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90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<title>Chapter�4.�Advanced DNS Features</title>
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2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<tr><th colspan="3" align="center">Chapter�4.�Advanced DNS Features</th></tr>
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2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<a accesskey="p" href="Bv9ARM.ch03.html">Prev</a>�</td>
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2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<td width="20%" align="right">�<a accesskey="n" href="Bv9ARM.ch05.html">Next</a>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</td>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</tr>
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90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<hr>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="chapter" lang="en">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="titlepage"><div><div><h2 class="title">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<a name="Bv9ARM.ch04"></a>Chapter�4.�Advanced DNS Features</h2></div></div></div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="toc">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p><b>Table of Contents</b></p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dl>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#notify">Notify</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#dynamic_update">Dynamic Update</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#journal">The journal file</a></span></dt></dl></dd>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#incremental_zone_transfers">Incremental Zone Transfers (IXFR)</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2570510">Split DNS</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2570529">Example split DNS setup</a></span></dt></dl></dd>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#tsig">TSIG</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dd><dl>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571030">Generate Shared Keys for Each Pair of Hosts</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571104">Copying the Shared Secret to Both Machines</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571114">Informing the Servers of the Key's Existence</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2563989">Instructing the Server to Use the Key</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2564115">TSIG Key Based Access Control</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2564163">Errors</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</dl></dd>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2571549">TKEY</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2571598">SIG(0)</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#DNSSEC">DNSSEC</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dd><dl>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571803">Generating Keys</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571950">Signing the Zone</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2572032">Configuring Servers</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</dl></dd>
010a51c427bfb6ab658fc0056955a1a5b69810beTinderbox User<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2572201">IPv6 Support in <acronym class="acronym">BIND</acronym> 9</a></span></dt>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dd><dl>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2572400">Address Lookups Using AAAA Records</a></span></dt>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2572421">Address to Name Lookups Using Nibble Format</a></span></dt>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User</dl></dd>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User</dl>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</div>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<div class="sect1" lang="en">
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<div class="titlepage"><div><div><h2 class="title" style="clear: both">
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<a name="notify"></a>Notify</h2></div></div></div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater <acronym class="acronym">DNS</acronym> NOTIFY is a mechanism that allows master
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater servers to notify their slave servers of changes to a zone's data. In
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater response to a <span><strong class="command">NOTIFY</strong></span> from a master server, the
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater slave will check to see that its version of the zone is the
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User current version and, if not, initiate a zone transfer.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
010a51c427bfb6ab658fc0056955a1a5b69810beTinderbox User For more information about <acronym class="acronym">DNS</acronym>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">NOTIFY</strong></span>, see the description of the
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">notify</strong></span> option in <a href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called &#8220;Boolean Options&#8221;</a> and
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User the description of the zone option <span><strong class="command">also-notify</strong></span> in
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont <a href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called &#8220;Zone Transfers&#8221;</a>. The <span><strong class="command">NOTIFY</strong></span>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont protocol is specified in RFC 1996.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
8e821eea5f57ac47a94305aa7ab0c3570d92a311Automatic Updater<h3 class="title">Note</h3>
aaaf8d4f4873d21e55c3ffb4f656203d08339865Mark Andrews As a slave zone can also be a master to other slaves, <span><strong class="command">named</strong></span>,
aaaf8d4f4873d21e55c3ffb4f656203d08339865Mark Andrews by default, sends <span><strong class="command">NOTIFY</strong></span> messages for every zone
731cc132f22dbc9e0ecd7035dce314a61076d31bAutomatic Updater it loads. Specifying <span><strong class="command">notify master-only;</strong></span> will
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont cause <span><strong class="command">named</strong></span> to only send <span><strong class="command">NOTIFY</strong></span> for master
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User zones that it loads.
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater </div>
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater</div>
8e821eea5f57ac47a94305aa7ab0c3570d92a311Automatic Updater<div class="sect1" lang="en">
8e821eea5f57ac47a94305aa7ab0c3570d92a311Automatic Updater<div class="titlepage"><div><div><h2 class="title" style="clear: both">
8e821eea5f57ac47a94305aa7ab0c3570d92a311Automatic Updater<a name="dynamic_update"></a>Dynamic Update</h2></div></div></div>
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Dynamic Update is a method for adding, replacing or deleting
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont records in a master server by sending it a special form of DNS
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont messages. The format and meaning of these messages is specified
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont in RFC 2136.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont Dynamic update is enabled by including an
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">allow-update</strong></span>, <span><strong class="command">update-policy</strong></span>
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater clause in the <span><strong class="command">zone</strong></span> statement, or by setting the
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">ddns-autconf</strong></span> option to <strong class="userinput"><code>yes</code></strong>.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater<p>
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater If the zone's <span><strong class="command">ddns-autoconf</strong></span> option is set to
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater <strong class="userinput"><code>yes</code></strong>, then updates to the zone
2a6d4c9948b3f4f31311bd799d114585a30419a9Automatic Updater will be permitted for the key <code class="filename">ddns.key</code>,
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User which will be generated by <span><strong class="command">named</strong></span> at startup.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
8ec3c085233cedb22b05da36e2773c8f357a7e45Automatic Updater<p>
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User The <span><strong class="command">tkey-gssapi-credential</strong></span> and
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">tkey-domain</strong></span> clauses in the
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User <span><strong class="command">options</strong></span> statement enable the
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User server to negotiate keys that can be matched against those
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User in <span><strong class="command">update-policy</strong></span> or
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User <span><strong class="command">allow-update</strong></span>.
