasis>Section 3</emphasis> is
<emphasis>task-oriented</emphasis> in its presentation and is
organized functionally, to aid in the process of installing the
<acronym>BIND</acronym> 9 software. The task-oriented section is followed by
<emphasis>Section 4</emphasis>, which contains more advanced
concepts that the system administrator may need for implementing
certain options. Section 5 describes the <acronym>BIND</acronym> 9 lightweight
resolver. The contents of <emphasis>Section 6</emphasis> are
organized as in a reference manual to aid in the ongoing
maintenance of the software. <emphasis>Section 7
</emphasis>addresses security considerations, and
<emphasis>Section 8</emphasis> contains troubleshooting help. The
main body of the document is followed by several
<emphasis>Appendices</emphasis> which contain useful reference
information, such as a <emphasis>Bibliography</emphasis> and
historic information related to <acronym>BIND</acronym> and the Domain Name
System.</para>
</sect1>
<sect1><title>Conventions Used in This Document</title>
<para>In this document, we use the following general typographic
conventions:</para>
<informaltable 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>a pathname, filename, URL, hostname,
mailing list name, or new term or concept</para></entry>
<entry colname = "2" rowsep = "1"><para><filename>Italic</filename></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>literal user
input</para></entry>
<entry colname = "2" rowsep = "1"><para><userinput>Fixed Width Bold</userinput></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>variable user
input</para></entry>
<entry colname = "2" rowsep = "1"><para><optional>Fixed Width Italic</optional></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>program output</para></entry>
<entry colname = "2"><para><computeroutput>Fixed Width Bold</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>Sans Serif Bold</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>Sans Serif Italic</varname></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>"meta-syntactic"
information (within brackets when optional)</para></entry>
<entry colname = "2" rowsep = "1"><para><optional>Fixed Width Italic</optional></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>Command line
input</para></entry>
<entry colname = "2" rowsep = "1"><para><userinput>Fixed Width Bold</userinput></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>Program output</para></entry>
<entry colname = "2" rowsep = "1"><para><computeroutput>Fixed Width</computeroutput></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>Optional input</para></entry>
<entry colname = "2"><para><optional>Text is enclosed in square brackets</optional></para></entry>
</row>
</tbody>
</tgroup></informaltable></para></sect1>
<sect1><title>Discussion of Domain Name System (<acronym>DNS</acronym>) Basics and
<acronym>BIND</acronym></title>
<para>The purpose of this document is to explain the installation
and basic upkeep of the <acronym>BIND</acronym> software package, and we begin by reviewing
the fundamentals of the domain naming system as they relate to <acronym>BIND</acronym>.
<acronym>BIND</acronym> consists of a <emphasis>nameserver</emphasis> (or "daemon")
called <command>named</command> and a <command>resolver</command> library.
The <acronym>BIND</acronym> server runs in the background, servicing queries on a well
known network port. The standard port for the User Datagram Protocol
(UDP) and Transmission Control Protocol (TCP), usually port 53,
is specified in<command> </command><filename>/etc/services</filename>.
The <emphasis>resolver</emphasis> is a set of routines residing
in a system library that provides the interface that programs can
use to access the domain name services.</para>
<sect2><title>Nameservers</title>
<para>A nameserver (NS) is a program that stores information about
named resources and responds to queries from programs called <emphasis>resolvers</emphasis> which
act as client processes. The basic function of an NS is to provide
information about network objects by answering queries.</para>
<para>With the nameserver, the network can be broken into a hierarchy
of domains. The name space is organized as a tree according to organizational
or administrative boundaries. Each node of the tree, called a domain,
is given a label. The name of the domain is the concatenation of
all the labels of the domains from the root to the current domain.
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 domain. The whole name space is partitioned into areas
called <emphasis>zones</emphasis>, each starting at a domain and
extending down to the leaf domains or to domains where other zones
start. Zones usually represent administrative boundaries. For example,
a domain name for a host at the company <emphasis>Example, Inc.</emphasis> would
be:</para>
<para><systemitem class="systemname">ourhost.example.com</systemitem></para>
<para>where <systemitem class="systemname">com</systemitem> is the top level domain to which <systemitem class="systemname">ourhost.example.com</systemitem> belongs, <systemitem class="systemname">example</systemitem> is
a subdomain of <systemitem class="systemname">com</systemitem>, and <systemitem class="systemname">ourhost</systemitem> is the
name of the host.</para>
<para>The specifications for the domain nameserver are defined in
the RFC 1034, RFC 1035 and RFC 974. These documents can be found
in
<filename>/usr/src/etc/named/doc</filename> in 4.4BSD or are available
via File Transfer Protocol (FTP) from
<ulink
url="ftp://www.isi.edu/in-notes/">ftp://www.isi.edu/in-notes/</ulink> or via the Web at <ulink url="http://www.ietf.org/rfc/">http://www.ietf.org/rfc/</ulink>.
(See Appendix C for complete information on finding and retrieving
RFCs.) It is also recommended that you read the related man pages: <command>named</command> and <command>resolver</command>.</para></sect2>
<sect2><title>Types of Zones</title>
<para>As we stated previously, a zone is a point of delegation in
the <acronym>DNS</acronym> tree. A zone consists of those contiguous parts of the domain
tree for which a domain 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 has one or more NS records in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.</para>
<para>To properly operate a nameserver, it is important to understand
the difference between a <emphasis>zone</emphasis> and a <emphasis>domain</emphasis>.</para>
<para>For instance, consider the <systemitem class="systemname">example.com</systemitem> domain
which includes names such as <systemitem class="systemname">host.aaa.example.com </systemitem>and <systemitem class="systemname">host.bbb.example.com</systemitem> even
though the <systemitem class="systemname">example.com</systemitem> zone includes only delegations
for the <systemitem class="systemname">aaa.example.com</systemitem> and <systemitem class="systemname">bbb.example.com</systemitem> 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
nameservers. 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 a Domain Nameserver, 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>
<para>Each zone will have one <emphasis>primary master</emphasis> (also
called <emphasis>primary</emphasis>) server which 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.
There there will be some number of <emphasis>slave</emphasis> (also
called <emphasis>secondary) </emphasis>servers, which load the zone
contents using the <acronym>DNS</acronym> protocol (that is, the secondary servers
will contact the primary and fetch the zone data using TCP). This
set of servers &mdash; the primary and all of its secondaries &mdash; should be
listed in the NS records in the parent zone and will constitute a <emphasis>delegation</emphasis>.
This set of servers must also be listed in the zone file itself,
usually under the <command>@</command> name which indicates the <emphasis>top
level</emphasis> or <emphasis>root</emphasis> of the current zone.
You can list servers in the zone's top-level <command>@</command> 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 in
the zone's <command>@</command>.</para>
<para>Any servers listed in the NS records must be configured as <emphasis>authoritative</emphasis> for
the zone. A server is authoritative for a zone when it has been
configured to answer questions for that zone with authority, which
it does by setting the "authoritative answer" (AA) bit in reply
packets. A server may be authoritative for more than one zone. The
authoritative data for a zone is composed of all of the Resource
Records (RRs) &mdash; the data associated with names in a tree-structured
name space &mdash; attached to all of the nodes from the top node of the
zone down to leaf nodes or nodes above cuts around the bottom edge
of the zone.</para>
<para>Adding a zone as a type master or type slave will tell the
server to answer questions for the zone authoritatively. If the
server is able to load the zone into memory without any errors it
will set the AA bit when it replies to queries for the zone. See
RFCs 1034 and 1035 for more information about the AA bit.</para></sect2>
<sect2><title>Servers</title>
<para>A <acronym>DNS</acronym> server can be master for some zones and slave for others
or can be only a master, or only a slave, or can serve no zones
and just answer queries via its <emphasis>cache</emphasis>. Master
servers are often also called <emphasis>primaries</emphasis> and
slave servers are often also called <emphasis>secondaries</emphasis>.
Both master/primary and slave/secondary servers are authoritative
for a zone.</para>
<para>All servers keep data in their cache until the data expires,
based on a Time To Live (TTL) field which is maintained for all
resource records.</para>
<sect3><title>Master Server</title>
<para>The <emphasis>primary master server</emphasis> is the ultimate
source of information about a domain. The primary master is an authoritative
server configured to be the source of zone transfer for one or more
secondary servers. The primary master server obtains data for the
zone from a file on disk.</para></sect3>
<sect3><title>Slave Server </title>
<para>A <emphasis>slave server</emphasis>, also called a <emphasis>secondary
server</emphasis>, is an authoritative server that uses zone transfers from
the primary master server to retrieve the zone data. Optionally,
the slave server obtains zone data from a cache on disk. Slave servers
provide necessary redundancy. All secondary/slave servers are named
in the NS RRs for the zone.</para></sect3>
<sect3><title>Caching Only Server</title>
<para>Some servers are <emphasis>caching only servers</emphasis>.
This means that the server caches the information that it receives
and uses it until the data expires. A caching only server is a server
that is not authoritative for any zone. This server services queries
and asks other servers, who have the authority, for the information
it needs.</para></sect3>
<sect3><title>Forwarding Server</title>
<para>Instead of interacting with the nameservers for the root and
other domains, a <emphasis>forwarding server</emphasis> always forwards
queries it cannot satisfy from its authoritative data or cache to
a fixed list of other servers. The forwarded queries are also known
as <emphasis>recursive queries</emphasis>, the same type as a client would
send to a server. There may be one or more servers forwarded to,
and they are queried in turn until the list is exhausted or an answer
is found. A forwarding server is typically used when you do not
wish all the servers at a given site to interact with the rest of
the Internet servers. A typical scenario would involve a number
of internal <acronym>DNS</acronym> servers and an Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <acronym>DNS</acronym> servers
on the internal server's behalf. An added benefit of using the forwarding
feature is that the central machine develops a much more complete
cache of information that all the workstations can take advantage
of.</para>
<para>There is no prohibition against declaring a server to be a
forwarder even though it has master and/or slave zones as well;
the effect will still be that anything in the local server's cache
or zones will be answered, and anything else will be forwarded using
the forwarders list.</para></sect3>
<sect3><title>Stealth Server</title>
<para>A <emphasis>stealth server</emphasis> is a server that answers
authoritatively for a zone, but is not listed in that zone's NS
records. Stealth servers can be used as a way to centralize distribution
of a zone, without having to edit the zone on a remote nameserver.
Where the master file for a zone resides on a stealth server in
this way, it is often referred to as a "hidden primary" configuration.
Stealth servers can also be a way to keep a local copy of a zone
for rapid access to the zone's records, even if all "official" nameservers
for the zone are inaccessible.</para>
</sect3>
</sect2>
</sect1>
</chapter>
<chapter id="ch02"><title><acronym>BIND</acronym> Resource Requirements</title>
<sect1><title>Hardware requirements</title>
<para><acronym>DNS</acronym> hardware requirements have traditionally been quite modest.
For many installations, servers that have been pensioned off from
active duty have performed admirably as <acronym>DNS</acronym> servers.</para>
<para>The DNSSEC and IPv6 features of <acronym>BIND</acronym> 9 may prove to be quite
CPU intensive however, so organizations that make heavy use of these
features may wish to consider larger systems for these applications.
<acronym>BIND</acronym> 9 is now fully multithreaded, allowing full utilization of
multiprocessor systems for installations that need it.</para></sect1>
<sect1><title>CPU Requirements</title>
<para>CPU requirements for <acronym>BIND</acronym> 9 range from i486-class machines
for serving of static zones without caching, to enterprise-class
machines if you intend to process many dynamic updates and DNSSEC
signed zones, serving many thousands of queries per second.</para></sect1>
<sect1><title>Memory Requirements </title>
<para>The memory of the server has to be large enough to fit the
cache and zones loaded off disk. Future releases of <acronym>BIND</acronym> 9 will
provide methods to limit the amount of memory used by the cache,
at the expense of reducing cache hit rates and causing more <acronym>DNS</acronym>
traffic. It is still good practice to have enough memory to load
all zone and cache data into memory &mdash; unfortunately, the best way
to determine this for a given installation is to watch the nameserver
in operation. After a few weeks the server process should reach
a relatively stable size where entries are expiring from the cache as
fast as they are being inserted. Ideally, the resource limits should
be set higher than this stable size.</para></sect1>
<sect1><title>Nameserver Intensive Environment Issues</title>
<para>For nameserver intensive environments, there are two alternative
configurations that may be used. The first is where clients and
any second-level internal nameservers query a main nameserver, which
has enough memory to build a large cache. This approach minimizes
the bandwidth used by external name lookups. The second alternative
is to set up second-level internal nameservers to make queries independently.
In this configuration, none of the individual machines needs to
have as much memory or CPU power as in the first alternative, but
this has the disadvantage of making many more external queries,
as none of the nameservers share their cached data.</para></sect1>
<sect1><title>Supported Operating Systems</title>
<para>ISC <acronym>BIND</acronym> 9 compiles and runs on the following operating
systems:</para>
<itemizedlist>
<listitem>
<simpara>IBM AIX 4.3</simpara>
</listitem>
<listitem>
<simpara>Compaq Digital/Tru64 UNIX 4.0D</simpara>
</listitem>
<listitem>
<simpara>HP HP-UX 11</simpara>
</listitem>
<listitem>
<simpara>IRIX64 6.5</simpara>
</listitem>
<listitem>
<simpara>Red Hat Linux 6.0, 6.1</simpara>
</listitem>
<listitem>
<simpara>Sun Solaris 2.6, 7, 8 (beta)</simpara>
</listitem>
<listitem>
<simpara>FreeBSD 3.4-STABLE</simpara>
</listitem>
<listitem>
<simpara>NetBSD-current with "unproven" pthreads</simpara>
</listitem>
</itemizedlist>
</sect1>
</chapter>
<chapter id="ch03">
<title>Nameserver Configuration</title>
<para>In this section we provide some suggested configurations along
with guidelines for their use. We also address the topic of reasonable
option setting.</para>
<sect1 id="sample_configuration">
<title>Sample Configurations</title>
<sect2>
<title>A Caching-only Nameserver</title>
<para>The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation. All queries
from outside clients are refused.</para>
<programlisting>
// Two corporate subnets we wish to allow queries from.
acl "corpnets" { 192.168.4.0/24; 192.168.7.0/24; };
options {
directory "/etc/namedb"; // Working directory
pid-file "named.pid"; // Put pid file in working dir
allow-query { "corpnets"; };
};
// Root server hints
zone "." { type hint; file "root.hint"; };
// Provide a reverse mapping for the loopback address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
</programlisting>
</sect2>
<sect2>
<title>An Authoritative-only Nameserver</title>
<para>This sample configuration is for an authoritative-only server
that is the master server for "<filename>example.com</filename>"
and a slave for the subdomain "<filename>eng.example.com</filename>".</para>
<programlisting>
options {
directory "/etc/namedb"; // Working directory
pid-file "named.pid"; // Put pid file in working dir
allow-query { any; }; // This is the default
recursion no; // Do not provide recursive service
};
// Root server hints
zone "." { type hint; file "root.hint"; };
// Provide a reverse mapping for the loopback address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the master server for example.com
zone "example.com" {
type master;
file "example.com.db";
// IP addresses of slave servers allowed to transfer example.com
allow-transfer {
192.168.4.14;
192.168.5.53;
};
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
type slave;
file "eng.example.com.bk";
// IP address of eng.example.com master server
masters { 192.168.4.12; };
};
</programlisting>
</sect2>
</sect1>
<sect1>
<title>Load Balancing</title>
<para>Primitive load balancing can be achieved in <acronym>DNS</acronym> using multiple
A records for one name.</para>
<para>For example, if you have three WWW servers with network addresses
of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a set of records such as the
following means that clients will connect to each machine one third
of the time:</para>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "5" colsep = "0" rowsep = "0"
tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.500in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "5" colnum = "5" colsep = "0" colwidth = "2.028in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>Name</para></entry>
<entry colname = "2"><para>TTL</para></entry>
<entry colname = "3"><para>CLASS</para></entry>
<entry colname = "4"><para>TYPE</para></entry>
<entry colname = "5"><para>Resource Record (RR) Data</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>www</literal></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.1</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.2</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.3</literal></para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>When a resolver queries for these records, <acronym>BIND</acronym> will rotate
them and respond to the query with the records in a different
order. In the example above, clients will randomly receive
records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
will use the first record returned and discard the rest.</para>
<para>For more detail on ordering responses, check the
<command>rrset-order</command> substatement in the
<command>options</command> statement, see <xref
endterm="rrset_ordering_title" linkend="rrset_ordering"/>. This substatement is not supported in
<acronym>BIND</acronym> 9, and only the ordering scheme described above is
available.</para>
</sect1>
<sect1 id="notify">
<title>Notify</title>
<para><acronym>DNS</acronym> Notify is a mechanism that allows master nameservers to
notify their slave servers of changes to a zone's data. In
response to a <command>NOTIFY</command> from a master server, the
slave will check to see that its version of the zone is the
current version and, if not, initiate a transfer.</para> <para><acronym>DNS</acronym>
Notify is fully documented in RFC 1996. See also the description
of the zone option <command>also-notify</command>, see <xref
linkend="zone_transfers"/>. For more information about
<command>notify</command>, see <xref
linkend="boolean_options"/>.</para>
</sect1>
<sect1>
<title>Nameserver Operations</title>
<sect2>
<title>Tools for Use With the Nameserver Daemon</title>
<para>There are several indispensable diagnostic, administrative
and monitoring tools available to the system administrator for controlling
and debugging the nameserver daemon. We describe several in this
section </para>
<sect3>
<title>Diagnostic Tools</title>
<variablelist>
<varlistentry>
<term><command>dig</command></term>
<listitem>
<para>The domain information groper (<command>dig</command>) is
a command line tool that can be used to gather information from
the Domain Name System servers. Dig has two modes: simple interactive
mode for a single query, and batch mode which executes a query for
each in a list of several query lines. All query options are accessible
from the command line.</para>
<cmdsynopsis label="Usage">
<command>dig</command>
<arg>@<replaceable>server</replaceable></arg>
<arg choice="plain"><replaceable>domain</replaceable></arg>
<arg><replaceable>query-type</replaceable></arg>
<arg><replaceable>query-class</replaceable></arg>
<arg>+<replaceable>query-option</replaceable></arg>
<arg>-<replaceable>dig-option</replaceable></arg>
<arg>%<replaceable>comment</replaceable></arg>
<!-- one of (SBR GROUP ARG COMMAND) -->
</cmdsynopsis>
<para>The usual simple use of dig will take the form</para>
<simpara><command>dig @server domain query-type query-class</command></simpara>
<para>For more information and a list of available commands and
options, see the <command>dig</command> man page.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>host</command></term>
<listitem>
<para>The <command>host</command> utility
provides a simple <acronym>DNS</acronym> lookup using a command-line interface for
looking up Internet hostnames. By default, the utility converts
between host names and Internet addresses, but its functionality
can be extended with the use of options.</para>
<cmdsynopsis label="Usage">
<!-- one of (SBR GROUP ARG COMMAND) -->
<command>host</command>
<arg>-aCdlrTwv</arg>
<arg>-c <replaceable>class</replaceable></arg>
<arg>-N <replaceable>ndots</replaceable></arg>
<arg>-t <replaceable>type</replaceable></arg>
<arg>-W <replaceable>timeout</replaceable></arg>
<arg>-R <replaceable>retries</replaceable></arg>
<arg choice="plain"><replaceable>hostname</replaceable></arg>
<arg><replaceable>server</replaceable></arg>
</cmdsynopsis>
<para>For more information and a list of available commands and
options, see the <command>host</command> man page.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nslookup</command></term>
<listitem>
<para><command>nslookup</command> is a program used to query Internet
domain nameservers. <command>nslookup</command> has two modes: interactive
and non-interactive. Interactive mode allows the user to query nameservers
for information about various hosts and domains or to print a list
of hosts in a domain. Non-interactive mode is used to print just
the name and requested information for a host or domain.</para>
<cmdsynopsis label="Usage">
<command>nslookup</command>
<arg rep="repeat">-option</arg>
<group>
<arg><replaceable>host-to-find</replaceable></arg>
<arg>- <arg>server</arg></arg>
</group>
</cmdsynopsis>
<para>Interactive mode is entered when no arguments are given (the
default nameserver will be used) or when the first argument is a
hyphen (`-') and the second argument is the host name or Internet address
of a nameserver.</para>
<para>Non-interactive mode is used when the name or Internet address
of the host to be looked up is given as the first argument. The
optional second argument specifies the host name or address of a nameserver.</para>
<para>Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of <command>nslookup</command>.
Use <command>dig</command> instead.</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="admin_tools">
<title>Administrative Tools</title>
<para>Administrative tools play an integral part in the management
of a server.</para>
<variablelist>
<varlistentry id="rndc" xreflabel="Remote Name Daemon Control application">
<term><command>rndc</command></term>
<listitem>
<para>The remote name daemon control
(<command>rndc</command>) program allows the system
administrator to control the operation of a nameserver.
