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<div class="chapter">
<div class="titlepage"><div><div><h1 class="title">
<a name="Bv9ARM.ch03"></a>Chapter�3.�Name Server Configuration</h1></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dt><span class="section"><a href="Bv9ARM.ch03.html#sample_configuration">Sample Configurations</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch03.html#cache_only_sample">A Caching-only Name Server</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch03.html#auth_only_sample">An Authoritative-only Name Server</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch03.html#load_balancing">Load Balancing</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch03.html#ns_operations">Name Server Operations</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch03.html#tools">Tools for Use With the Name Server Daemon</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch03.html#signals">Signals</a></span></dt>
</dl></dd>
</dl>
</div>
<p>
In this chapter we provide some suggested configurations, along
with guidelines for their use. We suggest reasonable values for
certain option settings.
</p>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sample_configuration"></a>Sample Configurations</h2></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="cache_only_sample"></a>A Caching-only Name Server</h3></div></div></div>
<p>
The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation. All
queries
from outside clients are refused using the <span class="command"><strong>allow-query</strong></span>
option. The same effect can be achieved using
suitable
firewall rules.
</p>
<pre class="programlisting">
// Two corporate subnets we wish to allow queries from.
acl corpnets { 192.168.4.0/24; 192.168.7.0/24; };
options {
// Working directory
directory "/etc/namedb";
allow-query { corpnets; };
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="auth_only_sample"></a>An Authoritative-only Name Server</h3></div></div></div>
<p>
This sample configuration is for an authoritative-only server
that is the primary server for "<code class="filename">example.com</code>"
and a secondary server for the subdomain "<code class="filename">eng.example.com</code>".
</p>
<pre class="programlisting">
options {
// Working directory
directory "/etc/namedb";
// Do not allow access to cache
allow-query-cache { none; };
// This is the default
allow-query { any; };
// Do not provide recursive service
recursion no;
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the primary server for example.com
zone "example.com" {
type master;
file "example.com.db";
// IP addresses of secondary servers allowed to
// transfer example.com
allow-transfer {
192.168.4.14;
192.168.5.53;
};
};
// We are a secondary server for eng.example.com
zone "eng.example.com" {
type slave;
file "eng.example.com.bk";
// IP address of eng.example.com primary server
masters { 192.168.4.12; };
};
</pre>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="load_balancing"></a>Load Balancing</h2></div></div></div>
<p>
A primitive form of load balancing can be achieved in
the <acronym class="acronym">DNS</acronym> by using multiple records
(such as multiple A records) for one name.
</p>
<p>
For example, assuming three HTTP servers with network addresses
of 10.0.0.1, 10.0.0.2, and 10.0.0.3, a set of records such as the
following means that clients will connect to each machine one-third
of the time:
</p>
<div class="informaltable"><table class="informaltable" border="1">
<colgroup>
<col width="0.875in" class="1">
<col width="0.500in" class="2">
<col width="0.750in" class="3">
<col width="0.750in" class="4">
<col width="2.028in" class="5">
</colgroup>
<tbody>
<tr>
<td>
<p>
Name
</p>
</td>
<td>
<p>
TTL
</p>
</td>
<td>
<p>
CLASS
</p>
</td>
<td>
<p>
TYPE
</p>
</td>
<td>
<p>
Resource Record (RR) Data
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="literal">www</code>
</p>
</td>
<td>
<p>
<code class="literal">600</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.1</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">600</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.2</code>
</p>
</td>
</tr>
<tr>
<td>
<p></p>
</td>
<td>
<p>
<code class="literal">600</code>
</p>
</td>
<td>
<p>
<code class="literal">IN</code>
</p>
</td>
<td>
<p>
<code class="literal">A</code>
</p>
</td>
<td>
<p>
<code class="literal">10.0.0.3</code>
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
When a resolver queries for these records, <acronym class="acronym">BIND</acronym> rotates
them and responds to the query with the records in a different
order. In the example above, clients randomly receive
records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
use the first record returned and discard the rest.