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User </p>
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User<p>
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User Updating of secure zones (zones using DNSSEC) follows RFC
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User 3007: RRSIG, NSEC and NSEC3 records affected by updates are
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User automatically regenerated by the server using an online
6ea2385360e9e2167e65f9286447da9eea189457Tinderbox User zone key. Update authorization is based on transaction
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User signatures and an explicit server policy.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<div class="sect2" lang="en">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="titlepage"><div><div><h3 class="title">
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<a name="journal"></a>The journal file</h3></div></div></div>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User All changes made to a zone using dynamic update are stored
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User in the zone's journal file. This file is automatically created
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User by the server when the first dynamic update takes place.
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User The name of the journal file is formed by appending the extension
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User <code class="filename">.jnl</code> to the name of the
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User corresponding zone
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User file unless specifically overridden. The journal file is in a
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User binary format and should not be edited manually.
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User </p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User The server will also occasionally write ("dump")
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User the complete contents of the updated zone to its zone file.
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User This is not done immediately after
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User each dynamic update, because that would be too slow when a large
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User zone is updated frequently. Instead, the dump is delayed by
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User up to 15 minutes, allowing additional updates to take place.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User When a server is restarted after a shutdown or crash, it will replay
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User the journal file to incorporate into the zone any updates that
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User took
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User place after the last zone dump.
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User </p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User<p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User Changes that result from incoming incremental zone transfers are
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User also
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont journalled in a similar way.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont The zone files of dynamic zones cannot normally be edited by
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont hand because they are not guaranteed to contain the most recent
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont dynamic changes &#8212; those are only in the journal file.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont The only way to ensure that the zone file of a dynamic zone
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont is up to date is to run <span><strong class="command">rndc stop</strong></span>.
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User If you have to make changes to a dynamic zone
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater manually, the following procedure will work: Disable dynamic updates
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User to the zone using
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">rndc freeze <em class="replaceable"><code>zone</code></em></strong></span>.
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater This will also remove the zone's <code class="filename">.jnl</code> file
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User and update the master file. Edit the zone file. Run
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater <span><strong class="command">rndc thaw <em class="replaceable"><code>zone</code></em></strong></span>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater to reload the changed zone and re-enable dynamic updates.
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater </p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater</div>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater</div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="sect1" lang="en">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="titlepage"><div><div><h2 class="title" style="clear: both">
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<a name="incremental_zone_transfers"></a>Incremental Zone Transfers (IXFR)</h2></div></div></div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User The incremental zone transfer (IXFR) protocol is a way for
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont slave servers to transfer only changed data, instead of having to
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont transfer the entire zone. The IXFR protocol is specified in RFC
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User 1995. See <a href="Bv9ARM.ch09.html#proposed_standards">Proposed Standards</a>.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User When acting as a master, <acronym class="acronym">BIND</acronym> 9
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User supports IXFR for those zones
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont where the necessary change history information is available. These
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater include master zones maintained by dynamic update and slave zones
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User whose data was obtained by IXFR. For manually maintained master
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User zones, and for slave zones obtained by performing a full zone
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater transfer (AXFR), IXFR is supported only if the option
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span><strong class="command">ixfr-from-differences</strong></span> is set
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User to <strong class="userinput"><code>yes</code></strong>.
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater </p>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User When acting as a slave, <acronym class="acronym">BIND</acronym> 9 will
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User attempt to use IXFR unless
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont it is explicitly disabled. For more information about disabling
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User IXFR, see the description of the <span><strong class="command">request-ixfr</strong></span> clause
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User of the <span><strong class="command">server</strong></span> statement.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="sect1" lang="en">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<div class="titlepage"><div><div><h2 class="title" style="clear: both">
0a7ed88633a680bb881868b75ded4d09a7bbbc50Automatic Updater<a name="id2570510"></a>Split DNS</h2></div></div></div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Setting up different views, or visibility, of the DNS space to
0a7ed88633a680bb881868b75ded4d09a7bbbc50Automatic Updater internal and external resolvers is usually referred to as a
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <span class="emphasis"><em>Split DNS</em></span> setup. There are several
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User reasons an organization would want to set up its DNS this way.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User One common reason for setting up a DNS system this way is
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont to hide "internal" DNS information from "external" clients on the
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Internet. There is some debate as to whether or not this is actually
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User useful.