If you run <command>rndc</command> without any options
it will display a usage message as follows:</para>
<cmdsynopsis label="Usage">
<command>rndc</command>
<arg>-c <replaceable>config</replaceable></arg>
<arg>-s <replaceable>server</replaceable></arg>
<arg>-p <replaceable>port</replaceable></arg>
<arg>-y <replaceable>key</replaceable></arg>
<arg choice="plain"><replaceable>command</replaceable></arg>
<arg rep="repeat"><replaceable>command</replaceable></arg>
</cmdsynopsis>
<para><command>command</command> is one of the following
for <command>named</command>:</para>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1"
colsep = "0" colwidth = "1.500in"/>
<colspec colname = "2" colnum = "2" colsep = "0"
colwidth = "3.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1">
<para><userinput>status</userinput><footnote id="nyi1">
<para>not yet implemented</para>
</footnote></para></entry>
<entry colname = "2"><para>Display ps(1) status of named.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>dumpdb</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Dump database and cache to /var/tmp/named_dump.db.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>reload</userinput></para></entry>
<entry colname = "2"><para>Reload configuration file and zones.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>stats</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Dump statistics to /var/tmp/named.stats.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>trace</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Increment debugging level by one.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1">
<para><userinput>notrace</userinput><footnoteref linkend="nyi1"/>
</para></entry>
<entry colname = "2"><para>Set debugging level to 0.</para></entry>
</row>
<row rowsep = "0">
<entry colname =
"1"><para><userinput>querylog</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Toggle query logging.</para></entry>
</row>
<row rowsep = "0">
<entry colname =
"1"><para><userinput>stop</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Stop the server.</para></entry>
</row>
<row rowsep = "0">
<entry colname =
"1"><para><userinput>restart</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Restart the server.</para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>As noted above, <command>reload</command> is the
only command available for <acronym>BIND</acronym> 9.0.0. The other
commands, and more, are planned to be implemented for
future releases.</para>
<para>A configuration file is required, since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
<command>rndc</command> configuration file is
<filename>/etc/rndc.conf</filename>, but an alternate
location can be specified with the <option>-c</option>
option.</para>
<para>The format of the configuration file is similar to
that of <filename>named.conf</filename>, but limited to
only three statements, the <command>options{}</command>,
<command>key{}</command> and <command>server{}</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 two clauses: <command>default-server</command> and <command>default-key</command>. <command>default-server</command> takes a
host name or address argument and represents the server that will
be contacted if no <option>-s</option>
option is provided on the command line. <command>default-key</command> takes
the name of key as its argument, as defined by a <command>key{}</command> statement.
In the future a <command>default-port</command> clause will be
added to specify the port to which <command>rndc</command> should
connect.</para>
<para>The <command>key{}</command> statement names a key with its
string argument. The string is required by the server to be a valid
domain name, though it need not actually be hierarchical; thus,
a string like "<userinput>rndc_key</userinput>" is a valid name.
The <command>key{}</command> statement has two clauses: <command>algorithm</command> and <command>secret</command>.
While the configuration parser will accept any string as the argument
to algorithm, currently only the string "<userinput>hmac-md5</userinput>"
has any meaning. The secret is a base-64 encoded string, typically
generated with either <command>dnssec-keygen</command> or <command>mmencode</command>.</para>
<para>The <command>server{}</command> statement uses the key clause
to associate a <command>key{}</command>-defined key with a server.
The argument to the <command>server{}</command> statement is a
host name or address (addresses must be double quoted). The argument
to the key clause is the name of the key as defined by the <command>key{}</command> statement.
A <command>port</command> clause will be added to a future release
to specify the port to which <command>rndc</command> should connect
on the given server.</para>
<para>A sample minimal configuration file is as follows:</para>
<programlisting>
key rndc_key {
algorithm "hmac-md5";
secret "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
default-server localhost;
default-key rndc_key;
};
</programlisting>
<para>This file, if installed as <filename>/etc/rndc.conf</filename>,
would allow the command:</para>
<para><prompt>$ </prompt><userinput>rndc reload</userinput></para>
<para>to connect to 127.0.0.1 port 953 and cause the nameserver
to reload, if a nameserver on the local machine were running with
following controls statements:</para>
<programlisting>
controls {
inet 127.0.0.1 allow { localhost; } keys { rndc_key; };
};
</programlisting>
<para>and it had an identical key statement for
<literal>rndc_key</literal>.</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
</sect2>
<sect2>
<title>Signals</title>
<para>Certain UNIX signals cause the name server to take specific
actions, as described in the following table. These signals can
be sent using the <command>kill</command> command.</para>
<informaltable 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><command>SIGHUP</command></para></entry>
<entry colname = "2"><para>Causes the server to read <filename>named.conf</filename> and
reload the database. </para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>SIGTERM</command></para></entry>
<entry colname = "2"><para>Causes the server to clean up and exit.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1">
<para><command>SIGINT</command></para>
</entry>
<entry colname = "2"><para>Causes the server to clean up and exit.</para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect2>
</sect1>
</chapter>
<chapter id="ch04">
<title>Advanced Concepts</title>
<sect1 id="dynamic_update">
<title>Dynamic Update</title>
<para>Dynamic update is the term used for the ability under
certain specified conditions to add, modify or delete records or
RRsets in the master zone files. Dynamic update is fully described
in RFC 2136.</para>
<para>Dynamic update is enabled on a zone-by-zone basis, by
including an <command>allow-update</command> or
<command>update-policy</command> clause in the
<command>zone</command> statement.</para>
<para>Updating of secure zones (zones using DNSSEC) is modelled
after the <emphasis>simple-secure-update</emphasis> proposal, a
work in progress in the DNS Extensions working group of the IETF.
(See <ulink
url="http://www.ietf.org/html.charters/dnsext-charter.html">http://www.ietf.org/html.charters/dnsext-charter.html</ulink>
for information about the DNS Extensions working group.) SIG and
NXT records affected by updates are automatically regenerated by
the server using an online zone key. Update authorization is based
on transaction signatures and an explicit server policy.</para>
<para>The zone files of dynamic zones must not be edited by hand.
The zone file on disk at any given time may not contain the latest
changes performed by dynamic update. The zone file is written to
disk only periodically, and changes that have occurred since the
zone file was last written to disk are stored only in the zone's
journal (<filename>.jnl</filename>) file. <acronym>BIND</acronym> 9 currently does
not update the zone file when it exits as <acronym>BIND</acronym> 8 does, so editing
the zone file manually is unsafe even when the server has been
shut down. </para>
</sect1>
<sect1 id="incremental_zone_transfers">
<title>Incremental Zone Transfers (IXFR)</title>
<para>The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is documented in RFC
1995. See <xref linkend="proposed_standards"/></para>
<para>When acting as a master, <acronym>BIND</acronym> 9 supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR, but not manually maintained master
zones nor slave zones obtained by performing a full zone transfer
(AXFR).</para>
<para>When acting as a slave, <acronym>BIND</acronym> 9 will attempt to use IXFR unless
it is explicitly disabled. For more information about disabling
IXFR, see the description of the <command>request-ixfr</command> clause
of the <command>server</command> statement.</para></sect1>
<sect1><title>Split DNS</title>
<para>Setting up different views, or visibility, of DNS space to
internal and external resolvers is usually referred to as a <emphasis>Split
DNS</emphasis> setup. There are several reasons an organization
would want to set up its DNS this way.</para>
<para>One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.</para>
<para>Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.</para>
<para>Here is an example of a split DNS setup:</para>
<para>Let's say a company named <emphasis>Example, Inc.</emphasis> (example.com)
has several corporate sites that have an internal network with reserved
Internet Protocol (IP) space and an external demilitarized zone (DMZ),
or "outside" section of a network, that is available to the public.</para>
<para><emphasis>Example, Inc.</emphasis> wants its internal clients
to be able to resolve external hostnames and to exchange mail with
people on the outside. The company also wants its internal resolvers
to have access to certain internal-only zones that are not available
at all outside of the internal network.</para>
<para>In order to accomplish this, the company will set up two sets
of nameservers. One set will be on the inside network (in the reserved
IP space) and the other set will be on bastion hosts, which are "proxy"
hosts that can talk to both sides of its network, in the DMZ.</para>
<para>The internal servers will be configured to forward all queries,
except queries for <filename>site1.internal</filename>, <filename>site2.internal</filename>, <filename>site1.example.com</filename>,
and <filename>site2.example.com</filename>, to the servers in the
DMZ. These internal servers will have complete sets of information
for <filename>site1.example.com</filename>, <filename>site2.example.com</filename>,<emphasis> </emphasis><filename>site1.internal</filename>,
and <filename>site2.internal</filename>.</para>
<para>To protect the<filename> site1.interna</filename><emphasis>l</emphasis> and<emphasis> </emphasis><filename>site2.internal</filename> domains,
the internal nameservers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.</para>
<para>The external servers, which are on the bastion hosts, will
be configured to serve the "public" version of the <filename>site1</filename> and <filename>site2.example.com</filename> zones.
This could include things such as the host records for public servers
(<filename>www.example.com</filename> and <filename>ftp.example.com</filename>),
and mail exchange (MX) records (<filename>a.mx.example.com</filename> and <filename>b.mx.example.com</filename>).</para>
<para>In addition, the public <filename>site1</filename> and <filename>site2.example.com</filename> zones
should have special MX records that contain wildcard (`*') records
pointing to the bastion hosts. This is needed because external mail
servers do not have any other way of looking up how to deliver mail
to those internal hosts. With the wildcard records, the mail will
be delivered to the bastion host, which can then forward it on to
internal hosts.</para>
<para>Here's an example of a wildcard MX record:</para>
<programlisting><literal>* IN MX 10 external1.example.com.</literal></programlisting>
<para>Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers on
the bastion hosts will need to be configured to point to the internal
nameservers for DNS resolution.</para>
<para>Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.</para>
<para>In order for all this to work properly, internal clients will
need to be configured to query <emphasis>only</emphasis> the internal
nameservers for DNS queries. This could also be enforced via selective
filtering on the network.</para>
<para>If everything has been set properly, <emphasis>Example, Inc.</emphasis>'s
internal clients will now be able to:</para>
<itemizedlist><listitem>
<simpara>Look up any hostnames in the <systemitem class="systemname">site1</systemitem> and
<systemitem class="systemname">site2.example.com</systemitem> zones.</simpara></listitem>
<listitem>
<simpara>Look up any hostnames in the <systemitem class="systemname">site1.internal</systemitem> and
<systemitem class="systemname">site2.internal</systemitem> domains.</simpara></listitem>
<listitem>
<simpara>Look up any hostnames on the Internet.</simpara></listitem>
<listitem>
<simpara>Exchange mail with internal AND external people.</simpara></listitem></itemizedlist>
<para>Hosts on the Internet will be able to:</para>
<itemizedlist><listitem>
<simpara>Look up any hostnames in the <systemitem class="systemname">site1</systemitem> and
<systemitem class="systemname">site2.example.com </systemitem>zones.</simpara></listitem>
<listitem>
<simpara>Exchange mail with anyone in the <systemitem class="systemname">site1</systemitem> and
<systemitem class="systemname">site2.example.com</systemitem> zones.</simpara></listitem></itemizedlist>
<para>Here is an example configuration for the setup we just
described above. Note that this is only configuration information;
for information on how to configure your zone files, see <xref
linkend="sample_configuration"/></para>
<para>Internal DNS server config:</para>
<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { <varname>bastion-ips-go-here</varname>; };
options {
...
...
forward only;
forwarders { // forward to external servers
<varname>bastion-ips-go-here</varname>;
};
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample slave zone
type master;
file "m/site1.example.com";
forwarders { }; // do normal iterative
// resolution (do not forward)
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</programlisting>
<para>External (bastion host) DNS server config:</para>
<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; externals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample slave zone
type master;
file "m/site1.foo.com";
allow-query { any; };
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-query { any; };
allow-transfer { internals; externals; }
};
</programlisting>
<para>In the <filename>resolv.conf</filename> (or equivalent) on
the bastion host(s):</para>
<programlisting>
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</programlisting>
</sect1>
<sect1 id="tsig"><title>TSIG</title>
<para>This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym>BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym>BIND</acronym>.</para>
<para><acronym>BIND</acronym> primarily supports TSIG for server to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym>BIND</acronym> 8 have limited support
for TSIG.</para>
<para>TSIG might be most useful for dynamic update. A primary
server for a dynamic zone should use access control to control
updates, but IP-based access control is insufficient. Key-based
access control is far superior, see <xref
linkend="proposed_standards"/>. The <command>nsupdate</command>
program supports TSIG via the <option>-k</option> and
<option>-y</option> command line options.</para>
<sect2><title>Generate Shared Keys for Each Pair of Hosts</title>
<para>A shared secret is generated to be shared between <emphasis>host1</emphasis> and <emphasis>host2</emphasis>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.</para>
<sect3><title>Automatic Generation</title>
<para>The following command will generate a 128 bit (16 byte) HMAC-MD5
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is 512 bits;
keys longer than that will be digested with MD5 to produce a 128
bit key.</para>
<para><userinput>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</userinput></para>
<para>The key is in the file <filename>Khost1-host2.+157+00000.private</filename>.
Nothing directly uses this file, but the base-64 encoded string
following "<literal>Key:</literal>"
can be extracted from the file and used as a shared secret:</para>
<programlisting>Key: La/E5CjG9O+os1jq0a2jdA==</programlisting>
<para>The string "<literal>La/E5CjG9O+os1jq0a2jdA==</literal>" can
be used as the shared secret.</para></sect3>
<sect3><title>Manual Generation</title>
<para>The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.</para>
<para>Also, a known string can be run through <command>mmencode</command> or
a similar program to generate base-64 encoded data.</para></sect3></sect2>
<sect2><title>Copying the Shared Secret to Both Machines</title>
<para>This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.</para></sect2>
<sect2><title>Informing the Servers of the Key's Existence</title>
<para>Imagine <emphasis>host1</emphasis> and <emphasis>host 2</emphasis> are
both servers. The following is added to each server's <filename>named.conf</filename> file:</para>
<programlisting>
key host1-host2. {
algorithm hmac-md5;
secret "La/E5CjG9O+os1jq0a2jdA==";
};
</programlisting>
<para>The algorithm, hmac-md5, is the only one supported by <acronym>BIND</acronym>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <filename>named.conf</filename> be non-world
readable, or the key directive be added to a non-world readable
file that is included by <filename>named.conf</filename>.</para>
<para>At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature succeeds, the response is signed by
the same key.</para></sect2>
<sect2><title>Instructing the Server to Use the Key</title>
<para>Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <filename>named.conf</filename> file
for <emphasis>host1</emphasis>, if the IP address of <emphasis>host2</emphasis> is
10.1.2.3:</para>
<programlisting>
server 10.1.2.3 {
keys { host1-host2. ;};
};
</programlisting>
<para>Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a world-readable
file.</para>
<para>If <emphasis>host1</emphasis> sends a message that is a response
to that address, the message will be signed with the specified key. <emphasis>host1</emphasis> will
expect any responses to signed messages to be signed with the same
key.</para>
<para>A similar statement must be present in <emphasis>host2</emphasis>'s
configuration file (with <emphasis>host1</emphasis>'s address) for <emphasis>host2</emphasis> to
sign non-response messages to <emphasis>host1</emphasis>.</para></sect2>
<sect2><title>TSIG Key Based Access Control</title>
<para><acronym>BIND</acronym> allows IP addresses and ranges to be specified in ACL
definitions and
<command>allow-{ query | transfer | update } </command>directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <command>key host1-host2.</command></para>
<para>An example of an allow-update directive would be:</para>
<programlisting>
allow-update { key host1-host2. ;};
</programlisting>
<para>This allows dynamic updates to succeed only if the request
was signed by a key named
"<command>host1-host2.</command>".</para> <para>You may want to read about the more
powerful <command>update-policy</command> statement in <xref
linkend="dynamic_update_policies"/>.</para>
</sect2>
<sect2>
<title>Errors</title>
<para>The processing of TSIG signed messages can result in
several errors. If a signed message is sent to a non-TSIG aware
server, a FORMERR will be returned, since the server will not
understand the record. This is a result of misconfiguration,
since the server must be explicitly configured to send a TSIG
signed message to a specific server.</para>
<para>If a TSIG aware server receives a message signed by an
unknown key, the response will be unsigned with the TSIG
extended error code set to BADKEY. If a TSIG aware server
receives a message with a signature that does not validate, the
response will be unsigned with the TSIG extended error code set
to BADSIG. If a TSIG aware server receives a message with a time
outside of the allowed range, the response will be signed with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified. In any of these cases, the message's rcode is set to
NOTAUTH.</para>
</sect2>
</sect1>
<sect1>
<title>TKEY</title>
<para><command>TKEY</command> is a mechanism for automatically
generating a shared secret between two hosts. There are several
"modes" of <command>TKEY</command> that specify how the key is
generated or assigned. <acronym>BIND</acronym> implements only one of these modes,
the Diffie-Hellman key exchange. Both hosts are required to have
a Diffie-Hellman KEY record (although this record is not required
to be present in a zone). The <command>TKEY</command> process
must use signed messages, signed either by TSIG or SIG(0). The
result of <command>TKEY</command> is a shared secret that can be
used to sign messages with TSIG. <command>TKEY</command> can also
be used to delete shared secrets that it had previously
generated.</para>
<para>The <command>TKEY</command> process is initiated by a client
or server by sending a signed <command>TKEY</command> query
(including any appropriate KEYs) to a TKEY-aware server. The
server response, if it indicates success, will contain a
<command>TKEY</command> record and any appropriate keys. After
this exchange, both participants have enough information to
determine the shared secret; the exact process depends on the
<command>TKEY</command> mode. When using the Diffie-Hellman
<command>TKEY</command> mode, Diffie-Hellman keys are exchanged,
and the shared secret is derived by both participants.</para>
</sect1>
<sect1>
<title>SIG(0)</title>
<para><acronym>BIND</acronym> 9 partially supports DNSSEC SIG(0) transaction
signatures as specified in RFC 2535. SIG(0) uses public/private
keys to authenticate messages. Access control is performed in the
same manner as TSIG keys; privileges can be granted or denied
based on the key name.</para>
<para>When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
will not attempt to locate and/or validate the key.</para>
<para><acronym>BIND</acronym> 9 does not ship with any tools that generate SIG(0)
signed messages.</para>
</sect1>
<sect1 id="DNSSEC">
<title>DNSSEC</title>
<para>Cryptographic authentication of DNS information is possible
through the DNS Security (<emphasis>DNSSEC</emphasis>) extensions,
defined in RFC 2535. This section describes the creation and use
of DNSSEC signed zones.</para>
<para>In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <acronym>BIND</acronym> 9 ships with several tools
that are used in this process, which are explained in more detail
below. In all cases, the "<option>-h</option>" option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset and signedkey files to be in the working directory.</para>
<para>There must also be communication with the administrators of
the parent and/or child zone to transmit keys and signatures. A
zone's security status must be indicated by the parent zone for a
DNSSEC capable resolver to trust its data.</para>
<para>For other servers to trust data in this zone, they must
either be statically configured with this zone's zone key or the
zone key of another zone above this one in the DNS tree.</para>
<sect2>
<title>Generating Keys</title>
<para>The <command>dnssec-keygen</command> program is used to
generate keys.</para>
<para>A secure zone must contain one or more zone keys. The
zone keys will sign all other records in the zone, as well as
the zone keys of any secure delegated zones. Zone keys must
have the same name as the zone, a name type of
<command>ZONE</command>, and must be usable for authentication.
It is recommended that zone keys be mandatory to implement a
cryptographic algorithm; currently the only key mandatory to
implement an algorithm is DSA.</para>
<para>The following command will generate a 768 bit DSA key for
the <filename>child.example</filename> zone:</para>
<para><userinput>dnssec-keygen -a DSA -b 768 -n ZONE child.example.</userinput></para>
<para>Two output files will be produced:
<filename>Kchild.example.+003+12345.key</filename> and
<filename>Kchild.example.+003+12345.private</filename> (where
12345 is an example of a key tag). The key file names contain
the key name (<filename>child.example.</filename>), algorithm (3
is DSA, 1 is RSA, etc.), and the key tag (12345 in this case).
The private key (in the <filename>.private</filename> file) is
used to generate signatures, and the public key (in the
<filename>.key</filename> file) is used for signature
verification.</para>
<para>To generate another key with the same properties (but with
a different key tag), repeat the above command.</para>
<para>The public keys should be inserted into the zone file with
<command>$INCLUDE</command> statements, including the
<filename>.key </filename>files.</para>
</sect2>
<sect2>
<title>Creating a Keyset</title>
<para>The <command>dnssec-makekeyset</command> program is used
to create a key set from one or more keys.</para>
<para>Once the zone keys have been generated, a key set must be
built for transmission to the administrator of the parent zone,
so that the parent zone can sign the keys with its own zone key
and correctly indicate the security status of this zone. When
building a key set, the list of keys to be included and the TTL
of the set must be specified, and the desired signature validity
period of the parent's signature may also be specified.</para>
<para>The list of keys to be inserted into the key set may also
included non-zone keys present at the top of the zone.
