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<div class="chapter">
<div class="titlepage"><div><div><h1 class="title">
<div class="toc">
<p><b>Table of Contents</b></p>
<dl class="toc">
<dd><dl><dt><span class="section"><a href="Bv9ARM.ch04.html#journal">The journal file</a></span></dt></dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#incremental_zone_transfers">Incremental Zone Transfers (IXFR)</a></span></dt>
<dd><dl><dt><span class="section"><a href="Bv9ARM.ch04.html#split_dns_sample">Example split DNS setup</a></span></dt></dl></dd>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.6.5">Generating a Shared Key</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.6.7">Instructing the Server to Use a Key</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.6.8">TSIG-Based Access Control</a></span></dt>
</dl></dd>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#dnssec_signing">Signing the Zone</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#dnssec_config">Configuring Servers</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#dnssec.dynamic.zones">DNSSEC, Dynamic Zones, and Automatic Signing</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.2">Converting from insecure to secure</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.7">Dynamic DNS update method</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.15">Fully automatic zone signing</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.24">Private-type records</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.33">Dynamic DNS update method</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.38">Automatic key rollovers</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.40">NSEC3PARAM rollovers via UPDATE</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.42">Converting from NSEC to NSEC3</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.44">Converting from NSEC3 to NSEC</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.46">Converting from secure to insecure</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.10.50">Periodic re-signing</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#rfc5011.support">Dynamic Trust Anchor Management</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.11.3">Validating Resolver</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.11.4">Authoritative Server</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#pkcs11">PKCS#11 (Cryptoki) support</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.12.8">OpenSSL-based PKCS#11</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.12.11">Specifying the engine on the command line</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.12.12">Running named with automatic zone re-signing</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#dlz-info">DLZ (Dynamically Loadable Zones)</a></span></dt>
<dd><dl>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#dyndb-info">DynDB (Dynamic Database)</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.14.6">Sample DynDB Module</a></span></dt>
</dl></dd>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.15.4">Principle of Operation</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.15.5">Configuring Catalog Zones</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.15.6">Catalog Zone format</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="Bv9ARM.ch04.html#ipv6">IPv6 Support in <acronym class="acronym">BIND</acronym> 9</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.16.6">Address Lookups Using AAAA Records</a></span></dt>
<dt><span class="section"><a href="Bv9ARM.ch04.html#id-1.5.16.7">Address to Name Lookups Using Nibble Format</a></span></dt>
</dl></dd>
</dl>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="notify"></a>Notify</h2></div></div></div>
<p>
<acronym class="acronym">DNS</acronym> NOTIFY is a mechanism that allows master
servers to notify their slave servers of changes to a zone's data. In
response to a <span class="command"><strong>NOTIFY</strong></span> from a master server, the
slave will check to see that its version of the zone is the
current version and, if not, initiate a zone transfer.
</p>
<p>
For more information about <acronym class="acronym">DNS</acronym>
<span class="command"><strong>NOTIFY</strong></span>, see the description of the
<span class="command"><strong>notify</strong></span> option in <a class="xref" href="Bv9ARM.ch06.html#boolean_options" title="Boolean Options">the section called “Boolean Options”</a> and
the description of the zone option <span class="command"><strong>also-notify</strong></span> in
<a class="xref" href="Bv9ARM.ch06.html#zone_transfers" title="Zone Transfers">the section called “Zone Transfers”</a>. The <span class="command"><strong>NOTIFY</strong></span>
protocol is specified in RFC 1996.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
As a slave zone can also be a master to other slaves, <span class="command"><strong>named</strong></span>,
by default, sends <span class="command"><strong>NOTIFY</strong></span> messages for every zone
it loads. Specifying <span class="command"><strong>notify master-only;</strong></span> will
cause <span class="command"><strong>named</strong></span> to only send <span class="command"><strong>NOTIFY</strong></span> for master
zones that it loads.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dynamic_update"></a>Dynamic Update</h2></div></div></div>
<p>
Dynamic Update is a method for adding, replacing or deleting
records in a master server by sending it a special form of DNS
messages. The format and meaning of these messages is specified
in RFC 2136.
</p>
<p>
Dynamic update is enabled by including an
<span class="command"><strong>allow-update</strong></span> or an <span class="command"><strong>update-policy</strong></span>
clause in the <span class="command"><strong>zone</strong></span> statement.
