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f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<title>Chapter�4.�Advanced DNS Features</title>
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f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="chapter" lang="en">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="titlepage"><div><div><h2 class="title">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<a name="Bv9ARM.ch04"></a>Chapter�4.�Advanced DNS Features</h2></div></div></div>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="toc">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p><b>Table of Contents</b></p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dl>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect1"><a href="Bv9ARM.ch04.html#notify">Notify</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect1"><a href="Bv9ARM.ch04.html#dynamic_update">Dynamic Update</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dd><dl><dt><span class="sect2"><a href="Bv9ARM.ch04.html#journal">The journal file</a></span></dt></dl></dd>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect1"><a href="Bv9ARM.ch04.html#incremental_zone_transfers">Incremental Zone Transfers (IXFR)</a></span></dt>
79291918d036d77d586b6eba265d8d2ac0a7fee5cilix<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2539940">Split DNS</a></span></dt>
1e944d29efb206f5d0b5d1069cb098e22169d548cilix<dt><span class="sect1"><a href="Bv9ARM.ch04.html#tsig">TSIG</a></span></dt>
1e944d29efb206f5d0b5d1069cb098e22169d548cilix<dd><dl>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540455">Generate Shared Keys for Each Pair of Hosts</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540529">Copying the Shared Secret to Both Machines</a></span></dt>
c0cd5511d3b975ebe07d019c1f5528108725e438johanengelen<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540539">Informing the Servers of the Key's Existence</a></span></dt>
c0cd5511d3b975ebe07d019c1f5528108725e438johanengelen<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540579">Instructing the Server to Use the Key</a></span></dt>
c0cd5511d3b975ebe07d019c1f5528108725e438johanengelen<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540705">TSIG Key Based Access Control</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540818">Errors</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm</dl></dd>
2e2b8bd323e3693f9d86f545ce049d3f1b45d1c2cilix<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2540832">TKEY</a></span></dt>
6c3e745a94ef6b25a4ef9f018d350a7535aa45afTed Gould<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2540881">SIG(0)</a></span></dt>
6c3e745a94ef6b25a4ef9f018d350a7535aa45afTed Gould<dt><span class="sect1"><a href="Bv9ARM.ch04.html#DNSSEC">DNSSEC</a></span></dt>
5cd969f185e1a05f873e023378d0831e71441da6joncruz<dd><dl>
797bee69297bbdd86c5cff2e0771a71d1e2ac69dcilix<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2540949">Generating Keys</a></span></dt>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2541086">Signing the Zone</a></span></dt>
a797dcb8e284cab19f60b3eff93a53a62abda263johanengelen<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2541234">Configuring Servers</a></span></dt>
fb5a72174252e0e79107dcad3bf5a2bbd73e349cjohanengelen</dl></dd>
d37634d73670180f99a3e0ea583621373d90ec4fJohan Engelen<dt><span class="sect1"><a href="Bv9ARM.ch04.html#id2541257">IPv6 Support in <span class="acronym">BIND</span> 9</a></span></dt>
bdd7add6c064afee52d2eabeaa18f745430e5a4djohanengelen<dd><dl>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2541317">Address Lookups Using AAAA Records</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<dt><span class="sect2"><a href="Bv9ARM.ch04.html#id2541338">Address to Name Lookups Using Nibble Format</a></span></dt>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm</dl></dd>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm</dl>
fb5a72174252e0e79107dcad3bf5a2bbd73e349cjohanengelen</div>
96ef6190a69e8101a3c3a8ef8b01cb35042d1f9dcilix<div class="sect1" lang="en">
fb5a72174252e0e79107dcad3bf5a2bbd73e349cjohanengelen<div class="titlepage"><div><div><h2 class="title" style="clear: both">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<a name="notify"></a>Notify</h2></div></div></div>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <span class="acronym">DNS</span> NOTIFY is a mechanism that allows
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm master
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm servers to notify their slave servers of changes to a zone's data. In
0903335a0099bd7ee779925f43a15a2216a0e863johanengelen response to a <span><strong class="command">NOTIFY</strong></span> from a master
0903335a0099bd7ee779925f43a15a2216a0e863johanengelen server, the
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm slave will check to see that its version of the zone is the
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm current version and, if not, initiate a zone transfer.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm </p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <span class="acronym">DNS</span>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm For more information about
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <span><strong class="command">NOTIFY</strong></span>, see the description of the
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <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
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm the description of the zone option <span><strong class="command">also-notify</strong></span> in
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <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>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz protocol is specified in RFC 1996.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm </p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm</div>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="sect1" lang="en">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="titlepage"><div><div><h2 class="title" style="clear: both">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<a name="dynamic_update"></a>Dynamic Update</h2></div></div></div>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
79291918d036d77d586b6eba265d8d2ac0a7fee5cilix Dynamic Update is a method for adding, replacing or deleting
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm records in a master server by sending it a special form of DNS
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm messages. The format and meaning of these messages is specified
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm in RFC 2136.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm </p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm Dynamic update is enabled by
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm including an <span><strong class="command">allow-update</strong></span> or
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <span><strong class="command">update-policy</strong></span> clause in the
ea3e4fdbdbf0a48ae887b096d301549da77d5707Johan Engelen <span><strong class="command">zone</strong></span> statement.
ea3e4fdbdbf0a48ae887b096d301549da77d5707Johan Engelen </p>
c0cd5511d3b975ebe07d019c1f5528108725e438johanengelen<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm Updating of secure zones (zones using DNSSEC) follows
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm RFC 3007: RRSIG and NSEC records affected by updates are automatically
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm regenerated by the server using an online zone key.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm Update authorization is based
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm on transaction signatures and an explicit server policy.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm </p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="sect2" lang="en">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<div class="titlepage"><div><div><h3 class="title">
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<a name="journal"></a>The journal file</h3></div></div></div>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm All changes made to a zone using dynamic update are stored
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm in the zone's journal file. This file is automatically created
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm by the server when the first dynamic update takes place.
ea3e4fdbdbf0a48ae887b096d301549da77d5707Johan Engelen The name of the journal file is formed by appending the extension
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm <code class="filename">.jnl</code> to the name of the
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm corresponding zone
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm file unless specifically overridden. The journal file is in a
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm binary format and should not be edited manually.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm </p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm<p>
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm The server will also occasionally write ("dump")
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm the complete contents of the updated zone to its zone file.
