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95317501208f3bf5b159e6a40801b7069f68c486Mark Andrews<title>Chapter�4.�Advanced DNS Features</title>
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b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews</table>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<hr>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews</div>
01163d188b89911c3a23fe1125a4cab6764a408cMark Andrews<div class="chapter" lang="en">
01163d188b89911c3a23fe1125a4cab6764a408cMark Andrews<div class="titlepage"><div><div><h2 class="title">
01163d188b89911c3a23fe1125a4cab6764a408cMark Andrews<a name="Bv9ARM.ch04"></a>Chapter�4.�Advanced DNS Features</h2></div></div></div>
01163d188b89911c3a23fe1125a4cab6764a408cMark Andrews<div class="toc">
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<p><b>Table of Contents</b></p>
648ba62b1f156cbca14d54d06c535385f1193d13Mark Andrews<dl>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#notify">Notify</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#dynamic_update">Dynamic Update</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#journal">The journal file</a></span></dt></dl></dd>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#incremental_zone_transfers">Incremental Zone Transfers (IXFR)</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2570513">Split DNS</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2570531">Example split DNS setup</a></span></dt></dl></dd>
35665db4e49e3e4c0e3776e635449f931f3732cfMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#tsig">TSIG</a></span></dt>
c6313caa6cd9d011ac075048d2b62fd3410162dfMark Andrews<dd><dl>
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571169">Generate Shared Keys for Each Pair of Hosts</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571242">Copying the Shared Secret to Both Machines</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571253">Informing the Servers of the Key's Existence</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571292">Instructing the Server to Use the Key</a></span></dt>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571486">TSIG Key Based Access Control</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571531">Errors</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews</dl></dd>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2571613">TKEY</a></span></dt>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2571662">SIG(0)</a></span></dt>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#DNSSEC">DNSSEC</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dd><dl>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571799">Generating Keys</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571878">Signing the Zone</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2571959">Configuring Servers</a></span></dt>
bdfd62f497fe0d5281c25b61271595a4c821a040Mark Andrews</dl></dd>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2572102">IPv6 Support in <acronym class="acronym">BIND</acronym> 9</a></span></dt>
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<dd><dl>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2572164">Address Lookups Using AAAA Records</a></span></dt>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2572185">Address to Name Lookups Using Nibble Format</a></span></dt>
64cde9d94a2f6c7050f00d9651df6b05e63d09f2Mark Andrews</dl></dd>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews</dl>
cbb94d52f98b48e8c3a8866dbf8c67860764f349Mark Andrews</div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="sect1" lang="en">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="titlepage"><div><div><h2 class="title" style="clear: both">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<a name="notify"></a>Notify</h2></div></div></div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <acronym class="acronym">DNS</acronym> NOTIFY is a mechanism that allows master
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews servers to notify their slave servers of changes to a zone's data. In
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews response to a <span><strong class="command">NOTIFY</strong></span> from a master server, the
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews slave will check to see that its version of the zone is the
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews current version and, if not, initiate a zone transfer.
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews </p>
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<p>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews For more information about <acronym class="acronym">DNS</acronym>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">NOTIFY</strong></span>, see the description of the
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <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
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews the description of the zone option <span><strong class="command">also-notify</strong></span> in
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <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>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews protocol is specified in RFC 1996.