</p>
<p>
If the zone's <span class="command"><strong>update-policy</strong></span> is set to
<strong class="userinput"><code>local</code></strong>, updates to the zone
will be permitted for the key <code class="varname">local-ddns</code>,
which will be generated by <span class="command"><strong>named</strong></span> at startup.
See <a class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called “Dynamic Update Policies”</a> for more details.
</p>
<p>
Dynamic updates using Kerberos signed requests can be made
<span class="command"><strong>tkey-gssapi-keytab</strong></span> option, or alternatively
by setting both the <span class="command"><strong>tkey-gssapi-credential</strong></span>
and <span class="command"><strong>tkey-domain</strong></span> options. Once enabled,
Kerberos signed requests will be matched against the update
policies for the zone, using the Kerberos principal as the
signer for the request.
</p>
<p>
Updating of secure zones (zones using DNSSEC) follows RFC
3007: RRSIG, NSEC and NSEC3 records affected by updates are
automatically regenerated by the server using an online
zone key. Update authorization is based on transaction
signatures and an explicit server policy.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="journal"></a>The journal file</h3></div></div></div>
<p>
All changes made to a zone using dynamic update are stored
in the zone's journal file. This file is automatically created
by the server when the first dynamic update takes place.
The name of the journal file is formed by appending the extension
<code class="filename">.jnl</code> to the name of the
corresponding zone
file unless specifically overridden. The journal file is in a
binary format and should not be edited manually.
</p>
<p>
The server will also occasionally write ("dump")
the complete contents of the updated zone to its zone file.
This is not done immediately after
each dynamic update, because that would be too slow when a large
zone is updated frequently. Instead, the dump is delayed by
up to 15 minutes, allowing additional updates to take place.
During the dump process, transient files will be created
with the extensions <code class="filename">.jnw</code> and
<code class="filename">.jbk</code>; under ordinary circumstances, these
will be removed when the dump is complete, and can be safely
ignored.
</p>
<p>
When a server is restarted after a shutdown or crash, it will replay
the journal file to incorporate into the zone any updates that
took
place after the last zone dump.
</p>
<p>
Changes that result from incoming incremental zone transfers are
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 class="command"><strong>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 class="command"><strong>rndc freeze <em class="replaceable"><code>zone</code></em></strong></span>.
This will update the zone's master file with the changes
stored in its <code class="filename">.jnl</code> file.
Edit the zone file. Run
<span class="command"><strong>rndc thaw <em class="replaceable"><code>zone</code></em></strong></span>
to reload the changed zone and re-enable dynamic updates.
</p>
<p>
<span class="command"><strong>rndc sync <em class="replaceable"><code>zone</code></em></strong></span>
will update the zone file with changes from the journal file
without stopping dynamic updates; this may be useful for viewing
the current zone state. To remove the <code class="filename">.jnl</code>
file after updating the zone file, use
<span class="command"><strong>rndc sync -clean</strong></span>.
</p>
</div>
</div>
<div class="section">
<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 class="xref" href="Bv9ARM.ch11.html#proposed_standards" title="Proposed Standards">Proposed Standards</a>.
</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 class="command"><strong>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 class="command"><strong>request-ixfr</strong></span> clause
of the <span class="command"><strong>server</strong></span> statement.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="split_dns"></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="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="split_dns_sample"></a>Example split DNS setup</h3></div></div></div>
<p>
Let's say a company named <span class="emphasis"><em>Example, Inc.</em></span>
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>,
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>,
</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
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>
<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 class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Look up any hostnames in the <code class="literal">site1</code>
and
</li>
<li class="listitem">
</li>
<li class="listitem">
Look up any hostnames on the Internet.
</li>
<li class="listitem">
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 class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Look up any hostnames in the <code class="literal">site1</code>
and
</li>
<li class="listitem">
Exchange mail with anyone in the <code class="literal">site1</code> and
</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 class="xref" href="Bv9ARM.ch03.html#sample_configuration" title="Sample Configurations">the section called “Sample Configurations”</a>.
</p>
<p>
Internal DNS server config:
</p>
<pre class="programlisting">
acl externals { <code class="varname">bastion-ips-go-here</code>; };
options {
...
...
forward only;
// forward to external servers
forwarders {
<code class="varname">bastion-ips-go-here</code>;
};
// sample allow-transfer (no one)
allow-transfer { none; };
// restrict query access
allow-query { internals; externals; };
// restrict recursion
allow-recursion { internals; };
...