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater Internal DNS information leaks out in many ways (via email headers,
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User for example) and most savvy "attackers" can find the information
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User they need using other means.
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater However, since listing addresses of internal servers that
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater external clients cannot possibly reach can result in
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater connection delays and other annoyances, an organization may
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater choose to use a Split DNS to present a consistent view of itself
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater to the outside world.
a3f8c8e20780e488141d200acdfea6c5f3303513Automatic Updater </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Another common reason for setting up a Split DNS system is
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont to allow internal networks that are behind filters or in RFC 1918
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User space (reserved IP space, as documented in RFC 1918) to resolve DNS
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User on the Internet. Split DNS can also be used to allow mail from outside
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater back in to the internal network.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<div class="sect2" lang="en">
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont<div class="titlepage"><div><div><h3 class="title">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<a name="id2570529"></a>Example split DNS setup</h3></div></div></div>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User Let's say a company named <span class="emphasis"><em>Example, Inc.</em></span>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User (<code class="literal">example.com</code>)
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User has several corporate sites that have an internal network with
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User reserved
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User Internet Protocol (IP) space and an external demilitarized zone (DMZ),
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User or "outside" section of a network, that is available to the public.
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User </p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User <span class="emphasis"><em>Example, Inc.</em></span> wants its internal clients
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User to be able to resolve external hostnames and to exchange mail with
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User people on the outside. The company also wants its internal resolvers
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User to have access to certain internal-only zones that are not available
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont at all outside of the internal network.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont In order to accomplish this, the company will set up two sets
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont of name servers. One set will be on the inside network (in the
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont reserved
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont IP space) and the other set will be on bastion hosts, which are
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User "proxy"
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User hosts that can talk to both sides of its network, in the DMZ.
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User The internal servers will be configured to forward all queries,
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont except queries for <code class="filename">site1.internal</code>, <code class="filename">site2.internal</code>, <code class="filename">site1.example.com</code>,
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User and <code class="filename">site2.example.com</code>, to the servers
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User in the
6f1205897504b8f50b1785975482c995888dd630Tinderbox User DMZ. These internal servers will have complete sets of information
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User for <code class="filename">site1.example.com</code>, <code class="filename">site2.example.com</code>, <code class="filename">site1.internal</code>,
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User and <code class="filename">site2.internal</code>.
6f1205897504b8f50b1785975482c995888dd630Tinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User To protect the <code class="filename">site1.internal</code> and <code class="filename">site2.internal</code> domains,
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater the internal name servers must be configured to disallow all queries
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User to these domains from any external hosts, including the bastion
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User hosts.
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater </p>
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater<p>
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater The external servers, which are on the bastion hosts, will
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater be configured to serve the "public" version of the <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones.
a3416b0a1b5482b6df32839445ca98c016945570Automatic Updater This could include things such as the host records for public servers
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User (<code class="filename">www.example.com</code> and <code class="filename">ftp.example.com</code>),
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User and mail exchange (MX) records (<code class="filename">a.mx.example.com</code> and <code class="filename">b.mx.example.com</code>).
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User In addition, the public <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User should have special MX records that contain wildcard (`*') records
010a51c427bfb6ab658fc0056955a1a5b69810beTinderbox User pointing to the bastion hosts. This is needed because external mail
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User servers do not have any other way of looking up how to deliver mail
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User to those internal hosts. With the wildcard records, the mail will
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User be delivered to the bastion host, which can then forward it on to
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater internal hosts.
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater </p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater<p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater Here's an example of a wildcard MX record:
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater </p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater<pre class="programlisting">* IN MX 10 external1.example.com.</pre>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater<p>
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User Now that they accept mail on behalf of anything in the internal
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User network, the bastion hosts will need to know how to deliver mail
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater to internal hosts. In order for this to work properly, the resolvers
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User on
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User the bastion hosts will need to be configured to point to the internal
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater name servers for DNS resolution.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater Queries for internal hostnames will be answered by the internal
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater servers, and queries for external hostnames will be forwarded back
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater out to the DNS servers on the bastion hosts.
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User In order for all this to work properly, internal clients will
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater need to be configured to query <span class="emphasis"><em>only</em></span> the internal
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User name servers for DNS queries. This could also be enforced via
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User selective
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater filtering on the network.
