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<div class="chapter" lang="en">
<div class="titlepage"><div><div><h2 class="title">
<a name="Bv9ARM.ch03"></a>Chapter 3. Name Server Configuration</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="Bv9ARM.ch03.html#sample_configuration">Sample Configurations</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch03.html#id2547334">A Caching-only Name Server</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch03.html#id2547350">An Authoritative-only Name Server</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="Bv9ARM.ch03.html#id2547372">Load Balancing</a></span></dt>
<dt><span class="sect1"><a href="Bv9ARM.ch03.html#id2547656">Name Server Operations</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="Bv9ARM.ch03.html#id2547661">Tools for Use With the Name Server Daemon</a></span></dt>
<dt><span class="sect2"><a href="Bv9ARM.ch03.html#id2548915">Signals</a></span></dt>
</dl></dd>
</dl>
</div>
<p>In this section we provide some suggested configurations along
with guidelines for their use. We also address the topic of reasonable
option setting.</p>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sample_configuration"></a>Sample Configurations</h2></div></div></div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2547334"></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><strong class="command">allow-query</strong></span>
option. Alternatively, the same effect could 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 {
directory "/etc/namedb"; // Working directory
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="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2547350"></a>An Authoritative-only Name Server</h3></div></div></div>
<p>This sample configuration is for an authoritative-only server
that is the master server for "<code class="filename">example.com</code>"
and a slave for the subdomain "<code class="filename">eng.example.com</code>".</p>
<pre class="programlisting">
options {
directory "/etc/namedb"; // Working directory
allow-query { any; }; // This is the default
recursion no; // Do not provide recursive service
};
// Provide a reverse mapping for the loopback address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the master server for example.com
zone "example.com" {
type master;
file "example.com.db";
// IP addresses of slave servers allowed to transfer example.com
allow-transfer {
192.168.4.14;
192.168.5.53;
};
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
type slave;
file "eng.example.com.bk";
// IP address of eng.example.com master server
masters { 192.168.4.12; };
};
</pre>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2547372"></a>Load Balancing</h2></div></div></div>
<p>A primitive form of load balancing can be achieved in
the <span class="acronym">DNS</span> by using multiple A records for one name.</p>
<p>For example, if you have three WWW servers with network addresses
of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a set of records such as the
following means that clients will connect to each machine one third
of the time:</p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
<col>
<col>
<col>
</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, <span class="acronym">BIND</span> will rotate
them and respond to the query with the records in a different
order. In the example above, clients will randomly receive
records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
will use the first record returned and discard the rest.</p>
<p>For more detail on ordering responses, check the
<span><strong class="command">rrset-order</strong></span> substatement in the
<span><strong class="command">options</strong></span> statement, see
<a href="Bv9ARM.ch06.html#rrset_ordering">RRset Ordering</a>.
This substatement is not supported in
<span class="acronym">BIND</span> 9, and only the ordering scheme described above is
available.</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2547656"></a>Name Server Operations</h2></div></div></div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2547661"></a>Tools for Use With the Name Server Daemon</h3></div></div></div>
<p>There are several indispensable diagnostic, administrative
and monitoring tools available to the system administrator for controlling
and debugging the name server daemon. We describe several in this
section </p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="diagnostic_tools"></a>Diagnostic Tools</h4></div></div></div>
<p>The <span><strong class="command">dig</strong></span>, <span><strong class="command">host</strong></span>, and
<span><strong class="command">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>
<dt><span class="term"><a name="dig"></a><span><strong class="command">dig</strong></span></span></dt>
<dd>
<p>The domain information groper (<span><strong class="command">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 dig will take the form</p>
<p><span><strong class="command">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><strong class="command">dig</strong></span> man page.</p>
</dd>
<dt><span class="term"><span><strong class="command">host</strong></span></span></dt>
<dd>
<p>The <span><strong class="command">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> [-aCdlrTwv] [-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>] <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><strong class="command">host</strong></span> man page.</p>
</dd>
<dt><span class="term"><span><strong class="command">nslookup</strong></span></span></dt>
<dd>
<p><span><strong class="command">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 will be used) or when the first argument is a
hyphen (`-') and the second argument is the host name or Internet address
of a name server.</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><strong class="command">nslookup</strong></span>.
Use <span><strong class="command">dig</strong></span> instead.</p>
</dd>
</dl></div>
</div>
<div class="sect3" lang="en">
<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>
<dt>
<a name="named-checkconf"></a><span class="term"><span><strong class="command">named-checkconf</strong></span></span>
</dt>
<dd>
<p>The <span><strong class="command">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><strong class="command">named-checkzone</strong></span></span>
</dt>
<dd>
<p>The <span><strong class="command">named-checkzone</strong></span> program checks a master 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>] <em class="replaceable"><code>zone</code></em> [<em class="replaceable"><code>filename</code></em>]</p></div>
</dd>
<dt>
<a name="rndc"></a><span class="term"><span><strong class="command">rndc</strong></span></span>
</dt>
<dd>
<p>The remote name daemon control
(<span><strong class="command">rndc</strong></span>) program allows the system
administrator to control the operation of a name server.