...
};
// sample master zone
zone "site1.example.com" {
type master;
file "m/site1.example.com";
// do normal iterative resolution (do not forward)
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
// sample slave zone
zone "site2.example.com" {
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 externals { bastion-ips-go-here; };
options {
...
...
// sample allow-transfer (no one)
allow-transfer { none; };
// default query access
allow-query { any; };
// restrict cache access
allow-query-cache { internals; externals; };
// restrict recursion
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>
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="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tsig"></a>TSIG</h2></div></div></div>
<p>
TSIG (Transaction SIGnatures) is a mechanism for authenticating DNS
messages, originally specified in RFC 2845. It allows DNS messages
to be cryptographically signed using a shared secret. TSIG can
be used in any DNS transaction, as a way to restrict access to
certain server functions (e.g., recursive queries) to authorized
clients when IP-based access control is insufficient or needs to
be overridden, or as a way to ensure message authenticity when it
is critical to the integrity of the server, such as with dynamic
UPDATE messages or zone transfers from a master to a slave server.
</p>
<p>
This is a guide to setting up TSIG in <acronym class="acronym">BIND</acronym>.
It describes the configuration syntax and the process of creating
TSIG keys.
</p>
<p>
<span class="command"><strong>named</strong></span> supports TSIG for server-to-server
communication, and some of the tools included with
<acronym class="acronym">BIND</acronym> support it for sending messages to
<span class="command"><strong>named</strong></span>:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<a class="xref" href="man.nsupdate.html" title="nsupdate"><span class="refentrytitle"><span class="application">nsupdate</span></span>(1)</a> supports TSIG via the
<code class="option">-k</code>, <code class="option">-l</code> and
<code class="option">-y</code> command line options, or via
the <span class="command"><strong>key</strong></span> command when running
interactively.
</li>
<li class="listitem">
<a class="xref" href="man.dig.html" title="dig"><span class="refentrytitle">dig</span>(1)</a> supports TSIG via the
<code class="option">-k</code> and <code class="option">-y</code> command
line options.
</li>
</ul></div>
<p>
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.6.5"></a>Generating a Shared Key</h3></div></div></div>
<p>
TSIG keys can be generated using the <span class="command"><strong>tsig-keygen</strong></span>
command; the output of the command is a <span class="command"><strong>key</strong></span> directive
key name, algorithm and size can be specified by command line parameters;
the defaults are "tsig-key", HMAC-SHA256, and 256 bits, respectively.
</p>
<p>
Any string which is a valid DNS name can be used as a key name.
For example, a key to be shared between servers called
<span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host2</em></span> could
be called "host1-host2.", and this key could be generated using:
</p>
<pre class="programlisting">
$ tsig-keygen host1-host2. > host1-host2.key
</pre>
<p>
This key may then be copied to both hosts. The key name and secret
must be identical on both hosts.
(Note: copying a shared secret from one server to another is beyond
the scope of the DNS. A secure transport mechanism should be used:
secure FTP, SSL, ssh, telephone, encrypted email, etc.)
</p>
<p>
<span class="command"><strong>tsig-keygen</strong></span> can also be run as
<span class="command"><strong>ddns-confgen</strong></span>, in which case its output includes
additional configuration text for setting up dynamic DNS in
<span class="command"><strong>named</strong></span>. See <a class="xref" href="man.ddns-confgen.html" title="ddns-confgen"><span class="refentrytitle"><span class="application">ddns-confgen</span></span>(8)</a>
for details.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.6.6"></a>Loading A New Key</h3></div></div></div>
<p>
For a key shared between servers called
<span class="emphasis"><em>host1</em></span> and <span class="emphasis"><em>host2</em></span>,
the following could be added to each server's
</p>
<pre class="programlisting">
key "host1-host2." {
algorithm hmac-sha256;
secret "DAopyf1mhCbFVZw7pgmNPBoLUq8wEUT7UuPoLENP2HY=";
};
</pre>
<p>
(This is the same key generated above using
<span class="command"><strong>tsig-keygen</strong></span>.)
</p>
<p>
Since this text contains a secret, it
world-readable, or that the <span class="command"><strong>key</strong></span> directive
be stored in a file which is not world-readable, and which is
<span class="command"><strong>include</strong></span> directive.