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews </p>
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews<h3 class="title">Note</h3>
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews As a slave zone can also be a master to other slaves, named,
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews by default, sends <span><strong class="command">NOTIFY</strong></span> messages for every zone
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews it loads. Specifying <span><strong class="command">notify master-only;</strong></span> will
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews cause named to only send <span><strong class="command">NOTIFY</strong></span> for master
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews zones that it loads.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </div>
8f8634e66351e292925dde8ab6b0418a0141f86aMark Andrews</div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="sect1" lang="en">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="titlepage"><div><div><h2 class="title" style="clear: both">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<a name="dynamic_update"></a>Dynamic Update</h2></div></div></div>
61a03692ab84504fb2bd85b71facfe0f6456b466Mark Andrews<p>
68843c99b695bf194b019d465f6d33e6297fd02aMark Andrews Dynamic Update is a method for adding, replacing or deleting
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews records in a master server by sending it a special form of DNS
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews messages. The format and meaning of these messages is specified
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews in RFC 2136.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews Dynamic update is enabled by including an
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">allow-update</strong></span> or <span><strong class="command">update-policy</strong></span>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews clause in the <span><strong class="command">zone</strong></span> statement. The
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews <span><strong class="command">tkey-gssapi-credential</strong></span> and
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">tkey-domain</strong></span> clauses in the
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">options</strong></span> statement enable the
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews server to negotiate keys that can be matched against those
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews in <span><strong class="command">update-policy</strong></span> or
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">allow-update</strong></span>.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews Updating of secure zones (zones using DNSSEC) follows RFC
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews 3007: RRSIG, NSEC and NSEC3 records affected by updates are
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews automatically regenerated by the server using an online
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews zone key. Update authorization is based on transaction
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews signatures and an explicit server policy.
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews </p>
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<div class="sect2" lang="en">
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<div class="titlepage"><div><div><h3 class="title">
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<a name="journal"></a>The journal file</h3></div></div></div>
d6dc0d4f584352d2e4305435599ae8c93776d9b4Mark Andrews<p>
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews All changes made to a zone using dynamic update are stored
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews in the zone's journal file. This file is automatically created
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews by the server when the first dynamic update takes place.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews The name of the journal file is formed by appending the extension
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <code class="filename">.jnl</code> to the name of the
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews corresponding zone
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews file unless specifically overridden. The journal file is in a
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews binary format and should not be edited manually.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews The server will also occasionally write ("dump")
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews the complete contents of the updated zone to its zone file.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews This is not done immediately after
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews each dynamic update, because that would be too slow when a large
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews zone is updated frequently. Instead, the dump is delayed by
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews up to 15 minutes, allowing additional updates to take place.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews When a server is restarted after a shutdown or crash, it will replay
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews the journal file to incorporate into the zone any updates that
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews took
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews place after the last zone dump.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews Changes that result from incoming incremental zone transfers are
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews also
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews journalled in a similar way.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews The zone files of dynamic zones cannot normally be edited by
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews hand because they are not guaranteed to contain the most recent
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews dynamic changes &#8212; those are only in the journal file.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews The only way to ensure that the zone file of a dynamic zone
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews is up to date is to run <span><strong class="command">rndc stop</strong></span>.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews If you have to make changes to a dynamic zone
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews manually, the following procedure will work: Disable dynamic updates
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews to the zone using
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews <span><strong class="command">rndc freeze <em class="replaceable"><code>zone</code></em></strong></span>.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews This will also remove the zone's <code class="filename">.jnl</code> file
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews and update the master file. Edit the zone file. Run
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews <span><strong class="command">rndc thaw <em class="replaceable"><code>zone</code></em></strong></span>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews to reload the changed zone and re-enable dynamic updates.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews</div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews</div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="sect1" lang="en">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<div class="titlepage"><div><div><h2 class="title" style="clear: both">
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<a name="incremental_zone_transfers"></a>Incremental Zone Transfers (IXFR)</h2></div></div></div>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews<p>
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews The incremental zone transfer (IXFR) protocol is a way for
b08e3be5dbfba22719ae9c428bd6853ac6f09798Mark Andrews slave servers to transfer only changed data, instead of having to
f91671c7dc877a52adc06d0a7d0ed1c7f6391e6eMark Andrews transfer the entire zone. The IXFR protocol is specified in RFC
f91671c7dc877a52adc06d0a7d0ed1c7f6391e6eMark Andrews 1995. See <a href="Bv9ARM.ch09.html#proposed_standards">Proposed Standards</a>.
d9b4174233b951f25cd53a2787b9f14314258c2fMark Andrews </p>
<p>
When acting as a master, <acronym class="acronym">BIND</acronym> 9
supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR. For manually maintained master
zones, and for slave zones obtained by performing a full zone
transfer (AXFR), IXFR is supported only if the option
<span><strong class="command">ixfr-from-differences</strong></span> is set
to <strong class="userinput"><code>yes</code></strong>.