<command>dnssec-makekeyset</command> may also be used at other
names in the zone.</para>
<para>The following command generates a key set containing the
above key and another key similarly generated, with a TTL of
3600 and a signature validity period of 10 days starting from
now.</para>
<para><userinput>dnssec-makekeyset -t 3600 -e +86400 Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>
<para>One output file is produced:
<filename>child.example.keyset</filename>. This file should be
transmitted to the parent to be signed. It includes the keys,
as well as signatures over the key set generated by the zone
keys themselves, which are used to prove ownership of the
private keys and encode the desired validity period.</para>
</sect2>
<sect2>
<title>Signing the Child's Keyset</title>
<para>The <command>dnssec-signkey</command> program is used to
sign one child's keyset.</para>
<para>If the <filename>child.example</filename> zone has any
delegations which are secure, for example,
<filename>grand.child.example</filename>, the
<filename>child.example</filename> administrator should receive
keyset files for each secure subzone. These keys must be signed
by this zone's zone keys.</para>
<para>The following command signs the child's key set with the
zone keys:</para>
<para><userinput>dnssec-signkey grand.child.example.keyset Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>
<para>One output file is produced:
<filename>grand.child.example.signedkey</filename>. This file
should be both transmitted back to the child and retained. It
includes all keys (the child's keys) from the keyset file and
signatures generated by this zone's zone keys.</para>
</sect2>
<sect2>
<title>Signing the Zone</title>
<para>The <command>dnssec-signzone</command> program is used to
sign a zone.</para>
<para>Any <filename>signedkey</filename> files corresponding to
secure subzones should be present, as well as a
<filename>signedkey</filename> file for this zone generated by
the parent (if there is one). The zone signer will generate
<literal>NXT</literal> and <literal>SIG</literal> records for
the zone, as well as incorporate the zone key signature from the
parent and indicate the security status at all delegation
points.</para>
<para>The following command signs the zone, assuming it is in a
file called <filename>zone.child.example</filename>. By
default, all zone keys which have an available private key are
used to generate signatures.</para>
<para><userinput>dnssec-signzone -o child.example zone.child.example</userinput></para>
<para>One output file is produced:
<filename>zone.child.example.signed</filename>. This file
should be referenced by <filename>named.conf</filename> as the
input file for the zone.</para>
</sect2>
<sect2><title>Configuring Servers</title>
<para>Unlike in <acronym>BIND</acronym> 8, data is not verified on load in <acronym>BIND</acronym> 9,
so zone keys for authoritative zones do not need to be specified
in the configuration file.</para>
<para>The public key for any security root must be present in
the configuration file's <command>trusted-keys</command>
statement, as described later in this document. </para>
</sect2>
</sect1>
<sect1>
<title>IPv6 Support in <acronym>BIND</acronym> 9</title>
<para><acronym>BIND</acronym> 9 fully supports all currently defined forms of IPv6
name to address and address to name lookups. It will also use
IPv6 addresses to make queries when running on an IPv6 capable
system.</para>
<para>For forward lookups, <acronym>BIND</acronym> 9 supports both A6 and AAAA
records. The use of AAAA records is deprecated, but it is still
useful for hosts to have both AAAA and A6 records to maintain
backward compatibility with installations where AAAA records are
still used. In fact, the stub resolvers currently shipped with
most operating system support only AAAA lookups, because following
A6 chains is much harder than doing A or AAAA lookups.</para>
<para>For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports the new
"bitstring" format used in the <emphasis>ip6.arpa</emphasis>
domain, as well as the older, deprecated "nibble" format used in
the <emphasis>ip6.int</emphasis> domain.</para>
<para><acronym>BIND</acronym> 9 includes a new lightweight resolver library and
resolver daemon which new applications may choose to use to avoid
the complexities of A6 chain following and bitstring labels, see <xref
linkend="ch05"/>.</para>
<sect2>
<title>Address Lookups Using AAAA Records</title>
<para>The AAAA record is a parallel to the IPv4 A record. It
specifies the entire address in a single record. For
example,</para>
<programlisting>
$ORIGIN example.com.
host 3600 IN AAAA 3ffe:8050:201:1860:42::1
</programlisting>
<para>While their use is deprecated, they are useful to support
older IPv6 applications. They should not be added where they
are not absolutely necessary.</para>
</sect2>
<sect2>
<title>Address Lookups Using A6 Records</title>
<para>The A6 record is more flexible than the AAAA record, and
is therefore more complicated. The A6 record can be used to
form a chain of A6 records, each specifying part of the IPv6
address. It can also be used to specify the entire record as
well. For example, this record supplies the same data as the
AAAA record in the previous example:</para>
<programlisting>
$ORIGIN example.com.
host 3600 IN A6 0 3ffe:8050:201:1860:42::1
</programlisting>
<sect3>
<title>A6 Chains</title>
<para>A6 records are designed to allow network
renumbering. This works when an A6 record only specifies the
part of the address space the domain owner controls. For
example, a host may be at a company named "company." It has
two ISPs which provide IPv6 address space for it. These two
ISPs fully specify the IPv6 prefix they supply.</para>
<para>In the company's address space:</para>
<programlisting>
$ORIGIN example.com.
host 3600 IN A6 64 0:0:0:0:42::1 company.example1.net.
host 3600 IN A6 64 0:0:0:0:42::1 company.example2.net.
</programlisting>
<para>ISP1 will use:</para>
<programlisting>
$ORIGIN example1.net.
company 3600 IN A6 0 3ffe:8050:201:1860::
</programlisting>
<para>ISP2 will use:</para>
<programlisting>
$ORIGIN example2.net.
company 3600 IN A6 0 1234:5678:90ab:fffa::
</programlisting>
<para>When <systemitem
class="systemname">host.example.com</systemitem> is looked up,
the resolver (in the resolver daemon or caching name server)
will find two partial A6 records, and will use the additional
name to find the remainder of the data.</para>
</sect3>
<sect3>
<title>A6 Records for DNS Servers</title>
<para>When an A6 record specifies the address of a name
server, it should use the full address rather than specifying
a partial address. For example:</para>
<programlisting>
$ORIGIN example.com.
@ 14400 IN NS ns0
14400 IN NS ns1
ns0 14400 IN A6 0 3ffe:8050:201:1860:42::1
ns1 14400 IN A 192.168.42.1
</programlisting>
<para>It is recommended that IPv4-in-IPv6 mapped addresses not
be used. If a host has an IPv4 address, use an A record, not
an A6, with <literal>::ffff:192.168.42.1</literal> as the
address.</para>
</sect3>
</sect2>
<sect2>
<title>Address to Name Lookups Using Nibble Format</title>
<para>While the use of nibble format to look up names is
deprecated, it is supported for backwards compatiblity with
existing IPv6 applications.</para>
<para>When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<literal>ip6.int.</literal> is appended to the resulting name.
For example, the following would provide reverse name lookup for
a host with address
<literal>3ffe:8050:201:1860:42::1</literal>.</para>
<programlisting>
$ORIGIN 0.6.8.1.1.0.2.0.0.5.0.8.e.f.f.3.ip6.int.
1.0.0.0.0.0.0.0.0.0.0.0.2.4.0.0 14400 IN PTR host.example.com.
</programlisting>
</sect2>
<sect2>
<title>Address to Name Lookups Using Bitstring Format</title>
<para>Bitstring labels can start and end on any bit boundary,
rather than on a multiple of 4 bits as in the nibble
format. They also use <emphasis>ip6.arpa</emphasis> rather than
<emphasis>ip6.int</emphasis>.</para>
<para>To replicate the previous example using bitstrings:</para>
<programlisting>
$ORIGIN \[x3ffe805002011860/64].ip6.arpa.
\[x0042000000000001/64] 14400 IN PTR host.example.com.
</programlisting>
</sect2>
<sect2>
<title>Using DNAME for Delegation of IPv6 Reverse Addresses</title>
<para>In IPV6, the same host may have many addresses from many
network providers. Since the trailing portion of the address
usually remains constant, <command>DNAME</command> can help
reduce the number of zone files used for reverse mapping that
need to be maintained.</para>
<para>For example, consider a host which has two providers
(<systemitem class="systemname">example.net</systemitem> and
<systemitem class="systemname">example2.net</systemitem>) and
therefore two IPv6 addresses. Since the host chooses its own 64
bit host address portion, the provider address is the only part
that changes:</para>
<programlisting>
$ORIGIN example.com.
host A6 64 ::1234:5678:1212:5675 cust1.example.net.
A6 64 ::1234:5678:1212:5675 subnet5.example2.net.
$ORIGIN example.net.
cust1 A6 48 0:0:0:dddd:: ipv6net.example.net.
ipv6net A6 0 aa:bb:cccc::
$ORIGIN example2.net.
subnet5 A6 48 0:0:0:1:: ipv6net2.example2.net.
ipv6net2 A6 0 6666:5555:4::
</programlisting>
<para>This sets up forward lookups. To handle the reverse lookups,
the provider <systemitem class="systemname">example.net</systemitem>
would have:</para>
<programlisting>
$ORIGIN \[x00aa00bbcccc/48].ip6.arpa.
\[xdddd/16] DNAME ipv6-rev.example.com.
</programlisting>
<para>and <systemitem
class="systemname">example2.net</systemitem> would have:</para>
<programlisting>
$ORIGIN \[x666655550004/48].ip6.arpa.
\[x0001/16] DNAME ipv6-rev.example.com.
</programlisting>
<para><systemitem class="systemname">example.com</systemitem>
needs only one zone file to handle both of these reverse
mappings:</para>
<programlisting>
$ORIGIN ipv6-rev.example.com.
\[x1234567812125675/64] PTR host.example.com.
</programlisting>
</sect2>
</sect1>
</chapter>
<chapter id="ch05"><title>The <acronym>BIND</acronym> 9 Lightweight Resolver</title>
<sect1><title>The Lightweight Resolver Library</title>
<para>Traditionally applications have been linked with a stub resolver
library that sends recursive DNS queries to a local caching name
server.</para>
<para>IPv6 introduces new complexity into the resolution process,
such as following A6 chains and DNAME records, and simultaneous
lookup of IPv4 and IPv6 addresses. These are hard or impossible
to implement in a traditional stub resolver.</para>
<para>Instead, <acronym>BIND</acronym> 9 provides resolution services to local clients
using a combination of a lightweight resolver library and a resolver
daemon process running on the local host. These communicate using
a simple UDP-based protocol, the "lightweight resolver protocol"
that is distinct from and simpler than the full DNS protocol.</para></sect1>
<sect1><title>Running a Resolver Daemon</title>
<para>To use the lightweight resolver interface, the system must
run the resolver daemon <command>lwresd</command>.</para>
<para>Applications using the lightweight resolver library will make
UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
The daemon will try to find the answer to the questions "what are the
addresses for host <systemitem class="systemname">foo.example.com</systemitem>?" and "what are
the names for IPv4 address 204.152.184.79?"</para>
<para>The daemon currently only looks in the DNS, but in the future
it may use other sources such as <literal>/etc/hosts</literal>,
NIS, etc.</para>
<para>The <command>lwresd</command> daemon is essentially a stripped-down,
caching-only name server that answers requests using the lightweight
resolver protocol rather than the DNS protocol. Because it needs
to run on each host, it is designed to require no or minimal configuration.
It uses the name servers listed on <command>nameserver</command> lines
in <filename>/etc/resolv.conf</filename> as forwarders, but is also
capable of doing the resolution autonomously if none are specified.</para></sect1></chapter>
<chapter id="ch06"><title><acronym>BIND</acronym> 9 Configuration Reference</title>
<para><acronym>BIND</acronym> 9 configuration is broadly similar to <acronym>BIND</acronym> 8.x; however,
there are a few new areas of configuration, such as views. <acronym>BIND</acronym>
8.x configuration files should work with few alterations in <acronym>BIND</acronym>
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in <acronym>BIND</acronym> 9.</para>
<para><acronym>BIND</acronym> 4 configuration files can be converted to the new format
using the shell script
<filename>contrib/named-bootconf/named-bootconf.sh</filename>.</para>
<sect1 id="configuration_file_elements"><title>Configuration File Elements</title>
<para>Following is a list of elements used throughout the <acronym>BIND</acronym> configuration
file documentation:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.855in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.770in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><varname>acl_name</varname></para></entry>
<entry colname = "2"><para>The name of an <varname>address_match_list</varname> as
defined by the <command>acl</command> statement.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>address_match_list</varname></para></entry>
<entry colname = "2"><para>A list of one or more <varname>ip_addr</varname><command>, </command><varname>ip_prefix</varname><command>, </command><varname>key_id</varname><command>, </command>or <varname>acl_name</varname> elements, see
<xref linkend="address_match_lists"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>domain_name</varname></para></entry>
<entry colname = "2"><para>A quoted string which will be used as
a DNS name, for example "<systemitem class="systemname">my.test.domain</systemitem>".</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>dotted_decimal</varname></para></entry>
<entry colname = "2"><para>One or more integers valued 0 through
255 separated only by dots (`.'), such as <command>123</command>, <command>45.67</command> or <command>89.123.45.67</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip4_addr</varname></para></entry>
<entry colname = "2"><para>An IPv4 address with exactly four elements
in <varname>dotted_decimal</varname> notation.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip6_addr</varname></para></entry>
<entry colname = "2"><para>An IPv6 address, such as <command>fe80::200:f8ff:fe01:9742</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_addr</varname></para></entry>
<entry colname = "2"><para>An <varname>ip4_addr</varname> or<command> </command><varname>ip6_addr</varname>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_port</varname></para></entry>
<entry colname = "2"><para>An IP port <varname>number</varname>.
<varname>number</varname> is limited to 0 through 65535, with values
below 1024 typically restricted to root-owned processes. In some
cases an asterisk (`*') character can be used as a placeholder to
select a random high-numbered port.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_prefix</varname></para></entry>
<entry colname = "2"><para>An IP network specified as an <varname>ip_addr</varname>,
followed by a slash (`/') and then the number of bits in the netmask.
Trailing zeros in a <varname>ip_addr</varname> may omitted.
For example, <command>127/8</command> is the network <command>127.0.0.0</command> with
netmask <command>255.0.0.0</command> and <command>1.2.3.0/28</command> is
network <command>1.2.3.0</command> with netmask <command>255.255.255.240</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>key_id</varname></para></entry>
<entry colname = "2"><para>A <varname>domain_name</varname> representing
the name of a shared key, to be used for transaction security.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>key_list</varname></para></entry>
<entry colname = "2"><para>A list of one or more <varname>key_id</varname>s,
separated by semicolons and ending with a semicolon.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>number</varname></para></entry>
<entry colname = "2"><para>A non-negative integer with an entire
range limited by the range of a C language signed integer (2,147,483,647
on a machine with 32 bit integers). Its acceptable value might further
be limited by the context in which it is used.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>path_name</varname></para></entry>
<entry colname = "2"><para>A quoted string which will be used as
a pathname, such as <filename>zones/master/my.test.domain</filename>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>size_spec</varname></para></entry>
<entry colname = "2"><para>A number, the word <userinput>unlimited</userinput>,
or the word <userinput>default</userinput>.</para><para>The maximum
value of <varname>size_spec</varname> is that of unsigned long integers
on the machine. An <varname>unlimited</varname> <varname>size_spec</varname> requests unlimited
use, or the maximum available amount. A <varname>default size_spec</varname> uses
the limit that was in force when the server was started.</para><para>A <varname>number</varname> can
optionally be followed by a scaling factor: <userinput>K</userinput> or <userinput>k</userinput><command> </command>for
kilobytes, <userinput>M</userinput> or <userinput>m</userinput> for
megabytes, and <userinput>G</userinput> or <userinput>g</userinput> for gigabytes,
which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.</para><para>Integer
storage overflow is currently silently ignored during conversion
of scaled values, resulting in values less than intended, possibly
even negative. Using <varname>unlimited</varname> is the best way
to safely set a really large number.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>yes_or_no</varname></para></entry>
<entry colname = "2"><para>Either <userinput>yes</userinput> or <userinput>no</userinput>.
The words <userinput>true</userinput> and <userinput>false</userinput> are
also accepted, as are the numbers <userinput>1</userinput> and <userinput>0</userinput>.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<sect2 id="address_match_lists"><title>Address Match Lists</title>
<sect3><title>Syntax</title>
<programlisting><varname>address_match_list</varname> = address_match_list_element ;
<optional> address_match_list_element; ... </optional>
<varname>address_match_list_element</varname> = <optional> ! </optional> (ip_address <optional>/length</optional> |
key key_id | acl_name | { address_match_list } )
</programlisting>
</sect3>
<sect3><title>Definition and Usage</title>
<para>Address match lists are primarily used to determine access
control for various server operations. They are also used to define
priorities for querying other nameservers and to set the addresses
on which <command>named</command> will listen for queries. The elements
which constitute an address match list can be any of the following:</para>
<itemizedlist><listitem>
<simpara>an IP address (IPv4 or IPv6)</simpara></listitem>
<listitem>
<simpara>an IP prefix (in the `/'-notation)</simpara></listitem>
<listitem>
<simpara>a key ID, as defined by the key statement</simpara></listitem>
<listitem>
<simpara>the name of an address match list previously defined with
the <command>acl</command> statement</simpara></listitem>
<listitem>
<simpara>a nested address match list enclosed in braces</simpara></listitem></itemizedlist>
<para>Elements can be negated with a leading exclamation mark (`!')
and the match list names "any," "none," "localhost" and "localnets"
are predefined. More information on those names can be found in
the description of the acl statement.</para>
<para>The addition of the key clause made the name of this syntactic
element something of a misnomer, since security keys can be used
to validate access without regard to a host or network address. Nonetheless,
the term "address match list" is still used throughout the documentation.</para>
<para>When a given IP address or prefix is compared to an address
match list, the list is traversed in order until an element matches.
The interpretation of a match depends on whether the list is being used
for access control, defining listen-on ports, or as a topology,
and whether the element was negated.</para>
<para>When used as an access control list, a non-negated match allows
access and a negated match denies access. If there is no match,
access is denied. The clauses <command>allow-query</command>, <command>allow-transfer</command>, <command>allow-update</command> and <command>blackhole</command> all
use address match lists this. Similarly, the listen-on option will cause
the server to not accept queries on any of the machine's addresses
which do not match the list.</para>
<para>When used with the topology clause, a non-negated match returns
a distance based on its position on the list (the closer the match
is to the start of the list, the shorter the distance is between
it and the server). A negated match will be assigned the maximum
distance from the server. If there is no match, the address will
get a distance which is further than any non-negated list element,
and closer than any negated element.</para>
<para>Because of the first-match aspect of the algorithm, an element
that defines a subset of another element in the list should come
before the broader element, regardless of whether either is negated. For
example, in
<command>1.2.3/24; ! 1.2.3.13;</command> the 1.2.3.13 element is
completely useless because the algorithm will match any lookup for
1.2.3.13 to the 1.2.3/24 element. Using <command>! 1.2.3.13; 1.2.3/24</command> fixes
that problem by having 1.2.3.13 blocked by the negation but all
other 1.2.3.* hosts fall through.</para></sect3></sect2>
<sect2>
<title>Comment Syntax</title>
<para>The <acronym>BIND</acronym> 9 comment syntax allows for comments to appear
anywhere that white space may appear in a <acronym>BIND</acronym> configuration
file. To appeal to programmers of all kinds, they can be written
in C, C++, or shell/perl constructs.</para>
<sect3>
<title>Syntax</title>
<para><programlisting>/* This is a <acronym>BIND</acronym> comment as in C */</programlisting>
<programlisting>// This is a <acronym>BIND</acronym> comment as in C++</programlisting>
<programlisting># This is a <acronym>BIND</acronym> comment as in common UNIX shells and perl</programlisting>
</para>
</sect3>
<sect3>
<title>Definition and Usage</title>
<para>Comments may appear anywhere that whitespace may appear in
a <acronym>BIND</acronym> configuration file.</para>
<para>C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.</para>
<para>C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:</para>
<para><programlisting>/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */
</programlisting></para>
<para>C++-style comments start with the two characters // (slash,
slash) and continue to the end of the physical line. They cannot
be continued across multiple physical lines; to have one logical
comment span multiple lines, each line must use the // pair.</para>
<para>For example:</para>
<para><programlisting>// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
</programlisting></para>
<para>Shell-style (or perl-style, if you prefer) comments start
with the character <literal>#</literal> (number sign) and continue to the end of the
physical line, as in C++ comments.</para>
<para>For example:</para>
<para><programlisting># This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.