</p>
<p>
server has been restarted or reconfigured, the server can recognize
the key. If the server receives a message signed by the
key, it will be able to verify the signature. If the signature
is valid, the response will be signed using the same key.
</p>
<p>
TSIG keys that are known to a server can be listed using the
command <span class="command"><strong>rndc tsig-list</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.6.7"></a>Instructing the Server to Use a Key</h3></div></div></div>
<p>
A server sending a request to another server must be told whether
to use a key, and if so, which key to use.
</p>
<p>
For example, a key may be specified for each server in the
<span class="command"><strong>masters</strong></span> statement in the definition of a
slave zone; in this case, all SOA QUERY messages, NOTIFY
messages, and zone transfer requests (AXFR or IXFR) will be
signed using the specified key. Keys may also be specified
in the <span class="command"><strong>also-notify</strong></span> statement of a master
or slave zone, causing NOTIFY messages to be signed using
the specified key.
</p>
<p>
Keys can also be specified in a <span class="command"><strong>server</strong></span>
directive. Adding the following on <span class="emphasis"><em>host1</em></span>,
if the IP address of <span class="emphasis"><em>host2</em></span> is 10.1.2.3, would
cause <span class="emphasis"><em>all</em></span> requests from <span class="emphasis"><em>host1</em></span>
to <span class="emphasis"><em>host2</em></span>, including normal DNS queries, to be
signed using the <span class="command"><strong>host1-host2.</strong></span> key:
</p>
<pre class="programlisting">
server 10.1.2.3 {
keys { host1-host2. ;};
};
</pre>
<p>
Multiple keys may be present in the <span class="command"><strong>keys</strong></span>
statement, but only the first one is used. As this directive does
not contain secrets, it can be used in a world-readable file.
</p>
<p>
Requests sent by <span class="emphasis"><em>host2</em></span> to <span class="emphasis"><em>host1</em></span>
would <span class="emphasis"><em>not</em></span> be signed, unless a similar
<span class="command"><strong>server</strong></span> directive were in <span class="emphasis"><em>host2</em></span>'s
configuration file.
</p>
<p>
Whenever any server sends a TSIG-signed DNS request, it will expect
the response to be signed with the same key. If a response is not
signed, or if the signature is not valid, the response will be
rejected.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.6.8"></a>TSIG-Based Access Control</h3></div></div></div>
<p>
TSIG keys may be specified in ACL definitions and ACL directives
such as <span class="command"><strong>allow-query</strong></span>, <span class="command"><strong>allow-transfer</strong></span>
and <span class="command"><strong>allow-update</strong></span>.
The above key would be denoted in an ACL element as
<span class="command"><strong>key host1-host2.</strong></span>
</p>
<p>
An example of an <span class="command"><strong>allow-update</strong></span> directive using
a TSIG key:
</p>
<pre class="programlisting">
allow-update { !{ !localnets; any; }; key host1-host2. ;};
</pre>
<p>
This allows dynamic updates to succeed only if the UPDATE
request comes from an address in <span class="command"><strong>localnets</strong></span>,
<span class="emphasis"><em>and</em></span> if it is signed using the
<span class="command"><strong>host1-host2.</strong></span> key.
</p>
<p>
See <a class="xref" href="Bv9ARM.ch06.html#dynamic_update_policies" title="Dynamic Update Policies">the section called “Dynamic Update Policies”</a> for a discussion of
the more flexible <span class="command"><strong>update-policy</strong></span> statement.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.6.9"></a>Errors</h3></div></div></div>
<p>
Processing of TSIG-signed messages can result in several errors:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
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.
</li>
<li class="listitem">
If a TSIG-aware server receives a message from a known key
but with an invalid signature, the response will be unsigned,
with the TSIG extended error code set to BADSIG.
</li>
<li class="listitem">
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.
</li>
</ul></div>
<p>
In all of the above cases, the server will return a response code
of NOTAUTH (not authenticated).
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="tkey"></a>TKEY</h2></div></div></div>
<p>
TKEY (Transaction KEY) is a mechanism for automatically negotiating
a shared secret between two hosts, originally specified in RFC 2930.
</p>
<p>
There are several TKEY "modes" that specify how a key is to be
generated or assigned. <acronym class="acronym">BIND</acronym> 9 implements only
one of these modes: Diffie-Hellman key exchange. Both hosts are
required to have a KEY record with algorithm DH (though this
record is not required to be present in a zone).