</p>
<p>
When acting as a slave, <acronym class="acronym">BIND</acronym> 9 will
attempt to use IXFR unless
it is explicitly disabled. For more information about disabling
IXFR, see the description of the <span><strong class="command">request-ixfr</strong></span> clause
of the <span><strong class="command">server</strong></span> statement.
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2570513"></a>Split DNS</h2></div></div></div>
<p>
Setting up different views, or visibility, of the DNS space to
internal and external resolvers is usually referred to as a
<span class="emphasis"><em>Split DNS</em></span> setup. There are several
reasons an organization would want to set up its DNS this way.
</p>
<p>
One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually
useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.
However, since listing addresses of internal servers that
external clients cannot possibly reach can result in
connection delays and other annoyances, an organization may
choose to use a Split DNS to present a consistent view of itself
to the outside world.
</p>
<p>
Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2570531"></a>Example split DNS setup</h3></div></div></div>
<p>
Let's say a company named <span class="emphasis"><em>Example, Inc.</em></span>
(<code class="literal">example.com</code>)
has several corporate sites that have an internal network with
reserved
Internet Protocol (IP) space and an external demilitarized zone (DMZ),
or "outside" section of a network, that is available to the public.
</p>
<p>
<span class="emphasis"><em>Example, Inc.</em></span> wants its internal clients
to be able to resolve external hostnames and to exchange mail with
people on the outside. The company also wants its internal resolvers
to have access to certain internal-only zones that are not available
at all outside of the internal network.
</p>
<p>
In order to accomplish this, the company will set up two sets
of name servers. One set will be on the inside network (in the
reserved
IP space) and the other set will be on bastion hosts, which are
"proxy"
hosts that can talk to both sides of its network, in the DMZ.
</p>
<p>
The internal servers will be configured to forward all queries,
except queries for <code class="filename">site1.internal</code>, <code class="filename">site2.internal</code>, <code class="filename">site1.example.com</code>,
and <code class="filename">site2.example.com</code>, to the servers
in the
DMZ. These internal servers will have complete sets of information
for <code class="filename">site1.example.com</code>, <code class="filename">site2.example.com</code>, <code class="filename">site1.internal</code>,
and <code class="filename">site2.internal</code>.
</p>
<p>
To protect the <code class="filename">site1.internal</code> and <code class="filename">site2.internal</code> domains,
the internal name servers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.
</p>
<p>
The external servers, which are on the bastion hosts, will
be configured to serve the "public" version of the <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones.
This could include things such as the host records for public servers
(<code class="filename">www.example.com</code> and <code class="filename">ftp.example.com</code>),
and mail exchange (MX) records (<code class="filename">a.mx.example.com</code> and <code class="filename">b.mx.example.com</code>).
</p>
<p>
In addition, the public <code class="filename">site1</code> and <code class="filename">site2.example.com</code> zones
should have special MX records that contain wildcard (`*') records
pointing to the bastion hosts. This is needed because external mail
servers do not have any other way of looking up how to deliver mail
to those internal hosts. With the wildcard records, the mail will
be delivered to the bastion host, which can then forward it on to
internal hosts.
</p>
<p>
Here's an example of a wildcard MX record:
</p>
<pre class="programlisting">* IN MX 10 external1.example.com.</pre>
<p>
Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers
on
the bastion hosts will need to be configured to point to the internal
name servers for DNS resolution.
</p>
<p>
Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.
</p>
<p>
In order for all this to work properly, internal clients will
need to be configured to query <span class="emphasis"><em>only</em></span> the internal
name servers for DNS queries. This could also be enforced via
selective
filtering on the network.
</p>
<p>
If everything has been set properly, <span class="emphasis"><em>Example, Inc.</em></span>'s
internal clients will now be able to:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
Look up any hostnames in the <code class="literal">site1</code>
and
<code class="literal">site2.example.com</code> zones.
</li>
<li>
Look up any hostnames in the <code class="literal">site1.internal</code> and
<code class="literal">site2.internal</code> domains.