</programlisting></para>
<warning>
<para>WARNING: you cannot use the semicolon (`;') character
to start a comment such as you would in a zone file. The
semicolon indicates the end of a configuration
statement.</para>
</warning>
</sect3>
</sect2>
</sect1>
<sect1 id="Configuration_File_Grammar">
<title>Configuration File Grammar</title>
<para>A <acronym>BIND</acronym> 9 configuration consists of statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of substatements, which are also
terminated with a semicolon.</para>
<para>The following statements are supported:</para>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0" tgroupstyle =
"2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.336in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.778in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>acl</command></para></entry>
<entry colname = "2"><para>defines a named IP address
matching list, for access control and other uses.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>controls</command></para></entry>
<entry colname = "2"><para>declares control channels to be used
by the <command>rndc</command> utility.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>include</command></para></entry>
<entry colname = "2"><para>includes a file.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>key</command></para></entry>
<entry colname = "2"><para>specifies key information for use in
authentication and authorization using TSIG.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>logging</command></para></entry>
<entry colname = "2"><para>specifies what the server logs, and where
the log messages are sent.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>options</command></para></entry>
<entry colname = "2"><para>controls global server configuration
options and sets defaults for other statements.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>server</command></para></entry>
<entry colname = "2"><para>sets certain configuration options on
a per-server basis.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>trusted-keys</command></para></entry>
<entry colname = "2"><para>defines trusted DNSSEC keys.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>view</command></para></entry>
<entry colname = "2"><para>defines a view.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>zone</command></para></entry>
<entry colname = "2"><para>defines a zone.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The <command>logging</command> and
<command>options</command> statements may only occur once per
configuration.</para>
<sect2>
<title><command>acl</command> Statement Grammar</title>
<programlisting><command>acl</command> acl-name {
address_match_list
};
</programlisting>
</sect2>
<sect2 id="acl">
<title><command>acl</command> Statement Definition and
Usage</title>
<para>The <command>acl</command> statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).</para>
<para>Note that an address match list's name must be defined
with <command>acl</command> before it can be used elsewhere; no
forward references are allowed.</para>
<para>The following ACLs are built-in:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.130in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>any</command></para></entry>
<entry colname = "2"><para>Matches all hosts.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>none</command></para></entry>
<entry colname = "2"><para>Matches no hosts.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>localhost</command></para></entry>
<entry colname = "2"><para>Matches the IP addresses of all interfaces
on the system.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>localnets</command></para></entry>
<entry colname = "2"><para>Matches any host on a network for which
the system has an interface.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
</sect2>
<sect2>
<title><command>controls</command> Statement Grammar</title>
<programlisting><command>controls</command> {
inet ( ip_addr | * ) <optional> port ip_port </optional> allow <replaceable> address_match_list </replaceable>
keys <replaceable> key_list </replaceable>;
<optional> inet ...; </optional>
};
</programlisting>
</sect2>
<sect2>
<title><command>controls</command> Statement Definition and
Usage</title>
<para>The <command>controls</command> statement declares control
channels to be used by system administrators to affect the
operation of the local nameserver. These control channels are
used by the <command>rndc</command> utility to send commands to
and retrieve non-DNS results from a nameserver.</para>
<para>An <command>inet</command> control channel is a TCP/IP
socket accessible to the Internet, created at the specified
<command>ip_port</command> on the specified
<command>ip_addr</command>. If no port is specified, port 953
is used by default. "*" cannot be used for
<command>ip_port</command>.</para>
<para>The ability to issue commands over the control channel is
restricted by the <command>allow</command> and
<command>keys</command> clauses. Connections to the control
channel are permitted based on the address permissions in
<command>address_match_list</command>. <command>key_id</command>
members of the <command>address_match_list</command> are
ignored, and instead are interpreted independently based the
<command>key_list</command>. Each <command>key_id</command> in
the <command>key_list</command> is allowed to be used to
authenticate commands and responses given over the control
channel by digitally signing each message between the server and
a command client (See <xref linkend="rndc"/> in <xref
linkend="admin_tools"/>). All commands to the
control channel must be signed by one of its specified keys to
be honored.</para>
<para> For the initial release of <acronym>BIND</acronym> 9.0.0, only one command
is possible over the command channel, the command to reload the
server. We will expand command set in future releases.</para>
<para>The UNIX control channel type of <acronym>BIND</acronym> 8 is not supported
in <acronym>BIND</acronym> 9.0.0, and is not expected to be added in future
releases. If it is present in the controls statement from a
<acronym>BIND</acronym> 8 configuration file, a non-fatal warning will be
logged.</para>
</sect2>
<sect2>
<title><command>include</command> Statement Grammar</title>
<programlisting>include <replaceable>filename</replaceable>;</programlisting>
</sect2>
<sect2>
<title><command>include</command> Statement Definition and
Usage</title>
<para>The <command>include</command> statement inserts the
specified file at the point that the <command>include</command>
statement is encountered. The <command>include</command>
statement facilitates the administration of configuration files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by a nameserver.</para>
</sect2>
<sect2>
<title><command>key</command> Statement Grammar</title>
<programlisting>key <replaceable>key_id</replaceable> {
algorithm <replaceable>string</replaceable>;
secret <replaceable>string</replaceable>;
};
</programlisting>
</sect2>
<sect2>
<title><command>key</command> Statement Definition and Usage</title>
<para>The <command>key</command> statement defines a shared
secret key for use with TSIG, see <xref linkend="tsig"/>.</para>
<para>The <replaceable>key_id</replaceable>, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a "server" statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.</para>
<para>The <replaceable>algorithm_id</replaceable> is a string
that specifies a security/authentication algorithm. The only
algorithm currently supported with TSIG authentication is
<literal>hmac-md5</literal>. The
<replaceable>secret_string</replaceable> is the secret to be
used by the algorithm, and is treated as a base-64 encoded
string.</para>
</sect2>
<sect2>
<title><command>logging</command> Statement Grammar</title>
<programlisting><command>logging</command> {
[ <command>channel</command> <replaceable>channel_name</replaceable> {
( <command>file</command> <replaceable>path name</replaceable>
[ <command>versions</command> ( <replaceable>number</replaceable> | <literal>unlimited</literal> ) ]
[ <command>size</command> <replaceable>size spec</replaceable> ]
| <command>syslog</command> ( <replaceable>syslog_facility</replaceable> )
| <literal>null</literal> );
[ <command>severity</command> (<option>critical</option> | <option>error</option> | <option>warning</option> | <option>notice</option> |
<option>info</option> | <option>debug</option> [ <replaceable>level</replaceable> ] | <option>dynamic</option> ); ]
[ <command>print-category</command> <option>yes</option> or <option>no</option>; ]
[ <command>print-severity</command> <option>yes</option> or <option>no</option>; ]
[ <command>print-time</command> <option>yes</option> or <option>no</option>; ]
}; ]
[ <command>category</command> <replaceable>category_name</replaceable> {
<replaceable>channel_name</replaceable> ; [ <replaceable>channel_nam</replaceable>e ; ... ]
}; ]
...
};
</programlisting>
</sect2>
<sect2><title><command>logging</command> Statement Definition and
Usage</title>
<para>The <command>logging</command> statement configures a wide
variety of logging options for the nameserver. Its <command>channel</command> phrase
associates output methods, format options and severity levels with
a name that can then be used with the <command>category</command> phrase
to select how various classes of messages are logged.</para>
<para>Only one <command>logging</command> statement is used to define
as many channels and categories as are wanted. If there is no <command>logging</command> statement,
the logging configuration will be:</para>
<programlisting><command>logging</command> {
category "default" { "default_syslog"; "default_debug"; };
};
</programlisting>
<para>In <acronym>BIND</acronym> 9, the logging configuration is only established when
the entire configuration file has been parsed. In <acronym>BIND</acronym> 8, it was
established as soon as the <command>logging</command> statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the "<option>-g</option>" option
was specified.</para>
<sect3><title>The <command>channel</command> Phrase</title>
<para>All log output goes to one or more <emphasis>channels</emphasis>;
you can make as many of them as you want.</para>
<para>Every channel definition must include a clause that says whether
messages selected for the channel go to a file, to a particular
syslog facility, 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 word <command>null</command> as the destination option
for the channel will cause all messages sent to it to be discarded;
in that case, other options for the channel are meaningless.</para>
<para>The <command>file</command> clause can include limitations
both on how large the file is allowed to become, and how many versions
of the file will be saved each time the file is opened.</para>
<para>The <command>size</command> option for files is simply a hard
ceiling on log growth. If the file ever exceeds the size, then <command>named</command> will
not write anything more to it until the file is reopened; exceeding
the size does not automatically trigger a reopen. The default behavior
is not to limit the size of the file.</para>
<para>If you use the <command>version</command> log file option,
then <command>named</command> will retain that many backup versions
of the file by renaming them when opening. For example, if you choose
to keep 3 old versions of the file <filename>lamers.log</filename> then
just before it is opened <filename>lamers.log.1</filename> is renamed
to <filename>lamers.log.2</filename>, <filename>lamers.log.0</filename> is
renamed to <filename>lamers.log.1</filename>, and <filename>lamers.log</filename> is
renamed to <filename>lamers.log.0</filename>. No rolled versions
are kept by default; any existing log file is simply appended. The <command>unlimited</command> keyword
is synonymous with <command>99</command> in current <acronym>BIND</acronym> releases.</para>
<para>Example usage of the size and versions options:</para>
<programlisting>channel "an_example_channel" {
file "example.log" versions 3 size 20m;
print-time yes;
print-category yes;
};
</programlisting>
<para>The argument for the <command>syslog</command> clause is a
syslog facility as described in the <command>syslog</command> man
page. How <command>syslog</command> will handle messages sent to
this facility is described in the <command>syslog.conf</command> man
page. If you have a system which uses a very old version of <command>syslog</command> that
only uses two arguments to the <command>openlog()</command> function,
then this clause is silently ignored.</para>
<para>The <command>severity</command> clause works like <command>syslog</command>'s
"priorities," except that they can also be used if you are writing
straight to a file rather than using <command>syslog</command>.
Messages which are not at least of the severity level given will
not be selected for the channel; messages of higher severity levels
will be accepted.</para>
<para>If you are using <command>syslog</command>, then the <command>syslog.conf</command> priorities
will also determine what eventually passes through. For example,
defining a channel facility and severity as <command>daemon</command> and <command>debug</command> but
only logging <command>daemon.warning</command> via <command>syslog.conf</command> will
cause messages of severity <command>info</command> and <command>notice</command> to
be dropped. If the situation were reversed, with <command>named</command> writing
messages of only <command>warning</command> or higher, then <command>syslogd</command> would
print all messages it received from the channel.</para>
<para>The 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>. <note>
<simpara>the latter
method is not yet implemented</simpara></note> The global debug level
can be set to zero, and debugging mode turned off, by running <command>ndc
notrace</command>. All debugging messages in the server have a debug
level, and higher debug levels give more detailed output. Channels
that specify a specific debug severity, for example:</para>
<programlisting>channel "specific_debug_level" {
file "foo";
severity debug 3;
};
</programlisting>
<para>will get debugging output of level 3 or less any time the
server is in debugging mode, regardless of the global debugging
level. Channels with <command>dynamic</command> severity use the
server's global level to determine what messages to print.</para>
<para>If <command>print-time</command> has been turned on, then
the date and time will be logged. <command>print-time</command> may
be specified for a <command>syslog</command> channel, but is usually
pointless since <command>syslog</command> also prints the date and
time. If <command>print-category</command> is requested, then the
category of the message will be logged as well. Finally, if <command>print-severity</command> is
on, then the severity level of the message will be logged. The <command>print-</command> options may
be used in any combination, and will always be printed in the following
order: time, category, severity. Here is an example where all three <command>print-</command> options
are on:</para>
<para><computeroutput>28-Feb-2000 15:05:32.863 general: notice: running</computeroutput></para>
<para>There are four predefined channels that are used for
<command>named</command>'s default logging as follows. How they are
used is described in <xref linkend="the_category_phrase"/>.
</para>
<programlisting>channel "default_syslog" {
syslog daemon; // end to syslog's daemon
// facility
severity info; // only send priority info
// and higher
};
channel "default_debug" {
file "named.run"; // write to named.run in
// the working directory
// Note: stderr is used instead
// of "named.run"
// if the server is started
// with the '-f' option.
severity dynamic // log at the server's
// current debug level
};
channel "default_stderr" { // writes to stderr
file "&lt;stderr&gt;"; // this is illustrative only;
// there's currently no way of
// specifying an internal file
// descriptor in the
// configuration language.
severity info; // only send priority info
// and higher
};
channel "null" {
null; // toss anything sent to
// this channel
};
</programlisting>
<para>The <command>default_debug</command> channel normally writes
to a file <filename>named.run</filename> in the server's working
directory. For security reasons, when the "<option>-u</option>"
command line option is used, the <filename>named.run</filename> file
is created only after <command>named</command> has changed to the
new UID, and any debug output generated while <command>named</command> is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the "<option>-g</option>"
option and redirect standard error to a file.</para>
<para>Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have defined.</para></sect3>
<sect3 id="the_category_phrase"><title>The <command>category</command> Phrase</title>
<para>There are many categories, so you can send the logs you want
to see wherever you want, without seeing logs you don't want. If
you don't specify a list of channels for a category, then log messages
in that category will be sent to the <command>default</command> category
instead. If you don't specify a default category, the following
"default default" is used:</para>
<programlisting>category "default" { "default_syslog"; "default_debug"; };
</programlisting>
<para>As an example, let's say you want to log security events to
a file, but you also want keep the default logging behavior. You'd
specify the following:</para>
<programlisting>channel "my_security_channel" {
file "my_security_file";
severity info;
};
category "security" {
"my_security_channel";
"default_syslog";
"default_debug";
};</programlisting>
<para>To discard all messages in a category, specify the <command>null</command> channel:</para>
<programlisting>category "xfer-out" { "null"; };
category "notify" { "null"; };
</programlisting>
<para>Following are the available categories and brief descriptions
of the types of log information they contain. More
categories may be added in future <acronym>BIND</acronym> releases.</para>
<informaltable
colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.150in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.350in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>default</command></para></entry>
<entry colname = "2"><para>The default category defines the logging
options for those categories where no specific configuration has been
defined.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>general</command></para></entry>
<entry colname = "2"><para>The catch-all. Many things still aren't
classified into categories, and they all end up here.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>database</command></para></entry>
<entry colname = "2"><para>Messages relating to the databases used
internally by the name server to store zone and cache data.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>security</command></para></entry>
<entry colname = "2"><para>Approval and denial of requests.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>config</command></para></entry>
<entry colname = "2"><para>Configuration file parsing and processing.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>resolver</command></para></entry>
<entry colname = "2"><para>DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name server.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>xfer-in</command></para></entry>
<entry colname = "2"><para>Zone transfers the server is receiving.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>xfer-out</command></para></entry>
<entry colname = "2"><para>Zone transfers the server is sending.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>notify</command></para></entry>
<entry colname = "2"><para>The NOTIFY protocol.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>client</command></para></entry>
<entry colname = "2"><para>Processing of client requests.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>network</command></para></entry>
<entry colname = "2"><para>Network operations.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>update</command></para></entry>
<entry colname = "2"><para>Dynamic updates.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
</sect3>
</sect2>
<sect2>
<title><command>options</command> Statement Grammar</title>
<para>This is the grammar of the <command>options</command>
statement in the <filename>named.conf</filename> file:</para>
<programlisting><command>options</command> {
<optional> version <replaceable>version_string</replaceable>; </optional>
<optional> directory <replaceable>path_name</replaceable>; </optional>
<optional> named-xfer <replaceable>path_name</replaceable>; </optional>
<optional> tkey-domain <replaceable>domainname</replaceable>; </optional>
<optional> tkey-dhkey <replaceable>key_name</replaceable> <replaceable>key_tag</replaceable>; </optional>
<optional> dump-file <replaceable>path_name</replaceable>; </optional>
<optional> memstatistics-file <replaceable>path_name</replaceable>; </optional>
<optional> pid-file <replaceable>path_name</replaceable>; </optional>
<optional> statistics-file <replaceable>path_name</replaceable>; </optional>
<optional> auth-nxdomain <replaceable>yes_or_no</replaceable>; </optional>
<optional> deallocate-on-exit <replaceable>yes_or_no</replaceable>; </optional>
<optional> dialup <replaceable>yes_or_no</replaceable>; </optional>
<optional> fake-iquery <replaceable>yes_or_no</replaceable>; </optional>
<optional> fetch-glue <replaceable>yes_or_no</replaceable>; </optional>
<optional> has-old-clients <replaceable>yes_or_no</replaceable>; </optional>
<optional> host-statistics <replaceable>yes_or_no</replaceable>; </optional>
<optional> multiple-cnames <replaceable>yes_or_no</replaceable>; </optional>
<optional> notify <replaceable>yes_or_no</replaceable>; </optional>
<optional> recursion <replaceable>yes_or_no</replaceable>; </optional>
<optional> rfc2308-type1 <replaceable>yes_or_no</replaceable>; </optional>
<optional> use-id-pool <replaceable>yes_or_no</replaceable>; </optional>
<optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable>; </optional>
<optional> forward ( <replaceable>only</replaceable> | <replaceable>first</replaceable> ); </optional>
<optional> forwarders { <optional> <replaceable>in_addr</replaceable> ; <optional> <replaceable>in_addr</replaceable> ; ... </optional> </optional> }; </optional>
<optional> check-names ( <replaceable>master</replaceable> | <replaceable>slave</replaceable> | <replaceable> response</replaceable> )( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-transfer { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-recursion { <replaceable>address_match_list</replaceable> }; </optional>
<optional> blackhole { <replaceable>address_match_list</replaceable> }; </optional>
<optional> listen-on <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
<optional> listen-on-v6 <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
<optional> query-source <optional> address ( <replaceable>ip_addr</replaceable> | <replaceable>*</replaceable> ) </optional> <optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional>; </optional>
<optional> max-transfer-time-in <replaceable>number</replaceable>; </optional>
<optional> max-transfer-time-out <replaceable>number</replaceable>; </optional>
<optional> max-transfer-idle-in <replaceable>number</replaceable>; </optional>
<optional> max-transfer-idle-out <replaceable>number</replaceable>; </optional>
<optional> tcp-clients <replaceable>number</replaceable>; </optional>
<optional> recursive-clients <replaceable>number</replaceable>; </optional>
<optional> serial-queries <replaceable>number</replaceable>; </optional>
<optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable>; </optional>
<optional> transfers-in <replaceable>number</replaceable>; </optional>
<optional> transfers-out <replaceable>number</replaceable>; </optional>
<optional> transfers-per-ns <replaceable>number</replaceable>; </optional>
<optional> transfer-source <replaceable>ip4_addr</replaceable>; </optional>
<optional> transfer-source-v6 <replaceable>ip6_addr</replaceable>; </optional>
<optional> also-notify { <replaceable>ip_addr</replaceable>; <optional> <replaceable>ip_addr</replaceable>; ... </optional> }; </optional>
<optional> max-ixfr-log-size <replaceable>number</replaceable>; </optional>
<optional> coresize <replaceable>size_spec</replaceable> ; </optional>
<optional> datasize <replaceable>size_spec</replaceable> ; </optional>
<optional> files <replaceable>size_spec</replaceable> ; </optional>
<optional> stacksize <replaceable>size_spec</replaceable> ; </optional>
<optional> cleaning-interval <replaceable>number</replaceable>; </optional>
<optional> heartbeat-interval <replaceable>number</replaceable>; </optional>
<optional> interface-interval <replaceable>number</replaceable>; </optional>
<optional> statistics-interval <replaceable>number</replaceable>; </optional>
<optional> topology <optional>{ <replaceable>address_match_list</replaceable> }</optional>; </optional>
<optional> sortlist <optional>{ <replaceable>address_match_list</replaceable> }</optional>; </optional>
<optional> rrset-order <optional>{ <replaceable>order_spec</replaceable> ; <optional> <replaceable>order_spec</replaceable> ; ... </optional> </optional> }</optional>;
<optional> lame-ttl <replaceable>number</replaceable>; </optional>
<optional> max-ncache-ttl <replaceable>number</replaceable>; </optional>
<optional> max-cache-ttl <replaceable>number</replaceable>; </optional>
<optional> sig-validity-interval <replaceable>number</replaceable> ; </optional>
<optional> min-roots <replaceable>number</replaceable>; </optional>
<optional> use-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> treat-cr-as-space <replaceable>yes_or_no</replaceable> ; </optional>
<optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> min-retry-time <replaceable>number</replaceable> ; </optional>
<optional> max-retry-time <replaceable>number</replaceable> ; </optional>
};
</programlisting>
</sect2>
<sect2><title><command>options</command> Statement Definition and
Usage</title>
<para>The <command>options</command> statement sets up global options
to be used by <acronym>BIND</acronym>. This statement may appear only once in a configuration
file. If more than one occurrence is found, the first occurrence
determines the actual options used, and a warning will be generated.
If there is no <command>options</command> statement, an options
block with each option set to its default will be used.<informaltable
colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.591in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.159in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>version</command></para></entry>
<entry colname = "2"><para>The version the server should report
via a query of name <filename>version.bind</filename> in class <command>chaos</command>.
The default is the real version number of this server.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>directory</command></para></entry>
<entry colname = "2"><para>The working directory of the server.
Any non-absolute pathnames in the configuration file will be taken
as relative to this directory. The default location for most server
output files (e.g. <filename>named.run</filename>) is this directory.
If a directory is not specified, the working directory defaults
to `<filename>.</filename>', the directory from which the server
was started. The directory specified should be an absolute path.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>named-xfer</command></para></entry>
<entry colname = "2"><para>
<emphasis>This option is obsolete.</emphasis>
It was used in <acronym>BIND</acronym> 8 to specify the pathname to the <command>named-xfer</command> program.
In <acronym>BIND</acronym> 9, no separate <command>named-xfer</command> program is
needed; its functionality is built into the name server.</para>
</entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>tkey-domain</command></para></entry>
<entry colname = "2"><para>The domain appended to the names of all
shared keys generated with <command>TKEY</command>. When a client
requests a <command>TKEY</command> exchange, it may or may not specify
the desired name for the key. If present, the name of the shared
key will be "<varname>client specified part</varname>" + "<varname>tkey-domain</varname>".
Otherwise, the name of the shared key will be "<varname>random hex
digits</varname>" + "<varname>tkey-domain</varname>". In most cases,
the <command>domainname</command> should be the server's domain
name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>tkey-dhkey</command></para></entry>
<entry colname = "2"><para>The Diffie-Hellman key used by the server
to generate shared keys with clients using the Diffie-Hellman mode
of <command>TKEY</command>. The server must be able to load the
public and private keys from files in the working directory. In
most cases, the keyname should be the server's host name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>dump-file</command></para></entry>
<entry colname = "2"><para>The pathname of the file the server dumps
the database to when it receives <command>SIGINT</command> signal
(<command>ndc dumpdb</command>). If not specified, the default is <filename>named_dump.db</filename>.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>memstatistics-file</command></para></entry>
<entry colname = "2"><para>The pathname of the file the server writes memory
usage statistics to on exit. If not specified, the default is <filename>named.memstats</filename>.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>pid-file</command></para></entry>
<entry colname = "2"><para>The pathname of the file the server writes
its process ID in. If not specified, the default is operating system
dependent, but is usually
<filename>/var/run/named.pid</filename> or <filename>/etc/named.pid</filename>.
The pid-file is used by programs that want to send signals to the running
nameserver.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>statistics-file</command></para></entry>
<entry colname = "2"><para>The pathname of the file the server appends statistics
to. If not specified, the default is <filename>named.stats</filename>.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
</tbody>
</tgroup></informaltable> </para>
<sect3 id="boolean_options"><title>Boolean Options</title>
<informaltable colsep = "0"
rowsep = "0"><tgroup cols = "2" colsep = "0"
rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.507in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "2.993in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>auth-nxdomain</command></para></entry>
<entry colname = "2"><para>If <userinput>yes</userinput>, then the <command>AA</command> bit
is always set on NXDOMAIN responses, even if the server is not actually
authoritative. The default is <userinput>no</userinput>; this is
a change from <acronym>BIND</acronym> 8. If you are using very old DNS software, you
may need to set it to <userinput>yes</userinput>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>deallocate-on-exit</command></para></entry>
<entry colname = "2"><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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>dialup</command></para></entry>
<entry colname = "2"><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>zone</command> statement,
in which case it overrides the <command>options dialup </command>statement.</para><para>If
the zone is a master then the server will send out a NOTIFY request
to all the slaves. This will trigger the zone serial number check
in the slave (providing it supports NOTIFY) allowing the slave to
verify the zone while the connection is active.</para><para>If the
zone is a slave or stub then the server will suppress the regular
"zone up to date" queries and only perform them when the
<command>heartbeat-interval</command> expires.</para><note>
<simpara>Not yet implemented
in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>fake-iquery</command></para></entry>
<entry colname = "2"><para>In <acronym>BIND</acronym> 8, this option was used to enable simulating
the obsolete DNS query type IQUERY. <acronym>BIND</acronym> 9 never does IQUERY simulation.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>fetch-glue</command></para></entry>
<entry colname = "2"><para>(Information present outside of the authoritative
nodes in the zone is called <emphasis>glue</emphasis> information).