</p>
<p>
The TKEY process is initiated by a client or server by sending
a query of type TKEY to a TKEY-aware server. The query must include
an appropriate KEY record in the additional section, and
must be signed using either TSIG or SIG(0) with a previously
established key. The server's response, if successful, will
contain a TKEY record in its answer section. After this transaction,
both participants will have enough information to calculate a
shared secret using Diffie-Hellman key exchange. The shared secret
can then be used by to sign subsequent transactions between the
two servers.
</p>
<p>
TSIG keys known by the server, including TKEY-negotiated keys, can
be listed using <span class="command"><strong>rndc tsig-list</strong></span>.
</p>
<p>
TKEY-negotiated keys can be deleted from a server using
<span class="command"><strong>rndc tsig-delete</strong></span>. This can also be done via
the TKEY protocol itself, by sending an authenticated TKEY query
specifying the "key deletion" mode.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sig0"></a>SIG(0)</h2></div></div></div>
<p>
<acronym class="acronym">BIND</acronym> partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC 2931.
is performed in the same manner as TSIG keys; privileges can be
granted or denied in ACL directives 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 recursively fetch 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 class="command"><strong>nsupdate</strong></span>.
</p>
</div>
<div class="section">
<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
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="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="dnssec_keys"></a>Generating Keys</h3></div></div></div>
<p>
The <span class="command"><strong>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 class="command"><strong>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
</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:
(where
12345 is an example of a key tag). The key filenames contain
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 class="command"><strong>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 class="command"><strong>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 class="command"><strong>$INCLUDE</strong></span> statements.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="dnssec_signing"></a>Signing the Zone</h3></div></div></div>
<p>
The <span class="command"><strong>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
default, all zone keys which have an available private key are
used to generate signatures.
</p>
<p>
</p>
<p>
One output file is produced:
file
as the
input file for the zone.
</p>
<p><span class="command"><strong>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="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="dnssec_config"></a>Configuring Servers</h3></div></div></div>
<p>
To enable <span class="command"><strong>named</strong></span> to respond appropriately
to DNS requests from DNSSEC aware clients,
<span class="command"><strong>dnssec-enable</strong></span> must be set to yes.
(This is the default setting.)
</p>
<p>
To enable <span class="command"><strong>named</strong></span> to validate answers from
other servers, the <span class="command"><strong>dnssec-enable</strong></span> option
must be set to <strong class="userinput"><code>yes</code></strong>, and the
<span class="command"><strong>dnssec-validation</strong></span> options must be set to
<strong class="userinput"><code>yes</code></strong> or <strong class="userinput"><code>auto</code></strong>.
</p>
<p>
If <span class="command"><strong>dnssec-validation</strong></span> is set to
<strong class="userinput"><code>auto</code></strong>, then a default
trust anchor for the DNS root zone will be used.
If it is set to <strong class="userinput"><code>yes</code></strong>, however,
then at least one trust anchor must be configured
with a <span class="command"><strong>trusted-keys</strong></span> or
<span class="command"><strong>managed-keys</strong></span> statement in
will not occur. The default setting is
<strong class="userinput"><code>yes</code></strong>.
</p>
<p>
<span class="command"><strong>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 class="command"><strong>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 class="command"><strong>managed-keys</strong></span> are trusted keys which are
automatically kept up to date via RFC 5011 trust anchor
maintenance.
</p>
<p>
<span class="command"><strong>trusted-keys</strong></span> and
<span class="command"><strong>managed-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 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 class="command"><strong>named</strong></span>
is immune to compromises in the DNSSEC components of the security
of parent zones.
</p>
<pre class="programlisting">
managed-keys {
/* Root Key */
"." initial-key 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
dgxbcDTClU0CRBdiieyLMNzXG3";
};
trusted-keys {
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
1OTQ09A0=";
/* Key for our reverse zone. */
xOdNax071L18QqZnQQQAVVr+i
LhGTnNGp3HoWQLUIzKrJVZ3zg
gy3WwNT6kZo6c0tszYqbtvchm
siaOdS0yOI6BgPsw+YZdzlYMa
IJGf4M4dyoKIhzdZyQ2bYQrjy
Q4LB0lC7aOnsMyYKHHYeRvPxj
IQXmdqgOJGq+vsevG06zW+1xg
59VvjSPsZJHeDCUyWYrvPZesZ
DIRvhDD52SKvbheeTJUm6Ehkz
};
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>
<p>
None of the keys listed in this example are valid. In particular,
the root key is not valid.