5a24d24c8fba3480d707c0c902379ddb36501e12Automatic Updater </p>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater<p>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater If everything has been set properly, <span class="emphasis"><em>Example, Inc.</em></span>'s
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User internal clients will now be able to:
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater<div class="itemizedlist"><ul type="disc">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Look up any hostnames in the <code class="literal">site1</code>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater and
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater <code class="literal">site2.example.com</code> zones.
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater </li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Look up any hostnames in the <code class="literal">site1.internal</code> and
79cf9524b15ca65f55fd6913e6cf01b5581c588aAutomatic Updater <code class="literal">site2.internal</code> domains.
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<li>Look up any hostnames on the Internet.</li>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater<li>Exchange mail with both internal and external people.</li>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater</ul></div>
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Hosts on the Internet will be able to:
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater<div class="itemizedlist"><ul type="disc">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Look up any hostnames in the <code class="literal">site1</code>
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater and
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater <code class="literal">site2.example.com</code> zones.
f8e3e03cacd16ffb923a9603fca23a9e1a1fee07Automatic Updater </li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User Exchange mail with anyone in the <code class="literal">site1</code> and
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User <code class="literal">site2.example.com</code> zones.
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User </li>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User</ul></div>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User Here is an example configuration for the setup we just
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User described above. Note that this is only configuration information;
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User for information on how to configure your zone files, see <a href="Bv9ARM.ch03.html#sample_configuration" title="Sample Configurations">the section called &#8220;Sample Configurations&#8221;</a>.
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User </p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User<p>
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User Internal DNS server config:
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User </p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<pre class="programlisting">
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox Useracl internals { 172.16.72.0/24; 192.168.1.0/24; };
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox Useracl externals { <code class="varname">bastion-ips-go-here</code>; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox Useroptions {
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User ...
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User ...
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User forward only;
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User // forward to external servers
794b79e6bbc3f5db1ea6ae154d739b9f1ef1a375Tinderbox User forwarders {
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User <code class="varname">bastion-ips-go-here</code>;
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User // sample allow-transfer (no one)
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-transfer { none; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User // restrict query access
010a51c427bfb6ab658fc0056955a1a5b69810beTinderbox User allow-query { internals; externals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User // restrict recursion
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-recursion { internals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User ...
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont ...
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont};
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont// sample master zone
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupontzone "site1.example.com" {
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User type master;
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User file "m/site1.example.com";
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User // do normal iterative resolution (do not forward)
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User forwarders { };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-query { internals; externals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-transfer { internals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User};
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User// sample slave zone
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox Userzone "site2.example.com" {
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User type slave;
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User file "s/site2.example.com";
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont masters { 172.16.72.3; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User forwarders { };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-query { internals; externals; };
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont allow-transfer { internals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User};
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupontzone "site1.internal" {
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont type master;
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont file "m/site1.internal";
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater forwarders { };
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont allow-query { internals; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-transfer { internals; }
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont};
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupontzone "site2.internal" {
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont type slave;
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont file "s/site2.internal";
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User masters { 172.16.72.3; };
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater forwarders { };
c7d32c0b0ff4c01f0d4479af3410d3c06044d48aAutomatic Updater allow-query { internals };
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont allow-transfer { internals; }
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont};
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont</pre>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User<p>
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User External (bastion host) DNS server config:
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User </p>
010a51c427bfb6ab658fc0056955a1a5b69810beTinderbox User<pre class="programlisting">
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox Useracl internals { 172.16.72.0/24; 192.168.1.0/24; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox Useracl externals { bastion-ips-go-here; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox Useroptions {
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User ...
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User ...
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont // sample allow-transfer (no one)
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User allow-transfer { none; };
bbbf2e27d3a981163dab139497d6b2dc85449db0Tinderbox User // default query access
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont allow-query { any; };
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User // restrict cache access
2eeb74d1cf5355dd98f6d507a10086e16bb08c4bTinderbox User allow-query-cache { internals; externals; };
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont // restrict recursion
90f35c2f2a1c660f3b96eec413036d238df395f6Francis Dupont allow-recursion { internals; externals; };
...
...
};
// sample slave zone
zone "site1.example.com" {
type master;
file "m/site1.foo.com";
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-transfer { internals; externals; }
};
</pre>
<p>
In the <code class="filename">resolv.conf</code> (or equivalent) on
the bastion host(s):
</p>
<pre class="programlisting">
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</pre>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tsig"></a>TSIG</h2></div></div></div>
<p>
This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym class="acronym">BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym class="acronym">BIND</acronym>.