If <userinput>yes</userinput> (the default), the server will fetch
glue resource records it doesn't have when constructing the additional
data section of a response. <command>fetch-glue </command><userinput>no</userinput><command> </command>can
be used in conjunction with <command>recursion </command><userinput>no</userinput><command> </command>to
prevent the server's cache from growing or becoming corrupted (at
the cost of requiring more work from the client).</para><note>
<simpara>Not yet
implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>has-old-clients</command></para></entry>
<entry colname = "2"><para>This option was incorrectly implemented
in <acronym>BIND</acronym> 8, and is ignored by <acronym>BIND</acronym> 9. To achieve the intended effect
of
<command>has-old-clients </command><userinput>yes</userinput>, specify
the two separate options <command>auth-nxdomain </command><userinput>yes</userinput> and <command>rfc2308-type1 </command><userinput>no</userinput> instead.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>host-statistics</command></para></entry>
<entry colname = "2"><para>If <userinput>yes</userinput>, then statistics
are kept for every host that the nameserver interacts with. The
default is <userinput>no</userinput>.</para><note>
<simpara>turning on <command>host-statistics</command> can consume
huge amounts of memory.</simpara></note><note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>maintain-ixfr-base</command></para></entry>
<entry colname = "2"><para><emphasis>This option is obsolete</emphasis>.
It was used in <acronym>BIND</acronym> 8 to determine whether a transaction log was
kept for Incremental Zone Transfer. <acronym>BIND</acronym> 9 maintains a transaction
log whenever possible. If you need to disable outgoing incremental zone
transfers, use <command>provide-ixfr </command><userinput>no</userinput>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>multiple-cnames</command></para></entry>
<entry colname = "2"><para>This option was used in <acronym>BIND</acronym> 8 to allow
a domain name to allow multiple CNAME records in violation of the
DNS standards. <acronym>BIND</acronym> 9 currently does not check for multiple CNAMEs
in zone data loaded from master files, but such checks may be introduced
in a later release. <acronym>BIND</acronym> 9 always strictly enforces the CNAME rules
in dynamic updates.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>notify</command></para></entry>
<entry colname = "2"><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 <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<varname>.</varname></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>recursion</command></para></entry>
<entry colname = "2"><para>If <userinput>yes</userinput>, and a
DNS query requests recursion, then the server will attempt to do
all the work required to answer the query. If recursion is off
and the server does not already know the answer, it will return a
referral response. The default is <userinput>yes</userinput>.
Note that setting <command>recursion no;</command> does not prevent
clients from getting data from the server's cache; it only
prevents new data from being cached as an effect of client queries.
Caching may still occur as an effect the server's internal
operation, such as NOTIFY address lookups.
See also <command>fetch-glue</command> above.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>rfc2308-type1</command></para></entry>
<entry colname = "2"><para>Setting this to <userinput>yes</userinput> will
cause the server to send NS records along with the SOA record for negative
answers. The default is <userinput>no</userinput>.</para>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>use-id-pool</command></para></entry>
<entry colname = "2"><para><emphasis>This option is obsolete</emphasis>.
<acronym>BIND</acronym> 9 always allocates query IDs from a pool.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>treat-cr-as-space</command></para></entry>
<entry colname = "2"><para>This option was used in <acronym>BIND</acronym> 8 to make
the server treat "<command>\r</command>" characters the same way
as <command>&#60;space> </command>" " or "<command>\t</command>",
to facilitate loading of zone files on a UNIX system that were generated
on an NT or DOS machine. In <acronym>BIND</acronym> 9, both UNIX "<command>\n</command>"
and NT/DOS "<command>\r\n</command>" newlines are always accepted,
and the option is ignored.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1">
<para><command>min-refresh-time</command></para>
<para><command>max-refresh-time</command></para>
<para><command>min-retry-time</command></para>
<para><command>max-retry-time</command></para>
</entry>
<entry colname = "2"><para>
These options control the server's behavior on refreshing a zone
(querying for SOA changes) or retrying failed transfers.
Usually the SOA values for the zone are used, but these values
are set by the master, giving slave server administrators little
control over their contents.
</para><para>
These options allow the administrator to set a minimum and maximum
refresh and retry time either per-zone, per-view, or per-server.
These options are valid for slave and stub zones, and clamp the SOA
refresh and retry times to the specified values.
</para>
<note><para>These options are not yet implemented in <acronym>BIND</acronym> 9.0.</para></note>
</entry>
</row>
</tbody>
</tgroup></informaltable></sect3>
<sect3><title>Forwarding</title>
<para>The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
nameservers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.</para>
<para><informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.973in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.527in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>forward</command></para></entry>
<entry colname = "2"><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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>forwarders</command></para></entry>
<entry colname = "2"><para>Specifies the IP addresses to be used
for forwarding. The default is the empty list (no forwarding).</para></entry>
</row>
</tbody>
</tgroup></informaltable></para>
<para>Forwarding can also be configured on a per-domain basis, allowing
for the global forwarding options to be overridden in a variety
of ways. You can set particular domains to use different forwarders,
or have a different <command>forward only/first</command> behavior,
or not forward at all, see <xref linkend="zone_statement_grammar"/>.</para></sect3>
<sect3 id="name_checking"><title>Name Checking</title>
<para>The server can check domain names based upon their expected
client contexts. For example, a domain name used as a hostname can
be checked for compliance with the RFCs defining valid hostnames.</para>
<para>Three checking methods are available:</para>
<para><informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.797in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.703in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>ignore</command></para></entry>
<entry colname = "2"><para>No checking is done.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>warn</command></para></entry>
<entry colname = "2"><para>Names are checked against their expected
client contexts. Invalid names are logged, but processing continues normally.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>fail</command></para></entry>
<entry colname = "2"><para>Names are checked against their expected
client contexts. Invalid names are logged, and the offending data
is rejected.</para></entry>
</row>
</tbody>
</tgroup></informaltable></para>
<para>The server can check names in three areas: master zone files,
slave zone files, and in responses to queries the server has initiated.
If <command>check-names response fail</command> has been specified,
and answering the client's question would require sending an invalid
name to the client, the server will send a REFUSED response code
to the client.</para>
<para>The defaults are:</para>
<programlisting> check-names master fail;
check-names slave warn;
check-names response ignore;
</programlisting>
<para><command>check-names</command> may also be specified in the <command>zone</command> statement,
in which case it overrides the <command>options check-names</command> statement.
When used in a <command>zone</command> statement, the area is not
specified because it can be deduced from the zone type.</para>
<note>
<para>Name checking is not yet implemented in <acronym>BIND</acronym> 9.</para></note></sect3>
<sect3 id="access_control"><title>Access Control</title>
<para>Access to the server can be restricted based on the IP address
of the requesting system. See <xref linkend="address_match_lists"/> for
details on how to specify IP address lists.</para>
<para><informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.375in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.125in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-query</command></para></entry>
<entry colname = "2"><para>Specifies which hosts are allowed to
ask ordinary questions. <command>allow-query</command> may also
be specified in the <command>zone</command> statement, in which
case it overrides the <command>options allow-query</command> statement. If
not specified, the default is to allow queries from all hosts.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-recursion</command></para></entry>
<entry colname = "2"><para>Specifies which hosts are allowed to
make recursive queries through this server. If not specified, the
default is to allow recursive queries from all hosts.
Note that disallowing recursive queries for a host does not prevent the
host from retrieving data that is already in the server's cache.
</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-transfer</command></para></entry>
<entry colname = "2"><para>Specifies which hosts are allowed to
receive zone transfers from the server. <command>allow-transfer</command> may
also be specified in the <command>zone</command> statement, in which
case it overrides the <command>options allow-transfer</command> statement.
If not specified, the default is to allow transfers from all hosts.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>blackhole</command></para></entry>
<entry colname = "2"><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>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
</tbody>
</tgroup></informaltable></para></sect3>
<sect3><title>Interfaces</title>
<para>The interfaces and ports that the server will answer queries
from may be specified using the <command>listen-on</command> option. <command>listen-on</command> takes
an optional port, and an <varname>address_match_list</varname>.
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be used.</para>
<para>Multiple <command>listen-on</command> statements are allowed.
For example,</para>
<programlisting>listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</programlisting>
<para>will enable the nameserver on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.</para>
<para>If no <command>listen-on</command> is specified, the
server will listen on port 53 on all interfaces.</para>
<para>The <command>listen-on-v6</command> option is used to
specify the ports on which the server will listen for incoming
queries sent using IPv6.</para>
<para>The server does not bind a separate socket to each IPv6
interface address as it does for IPv4. Instead, it always
listens on the IPv6 wildcard address. Therefore, the only
values allowed for the <varname>address_match_list</varname>
argument to the <command>listen-on-v6</command> statement are
<programlisting>{ any; }</programlisting> and
<programlisting>{ none;}</programlisting></para>
<para>Multiple <command>listen-on-v6</command> options can be
used to listen on multiple ports:</para>
<programlisting>listen-on-v6 port 53 { any; };
listen-on-v6 port 1234 { any; };
</programlisting>
<para>To make the server not listen on any IPv6 address, use</para>
<programlisting>listen-on-v6 { none; };
</programlisting>
<para>If no <command>listen-on-v6 </command>statement is specified,
the server will not listen on any IPv6 address.</para></sect3>
<sect3><title>Query Address</title>
<para>If the server doesn't know the answer to a question, it will
query other nameservers. <command>query-source</command> specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate <command>query-source-v6</command> option.
If <command>address</command> is <command>*</command> or is omitted,
a wildcard IP address (<command>INADDR_ANY</command>) will be used.
If <command>port</command> is <command>*</command> or is omitted,
a random unprivileged port will be used. The defaults are</para>
<programlisting>query-source address * port *;
query-source-v6 address * port *
</programlisting>
<note>
<para><command>query-source</command> currently applies only
to UDP queries; TCP queries always use a wildcard IP address and
a random unprivileged port.</para></note></sect3>
<sect3 id="zone_transfers"><title>Zone Transfers</title>
<para><acronym>BIND</acronym> has mechanisms in place to facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.750in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "2.750in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>also-notify</command></para></entry>
<entry colname = "2"><para>Defines a global list of IP addresses
that are also sent NOTIFY messages whenever a fresh copy of the
zone is loaded. This helps to ensure that copies of the zones will
quickly converge on stealth servers. If an <command>also-notify</command> list
is given in a <command>zone</command> statement, it will override
the <command>options also-notify</command> statement. When a <command>zone notify</command> statement
is set to <command>no</command>, the IP addresses in the global <command>also-notify</command> list will
not be sent NOTIFY messages for that zone. The default is the empty
list (no global notification list).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-time-in</command></para></entry>
<entry colname = "2"><para>Inbound zone transfers running longer than
this many minutes will be terminated. The default is 120 minutes
(2 hours).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-idle-in</command></para></entry>
<entry colname = "2"><para>Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60 minutes
(1 hour).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-time-out</command></para></entry>
<entry colname = "2"><para>Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120 minutes
(2 hours).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-idle-out</command></para></entry>
<entry colname = "2"><para>Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60 minutes (1
hour).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>serial-queries</command></para></entry>
<entry colname = "2"><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,
but more importantly each query uses a small amount of memory in
the slave server while waiting for the master server to respond.
The <command>serial-queries </command>option sets the maximum number
of concurrent serial-number queries allowed to be outstanding at
any given time. The default is 4.</para><note>
<simpara>If a server loads a large (tens or
hundreds of thousands) number of slave zones, then
this limit should be raised to the high hundreds
or low thousands, otherwise the slave server may
never actually become aware of zone changes in the
master servers. Beware, though, that setting this
limit arbitrarily high can spend a considerable
amount of your slave server's network, CPU, and
memory resources. As with all tunable limits, this
one should be changed gently and monitored for its
effects.</simpara>
</note>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfer-format</command></para></entry>
<entry colname = "2"><para>The server supports two zone transfer methods. <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. 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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfers-in</command></para></entry>
<entry colname = "2"><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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfers-out</command></para></entry>
<entry colname = "2"><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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfers-per-ns</command></para></entry>
<entry colname = "2"><para>The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote nameserver.
The default value is <literal>2</literal>. Increasing <command>transfers-per-ns</command> may
speed up the convergence of slave zones, but it also may increase
the load on the remote nameserver. <command>transfers-per-ns</command> may
be overridden on a per-server basis by using the <command>transfers</command> phrase
of the <command>server</command> statement.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfer-source</command></para></entry>
<entry colname = "2"><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. 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-zone basis by including a
<command>transfer-source</command> statement within the <command>zone</command> block
in the configuration file.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfer-source-v6</command></para></entry>
<entry colname = "2"><para>The same as <command>transfer-source</command>,
except zone transfers are performed using IPv6.</para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Resource Limits</title>
<para>The server's usage of many system resources can be
limited. Some operating systems don't support some of the
limits. On such systems, a warning will be issued if the
unsupported limit is used. Some operating systems don't
support limiting resources.</para> <para>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>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.500in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>coresize</command></para></entry>
<entry colname = "2"><para>The maximum size of a core dump. The default
is <literal>default</literal>.</para><note>
<simpara>Not yet implemented in <acronym>BIND</acronym>
9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>datasize</command></para></entry>
<entry colname = "2"><para>The maximum amount of data memory the server
may use. The default is <literal>default</literal>.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>files</command></para></entry>
<entry colname = "2"><para>The maximum number of files the server
may have open concurrently. The default is <literal>unlimited</literal>.
</para><note>
<simpara>on some operating systems the server cannot set an unlimited
value and cannot determine the maximum number of open files the
kernel can support. On such systems, choosing
<literal>unlimited</literal> will
cause the server to use the larger of the <command>rlim_max</command> for <command>RLIMIT_NOFILE</command> and
the value returned by <command>sysconf(_SC_OPEN_MAX)</command>.
If the actual kernel limit is larger than this value, use <command>limit
files </command>to specify the limit explicitly.</simpara></note><note><simpara>Not yet
implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-ixfr-log-size</command></para></entry>
<entry colname = "2"><para>The <command>max-ixfr-log-size</command> will
be used in a future release of the server to limit the size of the
transaction log kept for Incremental Zone Transfer.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>recursive-clients</command></para></entry>
<entry colname = "2"><para>The maximum number of simultaneous recursive
lookups the server will perform on behalf of clients. The default
is <literal>1000</literal>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>stacksize</command></para></entry>
<entry colname = "2"><para>The maximum amount of stack memory the server
may use. The default is <literal>default</literal>.</para><note>
<simpara>Not
yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>tcp-clients</command></para></entry>
<entry colname = "2"><para>The maximum number of simultaneous client TCP
connections that the server will accept. The default is <literal>100</literal>.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<note>
<para>Resource limits are not yet implemented in <acronym>BIND</acronym> 9.</para></note></sect3>
<sect3><title>Periodic Task Intervals</title>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.625in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "2.875in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>cleaning-interval</command></para></entry>
<entry colname = "2"><para>The server will remove expired resource records
from the cache every <command>cleaning-interval</command> minutes.
The default is 60 minutes.
If set to 0, no periodic cleaning will occur.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>heartbeat-interval</command></para></entry>
<entry colname = "2"><para>The server will perform zone maintenance tasks
for all zones marked <command>dialup yes</command> whenever this
interval expires. The default is 60 minutes. Reasonable values are up
to 1 day (1440 minutes). If set to 0, no zone maintenance for these zones will occur.</para><note>
<simpara>Not yet
implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>interface-interval</command></para></entry>
<entry colname = "2"><para>The server will scan the network interface list
every <command>interface-interval</command> minutes. The default
is 60 minutes. If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, listeners will be
started on any new interfaces (provided they are allowed by the
<command>listen-on</command> configuration). Listeners on interfaces
that have gone away will be cleaned up.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>statistics-interval</command></para></entry>
<entry colname = "2"><para>Nameserver statistics will be logged
every <command>statistics-interval</command> minutes. The default is
60. If set to 0, no statistics will be logged.</para><note>
<simpara>Not yet implemented in <acronym>BIND</acronym>9.</simpara></note></entry>
</row>
</tbody>
</tgroup></informaltable></sect3>
<sect3 id="topology"><title>Topology</title>
<para>All other things being equal, when the server chooses a nameserver
to query from a list of nameservers, it prefers the one that is
topologically closest to itself. The <command>topology</command> statement
takes an <command>address_match_list</command> and interprets it
in a special way. Each top-level list element is assigned a distance.
Non-negated elements get a distance based on their position in the
list, where the closer the match is to the start of the list, the
shorter the distance is between it and the server. A negated match
will be assigned the maximum distance from the server. If there
is no match, the address will get a distance which is further than
any non-negated list element, and closer than any negated element.
For example,</para>
<programlisting>topology {
10/8;
!1.2.3/24;
{ 1.2/16; 3/8; };
};</programlisting>
<para>will prefer servers on network 10 the most, followed by hosts
on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the
exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
is preferred least of all.</para>
<para>The default topology is</para>
<programlisting> topology { localhost; localnets; };
</programlisting>
<note><simpara>The <command>topology</command> option
is not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</sect3>
<sect3 id="the_sortlist_statement">
<title>The <command>sortlist</command> Statement</title>
<para>Resource Records (RRs) are the data associated with the names
in a domain name space. The data is maintained in the form of sets
of RRs. The order of RRs in a set is, by default, not significant.
Therefore, to control the sorting of records in a set of resource
records, or <varname>RRset</varname>, you must use the <command>sortlist</command> statement.</para>
<para>RRs are explained more fully in <xref
linkend="types_of_resource_records_and_when_to_use_them"/>. Specifications for RRs
are documented in RFC 1035.</para>
<para>When returning multiple RRs the nameserver will normally return
them in <varname>Round Robin</varname><varname> </varname>order,
that is, after each request the first RR is put at the end of the
list. The client resolver code should rearrange the RRs as appropriate,
that is, using any addresses on the local net in preference to other addresses.
However, not all resolvers can do this or are correctly configured.
When a client is using a local server the sorting can be performed
in the server, based on the client's address. This only requires
configuring the nameservers, not all the clients.</para>
<para>The <command>sortlist</command> statement (see below) takes
an <command>address_match_list </command>and interprets it even
more specifically than the <command>topology</command> statement
does (<xref linkend="topology"/>). Each top level statement in the <command>sortlist</command> must
itself be an explicit <command>address_match_list</command> with
one or two elements. The first element (which may be an IP address,
an IP prefix, an ACL name or a nested <command>address_match_list</command>)
of each top level list is checked against the source address of
the query until a match is found.</para>
<para>Once the source address of the query has been matched, if
the top level statement contains only one element, the actual primitive
element that matched the source address is used to select the address
in the response to move to the beginning of the response. If the
statement is a list of two elements, then the second element is
treated the same as the <command>address_match_list</command> in
a <command>topology</command> statement. Each top level element
is assigned a distance and the address in the response with the minimum
distance is moved to the beginning of the response.</para>
<para>In the following example, any queries received from any of
the addresses of the host itself will get responses preferring addresses
on any of the locally connected networks. Next most preferred are addresses
on the 192.168.1/24 network, and after that either the 192.168.2/24
or
192.168.3/24 network with no preference shown between these two
networks. Queries received from a host on the 192.168.1/24 network
will prefer other addresses on that network to the 192.168.2/24
and
192.168.3/24 networks. Queries received from a host on the 192.168.4/24
or the 192.168.5/24 network will only prefer other addresses on
their directly connected networks.</para>
<programlisting>sortlist {
{ localhost; // IF the local host
{ localnets; // THEN first fit on the
192.168.1/24; // following nets
{ 192,168.2/24; 192.168.3/24; }; }; };
{ 192.168.1/24; // IF on class C 192.168.1
{ 192.168.1/24; // THEN use .1, or .2 or .3
{ 192.168.2/24; 192.168.3/24; }; }; };
{ 192.168.2/24; // IF on class C 192.168.2
{ 192.168.2/24; // THEN use .2, or .1 or .3
{ 192.168.1/24; 192.168.3/24; }; }; };
{ 192.168.3/24; // IF on class C 192.168.3
{ 192.168.3/24; // THEN use .3, or .1 or .2
{ 192.168.1/24; 192.168.2/24; }; }; };
{ { 192.168.4/24; 192.168.5/24; }; // if .4 or .5, prefer that net
};
};</programlisting>
<para>The following example will give reasonable behavior for the
local host and hosts on directly connected networks. It is similar
to the behavior of the address sort in <acronym>BIND</acronym> 8.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>
<note><simpara>The <command>sortlist</command> option
is not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</sect3>
<sect3 id="rrset_ordering"><title id="rrset_ordering_title">RRset Ordering</title>
<para>When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the response.
For example, the records for a zone might be configured always to
be returned in the order they are defined in the zone file. Or perhaps
a random shuffle of the records as they are returned is wanted.
The <command>rrset-order</command> statement permits configuration
of the ordering made of the records in a multiple record response.
The default, if no ordering is defined, is a cyclic ordering (round
robin).</para>
<para>An <command>order_spec</command> is defined as follows:</para>
<programlisting><optional> class <replaceable>class_name</replaceable> </optional><optional> type <replaceable>type_name</replaceable> </optional><optional> name <replaceable>"domain_name"</replaceable></optional>
order <replaceable>ordering</replaceable>
</programlisting>
<para>If no class is specified, the default is <command>ANY</command>.
If no type is specified, the default is <command>ANY</command>.
