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Eric Luce 3827c16dce This is the initial addition of the XML version of the BIND v9 ARM. 
These files are based on the BIND v9 ARM in FrameMaker. After these
files are edited they will become the master source for the BIND v9 ARM.

Still need to include style sheets and the actual XML DocBook DTD
for those who do not have it.
2000-09-07 19:15:51 +00:00

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<chapter><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><title id="configuration_file_elements">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,
<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.
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><title id="address_match_lists">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>
<title id="Configuration_File_Grammar">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>
<title id="acl"><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 (<xref linkend="rndc"/>). 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, <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><title id="the_category_phrase">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>option</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> 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>
};
</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>
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><note>
<simpara>This option is obsolete.</simpara></note></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><title id="boolean_options">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><varname>This option is obsolete</varname>.
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, <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 not on,
the server will return a referral to the client if it doesn't know
the answer. The default is <userinput>yes</userinput>. 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><varname>This option is obsolete</varname>.
<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>
</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, <xref linkend="zone_statement_grammar"/>.</para></sect3>
<sect3><title id="name_checking">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><title id="access_control">Access Control</title>
<para>Access to the server can be restricted based on the IP address
of the requesting system. <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. </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 listen on port 53 on the IPv6 wildcard 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><title id="zone_transfers">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</para><para>(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><title id="topology">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>
<title id="the_sortlist_statement">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><title id="rrset_ordering">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><title id="tuning">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 NOT recommended.)
Default is <literal>600</literal> (10 minutes). Maximum value is
<programlisting><literal>1800</literal></programlisting> (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 <programlisting><literal>10800</literal></programlisting> 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>
<title><command id="server_statement_grammar">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><title><command id="server_statement_definition_and_usage">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 a 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><title id="zone_statement_grammar"><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><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><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
<programlisting><literal>DNS NOTIFY</literal></programlisting> 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<varname>.</varname></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><title id="dynamic_update_policies">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>
<title id="types_of_resource_records_and_when_to_use_them">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 - 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-a 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><title id="Setting_TTLs">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>
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