</p>
<p>
<acronym class="acronym">BIND</acronym> primarily supports TSIG for server
to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym class="acronym">BIND</acronym> 8 have limited support
for TSIG.
</p>
<p>
TSIG can also be useful for dynamic update. A primary
server for a dynamic zone should control access to the dynamic
update service, but IP-based access control is insufficient.
The cryptographic access control provided by TSIG
is far superior. The <span><strong class="command">nsupdate</strong></span>
program supports TSIG via the <code class="option">-k</code> and
<code class="option">-y</code> command line options or inline by use
of the <span><strong class="command">key</strong></span>.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2571030"></a>Generate Shared Keys for Each Pair of Hosts</h3></div></div></div>
<p>
A shared secret is generated to be shared between <span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host2</em></span>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.
</p>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2571047"></a>Automatic Generation</h4></div></div></div>
<p>
The following command will generate a 128-bit (16 byte) HMAC-MD5
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is 512 bits;
keys longer than that will be digested with MD5 to produce a
128-bit key.
</p>
<p>
<strong class="userinput"><code>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</code></strong>
</p>
<p>
The key is in the file <code class="filename">Khost1-host2.+157+00000.private</code>.
Nothing directly uses this file, but the base-64 encoded string
following "<code class="literal">Key:</code>"
can be extracted from the file and used as a shared secret:
</p>
<pre class="programlisting">Key: La/E5CjG9O+os1jq0a2jdA==</pre>
<p>
The string "<code class="literal">La/E5CjG9O+os1jq0a2jdA==</code>" can
be used as the shared secret.
</p>
</div>
<div class="sect3" lang="en">
<div class="titlepage"><div><div><h4 class="title">
<a name="id2571085"></a>Manual Generation</h4></div></div></div>
<p>
The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.
</p>
<p>
Also, a known string can be run through <span><strong class="command">mmencode</strong></span> or
a similar program to generate base-64 encoded data.
</p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2571104"></a>Copying the Shared Secret to Both Machines</h3></div></div></div>
<p>
This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2571114"></a>Informing the Servers of the Key's Existence</h3></div></div></div>
<p>
Imagine <span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host 2</em></span>
are
both servers. The following is added to each server's <code class="filename">named.conf</code> file:
</p>
<pre class="programlisting">
key host1-host2. {
algorithm hmac-md5;
secret "La/E5CjG9O+os1jq0a2jdA==";
};
</pre>
<p>
The algorithm, <code class="literal">hmac-md5</code>, is the only one supported by <acronym class="acronym">BIND</acronym>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <code class="filename">named.conf</code> be non-world
readable, or the key directive be added to a non-world readable
file that is included by
<code class="filename">named.conf</code>.
</p>
<p>
At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature is successfully verified, the
response is signed by the same key.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2563989"></a>Instructing the Server to Use the Key</h3></div></div></div>
<p>
Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <code class="filename">named.conf</code> file
for <span class="emphasis"><em>host1</em></span>, if the IP address of <span class="emphasis"><em>host2</em></span> is
10.1.2.3:
</p>
<pre class="programlisting">
server 10.1.2.3 {
keys { host1-host2. ;};
};
</pre>
<p>
Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a
world-readable
file.
</p>
<p>
If <span class="emphasis"><em>host1</em></span> sends a message that is a request
to that address, the message will be signed with the specified key. <span class="emphasis"><em>host1</em></span> will
expect any responses to signed messages to be signed with the same
key.
</p>
<p>
A similar statement must be present in <span class="emphasis"><em>host2</em></span>'s
configuration file (with <span class="emphasis"><em>host1</em></span>'s address) for <span class="emphasis"><em>host2</em></span> to
sign request messages to <span class="emphasis"><em>host1</em></span>.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2564115"></a>TSIG Key Based Access Control</h3></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> allows IP addresses and ranges
to be specified in ACL
definitions and
<span><strong class="command">allow-{ query | transfer | update }</strong></span>
directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <span><strong class="command">key host1-host2.</strong></span>
</p>
<p>
An example of an <span><strong class="command">allow-update</strong></span> directive would be:
</p>
<pre class="programlisting">
allow-update { key host1-host2. ;};
</pre>
<p>
This allows dynamic updates to succeed only if the request
was signed by a key named "<span><strong class="command">host1-host2.</strong></span>".
</p>
<p>
You may want to read about the more powerful
<span><strong class="command">update-policy</strong></span> statement in
<a href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called &#8220;Dynamic Update Policies&#8221;</a>.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2564163"></a>Errors</h3></div></div></div>
<p>
The processing of TSIG signed messages can result in
several errors. If a signed message is sent to a non-TSIG aware
server, a FORMERR (format error) will be returned, since the server will not
understand the record. This is a result of misconfiguration,
since the server must be explicitly configured to send a TSIG
signed message to a specific server.