If no name is specified, the default is "<command>*</command>".</para>
<para>The legal values for <command>ordering</command> are:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.750in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>fixed</command></para></entry>
<entry colname = "2"><para>Records are returned in the order they
are defined in the zone file.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>random</command></para></entry>
<entry colname = "2"><para>Records are returned in some random order.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>cyclic</command></para></entry>
<entry colname = "2"><para>Records are returned in a round-robin
order.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>For example:</para>
<programlisting>rrset-order {
class IN type A name "host.example.com" order random;
order cyclic;
};
</programlisting>
<para>will cause any responses for type A records in class IN that
have "<systemitem class="systemname">host.example.com</systemitem>" 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>If no <command>rrset-order</command> statement is specified,
then a default one of:
<programlisting>rrset-order { class ANY type ANY name "*"; order cyclic ; };
</programlisting>
is used.</para>
<note><simpara>The <command>rrset-order</command> statement
is not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</sect3>
<sect3 id="tuning"><title>Tuning</title>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.250in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.250in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>lame-ttl</command></para></entry>
<entry colname = "2"><para>Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
<emphasis role="bold">NOT</emphasis> recommended.)
Default is <literal>600</literal> (10 minutes). Maximum value is
<literal>1800</literal> (30 minutes).</para>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
</entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-ncache-ttl</command></para></entry>
<entry colname = "2"><para>To reduce network traffic and increase performance
the server stores negative answers. <command>max-ncache-ttl</command> is
used to set a maximum retention time for these answers in the server
in seconds. The default
<command>max-ncache-ttl</command> is <literal>10800</literal> seconds (3 hours).
<command>max-ncache-ttl</command> cannot exceed 7 days and will
be silently truncated to 7 days if set to a greater value.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-cache-ttl</command></para></entry>
<entry colname = "2"><para><command>max-cache-ttl</command> sets
the maximum time for which the server will cache ordinary (positive)
answers. The default is one week (7 days).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>min-roots</command></para></entry>
<entry colname = "2"><para>The minimum number of root servers that
is required for a request for the root servers to be accepted. Default
is <userinput>2</userinput>.</para>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym>
9.</simpara></note>
</entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>sig-validity-interval</command></para></entry>
<entry colname = "2"><para>Specifies the number of days into the
future when DNSSEC signatures automatically generated as a result
of dynamic updates (<xref linkend="dynamic_update"/>)
will expire. The default is <literal>30</literal> days. The signature
inception time is unconditionally set to one hour before the current time
to allow for a limited amount of clock skew.</para></entry>
</row>
</tbody>
</tgroup></informaltable></sect3>
<sect3>
<title>Deprecated Features</title>
<para><command>use-ixfr</command> is deprecated in <acronym>BIND</acronym> 9. 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>
</sect3></sect2>
<sect2 id="server_statement_grammar">
<title><command>server</command>
Statement Grammar</title>
<programlisting>server <replaceable>ip_addr</replaceable> {
<optional> bogus <replaceable>yes_or_no</replaceable> ; </optional>
<optional> provide-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> request-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> transfers <replaceable>number</replaceable> ; </optional>
<optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable> ; ]</optional>
<optional> keys <replaceable>{ string ; <optional> string ; <optional>...</optional></optional> }</replaceable> ; </optional>
};
</programlisting>
</sect2>
<sect2 id="server_statement_definition_and_usage"><title><command>server</command> Statement Definition
and Usage</title>
<para>The <command>server</command> statement defines the characteristics
to be associated with a remote nameserver.</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>
<note>
<simpara>The <command>bogus</command> clause
is not yet implemented in <acronym>BIND</acronym> 9.</simpara></note>
<para>The <command>provide-ixfr</command> clause determines whether
the local server, acting as master, will respond with an incremental
zone transfer when the given remote server, a slave, requests it.
If set to <command>yes</command>, incremental transfer will be provided
whenever possible. If set to <command>no</command>, all transfers
to the remote server will be nonincremental. If not set, the value
of the <command>provide-ixfr </command>option in the global options block
is used as a default.</para>
<para>The <command>request-ixfr</command> clause determines whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the <command>request-ixfr</command> option in the global
options block is used as a default.</para>
<para>IXFR requests to servers that do not support IXFR will automatically
fall back to AXFR. Therefore, there is no need to manually list
which servers support IXFR and which ones do not; the global default
of <command>yes</command> should always work. The purpose of the <command>provide-ixfr</command> and <command>request-ixfr</command> clauses is
to make it possible to disable the use of IXFR even when both master
and slave claim to support it, for example if one of the servers
is buggy and crashes or corrupts data when IXFR is used.</para>
<para>The server supports two zone transfer methods. The first, <command>one-answer</command>,
uses one DNS message per resource record transferred. <command>many-answers</command> packs
as many resource records as possible into a message. <command>many-answers</command> is
more efficient, but is only known to be understood by <acronym>BIND</acronym> 9, <acronym>BIND</acronym>
8.x, and patched versions of <acronym>BIND</acronym> 4.9.5. You can specify which method
to use for a server with the <command>transfer-format </command>option.
If <command>transfer-format </command>is not specified, the <command>transfer-format</command> specified
by the <command>options</command> statement will be used.</para>
<para><command>transfers</command> is used to limit the number of
concurrent inbound zone transfers from the specified server. If
no <command>transfers</command> clause is specified, the limit is
set according to the <command>transfers-per-ns</command> option.</para>
<para>The <command>keys</command> clause is used to identify a <command>key_id </command>defined
by the <command>key</command> statement, to be used for transaction
security when talking to the remote server. The <command>key</command> statement
must come before the <command>server</command> statement that references
it. When a request is sent to the remote server, a request signature
will be generated using the key specified here and appended to the
message. A request originating from the remote server is not required
to be signed by this key.</para>
<para>Although the grammar of the <command>keys</command> clause
allows for multiple keys, only a single key per server is currently
supported.</para></sect2>
<sect2><title><command>trusted-keys</command> Statement Grammar</title>
<programlisting>trusted-keys {
<replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ;
<optional> <replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; <optional>...</optional></optional>
};
</programlisting>
</sect2>
<sect2><title><command>trusted-keys</command> Statement Definition
and Usage</title>
<para>The <command>trusted-keys</command> statement defines DNSSEC
security roots. DNSSEC is described in <xref linkend="DNSSEC"/>. A security root is defined when the public key for a non-authoritative
zone is known, but cannot be securely obtained through DNS, either
because it is the DNS root zone or its parent zone is unsigned.
Once a key has been configured as a trusted key, it is treated as
if it had been validated and proven secure. The resolver attempts
DNSSEC validation on all DNS data in subdomains of a security root.</para>
<para>The <command>trusted-keys</command> statement can contain
multiple key entries, each consisting of the key's domain name,
flags, protocol, algorithm, and the base-64 representation of the
key data.</para></sect2>
<sect2><title><command>view</command> Statement Grammar</title>
<programlisting>view <replaceable>view_name</replaceable> {
match-clients { <replaceable>address_match_list</replaceable> } ;
<optional> <replaceable>view_option</replaceable>; ...</optional>
<optional> <replaceable>zone_statement</replaceable>; ...</optional>
};
</programlisting></sect2>
<sect2><title><command>view</command> Statement Definition and Usage</title>
<para>The <command>view</command> statement is a powerful new feature
of <acronym>BIND</acronym> 9 that lets a name server answer a DNS query differently
depending on who is asking. It is particularly useful for implementing
split DNS setups without having to run multiple servers.</para>
<para>Each <command>view</command> statement defines a view of the
DNS namespace that will be seen by those clients whose IP addresses
match the <varname>address_match_list</varname> of the view's <command>match-clients</command> clause.
The order of the <command>view</command> statements is significant-a
client query will be resolved in the context of the first <command>view</command> whose <command>match-clients </command>list
matches the client's IP address.</para>
<para>Zones defined within a <command>view</command> statement will
be only be accessible to clients that match the <command>view</command>.
By defining a zone of the same name in multiple views, different
zone data can be given to different clients, for example, "internal"
and "external" clients in a split DNS setup.</para>
<para>Many of the options given in the <command>options</command> statement
can also be used within a <command>view</command> statement, and then
apply only when resolving queries with that view. When no view-specific
value is given, the value in the <command>options</command> statement
is used as a default. Also, zone options can have default values specified
in the <command>view</command> statement; these view-specific defaults
take precedence over those in the <command>options</command> statement. </para>
<para>Views are class specific. If no class is given, class IN
is assumed.</para>
<para>If there are no <command>view</command> statements in the
config file, a default view that matches any client is automatically
created in class IN, and any <command>zone</command> statements
specified on the top level of the configuration file are considered
to be part of this default view. If any explicit <command>view</command> statements
are present, all <command>zone</command> statements must occur inside <command>view</command> statements.</para>
<para>Here is an example of a typical split DNS setup implemented
using <command>view</command> statements.</para>
<programlisting>view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal clients only.
recursion yes;
// Provide a complete view of the example.com zone
// including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com zone
// containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
</programlisting>
</sect2>
<sect2 id="zone_statement_grammar"><title><command>zone</command>
Statement Grammar</title>
<programlisting>zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> <optional>{
type ( master | slave | hint | stub | forward ) ;
<optional> allow-query { <replaceable>address_match_list</replaceable> } ; </optional>
<optional> allow-transfer { <replaceable>address_match_list</replaceable> } ; </optional>
<optional> allow-update { <replaceable>address_match_list</replaceable> } ; </optional>
<optional> update-policy { <replaceable>update_policy_rule</replaceable> <optional>...</optional> } ; </optional>
<optional> allow-update-forwarding { <replaceable>address_match_list</replaceable> } ; </optional>
<optional> also-notify { <optional> <replaceable>ip_addr</replaceable> ; <optional><replaceable>ip_addr</replaceable> ; <optional>...</optional></optional></optional> } ; </optional>
<optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
<optional> dialup <replaceable>true_or_false</replaceable> ; </optional>
<optional> file <replaceable>string</replaceable> ; </optional>
<optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> ; <optional> <replaceable>ip_addr</replaceable> ; <optional>...</optional></optional></optional> } ; </optional>
<optional> ixfr-base <replaceable>string</replaceable> ; </optional>
<optional> ixfr-tmp-file <replaceable>string</replaceable> ; </optional>
<optional> maintain-ixfr-base <replaceable>true_or_false</replaceable> ; </optional>
<optional> masters <optional>port <replaceable>number</replaceable></optional> { <replaceable>ip_addr</replaceable> ; <optional><replaceable>ip_addr</replaceable> ; <optional>...</optional></optional> } ; </optional>
<optional> max-ixfr-log-size <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-idle-in <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-idle-out <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-in <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-out <replaceable>number</replaceable> ; </optional>
<optional> notify <replaceable>true_or_false</replaceable> ; </optional>
<optional> pubkey <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; </optional>
<optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) ; </optional>
<optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) ; </optional>
<optional> sig-validity-interval <replaceable>number</replaceable> ; </optional>
}</optional>;
</programlisting>
</sect2>
<sect2><title><command>zone</command> Statement Definition and Usage</title>
<sect3><title>Zone Types</title>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0"
tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.908in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.217in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><varname>master</varname></para></entry>
<entry colname = "2"><para>The server has a master copy of the data
for the zone and will be able to provide authoritative answers for
it.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>slave</varname></para></entry>
<entry colname = "2"><para>A slave zone is a replica of a master
zone. The masters list specifies one or more IP addresses that the
slave contacts to update its copy of the zone. If a port is specified,
the slave then checks to see if the zone is current and zone transfers
will be done to the port given. If a file is specified, then the
replica will be written to this file whenever the zone is changed,
and reloaded from this file on a server restart. Use of a file is
recommended, since it often speeds server start-up and eliminates
a needless waste of bandwidth. Note that for large numbers (in the
tens or hundreds of thousands) of zones per server, it is best to
use a two level naming scheme for zone file names. For example,
a slave server for the zone <systemitem class="systemname">example.com</systemitem> might place
the zone contents into a file called
<filename>ex/example.com</filename> where <filename>ex/ </filename>is
just the first two letters of the zone name. (Most operating systems
behave very slowly if you put 100K files into a single directory.)</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>stub</varname></para></entry>
<entry colname = "2"><para>A stub zone is similar to a slave zone,
except that it replicates only the NS records of a master zone instead
of the entire zone. Stub zones are not a standard part of the DNS;
they are a peculiarity of <acronym>BIND</acronym> 4 and <acronym>BIND</acronym> 8 that relies heavily
on the particular way the zone data is structured in those servers.
<acronym>BIND</acronym> 9 attempts to emulate the <acronym>BIND</acronym> 4/8 stub zone feature for backwards compatibility,
but we do not recommend its use in new configurations.</para><para>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></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>forward</varname></para></entry>
<entry colname = "2"><para>A "forward zone" is a way to configure
forwarding on a per-domain basis. A <command>zone</command> statement
of type <command>forward</command> can contain a <command>forward</command> and/or <command>forwarders</command> statement,
which will apply to queries within the domain given by the zone
name. If no <command>forwarders</command> statement is present or
an empty list for <command>forwarders</command> is given, then no
forwarding will be done for the domain, cancelling the effects of
any forwarders in the <command>options</command> statement. Thus
if you want to use this type of zone to change the behavior of the
global <command>forward</command> option (that is, "forward first
to", then "forward only", or vice versa, but want to use the same
servers as set globally) you need to respecify the global forwarders.</para>
<note>
<simpara>Domain-specific
forwarding is not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>hint</varname></para></entry>
<entry colname = "2"><para>The initial set of root nameservers is
specified using a "hint zone". When the server starts up, it uses
the root hints to find a root nameserver and get the most recent
list of root nameservers. If no hint zone is specified for class
IN, the server users a compiled-in default set of root servers hints.
Classes other than IN have no built-in defaults hints.</para></entry>
</row>
</tbody>
</tgroup></informaltable></sect3>
<sect3><title>Class</title>
<para>The zone's name may optionally be followed by a class. If
a class is not specified, class <literal>IN</literal> (for <varname>Internet</varname>),
is assumed. This is correct for the vast majority of cases.</para>
<para>The <literal>hesiod</literal> class is
named for an information service from MIT's Project Athena. It is
used to share information about various systems databases, such
as users, groups, printers and so on. The keyword
<literal>HS</literal> is
a synonym for hesiod.</para>
<para>Another MIT development is CHAOSnet, a LAN protocol created
in the mid-1970s. Zone data for it can be specified with the <literal>CHAOS</literal> class.</para></sect3>
<sect3>
<title>Zone Options</title>
<informaltable colsep = "0"
rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.653in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "2.847in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-query</command></para></entry>
<entry colname = "2"><para>See the description of
<command>allow-query</command> in <xref linkend="access_control"/></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-transfer</command></para></entry>
<entry colname = "2"><para>See the description of <command>allow-transfer</command> in <xref linkend="access_control"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-update</command></para></entry>
<entry colname = "2"><para>Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is to deny
updates from all hosts.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>update-policy</command></para></entry>
<entry colname = "2"><para>Specifies a "Simple Secure Update" policy. See
<xref linkend="dynamic_update_policies"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>allow-update-forwarding</command></para></entry>
<entry colname = "2"><para>Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to the
master. The default is to deny update forwarding from all hosts.</para><note>
<simpara>Update
forwarding is not yet implemented.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>also-notify</command></para></entry>
<entry colname = "2"><para>Only meaningful if <command>notify</command> is
active for this zone. The set of machines that will receive a
<literal>DNS NOTIFY</literal> message
for this zone is made up of all the listed nameservers (other than
the primary master) for the zone plus any IP addresses specified
with <command>also-notify</command>.
<command>also-notify</command> is not meaningful for stub zones.
The default is the empty list.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>check-names</command></para></entry>
<entry colname = "2"><para>See <xref
linkend="name_checking"/>.</para>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>dialup</command></para></entry>
<entry colname = "2"><para>See the description of
<command>dialup</command> under <xref linkend="boolean_options"/>.
<note><simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>forward</command></para></entry>
<entry colname = "2"><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>
<note>
<simpara>Not yet implemented in <acronym>BIND</acronym> 9.</simpara></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>forwarders</command></para></entry>
<entry colname = "2"><para>Used to override the list of global forwarders.
If it is not specified in a zone of type <command>forward</command>,
no forwarding is done for the zone; the global options are not used.</para><note>
<para>Not
yet implemented in <acronym>BIND</acronym> 9.</para></note></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>ixfr-base</command></para></entry>
<entry colname = "2"><para>Was used in <acronym>BIND</acronym> 8 to specify the name
of the transaction log (journal) file for dynamic update and IXFR.
<acronym>BIND</acronym> 9 ignores the option and constructs the name of the journal
file by appending ".<filename>jnl</filename>" to the name of the
zone file.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-time-in</command></para></entry>
<entry colname = "2"><para>See the description of
<command>max-transfer-time-in</command> under <xref linkend="zone_transfers"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-idle-in</command></para></entry>
<entry colname = "2"><para>See the description of
<command>max-transfer-idle-in</command> under <xref linkend="zone_transfers"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-time-out</command></para></entry>
<entry colname = "2"><para>See the description of
<command>max-transfer-time-out</command> under <xref linkend="zone_transfers"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>max-transfer-idle-out</command></para></entry>
<entry colname = "2"><para>See the description of
<command>max-transfer-idle-out</command> under <xref linkend="zone_transfers"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>notify</command></para></entry>
<entry colname = "2"><para>See the description of
<command>notify</command> under <xref linkend="boolean_options"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>pubkey</command></para></entry>
<entry colname = "2"><para>In <acronym>BIND</acronym> 8, this option was intended for specifying
a public zone key for verification of signatures in DNSSEC signed
zones when they are loaded from disk. <acronym>BIND</acronym> 9 does not verify signatures
on loading and ignores the option.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>sig-validity-interval</command></para></entry>
<entry colname = "2"><para>See the description of
<command>sig-validity-interval</command> under <xref linkend="tuning"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>transfer-source</command></para></entry>
<entry colname = "2"><para>Determines which local address will be bound
to the IPv4 TCP connection used to fetch this zone. If not set,
it defaults to a system controlled value which will usually be the
address of the interface "closest to" the remote end. If the remote
end user is an <command>allow-transfer</command> option for this
zone, the address, supplied by the <command>transfer-source</command> option,
needs to be specified in that <command>allow-transfer</command> option.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>transfer-source-v6</para></entry>
<entry colname = "2"><para>Similar to transfer-source, but for zone transfers
performed using IPv6.</para></entry>
</row>
</tbody>
</tgroup></informaltable></sect3>
<sect3 id="dynamic_update_policies"><title>Dynamic Update Policies</title>
<para><acronym>BIND</acronym> 9 supports two alternative methods of granting clients
the right to perform dynamic updates to a zone, configured by the <command>allow-update</command> and <command>update-policy</command> option,
respectively.</para>
<para>The <command>allow-update</command> clause works the same
way as in previous versions of <acronym>BIND</acronym>. It grants given clients the
permission to update any record of any name in the zone.</para>
<para>The <command>update-policy</command> clause is new in <acronym>BIND</acronym>
9 and allows more fine-grained control over what updates are allowed.
A set of rules is specified, where each rule either grants or denies
permissions for one or more names to be updated by one or more identities.
If the dynamic update request message is signed (that is, it includes
either a TSIG or SIG(0) record), the identity of the signer can
be determined.</para>
<para>Rules are specified in the <command>update-policy</command> zone
option, and are only meaningful for master zones. When the <command>update-policy</command> statement
is present, it is a configuration error for the <command>allow-update</command> statement
to be present. The <command>update-policy</command> statement only
examines the signer of a message; the source address is not relevant.</para>
<para>This is how a rule definition looks:</para>
<programlisting>
( <command>grant</command> | <command>deny</command> ) <replaceable>identity</replaceable> <replaceable>nametype</replaceable> <replaceable>name</replaceable> <optional> <replaceable>types</replaceable> </optional>
</programlisting>
<para>Each rule grants or denies privileges. Once a message has
successfully matched a rule, the operation is immediately granted
or denied and no further rules are examined. A rule is matched
when the signer matches the identity field, the name matches the
name field, and the type is specified in the type field.</para>
<para>The identity field specifies a name or a wildcard name. The
nametype field has 4 values: <varname>name</varname>, <varname>subdomain</varname>, <varname>wildcard</varname>,
and <varname>self</varname>
</para>
<informaltable>
<tgroup cols = "2" colsep = "0"
rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.819in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.681in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><varname>name</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is the
same as the name in the name field.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>subdomain</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is a subdomain
of the name in the name field.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>wildcard</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is a valid
expansion of the wildcard name in the name field.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>self</varname></para></entry>
<entry colname = "2"><para>Matches when the updated name is the
same as the message signer. The name field is ignored.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>If no types are specified, the rule matches all types except
SIG, NS, SOA, and NXT. Types may be specified by name, including
"ANY" (ANY matches all types except NXT, which can never be updated).
</para>
</sect3>
</sect2>
</sect1>
<sect1>
<title>Zone File</title>
<sect2 id="types_of_resource_records_and_when_to_use_them">
<title>Types of Resource Records and When to Use Them</title>
<para>This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been identified
and implemented in the DNS. These are also included.</para>
<sect3>
<title>Resource Records</title>
<para>A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by nameservers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See <xref
linkend="the_sortlist_statement"/> and <xref
linkend="rrset_ordering"/>.</para>
<para>The components of a Resource Record are:</para>
<informaltable colsep = "0"
rowsep = "0"><tgroup cols = "2" colsep = "0"
rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.000in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.500in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>owner name</para></entry>
<entry colname = "2"><para>the domain name where the RR is found.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>type</para></entry>
<entry colname = "2"><para>an encoded 16 bit value that specifies
the type of the resource in this resource record. Types refer to
abstract resources.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>TTL</para></entry>
<entry colname = "2"><para>the time to live of the RR. This field
is a 32 bit integer in units of seconds, and is primarily used by
resolvers when they cache RRs. The TTL describes how long a RR can
be cached before it should be discarded.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>class</para></entry>
<entry colname = "2"><para>an encoded 16 bit value that identifies
a protocol family or instance of a protocol.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RDATA</para></entry>
<entry colname = "2"><para>the type and sometimes class-dependent
data that describes the resource.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The following are <emphasis>types</emphasis> of valid RRs
(some of these listed, although not obsolete, are experimental (x)
or historical (h) and no longer in general use):</para>
<informaltable colsep = "0"
rowsep = "0"><tgroup cols = "2" colsep = "0"
rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.625in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>A</para></entry>
<entry colname = "2"><para>a host address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>A6</para></entry>
<entry colname = "2"><para>an IPv6 address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>AAAA</para></entry>
<entry colname = "2"><para>Obsolete format of IPv6 address</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>AFSDB</para></entry>
<entry colname = "2"><para>(x) location of AFS database servers.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>CNAME</para></entry>
<entry colname = "2"><para>identifies the canonical name of an alias.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>DNAME</para></entry>
<entry colname = "2"><para>for delegation of reverse addresses.