</p>
<p>
For more detail on ordering responses, check the
<span class="command"><strong>rrset-order</strong></span> sub-statement in the
<span class="command"><strong>options</strong></span> statement, see
<a class="xref" href="Bv9ARM.ch06.html#rrset_ordering" title="RRset Ordering">RRset Ordering</a>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="ns_operations"></a>Name Server Operations</h2></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="tools"></a>Tools for Use With the Name Server Daemon</h3></div></div></div>
<p>
This section describes several indispensable diagnostic,
administrative, and monitoring tools available to the system
administrator for controlling and debugging the name server
daemon.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="diagnostic_tools"></a>Diagnostic Tools</h4></div></div></div>
<p>
The <span class="command"><strong>dig</strong></span>, <span class="command"><strong>host</strong></span>, and
<span class="command"><strong>nslookup</strong></span> programs are all command-line tools
for manually querying name servers. They differ in style and
output format.
</p>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term"><a name="dig"></a><span class="command"><strong>dig</strong></span></span></dt>
<dd>
<p>
<span class="command"><strong>dig</strong></span>
is the most versatile and complete of these lookup tools.
It has two modes: simple interactive
mode for a single query, and batch mode, which executes a
query for
each in a list of several query lines. All query options are
accessible
from the command line.
</p>
<div class="cmdsynopsis"><p><code class="command">dig</code> [@<em class="replaceable"><code>server</code></em>] <em class="replaceable"><code>domain</code></em> [<em class="replaceable"><code>query-type</code></em>] [<em class="replaceable"><code>query-class</code></em>] [+<em class="replaceable"><code>query-option</code></em>] [-<em class="replaceable"><code>dig-option</code></em>] [%<em class="replaceable"><code>comment</code></em>]</p></div>
<p>
The usual simple use of <span class="command"><strong>dig</strong></span> takes the form
</p>
<p class="simpara">
<span class="command"><strong>dig @server domain query-type query-class</strong></span>
</p>
<p>
For more information and a list of available commands and
options, see the <span class="command"><strong>dig</strong></span> man
page.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>host</strong></span></span></dt>
<dd>
<p>
The <span class="command"><strong>host</strong></span> utility emphasizes
simplicity
and ease of use. By default, it converts
between host names and Internet addresses, but its
functionality
can be extended with the use of options.
</p>
<div class="cmdsynopsis"><p><code class="command">host</code> [-aCdlnrsTwv] [-c <em class="replaceable"><code>class</code></em>] [-N <em class="replaceable"><code>ndots</code></em>] [-t <em class="replaceable"><code>type</code></em>] [-W <em class="replaceable"><code>timeout</code></em>] [-R <em class="replaceable"><code>retries</code></em>] [-m <em class="replaceable"><code>flag</code></em>] [-4] [-6] <em class="replaceable"><code>hostname</code></em> [<em class="replaceable"><code>server</code></em>]</p></div>
<p>
For more information and a list of available commands and
options, see the <span class="command"><strong>host</strong></span> man
page.
</p>
</dd>
<dt><span class="term"><span class="command"><strong>nslookup</strong></span></span></dt>
<dd>
<p><span class="command"><strong>nslookup</strong></span>
has two modes: interactive and
non-interactive. Interactive mode allows the user to
query name servers for information about various
hosts and domains, or to print a list of hosts in a
domain. Non-interactive mode is used to print just
the name and requested information for a host or
domain.
</p>
<div class="cmdsynopsis"><p><code class="command">nslookup</code> [-option...] [[<em class="replaceable"><code>host-to-find</code></em>] | [- [server]]]</p></div>
<p>
Interactive mode is entered when no arguments are given (the
default name server is used) or when the first argument
is a
hyphen ("-") and the second argument is the host name or
Internet address
of a name server.
</p>
<p>
Non-interactive mode is used when the name or Internet
address
of the host to be looked up is given as the first argument.
The
optional second argument specifies the host name or address
of a name server.
</p>
<p>
Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of <span class="command"><strong>nslookup</strong></span>.
Use <span class="command"><strong>dig</strong></span> instead.
</p>
</dd>
</dl></div>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="admin_tools"></a>Administrative Tools</h4></div></div></div>
<p>
Administrative tools play an integral part in the management
of a server.
</p>
<div class="variablelist"><dl class="variablelist">
<dt>
<a name="named-checkconf"></a><span class="term"><span class="command"><strong>named-checkconf</strong></span></span>
</dt>
<dd>
<p>
The <span class="command"><strong>named-checkconf</strong></span> program
checks the syntax of a <code class="filename">named.conf</code> file.