</p>
<p>
If a TSIG aware server receives a message signed by an
unknown key, the response will be unsigned with the TSIG
extended error code set to BADKEY. If a TSIG aware server
receives a message with a signature that does not validate, the
response will be unsigned with the TSIG extended error code set
to BADSIG. If a TSIG aware server receives a message with a time
outside of the allowed range, the response will be signed with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified. In any of these cases, the message's rcode (response code) is set to
NOTAUTH (not authenticated).
</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2571549"></a>TKEY</h2></div></div></div>
<p><span><strong class="command">TKEY</strong></span>
is a mechanism for automatically generating a shared secret
between two hosts. There are several "modes" of
<span><strong class="command">TKEY</strong></span> that specify how the key is generated
or assigned. <acronym class="acronym">BIND</acronym> 9 implements only one of
these modes, the Diffie-Hellman key exchange. Both hosts are
required to have a Diffie-Hellman KEY record (although this
record is not required to be present in a zone). The
<span><strong class="command">TKEY</strong></span> process must use signed messages,
signed either by TSIG or SIG(0). The result of
<span><strong class="command">TKEY</strong></span> is a shared secret that can be used to
sign messages with TSIG. <span><strong class="command">TKEY</strong></span> can also be
used to delete shared secrets that it had previously
generated.
</p>
<p>
The <span><strong class="command">TKEY</strong></span> process is initiated by a
client
or server by sending a signed <span><strong class="command">TKEY</strong></span>
query
(including any appropriate KEYs) to a TKEY-aware server. The
server response, if it indicates success, will contain a
<span><strong class="command">TKEY</strong></span> record and any appropriate keys.
After
this exchange, both participants have enough information to
determine the shared secret; the exact process depends on the
<span><strong class="command">TKEY</strong></span> mode. When using the
Diffie-Hellman
<span><strong class="command">TKEY</strong></span> mode, Diffie-Hellman keys are
exchanged,
and the shared secret is derived by both participants.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2571598"></a>SIG(0)</h2></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> 9 partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC 2931.
SIG(0)
uses public/private keys to authenticate messages. Access control
is performed in the same manner as TSIG keys; privileges can be
granted or denied based on the key name.
</p>
<p>
When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
will not attempt to locate and/or validate the key.
</p>
<p>
SIG(0) signing of multiple-message TCP streams is not
supported.
</p>
<p>
The only tool shipped with <acronym class="acronym">BIND</acronym> 9 that
generates SIG(0) signed messages is <span><strong class="command">nsupdate</strong></span>.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="DNSSEC"></a>DNSSEC</h2></div></div></div>
<p>
Cryptographic authentication of DNS information is possible
through the DNS Security (<span class="emphasis"><em>DNSSEC-bis</em></span>) extensions,
defined in RFC 4033, RFC 4034, and RFC 4035.
This section describes the creation and use of DNSSEC signed zones.
</p>
<p>
In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <acronym class="acronym">BIND</acronym>
9 ships
with several tools
that are used in this process, which are explained in more detail
below. In all cases, the <code class="option">-h</code> option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset files to be in the working directory or the
directory specified by the <code class="option">-d</code> option, and
that the tools shipped with BIND 9.2.x and earlier are not compatible
with the current ones.
</p>
<p>
There must also be communication with the administrators of
the parent and/or child zone to transmit keys. A zone's security
status must be indicated by the parent zone for a DNSSEC capable
resolver to trust its data. This is done through the presence
or absence of a <code class="literal">DS</code> record at the
delegation
point.
</p>
<p>
For other servers to trust data in this zone, they must
either be statically configured with this zone's zone key or the
zone key of another zone above this one in the DNS tree.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2571803"></a>Generating Keys</h3></div></div></div>
<p>
The <span><strong class="command">dnssec-keygen</strong></span> program is used to
generate keys.
</p>
<p>
A secure zone must contain one or more zone keys. The
zone keys will sign all other records in the zone, as well as
the zone keys of any secure delegated zones. Zone keys must
have the same name as the zone, a name type of
<span><strong class="command">ZONE</strong></span>, and must be usable for
authentication.
It is recommended that zone keys use a cryptographic algorithm
designated as "mandatory to implement" by the IETF; currently
the only one is RSASHA1.
</p>
<p>
The following command will generate a 768-bit RSASHA1 key for
the <code class="filename">child.example</code> zone:
</p>
<p>
<strong class="userinput"><code>dnssec-keygen -a RSASHA1 -b 768 -n ZONE child.example.</code></strong>
</p>
<p>
Two output files will be produced:
<code class="filename">Kchild.example.+005+12345.key</code> and
<code class="filename">Kchild.example.+005+12345.private</code>
(where
12345 is an example of a key tag). The key filenames contain
the key name (<code class="filename">child.example.</code>),
algorithm (3
is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in
this case).