Replaces the domain name specified with another name to be looked
up. Described in RFC 2672.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>HINFO</para></entry>
<entry colname = "2"><para>identifies the CPU and OS used by a host.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>ISDN</para></entry>
<entry colname = "2"><para>(x) representation of ISDN addresses.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>KEY</para></entry>
<entry colname = "2"><para>stores a public key associated with a
DNS name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>LOC</para></entry>
<entry colname = "2"><para>(x) for storing GPS info. See RFC 1876.
Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>MX</para></entry>
<entry colname = "2"><para>identifies a mail exchange for the domain.
See RFC 974 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NS</para></entry>
<entry colname = "2"><para>the authoritative nameserver for the
domain.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NXT</para></entry>
<entry colname = "2"><para>used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do not exist in
a zone and indicate what RR types are present for an existing name.
See RFC 2535 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>PTR</para></entry>
<entry colname = "2"><para>a pointer to another part of the domain
name space.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RP</para></entry>
<entry colname = "2"><para>(x) information on persons responsible
for the domain. Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RT</para></entry>
<entry colname = "2"><para>(x) route-through binding for hosts that
do not have their own direct wide area network addresses. Experimental.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SIG</para></entry>
<entry colname = "2"><para>("signature") contains data authenticated
in the secure DNS. See RFC 2535 for details.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SOA</para></entry>
<entry colname = "2"><para>identifies the start of a zone of authority.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SRV</para></entry>
<entry colname = "2"><para>information about well known network
services (replaces WKS).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>WKS</para></entry>
<entry colname = "2"><para>(h) information about which well known
network services, such as SMTP, that a domain supports. Historical,
replaced by newer RR SRV.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>X25</para></entry>
<entry colname = "2"><para>(x) representation of X.25 network addresses. Experimental.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The following <emphasis>classes</emphasis> of resource records
are currently valid in the DNS:</para><informaltable colsep = "0"
rowsep = "0"><tgroup cols = "2" colsep = "0" rowsep = "0"
tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.625in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>IN</para></entry>
<entry colname = "2"><para>the Internet system.</para></entry>
</row>
<row rowsep = "0">
<entry nameend = "2" namest = "1"><para>For information about other,
older classes of RRs, see <xref linkend="classes_of_resource_records"/>.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para><emphasis>RDATA</emphasis> is the type-dependent or class-dependent
data that describes the resource:</para><informaltable colsep = "0"
rowsep = "0"><tgroup cols = "2" colsep = "0" rowsep = "0"
tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.625in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>A</para></entry>
<entry colname = "2"><para>for the IN class, a 32 bit IP address.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>A6</para></entry>
<entry colname = "2"><para>maps a domain name to an IPv6 address,
with a provision for indirection for leading "prefix" bits.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>CNAME</para></entry>
<entry colname = "2"><para>a domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>DNAME</para></entry>
<entry colname = "2"><para>provides alternate naming to an entire
subtree of the domain name space, rather than to a single node.
It causes some suffix of a queried name to be substituted with
a name from the DNAME record's RDATA.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>MX</para></entry>
<entry colname = "2"><para>a 16 bit preference value (lower is better)
followed by a host name willing to act as a mail exchange for the
owner domain.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NS</para></entry>
<entry colname = "2"><para>a fully qualified domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>PTR</para></entry>
<entry colname = "2"><para>a fully qualified domain name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SOA</para></entry>
<entry colname = "2"><para>several fields.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The owner name is often implicit, rather than forming an integral
part of the RR. For example, many nameservers internally form tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA) that
fits the needs of the resource being described.</para>
<para>The meaning of the TTL field is a time limit on how long an
RR can be kept in a cache. This limit does not apply to authoritative
data in zones; it is also timed out, but by the refreshing policies
for the zone. The TTL is assigned by the administrator for the
zone where the data originates. While short TTLs can be used to
minimize caching, and a zero TTL prohibits caching, the realities
of Internet performance suggest that these times should be on the
order of days for the typical host. If a change can be anticipated,
the TTL can be reduced prior to the change to minimize inconsistency
during the change, and then increased back to its former value following
the change.</para>
<para>The data in the RDATA section of RRs is carried as a combination
of binary strings and domain names. The domain names are frequently
used as "pointers" to other data in the DNS.</para></sect3>
<sect3><title>Textual expression of RRs</title>
<para>RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form when
stored in a nameserver or resolver. In the examples provided in
RFC 1034, a style similar to that used in master files was employed
in order to show the contents of RRs. In this format, most RRs
are shown on a single line, although continuation lines are possible
using parentheses.</para>
<para>The start of the line gives the owner of the RR. If a line
begins with a blank, then the owner is assumed to be the same as
that of the previous RR. Blank lines are often included for readability.</para>
<para>Following the owner, we list the TTL, type, and class of the
RR. Class and type use the mnemonics defined above, and TTL is
an integer before the type field. In order to avoid ambiguity in
parsing, type and class mnemonics are disjoint, TTLs are integers,
and the type mnemonic is always last. The IN class and TTL values
are often omitted from examples in the interests of clarity.</para>
<para>The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.</para>
<para>For example, we might show the RRs carried in a message as:</para> <informaltable
colsep = "0" rowsep = "0"><tgroup cols = "3"
colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.381in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "1.020in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "2.099in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><literal>ISI.EDU.</literal></para></entry>
<entry colname = "2"><para><literal>MX</literal></para></entry>
<entry colname = "3"><para><literal>10 VENERA.ISI.EDU.</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>MX</literal></para></entry>
<entry colname = "3"><para><literal>10 VAXA.ISI.EDU</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>VENERA.ISI.EDU</literal></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>128.9.0.32</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>10.1.0.52</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>VAXA.ISI.EDU</literal></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>10.2.0.27</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>128.9.0.33</literal></para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The MX RRs have an RDATA section which consists of a 16 bit
number followed by a domain name. The address RRs use a standard
IP address format to contain a 32 bit internet address.</para>
<para>This example shows six RRs, with two RRs at each of three
domain names.</para>
<para>Similarly we might see:</para><informaltable colsep = "0"
rowsep = "0"><tgroup cols = "3" colsep = "0" rowsep = "0"
tgroupstyle = "4Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.491in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "1.067in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "2.067in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><literal>XX.LCS.MIT.EDU. IN</literal></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>10.0.0.44</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>CH</literal></para></entry>
<entry colname = "2"><para><literal>A</literal></para></entry>
<entry colname = "3"><para><literal>MIT.EDU. 2420</literal></para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>This example shows two addresses for <systemitem class="systemname">XX.LCS.MIT.EDU</systemitem>,
each of a different class.</para></sect3></sect2>
<sect2><title>Discussion of MX Records</title>
<para>As described above, domain servers store information as a
series of resource records, each of which contains a particular
piece of information about a given domain name (which is usually,
but not always, a host). The simplest way to think of a RR is as
a typed pair of datum, a domain name matched with relevant data,
and stored with some additional type information to help systems determine
when the RR is relevant.</para>
<para>MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest priority.
Priority numbers do not have any absolute meaning &mdash; they are relevant
only respective to other MX records for that domain name. The domain
name given is the machine to which the mail will be delivered. It <emphasis>must</emphasis> have
an associated A record &mdash; CNAME is not sufficient.</para>
<para>For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored. Instead,
the mail will be delivered to the server specified in the MX record
pointed to by the CNAME.</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "5"
colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.708in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.444in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.444in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.976in"/>
<colspec colname = "5" colnum = "5" colsep = "0" colwidth = "1.553in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><literal>example.com.</literal></para></entry>
<entry colname = "2"><para><literal>IN</literal></para></entry>
<entry colname = "3"><para><literal>MX</literal></para></entry>
<entry colname = "4"><para><literal>10</literal></para></entry>
<entry colname = "5"><para><literal>mail.example.com.</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>IN</literal></para></entry>
<entry colname = "3"><para><literal>MX</literal></para></entry>
<entry colname = "4"><para><literal>10</literal></para></entry>
<entry colname = "5"><para><literal>mail2.example.com.</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>IN</literal></para></entry>
<entry colname = "3"><para><literal>MX</literal></para></entry>
<entry colname = "4"><para><literal>20</literal></para></entry>
<entry colname = "5"><para><literal>mail.backup.org.</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>mail.example.com.</literal></para></entry>
<entry colname = "2"><para><literal>IN</literal></para></entry>
<entry colname = "3"><para><literal>A</literal></para></entry>
<entry colname = "4"><para><literal>10.0.0.1</literal></para></entry>
<entry colname = "5"><para></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>mail2.example.com.</literal></para></entry>
<entry colname = "2"><para><literal>IN</literal></para></entry>
<entry colname = "3"><para><literal>A</literal></para></entry>
<entry colname = "4"><para><literal>10.0.0.2</literal></para></entry>
<entry colname = "5"><para></para></entry>
</row>
</tbody>
</tgroup></informaltable><para>For example:</para>
<para>Mail delivery will be attempted to <systemitem class="systemname">mail.example.com</systemitem> and <systemitem class="systemname">mail2.example.com</systemitem> (in
any order), and if neither of those succeed, delivery to <systemitem class="systemname">mail.backup.org</systemitem> will
be attempted.</para></sect2>
<sect2 id="Setting_TTLs"><title>Setting TTLs</title>
<para>The time to live of the RR field is a 32 bit integer represented
in units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached before it
should be discarded. The following three types of TTL are currently
used in a zone file.</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.375in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>SOA</para></entry>
<entry colname = "2"><para>The last field in the SOA is the negative
caching TTL. This controls how long other servers will cache no-such-domain
(NXDOMAIN) responses from you.</para><para>The maximum time for
negative caching is 3 hours (3h).</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>$TTL</para></entry>
<entry colname = "2"><para>The $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every RR without
a specific TTL set.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RR TTLs</para></entry>
<entry colname = "2"><para>Each RR can have a TTL as the second
field in the RR, which will control how long other servers can cache
the it.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, <literal>1h30m</literal>. </para></sect2>
<sect2><title>Inverse Mapping in IPv4</title>
<para>Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the <emphasis>in-addr.arpa</emphasis> domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally, multiple
PTR records if the machine has more than one name. For example,
in the <optional>example.com</optional> domain:</para>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0"
tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.125in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><literal>$ORIGIN</literal></para></entry>
<entry colname = "2"><para><literal>2.1.10.in-addr.arpa</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>3</literal></para></entry>
<entry colname = "2"><para><literal>IN PTR foo.example.com.</literal></para></entry>
</row>
</tbody>
</tgroup></informaltable>
<note>
<para>The <command>$ORIGIN</command> lines in the examples
are for providing context to the examples only-they do not necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.</para></note></sect2>
<sect2><title>Other Zone File Directives</title>
<para>The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format itself
is class independent all records in a Master File must be of the same
class.</para>
<para>Master File Directives include <command>$ORIGIN</command>, <command>$INCLUDE</command>,
and <command>$TTL.</command></para>
<sect3><title>The <command>$ORIGIN</command> Directive</title>
<para>Syntax: <command>$ORIGIN
</command><replaceable>domain-name</replaceable> <optional> <replaceable>comment</replaceable></optional></para>
<para><command>$ORIGIN </command>sets the domain name that will
be appended to any unqualified records. When a zone is first read
in there is an implicit <command>$ORIGIN </command>&#60;<varname>zone-name</varname>><command>.</command> The
current <command>$ORIGIN</command> is appended to the domain specified
in the <command>$ORIGIN</command> argument if it is not absolute.</para>
<programlisting><literal>$ORIGIN example.com
WWW CNAME MAIN-SERVER</literal></programlisting>
<para>is equivalent to</para>
<programlisting><literal>WWW.EXAMPLE.COM CNAME MAIN-SERVER.EXAMPLE.COM.</literal></programlisting></sect3>
<sect3><title>The <command>$INCLUDE</command> Directive</title>
<para>Syntax: <command>$INCLUDE</command>
<replaceable>filename</replaceable> <optional>
<replaceable>origin</replaceable> </optional> <optional> <replaceable>comment</replaceable> </optional></para>
<para>Read and process the file <filename>filename</filename> as
if it were included into the file at this point. If <command>origin</command> is
specified the file is processed with <command>$ORIGIN</command> set
to that value, otherwise the current <command>$ORIGIN</command> is
used.</para>
<note>
<para>The behavior when <command>origin</command> is
specified differs from that described in RFC 1035. The origin and
current domain revert to the values they were prior to the <command>$INCLUDE</command> once
the file has been read.</para></note></sect3>
<sect3><title>The <command>$TTL</command> Directive</title>
<para>Syntax: <command>$TTL</command>
<replaceable>default-ttl</replaceable> <optional>
<replaceable>comment</replaceable> </optional></para>
<para>Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647 seconds.</para>
<para><command>$TTL</command> is defined in RFC 2308.</para></sect3></sect2>
<sect2><title><acronym>BIND</acronym> Master File Extension: the <command>$GENERATE</command> Directive</title>
<para>Syntax: <command>$GENERATE</command> <replaceable>range</replaceable> <replaceable>hs</replaceable> <replaceable>type</replaceable> <replaceable>rhs</replaceable> <optional> <replaceable>comment</replaceable> </optional></para>
<para><command>$GENERATE</command> is used to create a series of
resource records that only differ from each other by an iterator. <command>$GENERATE </command>can
be used to easily generate the sets of records required to support
sub /24 reverse delegations described in RFC 2317: Classless IN-ADDR.ARPA
delegation.</para>
<programlisting><literal>$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 0 NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</literal></programlisting>
<para>is equivalent to</para>
<programlisting><literal>0.0.0.192.IN-ADDR.ARPA NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA CNAME 1.0.0.0.192.IN-ADDR.ARPA
2.0.0.192.IN-ADDR.ARPA CNAME 2.0.0.0.192.IN-ADDR.ARPA
...
127.0.0.192.IN-ADDR.ARPA CNAME 127.0.0.0.192.IN-ADDR.ARPA
.</literal></programlisting>
<informaltable colsep = "0" rowsep = "0">
<tgroup cols = "2" colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.250in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>range</command></para></entry>
<entry colname = "2"><para>This can be one of two forms: start-stop
or start-stop/step. If the first form is used then step is set to
1. All of start, stop and step must be positive.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>lhs</command></para></entry>
<entry colname = "2"><para><command>lhs</command> describes the
owner name of the resource records to be created. Any single <command>$</command> symbols
within the <command>lhs</command> side are replaced by the iterator
value. To get a $ in the output use a double <command>$</command>,
e.g. <command>$$</command>. If the <command>lhs</command> is not
absolute, the current <command>$ORIGIN </command>is appended to
the name.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>type</command></para></entry>
<entry colname = "2"><para>At present the only supported types are
PTR, CNAME and NS.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>rhs</command></para></entry>
<entry colname = "2"><para>rhs is a domain name. It is processed
similarly to lhs.</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>The <command>$GENERATE</command> directive is a <acronym>BIND</acronym> extension
and not part of the standard zone file format.
<note>
<simpara>It is not yet implemented in <acronym>BIND</acronym> 9.</simpara>
</note>
</para>
</sect2>
</sect1>
</chapter>
<chapter id="ch07"><title><acronym>BIND</acronym> 9 Security Considerations</title>
<sect1 id="Access_Control_Lists"><title>Access Control Lists</title>
<para>Access Control Lists (ACLs), are address match lists that
you can set up and nickname for future use in <command>allow-query</command>, <command>allow-recursion</command>, <command>blackhole</command>, <command>allow-transfer</command>,
etc.</para>
<para>Using ACLs allows you to have finer control over who can access
your nameserver, without cluttering up your config files with huge
lists of IP addresses.</para>
<para>It is a <emphasis>good idea</emphasis> to use ACLs, and to
control access to your server. Limiting access to your server by
outside parties can help prevent spoofing and DoS attacks against
your server.</para>
<para>Here is an example of how to properly apply ACLs:</para>
<programlisting>
// Set up an ACL named "bogusnets" that will block RFC1918 space,
// which is commonly used in spoofing attacks.
acl bogusnets { 0.0.0.0/8; 1.0.0.0/8; 2.0.0.0/8; 192.0.2.0/24; 224.0.0.0/3; 10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16; };
// Set up an ACL called our-nets. Replace this with the real IP numbers.
acl our-nets { x.x.x.x/24; x.x.x.x/21; };
options {
...
...
allow-query { our-nets; };
allow-recursion { our-nets; };
...
blackhole { bogusnets; };
...
};
zone "example.com" {
type master;
file "m/example.com";
allow-query { any; };
};
</programlisting>
<para>This allows recursive queries of the server from the outside
unless recursion has been previously disabled.</para>
<para>For more information on how to use ACLs to protect your server,
see the <emphasis>AUSCERT</emphasis> advisory at
<ulink url="ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos">ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos</ulink></para></sect1>
<sect1><title><command>chroot</command> and <command>setuid</command> (for
UNIX servers)</title>
<para>On UNIX servers, it is possible to run <acronym>BIND</acronym> in a <emphasis>chrooted</emphasis> environment
(<command>chroot()</command>) by specifying the "<option>-t</option>"
option. This can help improve system security by placing <acronym>BIND</acronym> in
a "sandbox," which will limit the damage done if a server is compromised.</para>
<para>Another useful feature in the UNIX version of <acronym>BIND</acronym> is the
ability to run the daemon as a nonprivileged user ( <option>-u</option> <replaceable>user</replaceable> ).
We suggest running as a nonprivileged user when using the <command>chroot</command> feature.</para>
<para>Here is an example command line to load <acronym>BIND</acronym> in a <command>chroot()</command> sandbox,
<command>/var/named</command>, and to run <command>named</command> <command>setuid</command> to
user 202:</para>
<para><userinput>/usr/local/bin/named -u 202 -t /var/named</userinput></para>
<sect2><title>The <command>chroot</command> Environment</title>
<para>In order for a <command>chroot()</command> environment to
work properly in a particular directory (for example, <filename>/var/named</filename>),
you will need to set up an environment that includes everything
<acronym>BIND</acronym> needs to run. From <acronym>BIND</acronym>'s point of view, <filename>/var/named</filename> is
the root of the filesystem. You will need <filename>/dev/null</filename>,
and any library directories and files that <acronym>BIND</acronym> needs to run on
your system. Please consult your operating system's instructions
if you need help figuring out which library files you need to copy
over to the <command>chroot()</command> sandbox.</para>
<para>If you are running an operating system that supports static
binaries, you can also compile <acronym>BIND</acronym> statically and avoid the need
to copy system libraries over to your <command>chroot()</command> sandbox.</para></sect2>
<sect2><title>Using the <command>setuid</command> Function </title>
<para>Prior to running the <command>named</command> daemon, use
the <command>touch</command> utility (to change file access and
modification times) or the <command>chown</command> utility (to
set the user id and/or group id) on files to which you want <acronym>BIND</acronym>
to write.</para></sect2></sect1>
<sect1><title>Dynamic Updates</title>
<para>Access to the dynamic update facility should be strictly limited.
In earlier versions of <acronym>BIND</acronym> the only way to do this was based on
the IP address of the host requesting the update. <acronym>BIND9</acronym> also
supports authenticating updates cryptographically by means of transaction
signatures (TSIG). The use of TSIG is strongly recommended.</para>
<para>Some sites choose to keep all dynamically updated DNS data
in a subdomain and delegate that subdomain to a separate zone. This
way, the top-level zone containing critical data such as the IP addresses
of public web and mail servers need not allow dynamic update at
all.</para></sect1></chapter>
<chapter id="ch08">
<title>Troubleshooting</title>
<sect1>
<title>Common Problems</title>
<sect2>
<title>It's not working; how can I figure out what's wrong?</title>
<para>The best solution to solving installation and
configuration issues is to take preventative measures by setting
up logging files beforehand (see the sample configurations in
<xref linkend="sample_configuration"/>). The log files provide a
source of hints and information that can be used to figure out
what went wrong and how to fix the problem.</para>
</sect2>
</sect1>
<sect1>
<title>Incrementing and Changing the Serial Number</title>
<para>Zone serial numbers are just numbers-they aren't date
related. A lot of people set them to a number that represents a
date, usually of the form YYYYMMDDRR. A number of people have been
testing these numbers for Y2K compliance and have set the number
to the year 2000 to see if it will work. They then try to restore
the old serial number. This will cause problems because serial
numbers are used to indicate that a zone has been updated. If the
serial number on the slave server is lower than the serial number
on the master, the slave server will attempt to update its copy of
the zone.</para>
<para>Setting the serial number to a lower number on the master
server than the slave server means that the slave will not perform
updates to its copy of the zone.</para>
<para>The solution to this is to add 2147483647 (2^31-1) to the
number, reload the zone and make sure all slaves have updated to
the new zone serial number, then reset the number to what you want
it to be, and reload the zone again.</para>
</sect1>
<sect1>
<title>Where Can I Get Help?</title>
<para>The Internet Software Consortium (<acronym>ISC</acronym>) offers a wide range
of support and service agreements for <acronym>BIND</acronym> and <acronym>DHCP</acronym> servers. Four
levels of premium support are available and each level includes
support for all <acronym>ISC</acronym> programs, significant discounts on products
and training, and a recognized priority on bug fixes and
non-funded feature requests. In addition, <acronym>ISC</acronym> offers a standard
support agreement package which includes services ranging from bug
fix announcements to remote support. It also includes training in
<acronym>BIND</acronym> and <acronym>DHCP</acronym>.</para>
<para>To discuss arrangements for support, contact
<ulink url="email:info@isc.org">info@isc.org</ulink> or visit the
<acronym>ISC</acronym> web page at <ulink
url="http://www.isc.org/services/support/">http://www.isc.org/services/support/</ulink>
to read more.</para>
</sect1>
</chapter>
<appendix id="ch09">
<title>Appendices</title>
<sect1>
<title>Acknowledgements</title>
<sect2>
<title>A Brief History of the <acronym>DNS</acronym> and <acronym>BIND</acronym></title>
<para>Although the "official" beginning of the Domain Name
System occurred in 1984 with the publication of RFC 920, the
core of the new system was described in 1983 in RFCs 882 and
883. From 1984 to 1987, the ARPAnet (the precursor to today's
Internet) became a testbed of experimentation for developing the
new naming/addressing scheme in an rapidly expanding,
operational network environment. New RFCs were written and
published in 1987 that modified the original documents to
incorporate improvements based on the working model. RFC 1034,
"Domain Names-Concepts and Facilities," and RFC 1035, "Domain
Names-Implementation and Specification" were published and
became the standards upon which all <acronym>DNS</acronym> implementations are
built.