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm This is not done immediately after
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm each dynamic update, because that would be too slow when a large
f07bfd5a05d43a6d11f7cd442f085149092dea88pjrm zone is updated frequently. Instead, the dump is delayed by
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz up to 15 minutes, allowing additional updates to take place.
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz </p>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz<p>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz When a server is restarted after a shutdown or crash, it will replay
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz the journal file to incorporate into the zone any updates that
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz took
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz place after the last zone dump.
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz </p>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz<p>
e7333a0a54c8d33b7397406dd76938aa430836d5joncruz Changes that result from incoming incremental zone transfers are
a4030d5ca449e7e384bc699cd249ee704faaeab0Chris Morgan also
journalled in a similar way.
</p>
<p>
The zone files of dynamic zones cannot normally be edited by
hand because they are not guaranteed to contain the most recent
dynamic changes - those are only in the journal file.
The only way to ensure that the zone file of a dynamic zone
is up to date is to run <span><strong class="command">rndc stop</strong></span>.
</p>
<p>
If you have to make changes to a dynamic zone
manually, the following procedure will work: Disable dynamic updates
to the zone using
<span><strong class="command">rndc freeze <em class="replaceable"><code>zone</code></em></strong></span>.
This will also remove the zone's <code class="filename">.jnl</code> file
and update the master file. Edit the zone file. Run
<span><strong class="command">rndc unfreeze <em class="replaceable"><code>zone</code></em></strong></span>
to reload the changed zone and re-enable dynamic updates.
</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="incremental_zone_transfers"></a>Incremental Zone Transfers (IXFR)</h2></div></div></div>
<p>
The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is specified in RFC
1995. See <a href="Bv9ARM.ch09.html#proposed_standards">Proposed Standards</a>.
</p>
<p>
When acting as a master, <span class="acronym">BIND</span> 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, <span class="acronym">BIND</span> 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="id2539940"></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.
</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>
<p>
Here is an example of a split DNS setup:
</p>
<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>,<span class="emphasis"><em></em></span> <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 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 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 <span class="acronym">BIND</span>. 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 <span class="acronym">BIND</span>.
</p>
<p>
<span class="acronym">BIND</span> primarily supports TSIG for server
to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <span class="acronym">BIND</span> 8 have limited support
for TSIG.
</p>
<p>
TSIG might be most useful for dynamic update. A primary
server for a dynamic zone should use access control to control
updates, 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.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2540455"></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="id2540472"></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="id2540510"></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="id2540529"></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="id2540539"></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 <span class="acronym">BIND</span>.
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="id2540579"></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="id2540705"></a>TSIG Key Based Access Control</h3></div></div></div>
<p>
<span class="acronym">BIND</span> 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="id2540818"></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 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 is set to
NOTAUTH.
</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2540832"></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. <span class="acronym">BIND</span> 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="id2540881"></a>SIG(0)</h2></div></div></div>
<p>
<span class="acronym">BIND</span> 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 <span class="acronym">BIND</span> 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 &lt;TBA&gt;. 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. <span class="acronym">BIND</span>
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">-h</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 presense
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="id2540949"></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 file names 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 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="id2541086"></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> 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">'-d'</code> is specified.
If <code class="literal">'-d'</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
administators 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="id2541234"></a>Configuring Servers</h3></div></div></div>
<p>
Unlike <span class="acronym">BIND</span> 8,
<span class="acronym">BIND</span> 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>
The public key for any security root must be present in
the configuration file's <span><strong class="command">trusted-keys</strong></span>
statement, as described later in this document.
</p>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2541257"></a>IPv6 Support in <span class="acronym">BIND</span> 9</h2></div></div></div>
<p>
<span class="acronym">BIND</span> 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, <span class="acronym">BIND</span> 9 supports
only AAAA
records. The use of A6 records is deprecated by RFC 3363, and the
support for forward lookups in <span class="acronym">BIND</span> 9
is
removed accordingly.
However, authoritative <span class="acronym">BIND</span> 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, <span class="acronym">BIND</span> 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.
<span class="acronym">BIND</span> 9 formerly
supported the "binary label" (also known as "bitstring") format.
The support of binary labels, however, is now completely removed
according to the changes in RFC 3363.
Any applications in <span class="acronym">BIND</span> 9 do not
understand
the format any more, and will return an error if given.
In particular, an authoritative <span class="acronym">BIND</span> 9
name
server rejects to 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="id2541317"></a>Address Lookups Using AAAA Records</h3></div></div></div>
<p>
The AAAA record is a parallel to the IPv4 A record. It
specifies the entire address in a single record. For
example,
</p>
<pre class="programlisting">
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
</pre>
<p>
It is recommended that IPv4-in-IPv6 mapped addresses not
be used. 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="id2541338"></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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