</li>
<li>Look up any hostnames on the Internet.</li>
<li>Exchange mail with both internal and external people.</li>
</ul></div>
<p>
Hosts on the Internet will be able to:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
Look up any hostnames in the <code class="literal">site1</code>
and
<code class="literal">site2.example.com</code> zones.
</li>
<li>
Exchange mail with anyone in the <code class="literal">site1</code> and
<code class="literal">site2.example.com</code> zones.
</li>
</ul></div>
<p>
Here is an example configuration for the setup we just
described above. Note that this is only configuration information;
for information on how to configure your zone files, see <a href="Bv9ARM.ch03.html#sample_configuration" title="Sample Configurations">the section called &#8220;Sample Configurations&#8221;</a>.
</p>
<p>
Internal DNS server config:
</p>
<pre class="programlisting">
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { <code class="varname">bastion-ips-go-here</code>; };
options {
...
...
forward only;
forwarders { // forward to external servers
<code class="varname">bastion-ips-go-here</code>;
};
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample master zone
type master;
file "m/site1.example.com";
forwarders { }; // do normal iterative
// resolution (do not forward)
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site2.example.com" { // sample slave zone
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</pre>
<p>
External (bastion host) DNS server config:
</p>
<pre class="programlisting">
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { any; }; // default query access
allow-query-cache { internals; externals; }; // restrict cache access
allow-recursion { internals; externals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample slave zone
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="id2571169"></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="id2571186"></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="id2571224"></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="id2571242"></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="id2571253"></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, hmac-md5, 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="id2571292"></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="id2571486"></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 allow-update 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="id2571531"></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="id2571613"></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="id2571662"></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 RFC2931.
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="id2571799"></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="id2571878"></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="id2571959"></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.
</p>
<p>
To enable <span><strong class="command">named</strong></span> to validate answers from
other servers both <span><strong class="command">dnssec-enable</strong></span> and
<span><strong class="command">dnssec-validation</strong></span> must be set and some
<span><strong class="command">trusted-keys</strong></span> must be configured
into <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 named 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+CXd0rVXyYmobt7sEEfK3clRbGaTwSJxrGkxJWoZu6I7PzJu/
E9gx4UC1zGAHlXKdE4zYIpRhaBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3
zy2Xy4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYghf+6fElrmLkdaz
MQ2OCnACR817DF4BBa7UR/beDHyp5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M
/lUUVRbkeg1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq66gKodQj+M
iA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ97S+LKUTpQcq27R7AT3/V5hRQxScI
Nqwcz4jYqZD2fQdgxbcDTClU0CRBdiieyLMNzXG3";
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM65KbhTjrW1ZaARmPhEZZe
3Y9ifgEuq7vZ/zGZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb4JKUbb
OTcM8pwXlj0EiX3oDFVmjHO444gLkBO UKUf/mC7HvfwYH/Be22GnC
lrinKJp1Og4ywzO9WglMk7jbfW33gUKvirTHr25GL7STQUzBb5Usxt
8lgnyTUHs1t3JwCY5hKZ6CqFxmAVZP20igTixin/1LcrgX/KMEGd/b
iuvF4qJCyduieHukuY3H4XMAcR+xia2 nIUPvm/oyWR8BW/hWdzOvn
SCThlHf3xiYleDbt/o1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwcxOdNax071L18QqZnQQQA
VVr+iLhGTnNGp3HoWQLUIzKrJVZ3zggy3WwNT6kZo6c0
tszYqbtvchmgQC8CzKojM/W16i6MG/ea fGU3siaOdS0
yOI6BgPsw+YZdzlYMaIJGf4M4dyoKIhzdZyQ2bYQrjyQ
4LB0lC7aOnsMyYKHHYeRv PxjIQXmdqgOJGq+vsevG06
zW+1xgYJh9rCIfnm1GX/KMgxLPG2vXTD/RnLX+D3T3UL
7HJYHJhAZD5L59VvjSPsZJHeDCUyWYrvPZesZDIRvhDD
52SKvbheeTJUm6EhkzytNN2SN96QRk8j/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>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2572102"></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="id2572164"></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="id2572185"></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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