</para>
<para>The first working domain name server, called "Jeeves," was
written in 1983-84 by Paul Mockapetris for operation on DEC Tops-20
machines located at the University of Southern California's Information
Sciences Institute (USC-ISI) and SRI International's Network Information
Center (SRI-NIC). A <acronym>DNS</acronym> server for Unix machines, the Berkeley Internet
Name Domain (<acronym>BIND</acronym>) package, was written soon after by a group of
graduate students at the University of California at Berkeley under
a grant from the US Defense Advanced Research Projects Administration
(DARPA). Versions of <acronym>BIND</acronym> through 4.8.3 were maintained by the Computer
Systems Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark
Painter, David Riggle and Songnian Zhou made up the initial <acronym>BIND</acronym>
project team. After that, additional work on the software package
was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment Corporation
employee on loan to the CSRG, worked on <acronym>BIND</acronym> for 2 years, from 1985
to 1987. Many other people also contributed to <acronym>BIND</acronym> development
during that time: Doug Kingston, Craig Partridge, Smoot Carl-Mitchell,
Mike Muuss, Jim Bloom and Mike Schwartz. <acronym>BIND</acronym> maintenance was subsequently
handled by Mike Karels and O. Kure.</para>
<para><acronym>BIND</acronym> versions 4.9 and 4.9.1 were released by Digital Equipment
Corporation (now Compaq Computer Corporation). Paul Vixie, then
a DEC employee, became <acronym>BIND</acronym>'s primary caretaker. Paul was assisted
by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan Beecher, Andrew
Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat
Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe
Wolfhugel, and others.</para>
<para><acronym>BIND</acronym> Version 4.9.2 was sponsored by Vixie Enterprises. Paul
Vixie became <acronym>BIND</acronym>'s principal architect/programmer.</para>
<para><acronym>BIND</acronym> versions from 4.9.3 onward have been developed and maintained
by the Internet Software Consortium with support being provided
by ISC's sponsors. As co-architects/programmers, Bob Halley and
Paul Vixie released the first production-ready version of <acronym>BIND</acronym> version
8 in May 1997.</para>
<para><acronym>BIND</acronym> development work is made possible today by the sponsorship
of several corporations, and by the tireless work efforts of numerous
individuals.</para>
</sect2>
</sect1>
<sect1 id="historical_dns_information">
<title>Historical <acronym>DNS</acronym> Information</title>
<sect2 id="classes_of_resource_records">
<title>Classes of Resource Records</title>
<sect3>
<title>HS = hesiod</title>
<para>The <optional>hesiod</optional> class is an information service
developed by MIT's Project Athena. It is used to share information
about various systems databases, such as users, groups, printers
and so on. The keyword <command>hs</command> is a synonym for
hesiod.</para>
</sect3>
<sect3>
<title>CH = chaos</title>
<para>The <command>chaos</command> class is used to specify zone
data for the MIT-developed CHAOSnet, a LAN protocol created in the
mid-1970s.</para>
</sect3>
</sect2>
</sect1>
<sect1>
<title>General <acronym>DNS</acronym> Reference Information</title>
<sect2>
<title>IPv6 addresses (A6)</title>
<para>IPv6 addresses are 128-bit identifiers for interfaces and
sets of interfaces which were introduced in the <acronym>DNS</acronym> to facilitate
scalable Internet routing. There are three types of addresses: <emphasis>Unicast</emphasis>,
an identifier for a single interface; <emphasis>Anycast</emphasis>,
an identifier for a set of interfaces; and <emphasis>Multicast</emphasis>,
an identifier for a set of interfaces. Here we describe the global
Unicast address scheme. For more information, see RFC 2374.</para>
<para>The aggregatable global Unicast address format is as follows:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "6"
colsep = "0" rowsep = "0" tgroupstyle = "1Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.477in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.501in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.523in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.731in"/>
<colspec colname = "5" colnum = "5" colsep = "0" colwidth = "1.339in"/>
<colspec colname = "6" colnum = "6" colsep = "0" colwidth = "2.529in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>3</para></entry>
<entry colname = "2" colsep = "1" rowsep = "1"><para>13</para></entry>
<entry colname = "3" colsep = "1" rowsep = "1"><para>8</para></entry>
<entry colname = "4" colsep = "1" rowsep = "1"><para>24</para></entry>
<entry colname = "5" colsep = "1" rowsep = "1"><para>16</para></entry>
<entry colname = "6" rowsep = "1"><para>64 bits</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>FP</para></entry>
<entry colname = "2" colsep = "1"><para>TLA ID</para></entry>
<entry colname = "3" colsep = "1"><para>RES</para></entry>
<entry colname = "4" colsep = "1"><para>NLA ID</para></entry>
<entry colname = "5" colsep = "1"><para>SLA ID</para></entry>
<entry colname = "6"><para>Interface ID</para></entry>
</row>
<row rowsep = "0">
<entry nameend = "4" namest = "1"><para>&#60;------ Public Topology
------></para></entry>
<entry colname = "5"><para></para></entry>
<entry colname = "6"><para></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para></para></entry>
<entry colname = "3"><para></para></entry>
<entry colname = "4"><para></para></entry>
<entry colname = "5"><para>&#60;-Site Topology-></para></entry>
<entry colname = "6"><para></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para></para></entry>
<entry colname = "3"><para></para></entry>
<entry colname = "4"><para></para></entry>
<entry colname = "5"><para></para></entry>
<entry colname = "6"><para>&#60;------ Interface Identifier ------></para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>Where
<informaltable colsep = "0" rowsep = "0"><tgroup
cols = "3" colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.375in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.250in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "3.500in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>FP</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Format Prefix (001)</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>TLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Top-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>RES</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Reserved for future use</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>NLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Next-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>SLA ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Site-Level Aggregation Identifier</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para>INTERFACE ID</para></entry>
<entry colname = "2"><para>=</para></entry>
<entry colname = "3"><para>Interface Identifier</para></entry>
</row>
</tbody>
</tgroup></informaltable></para>
<para>The <emphasis>Public Topology</emphasis> is provided by the
upstream provider or ISP, and (roughly) corresponds to the IPv4 <emphasis>network</emphasis> section
of the address range. The <emphasis>Site Topology</emphasis> is
where you can subnet this space, much the same as subnetting an
IPv4 /16 network into /24 subnets. The <emphasis>Interface Identifier</emphasis> is
the address of an individual interface on a given network. (With
IPv6, addresses belong to interfaces rather than machines.)</para>
<para>The subnetting capability of IPv6 is much more flexible than
that of IPv4: subnetting can now be carried out on bit boundaries,
in much the same way as Classless InterDomain Routing (CIDR).</para>
<para>The internal structure of the Public Topology for an A6 global
unicast address consists of:</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "4"
colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.506in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.662in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.556in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.825in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>3</para></entry>
<entry colname = "2" colsep = "1" rowsep = "1"><para>13</para></entry>
<entry colname = "3" colsep = "1" rowsep = "1"><para>8</para></entry>
<entry colname = "4" rowsep = "1"><para>24</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>FP</para></entry>
<entry colname = "2" colsep = "1"><para>TLA ID</para></entry>
<entry colname = "3" colsep = "1"><para>RES</para></entry>
<entry colname = "4"><para>NLA ID</para></entry>
</row>
</tbody>
</tgroup></informaltable>
<para>A 3 bit FP (Format Prefix) of 001 indicates this is a global
Unicast address. FP lengths for other types of addresses may vary.</para>
<para>13 TLA (Top Level Aggregator) bits give the prefix of your
top-level IP backbone carrier.</para>
<para>8 Reserved bits</para>
<para>24 bits for Next Level Aggregators. This allows organizations
with a TLA to hand out portions of their IP space to client organizations,
so that the client can then split up the network further by filling
in more NLA bits, and hand out IPv6 prefixes to their clients, and
so forth.</para>
<para>There is no particular structure for the Site topology section.
Organizations can allocate these bits in any way they desire.</para>
<para>The Interface Identifier must be unique on that network. On
ethernet networks, one way to ensure this is to set the address
to the first three bytes of the hardware address, "FFFE", then the
last three bytes of the hardware address. The lowest significant
bit of the first byte should then be complemented. Addresses are
written as 32-bit blocks separated with a colon, and leading zeros
of a block may be omitted, for example:</para>
<para><command>3ffe:8050:201:9:a00:20ff:fe81:2b32</command></para>
<para>IPv6 address specifications are likely to contain long strings
of zeros, so the architects have included a shorthand for specifying
them. The double colon (`::') indicates the longest possible string
of zeros that can fit, and can be used only once in an address.</para>
</sect2>
</sect1>
<sect1 id="bibliography">
<title>Bibliography (and Suggested Reading)</title>
<sect2 id="rfcs">
<title>Request for Comments (RFCs)</title>
<para>Specification documents for the Internet protocol suite, including
the <acronym>DNS</acronym>, are published as part of the Request for Comments (RFCs)
series of technical notes. The standards themselves are defined
by the Internet Engineering Task Force (IETF) and the Internet Engineering
Steering Group (IESG). RFCs can be obtained online via FTP at
<ulink url="ftp://www.isi.edu/in-notes/">ftp://www.isi.edu/in-notes/RFC<replaceable>xxx</replaceable>.txt</ulink> (where <replaceable>xxx</replaceable> is
the number of the RFC). RFCs are also available via the Web at <ulink
url="http://www.ietf.org/rfc/">http://www.ietf.org/rfc/</ulink>.</para>
<bibliography>
<bibliodiv>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<title>Standards</title>
<biblioentry>
<abbrev>RFC974</abbrev>
<author>
<surname>Partridge</surname>
<firstname>C.</firstname>
</author>
<title>Mail Routing and the Domain System</title>
<pubdate>January 1986</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1034</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P.V.</firstname>
</author>
<title>Domain Names &mdash; Concepts and Facilities</title>
<pubdate>November 1987</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1035</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P. V.</firstname>
</author> <title>Domain Names &mdash; Implementation and
Specification</title>
<pubdate>November 1987</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv id="proposed_standards" xreflabel="Proposed Standards">
<title>Proposed Standards</title>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<biblioentry>
<abbrev>RFC2181</abbrev>
<author>
<surname>Elz</surname>
<firstname>R., R. Bush</firstname>
</author>
<title>Clarifications to the <acronym>DNS</acronym> Specification</title>
<pubdate>July 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2308</abbrev>
<author>
<surname>Andrews</surname>
<firstname>M.</firstname>
</author>
<title>Negative Caching of <acronym>DNS</acronym> Queries</title>
<pubdate>March 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1995</abbrev>
<author>
<surname>Ohta</surname>
<firstname>M.</firstname>
</author>
<title>Incremental Zone Transfer in <acronym>DNS</acronym></title>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1996</abbrev>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<title>A Mechanism for Prompt Notification of Zone Changes</title>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2136</abbrev>
<authorgroup>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<author>
<firstname>S.</firstname>
<surname>Thomson</surname>
</author>
<author>
<firstname>Y.</firstname>
<surname>Rekhter</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Bound</surname>
</author>
</authorgroup>
<title>Dynamic Updates in the Domain Name System</title>
<pubdate>April 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2845</abbrev>
<authorgroup>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<author>
<firstname>O.</firstname>
<surname>Gudmundsson</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Eastlake</surname>
<lineage>3rd</lineage></author>
<author>
<firstname>B.</firstname>
<surname>Wellington</surname>
</author></authorgroup>
<title>Secret Key Transaction Authentication for <acronym>DNS</acronym> (TSIG)</title>
<pubdate>May 2000</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Proposed Standards Still Under Development</title>
<note>
<para><emphasis>Note:</emphasis> the following list of
RFCs are undergoing major revision by the IETF.</para>
</note>
<biblioentry>
<abbrev>RFC1886</abbrev>
<authorgroup>
<author>
<surname>Thomson</surname>
<firstname>S.</firstname>
</author>
<author>
<firstname>C.</firstname>
<surname>Huitema</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> Extensions to support IP version 6</title>
<pubdate>December 1995</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2065</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
<firstname>D.</firstname>
</author>
<author>
<firstname>C.</firstname>
<surname>Kaufman</surname>
</author>
</authorgroup>
<title>Domain Name System Security Extensions</title>
<pubdate>January 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2137</abbrev>
<author>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
<firstname>D.</firstname>
</author>
<title>Secure Domain Name System Dynamic Update</title>
<pubdate>April 1997</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Other Important RFCs About <acronym>DNS</acronym> Implementation</title>
<biblioentry>
<abbrev>RFC1535</abbrev>
<author>
<surname>Gavron</surname>
<firstname>E.</firstname>
</author>
<title>A Security Problem and Proposed Correction With Widely Deployed <acronym>DNS</acronym> Software.</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1536</abbrev>
<authorgroup>
<author>
<surname>Kumar</surname>
<firstname>A.</firstname>
</author>
<author>
<firstname>J.</firstname>
<surname>Postel</surname>
</author>
<author>
<firstname>C.</firstname>
<surname>Neuman</surname></author>
<author>
<firstname>P.</firstname>
<surname>Danzig</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Miller</surname>
</author>
</authorgroup>
<title>Common <acronym>DNS</acronym> Implementation Errors and Suggested Fixes</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1982</abbrev>
<authorgroup>
<author>
<surname>Elz</surname>
<firstname>R.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Bush</surname>
</author>
</authorgroup>
<title>Serial Number Arithmetic</title>
<pubdate>August 1996</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Resource Record Types</title>
<biblioentry>
<abbrev>RFC1183</abbrev>
<authorgroup>
<author>
<surname>Everhart</surname>
<firstname>C.F.</firstname>
</author>
<author>
<firstname>L. A.</firstname>
<surname>Mamakos</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Ullmann</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Mockapetris</surname>
</author>
</authorgroup>
<title>New <acronym>DNS</acronym> RR Definitions</title>
<pubdate>October 1990</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1706</abbrev>
<authorgroup>
<author>
<surname>Manning</surname>
<firstname>B.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Colella</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> NSAP Resource Records</title>
<pubdate>October 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2168</abbrev>
<authorgroup>
<author>
<surname>Daniel</surname>
<firstname>R.</firstname>
</author>
<author>
<firstname>M.</firstname>
<surname>Mealling</surname>
</author>
</authorgroup>
<title>Resolution of Uniform Resource Identifiers using
the Domain Name System</title>
<pubdate>June 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1876</abbrev>
<authorgroup>
<author>
<surname>Davis</surname>
<firstname>C.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
<author>
<firstname>T.</firstname>
<firstname>Goodwin</firstname>
</author>
<author>
<firstname>I.</firstname>
<surname>Dickinson</surname>
</author>
</authorgroup>
<title>A Means for Expressing Location Information in the Domain
Name System</title>
<pubdate>January 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2052</abbrev>
<authorgroup>
<author>
<surname>Gulbrandsen</surname>
<firstname>A.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>A <acronym>DNS</acronym> RR for Specifying the Location of
Services.</title>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2163</abbrev>
<author>
<surname>Allocchio</surname>
<firstname>A.</firstname>
</author>
<title>Using the Internet <acronym>DNS</acronym> to Distribute MIXER
Conformant Global Address Mapping</title>
<pubdate>January 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2230</abbrev>
<author>
<surname>Atkinson</surname>
<firstname>R.</firstname>
</author>
<title>Key Exchange Delegation Record for the <acronym>DNS</acronym></title>
<pubdate>October 1997</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title><acronym>DNS</acronym> and the Internet</title>
<biblioentry>
<abbrev>RFC1101</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P. V.</firstname>
</author>
<title><acronym>DNS</acronym> Encoding of Network Names and Other Types</title>
<pubdate>April 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1123</abbrev>
<author>
<surname>Braden</surname>
<surname>R.</surname>
</author>
<title>Requirements for Internet Hosts - Application and Support</title>
<pubdate>October 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1591</abbrev>
<author>
<surname>Postel</surname>
<firstname>J.</firstname></author>
<title>Domain Name System Structure and Delegation</title>
<pubdate>March 1994</pubdate></biblioentry>
<biblioentry>
<abbrev>RFC2317</abbrev>
<authorgroup>
<author>
<surname>Eidnes</surname>
<firstname>H.</firstname>
</author>
<author>
<firstname>G.</firstname>
<surname>de Groot</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>Classless IN-ADDR.ARPA Delegation</title>
<pubdate>March 1998</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title><acronym>DNS</acronym> Operations</title>
<biblioentry>
<abbrev>RFC1537</abbrev>
<author>
<surname>Beertema</surname>
<firstname>P.</firstname>
</author>
<title>Common <acronym>DNS</acronym> Data File Configuration Errors</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1912</abbrev>
<author>
<surname>Barr</surname>
<firstname>D.</firstname>
</author>
<title>Common <acronym>DNS</acronym> Operational and Configuration Errors</title>
<pubdate>February 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1912</abbrev>
<author>
<surname>Barr</surname>
<firstname>D.</firstname>
</author>
<title>Common <acronym>DNS</acronym> Operational and Configuration Errors</title>
<pubdate>February 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2010</abbrev>
<authorgroup>
<author>
<surname>Manning</surname>
<firstname>B.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>Operational Criteria for Root Name Servers.</title>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2219</abbrev>
<authorgroup>
<author>
<surname>Hamilton</surname>
<firstname>M.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Wright</surname>
</author>
</authorgroup>
<title>Use of <acronym>DNS</acronym> Aliases for Network Services.</title>
<pubdate>October 1997</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Other <acronym>DNS</acronym>-related RFCs</title>
<note>
<para>Note: the following list of RFCs, although
<acronym>DNS</acronym>-related, are not concerned with implementing software.</para>
</note>
<biblioentry>
<abbrev>RFC1464</abbrev>
<author>
<surname>Rosenbaum</surname>
<firstname>R.</firstname>
</author>
<title>Using the Domain Name System To Store Arbitrary String Attributes</title>
<pubdate>May 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1713</abbrev>
<author>
<surname>Romao</surname>
<firstname>A.</firstname>
</author>
<title>Tools for <acronym>DNS</acronym> Debugging</title>
<pubdate>November 1994</pubdate></biblioentry>
<biblioentry>
<abbrev>RFC1794</abbrev>
<author>
<surname>Brisco</surname>
<firstname>T.</firstname>
</author>
<title><acronym>DNS</acronym> Support for Load Balancing</title>
<pubdate>April 1995</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2240</abbrev>
<author>
<surname>Vaughan</surname>
<firstname>O.</firstname></author>
<title>A Legal Basis for Domain Name Allocation</title>
<pubdate>November 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2345</abbrev>
<authorgroup>
<author>
<surname>Klensin</surname>
<firstname>J.</firstname>
</author>
<author>
<firstname>T.</firstname>
<surname>Wolf</surname>
</author>
<author>
<firstname>G.</firstname>
<surname>Oglesby</surname>
</author>
</authorgroup>
<title>Domain Names and Company Name Retrieval</title>
<pubdate>May 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2352</abbrev>
<author>
<surname>Vaughan</surname>
<firstname>O.</firstname>
</author>
<title>A Convention For Using Legal Names as Domain Names</title>
<pubdate>May 1998</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Obsolete and Unimplemented Experimental RRs</title>
<biblioentry>
<abbrev>RFC1712</abbrev>
<authorgroup>
<author>
<surname>Farrell</surname>
<firstname>C.</firstname>
</author>
<author>
<firstname>M.</firstname>
<surname>Schulze</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Pleitner</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Baldoni</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> Encoding of Geographical
Location</title>
<pubdate>November 1994</pubdate>
</biblioentry>
</bibliodiv>
</bibliography>
</sect2>
<sect2 id="internet_drafts">
<title>Internet Drafts</title>
<para>Internet Drafts (IDs) are rough-draft working documents of
the Internet Engineering Task Force. They are, in essence, RFCs
in the preliminary stages of development. Implementors are cautioned not
to regard IDs as archival, and they should not be quoted or cited
in any formal documents unless accompanied by the disclaimer that
they are "works in progress." IDs have a lifespan of six months
after which they are deleted unless updated by their authors.
</para>
</sect2>
<sect2>
<title>Other Documents About <acronym>BIND</acronym></title>
<para></para>
<bibliography>
<biblioentry>
<authorgroup>
<author>
<surname>Albitz</surname>
<firstname>Paul</firstname>
</author>
<author>
<firstname>Cricket</firstname>
<surname>Liu</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> and <acronym>BIND</acronym></title>
<copyright>
<year>1998</year>
<holder>Sebastopol, CA: O'Reilly and Associates</holder>
</copyright>
</biblioentry>
</bibliography>
</sect2>
</sect1>
</appendix>
</book>
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