</p>
<div class="cmdsynopsis"><p><code class="command">named-checkconf</code> [-jvz] [-t <em class="replaceable"><code>directory</code></em>] [<em class="replaceable"><code>filename</code></em>]</p></div>
</dd>
<dt>
<a name="named-checkzone"></a><span class="term"><span class="command"><strong>named-checkzone</strong></span></span>
</dt>
<dd>
<p>
The <span class="command"><strong>named-checkzone</strong></span> program
checks a zone file for
syntax and consistency.
</p>
<div class="cmdsynopsis"><p><code class="command">named-checkzone</code> [-djqvD] [-c <em class="replaceable"><code>class</code></em>] [-o <em class="replaceable"><code>output</code></em>] [-t <em class="replaceable"><code>directory</code></em>] [-w <em class="replaceable"><code>directory</code></em>] [-k <em class="replaceable"><code>(ignore|warn|fail)</code></em>] [-n <em class="replaceable"><code>(ignore|warn|fail)</code></em>] [-W <em class="replaceable"><code>(ignore|warn)</code></em>] <em class="replaceable"><code>zone</code></em> [<em class="replaceable"><code>filename</code></em>]</p></div>
</dd>
<dt>
<a name="named-compilezone"></a><span class="term"><span class="command"><strong>named-compilezone</strong></span></span>
</dt>
<dd><p>
This tool is similar to <span class="command"><strong>named-checkzone,</strong></span> but
it always dumps the zone content to a specified file
(typically in a different format).
</p></dd>
<dt>
<a name="rndc"></a><span class="term"><span class="command"><strong>rndc</strong></span></span>
</dt>
<dd>
<p>
The remote name daemon control
(<span class="command"><strong>rndc</strong></span>) program allows the
system
administrator to control the operation of a name server.
If <span class="command"><strong>rndc</strong></span> is run without any
options,
it displays a usage message as follows:
</p>
<div class="cmdsynopsis"><p><code class="command">rndc</code> [-c <em class="replaceable"><code>config</code></em>] [-s <em class="replaceable"><code>server</code></em>] [-p <em class="replaceable"><code>port</code></em>] [-y <em class="replaceable"><code>key</code></em>] <em class="replaceable"><code>command</code></em> [<em class="replaceable"><code>command</code></em>...]</p></div>
<p>See <a class="xref" href="man.rndc.html" title="rndc"><span class="refentrytitle"><span class="application">rndc</span></span>(8)</a> for details of
the available <span class="command"><strong>rndc</strong></span> commands.
</p>
<p>
<span class="command"><strong>rndc</strong></span> requires a configuration file,
since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
<span class="command"><strong>rndc</strong></span> configuration file is
<code class="filename">/etc/rndc.conf</code>, but an
alternate
location can be specified with the <code class="option">-c</code>
option. If the configuration file is not found,
<span class="command"><strong>rndc</strong></span> also looks in
<code class="filename">/etc/rndc.key</code> (or whatever
<code class="varname">sysconfdir</code> was defined when
the <acronym class="acronym">BIND</acronym> build was
configured).
The <code class="filename">rndc.key</code> file is
generated by
running <span class="command"><strong>rndc-confgen -a</strong></span> as
described in
<a class="xref" href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and Usage">the section called “<span class="command"><strong>controls</strong></span> Statement Definition and
Usage”</a>.
</p>
<p>
The format of the configuration file is similar to
that of <code class="filename">named.conf</code>, but is
limited to
only four statements: the <span class="command"><strong>options</strong></span>,
<span class="command"><strong>key</strong></span>, <span class="command"><strong>server</strong></span>, and
<span class="command"><strong>include</strong></span>
statements. These statements are what associate the
secret keys to the servers with which they are meant to
be shared. The order of statements is not
significant.
</p>
<p>
The <span class="command"><strong>options</strong></span> statement has
three clauses:
<span class="command"><strong>default-server</strong></span>, <span class="command"><strong>default-key</strong></span>,
and <span class="command"><strong>default-port</strong></span>.
<span class="command"><strong>default-server</strong></span> takes a
host name or address argument and represents the server
that
is contacted if no <code class="option">-s</code>
option is provided on the command line.
<span class="command"><strong>default-key</strong></span> takes
the name of a key as its argument, as defined by a <span class="command"><strong>key</strong></span> statement.
<span class="command"><strong>default-port</strong></span> specifies the
port to which
<span class="command"><strong>rndc</strong></span> should connect if no
port is given on the command line or in a
<span class="command"><strong>server</strong></span> statement.