If you run <span><strong class="command">rndc</strong></span> without any options
it will display 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><span><strong class="command">command</strong></span> is one of the following:</p>
<div class="variablelist"><dl>
<dt><span class="term"><strong class="userinput"><code>reload</code></strong></span></dt>
<dd><p>Reload configuration file and zones.</p></dd>
<dt><span class="term"><strong class="userinput"><code>reload <em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</code></strong></span></dt>
<dd><p>Reload the given zone.</p></dd>
<dt><span class="term"><strong class="userinput"><code>refresh <em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</code></strong></span></dt>
<dd><p>Schedule zone maintenance for the given zone.</p></dd>
<dt><span class="term"><strong class="userinput"><code>retransfer <em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</code></strong></span></dt>
<dd><p>Retransfer the given zone from the master.</p></dd>
<dt><span class="term"><strong class="userinput"><code>freeze [<span class="optional"><em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</span>]</code></strong></span></dt>
<dd><p>Suspend updates to a dynamic zone. If no zone is specified
then all zones are suspended. This allows manual
edits to be made to a zone normally updated by dynamic update. It
also causes changes in the journal file to be synced into the master
and the journal file to be removed. All dynamic update attempts will
be refused while the zone is frozen.</p></dd>
<dt><span class="term"><strong class="userinput"><code>thaw [<span class="optional"><em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</span>]</code></strong></span></dt>
<dd><p>Enable updates to a frozen dynamic zone. If no zone is
specified then all frozen zones are enabled. This causes
the server to reload the zone from disk, and re-enables dynamic updates
after the load has completed. After a zone is thawed, dynamic updates
will no longer be refused.</p></dd>
<dt><span class="term"><strong class="userinput"><code>notify <em class="replaceable"><code>zone</code></em>
[<span class="optional"><em class="replaceable"><code>class</code></em>
[<span class="optional"><em class="replaceable"><code>view</code></em></span>]</span>]</code></strong></span></dt>
<dd><p>Resend NOTIFY messages for the zone</p></dd>
<dt><span class="term"><strong class="userinput"><code>reconfig</code></strong></span></dt>
<dd><p>Reload the configuration file and load new zones,
but do not reload existing zone files even if they have changed.
This is faster than a full <span><strong class="command">reload</strong></span> when there
is a large number of zones because it avoids the need to examine the
modification times of the zones files.
</p></dd>
<dt><span class="term"><strong class="userinput"><code>stats</code></strong></span></dt>
<dd><p>Write server statistics to the statistics file.</p></dd>
<dt><span class="term"><strong class="userinput"><code>querylog</code></strong></span></dt>
<dd><p>Toggle query logging. Query logging can also be enabled
by explicitly directing the <span><strong class="command">queries</strong></span>
<span><strong class="command">category</strong></span> to a <span><strong class="command">channel</strong></span> in the
<span><strong class="command">logging</strong></span> section of
<code class="filename">named.conf</code>.</p></dd>
<dt><span class="term"><strong class="userinput"><code>dumpdb [<span class="optional">-all|-cache|-zone</span>] [<span class="optional"><em class="replaceable"><code>view ...</code></em></span>]</code></strong></span></dt>
<dd><p>Dump the server's caches (default) and / or zones to the
dump file for the specified views. If no view is specified all
views are dumped.</p></dd>
<dt><span class="term"><strong class="userinput"><code>stop [<span class="optional">-p</span>]</code></strong></span></dt>
<dd><p>Stop the server, making sure any recent changes
made through dynamic update or IXFR are first saved to the master files
of the updated zones. If -p is specified named's process id is returned.</p></dd>
<dt><span class="term"><strong class="userinput"><code>halt [<span class="optional">-p</span>]</code></strong></span></dt>
<dd><p>Stop the server immediately. Recent changes
made through dynamic update or IXFR are not saved to the master files,
but will be rolled forward from the journal files when the server
is restarted. If -p is specified named's process id is returned.</p></dd>
<dt><span class="term"><strong class="userinput"><code>trace</code></strong></span></dt>
<dd><p>Increment the servers debugging level by one. </p></dd>
<dt><span class="term"><strong class="userinput"><code>trace <em class="replaceable"><code>level</code></em></code></strong></span></dt>
<dd><p>Sets the server's debugging level to an explicit
value.</p></dd>
<dt><span class="term"><strong class="userinput"><code>notrace</code></strong></span></dt>
<dd><p>Sets the server's debugging level to 0.</p></dd>
<dt><span class="term"><strong class="userinput"><code>flush</code></strong></span></dt>
<dd><p>Flushes the server's cache.</p></dd>
<dt><span class="term"><strong class="userinput"><code>flushname</code></strong> <em class="replaceable"><code>name</code></em></span></dt>
<dd><p>Flushes the given name from the server's cache.</p></dd>
<dt><span class="term"><strong class="userinput"><code>status</code></strong></span></dt>
<dd><p>Display status of the server.