The private key (in the <code class="filename">.private</code>
file) is
used to generate signatures, and the public key (in the
<code class="filename">.key</code> file) is used for signature
verification.
</p>
<p>
To generate another key with the same properties (but with
a different key tag), repeat the above command.
</p>
<p>
The <span><strong class="command">dnssec-keyfromlabel</strong></span> program is used
to get a key pair from a crypto hardware and build the key
files. Its usage is similar to <span><strong class="command">dnssec-keygen</strong></span>.
</p>
<p>
The public keys should be inserted into the zone file by
including the <code class="filename">.key</code> files using
<span><strong class="command">$INCLUDE</strong></span> statements.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2571950"></a>Signing the Zone</h3></div></div></div>
<p>
The <span><strong class="command">dnssec-signzone</strong></span> program is used
to sign a zone.
</p>
<p>
Any <code class="filename">keyset</code> files corresponding to
secure subzones should be present. The zone signer will
generate <code class="literal">NSEC</code>, <code class="literal">NSEC3</code>
and <code class="literal">RRSIG</code> records for the zone, as
well as <code class="literal">DS</code> for the child zones if
<code class="literal">'-g'</code> is specified. If <code class="literal">'-g'</code>
is not specified, then DS RRsets for the secure child
zones need to be added manually.
</p>
<p>
The following command signs the zone, assuming it is in a
file called <code class="filename">zone.child.example</code>. By
default, all zone keys which have an available private key are
used to generate signatures.
</p>
<p>
<strong class="userinput"><code>dnssec-signzone -o child.example zone.child.example</code></strong>
</p>
<p>
One output file is produced:
<code class="filename">zone.child.example.signed</code>. This
file
should be referenced by <code class="filename">named.conf</code>
as the
input file for the zone.
</p>
<p><span><strong class="command">dnssec-signzone</strong></span>
will also produce a keyset and dsset files and optionally a
dlvset file. These are used to provide the parent zone
administrators with the <code class="literal">DNSKEYs</code> (or their
corresponding <code class="literal">DS</code> records) that are the
secure entry point to the zone.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2572032"></a>Configuring Servers</h3></div></div></div>
<p>
To enable <span><strong class="command">named</strong></span> to respond appropriately
to DNS requests from DNSSEC aware clients,
<span><strong class="command">dnssec-enable</strong></span> must be set to yes.
(This is the default setting.)
</p>
<p>
To enable <span><strong class="command">named</strong></span> to validate answers from
other servers, the <span><strong class="command">dnssec-enable</strong></span> and
<span><strong class="command">dnssec-validation</strong></span> options must both be
set to yes (the default setting in <acronym class="acronym">BIND</acronym> 9.5
and later), and at least one trust anchor must be configured
with a <span><strong class="command">trusted-keys</strong></span> statement in
<code class="filename">named.conf</code>.
</p>
<p>
<span><strong class="command">trusted-keys</strong></span> are copies of DNSKEY RRs
for zones that are used to form the first link in the
cryptographic chain of trust. All keys listed in
<span><strong class="command">trusted-keys</strong></span> (and corresponding zones)
are deemed to exist and only the listed keys will be used
to validated the DNSKEY RRset that they are from.
</p>
<p>
<span><strong class="command">trusted-keys</strong></span> are described in more detail
later in this document.
</p>
<p>
Unlike <acronym class="acronym">BIND</acronym> 8, <acronym class="acronym">BIND</acronym>
9 does not verify signatures on load, so zone keys for
authoritative zones do not need to be specified in the
configuration file.
</p>
<p>
After DNSSEC gets established, a typical DNSSEC configuration
will look something like the following. It has a one or
more public keys for the root. This allows answers from
outside the organization to be validated. It will also
have several keys for parts of the namespace the organization
controls. These are here to ensure that <span><strong class="command">named</strong></span> is immune
to compromises in the DNSSEC components of the security
of parent zones.