</p>
<p>
The <span class="command"><strong>key</strong></span> statement defines a
key to be used
by <span class="command"><strong>rndc</strong></span> when authenticating
with
<span class="command"><strong>named</strong></span>. Its syntax is
identical to the
<span class="command"><strong>key</strong></span> statement in <code class="filename">named.conf</code>.
The keyword <strong class="userinput"><code>key</code></strong> is
followed by a key name, which must be a valid
domain name, though it need not actually be hierarchical;
thus,
a string like "<strong class="userinput"><code>rndc_key</code></strong>" is a valid
name.
The <span class="command"><strong>key</strong></span> statement has two
clauses:
<span class="command"><strong>algorithm</strong></span> and <span class="command"><strong>secret</strong></span>.
While the configuration parser accepts any string as the
argument
to <span class="command"><strong>algorithm</strong></span>, currently only the strings
"<strong class="userinput"><code>hmac-md5</code></strong>",
"<strong class="userinput"><code>hmac-sha1</code></strong>",
"<strong class="userinput"><code>hmac-sha224</code></strong>",
"<strong class="userinput"><code>hmac-sha256</code></strong>",
"<strong class="userinput"><code>hmac-sha384</code></strong>",
and "<strong class="userinput"><code>hmac-sha512</code></strong>"
have any meaning. The secret is a Base64-encoded string
as specified in RFC 3548.
</p>
<p>
The <span class="command"><strong>server</strong></span> statement
associates a key
defined using the <span class="command"><strong>key</strong></span>
statement with a server.
The keyword <strong class="userinput"><code>server</code></strong> is followed by a
host name or address. The <span class="command"><strong>server</strong></span> statement
has two clauses: <span class="command"><strong>key</strong></span> and <span class="command"><strong>port</strong></span>.
The <span class="command"><strong>key</strong></span> clause specifies the
name of the key
to be used when communicating with this server, and the
<span class="command"><strong>port</strong></span> clause can be used to
specify the port <span class="command"><strong>rndc</strong></span> should
connect
to on the server.
</p>
<p>
A sample minimal configuration file is as follows:
</p>
<pre class="programlisting">
key rndc_key {
algorithm "hmac-sha256";
secret
"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
default-server 127.0.0.1;
default-key rndc_key;
};
</pre>
<p>
This file, if installed as <code class="filename">/etc/rndc.conf</code>,
allows the command:
</p>
<p>
<code class="prompt">$ </code><strong class="userinput"><code>rndc reload</code></strong>
</p>
<p>
to connect to 127.0.0.1 port 953 and causes the name server
to reload, if a name server on the local machine is
running with
following controls statements:
</p>
<pre class="programlisting">
controls {
inet 127.0.0.1
allow { localhost; } keys { rndc_key; };
};
</pre>
<p>
and it has an identical key statement for
<code class="literal">rndc_key</code>.
</p>
<p>
Running the <span class="command"><strong>rndc-confgen</strong></span>
program
conveniently creates an <code class="filename">rndc.conf</code>
file, and also displays the
corresponding <span class="command"><strong>controls</strong></span>
statement needed to
add to <code class="filename">named.conf</code>.
Alternatively,
it is possible to run <span class="command"><strong>rndc-confgen -a</strong></span>
to set up
an <code class="filename">rndc.key</code> file and not
modify
<code class="filename">named.conf</code> at all.
</p>
</dd>
</dl></div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="signals"></a>Signals</h3></div></div></div>
<p>
Certain Unix signals cause the name server to take specific
actions, as described in the following table. These signals can
be sent using the <span class="command"><strong>kill</strong></span> command.
</p>
<div class="informaltable"><table class="informaltable" border="1">
<colgroup>
<col width="1.125in" class="1">
<col width="4.000in" class="2">
</colgroup>
<tbody>
<tr>
<td>
<p><span class="command"><strong>SIGHUP</strong></span></p>
</td>
<td>
<p>
Causes the server to read <code class="filename">named.conf</code> and
reload the database.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>SIGTERM</strong></span></p>
</td>
<td>
<p>
Causes the server to clean up and exit.
</p>
</td>
</tr>
<tr>
<td>
<p><span class="command"><strong>SIGINT</strong></span></p>
</td>
<td>
<p>
Causes the server to clean up and exit.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
</div>
</div>
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<td width="40%" align="right" valign="top">�Chapter�4.�Advanced DNS Features</td>
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<p xmlns:db="http://docbook.org/ns/docbook" style="text-align: center;">BIND 9.11.36 (Extended Support Version)</p>
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