Note the number of zones includes the internal <span><strong class="command">bind/CH</strong></span> zone
and the default <span><strong class="command">./IN</strong></span> hint zone if there is not a
explicit root zone configured.</p></dd>
<dt><span class="term"><strong class="userinput"><code>recursing</code></strong></span></dt>
<dd><p>Dump the list of queries named is currently recursing
on.
</p></dd>
</dl></div>
<p>In <span class="acronym">BIND</span> 9.2, <span><strong class="command">rndc</strong></span>
supports all the commands of the BIND 8 <span><strong class="command">ndc</strong></span>
utility except <span><strong class="command">ndc start</strong></span> and
<span><strong class="command">ndc restart</strong></span>, which were also
not supported in <span><strong class="command">ndc</strong></span>'s channel mode.</p>
<p>A configuration file is required, since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
<span><strong class="command">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><strong class="command">rndc</strong></span> will also look in
<code class="filename">/etc/rndc.key</code> (or whatever
<code class="varname">sysconfdir</code> was defined when
the <span class="acronym">BIND</span> build was configured).
The <code class="filename">rndc.key</code> file is generated by
running <span><strong class="command">rndc-confgen -a</strong></span> as described in
<a href="Bv9ARM.ch06.html#controls_statement_definition_and_usage" title="controls Statement Definition and Usage">the section called “<span><strong class="command">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 limited to
only four statements, the <span><strong class="command">options</strong></span>,
<span><strong class="command">key</strong></span>, <span><strong class="command">server</strong></span> and
<span><strong class="command">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><strong class="command">options</strong></span> statement has three clauses:
<span><strong class="command">default-server</strong></span>, <span><strong class="command">default-key</strong></span>,
and <span><strong class="command">default-port</strong></span>.
<span><strong class="command">default-server</strong></span> takes a
host name or address argument and represents the server that will
be contacted if no <code class="option">-s</code>
option is provided on the command line.
<span><strong class="command">default-key</strong></span> takes
the name of a key as its argument, as defined by a <span><strong class="command">key</strong></span> statement.
<span><strong class="command">default-port</strong></span> specifies the port to which
<span><strong class="command">rndc</strong></span> should connect if no
port is given on the command line or in a
<span><strong class="command">server</strong></span> statement.</p>
<p>The <span><strong class="command">key</strong></span> statement defines an key to be used
by <span><strong class="command">rndc</strong></span> when authenticating with
<span><strong class="command">named</strong></span>. Its syntax is identical to the
<span><strong class="command">key</strong></span> statement in named.conf.
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><strong class="command">key</strong></span> statement has two clauses:
<span><strong class="command">algorithm</strong></span> and <span><strong class="command">secret</strong></span>.
While the configuration parser will accept any string as the argument
to algorithm, currently only the string "<strong class="userinput"><code>hmac-md5</code></strong>"
has any meaning. The secret is a base-64 encoded string.</p>
<p>The <span><strong class="command">server</strong></span> statement associates a key
defined using the <span><strong class="command">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><strong class="command">server</strong></span> statement
has two clauses: <span><strong class="command">key</strong></span> and <span><strong class="command">port</strong></span>.
The <span><strong class="command">key</strong></span> clause specifies the name of the key
to be used when communicating with this server, and the
<span><strong class="command">port</strong></span> clause can be used to
specify the port <span><strong class="command">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-md5";
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>,
would allow 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 cause the name server
to reload, if a name server on the local machine were running with
following controls statements:</p>
<pre class="programlisting">
controls {
inet 127.0.0.1 allow { localhost; } keys { rndc_key; };
};
</pre>
<p>and it had an identical key statement for
<code class="literal">rndc_key</code>.</p>
<p>Running the <span><strong class="command">rndc-confgen</strong></span> program will
conveniently create a <code class="filename">rndc.conf</code>
file for you, and also display the
corresponding <span><strong class="command">controls</strong></span> statement that you need to
add to <code class="filename">named.conf</code>. Alternatively,
you can run <span><strong class="command">rndc-confgen -a</strong></span> to set up
a <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="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2548915"></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><strong class="command">kill</strong></span> command.</p>
<div class="informaltable"><table border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td><p><span><strong class="command">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><strong class="command">SIGTERM</strong></span></p></td>
<td><p>Causes the server to clean up and exit.</p></td>
</tr>
<tr>
<td>
<p><span><strong class="command">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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