</p>
<pre class="programlisting">
trusted-keys {
/* Root Key */
"." 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
JxrGkxJWoZu6I7PzJu/E9gx4UC1zGAHlXKdE4zYIpRh
aBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3zy2Xy
4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYg
hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M/lUUVRbke
g1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq
66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
97S+LKUTpQcq27R7AT3/V5hRQxScINqwcz4jYqZD2fQ
dgxbcDTClU0CRBdiieyLMNzXG3";
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
kBOUKUf/mC7HvfwYH/Be22GnClrinKJp1O
g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
FxmAVZP20igTixin/1LcrgX/KMEGd/biuv
F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
/oyWR8BW/hWdzOvnSCThlHf3xiYleDbt/o
1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc
xOdNax071L18QqZnQQQAVVr+i
LhGTnNGp3HoWQLUIzKrJVZ3zg
gy3WwNT6kZo6c0tszYqbtvchm
gQC8CzKojM/W16i6MG/eafGU3
siaOdS0yOI6BgPsw+YZdzlYMa
IJGf4M4dyoKIhzdZyQ2bYQrjy
Q4LB0lC7aOnsMyYKHHYeRvPxj
IQXmdqgOJGq+vsevG06zW+1xg
YJh9rCIfnm1GX/KMgxLPG2vXT
D/RnLX+D3T3UL7HJYHJhAZD5L
59VvjSPsZJHeDCUyWYrvPZesZ
DIRvhDD52SKvbheeTJUm6Ehkz
ytNN2SN96QRk8j/iI8ib";
};
options {
...
dnssec-enable yes;
dnssec-validation yes;
};
</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
None of the keys listed in this example are valid. In particular,
the root key is not valid.
</div>
<p>
When DNSSEC validation is enabled and properly configured,
the resolver will reject any answers from signed, secure zones
which fail to validate, and will return SERVFAIL to the client.
</p>
<p>
Responses may fail to validate for any of several reasons,
including missing, expired, or invalid signatures, a key which
does not match the DS RRset in the parent zone, or an insecure
response from a zone which, according to its parent, should have
been secure.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
When the validator receives a response from an unsigned zone
that has a signed parent, it must confirm with the parent
that the zone was intentionally left unsigned. It does
this by verifying, via signed and validated NSEC/NSEC3 records,
that the parent zone contains no DS records for the child.
</p>
<p>
If the validator <span class="emphasis"><em>can</em></span> prove that the zone
is insecure, then the response is accepted. However, if it
cannot, then it must assume an insecure response to be a
forgery; it rejects the response and logs an error.
</p>
<p>
The logged error reads "insecurity proof failed" and
"got insecure response; parent indicates it should be secure".
(Prior to BIND 9.7, the logged error was "not insecure".
This referred to the zone, not the response.)
</p>
</div>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2572201"></a>IPv6 Support in <acronym class="acronym">BIND</acronym> 9</h2></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> 9 fully supports all currently
defined forms of IPv6 name to address and address to name
lookups. It will also use IPv6 addresses to make queries when
running on an IPv6 capable system.
</p>
<p>
For forward lookups, <acronym class="acronym">BIND</acronym> 9 supports
only AAAA records. RFC 3363 deprecated the use of A6 records,
and client-side support for A6 records was accordingly removed
from <acronym class="acronym">BIND</acronym> 9.
However, authoritative <acronym class="acronym">BIND</acronym> 9 name servers still
load zone files containing A6 records correctly, answer queries
for A6 records, and accept zone transfer for a zone containing A6
records.
</p>
<p>
For IPv6 reverse lookups, <acronym class="acronym">BIND</acronym> 9 supports
the traditional "nibble" format used in the
<span class="emphasis"><em>ip6.arpa</em></span> domain, as well as the older, deprecated
<span class="emphasis"><em>ip6.int</em></span> domain.
Older versions of <acronym class="acronym">BIND</acronym> 9
supported the "binary label" (also known as "bitstring") format,
but support of binary labels has been completely removed per
RFC 3363.
Many applications in <acronym class="acronym">BIND</acronym> 9 do not understand
the binary label format at all any more, and will return an
error if given.
In particular, an authoritative <acronym class="acronym">BIND</acronym> 9
name server will not load a zone file containing binary labels.
</p>
<p>
For an overview of the format and structure of IPv6 addresses,
see <a href="Bv9ARM.ch09.html#ipv6addresses" title="IPv6 addresses (AAAA)">the section called &#8220;IPv6 addresses (AAAA)&#8221;</a>.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2572400"></a>Address Lookups Using AAAA Records</h3></div></div></div>
<p>
The IPv6 AAAA record is a parallel to the IPv4 A record,
and, unlike the deprecated A6 record, specifies the entire
IPv6 address in a single record. For example,
</p>
<pre class="programlisting">
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
</pre>
<p>
Use of IPv4-in-IPv6 mapped addresses is not recommended.
If a host has an IPv4 address, use an A record, not
a AAAA, with <code class="literal">::ffff:192.168.42.1</code> as
the address.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2572421"></a>Address to Name Lookups Using Nibble Format</h3></div></div></div>
<p>
When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<code class="literal">ip6.arpa.</code> is appended to the
resulting name.
For example, the following would provide reverse name lookup for
a host with address
<code class="literal">2001:db8::1</code>.
</p>
<pre class="programlisting">
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
host.example.com. )
</pre>
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