</p>
</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
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".
</p>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dnssec.dynamic.zones"></a>DNSSEC, Dynamic Zones, and Automatic Signing</h2></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.2"></a>Converting from insecure to secure</h3></div></div></div>
</div>
<p>Changing a zone from insecure to secure can be done in two
ways: using a dynamic DNS update, or the
<span class="command"><strong>auto-dnssec</strong></span> zone option.</p>
<p>For either method, you need to configure
<span class="command"><strong>named</strong></span> so that it can see the
<code class="filename">K*</code> files which contain the public and private
parts of the keys that will be used to sign the zone. These files
will have been generated by
<span class="command"><strong>dnssec-keygen</strong></span>. You can do this by placing them
in the key-directory, as specified in
<pre class="programlisting">
zone example.net {
type master;
update-policy local;
key-directory "dynamic/example.net";
};
</pre>
<p>If one KSK and one ZSK DNSKEY key have been generated, this
configuration will cause all records in the zone to be signed
with the ZSK, and the DNSKEY RRset to be signed with the KSK as
well. An NSEC chain will be generated as part of the initial
signing process.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.7"></a>Dynamic DNS update method</h3></div></div></div>
</div>
<p>To insert the keys via dynamic update:</p>
<pre class="screen">
% nsupdate
> ttl 3600
> update add example.net DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8=
> update add example.net DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk=
> send
</pre>
<p>While the update request will complete almost immediately,
the zone will not be completely signed until
<span class="command"><strong>named</strong></span> has had time to walk the zone and
generate the NSEC and RRSIG records. The NSEC record at the apex
will be added last, to signal that there is a complete NSEC
chain.</p>
<p>If you wish to sign using NSEC3 instead of NSEC, you should
add an NSEC3PARAM record to the initial update request. If you
wish the NSEC3 chain to have the OPTOUT bit set, set it in the
flags field of the NSEC3PARAM record.</p>
<pre class="screen">
% nsupdate
> ttl 3600
> update add example.net DNSKEY 256 3 7 AwEAAZn17pUF0KpbPA2c7Gz76Vb18v0teKT3EyAGfBfL8eQ8al35zz3Y I1m/SAQBxIqMfLtIwqWPdgthsu36azGQAX8=
> update add example.net DNSKEY 257 3 7 AwEAAd/7odU/64o2LGsifbLtQmtO8dFDtTAZXSX2+X3e/UNlq9IHq3Y0 XtC0Iuawl/qkaKVxXe2lo8Ct+dM6UehyCqk=
> update add example.net NSEC3PARAM 1 1 100 1234567890
> send
</pre>
<p>Again, this update request will complete almost
immediately; however, the record won't show up until
relevant chain. A private type record will be created to record
the state of the operation (see below for more details), and will
be removed once the operation completes.</p>
is happening, other updates are possible as well.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.15"></a>Fully automatic zone signing</h3></div></div></div>
</div>
<p>To enable automatic signing, add the
<span class="command"><strong>auto-dnssec</strong></span> option to the zone statement in
<span class="command"><strong>auto-dnssec</strong></span> has two possible arguments:
<code class="constant">allow</code> or
<code class="constant">maintain</code>.</p>
<p>With
<span class="command"><strong>auto-dnssec allow</strong></span>,
<span class="command"><strong>named</strong></span> can search the key directory for keys
matching the zone, insert them into the zone, and use them to
sign the zone. It will do so only when it receives an
<span class="command"><strong>rndc sign <zonename></strong></span>.</p>
<p>
<span class="command"><strong>auto-dnssec maintain</strong></span> includes the above
functionality, but will also automatically adjust the zone's
DNSKEY records on schedule according to the keys' timing metadata.
(See <a class="xref" href="man.dnssec-keygen.html" title="dnssec-keygen"><span class="refentrytitle"><span class="application">dnssec-keygen</span></span>(8)</a> and
<a class="xref" href="man.dnssec-settime.html" title="dnssec-settime"><span class="refentrytitle"><span class="application">dnssec-settime</span></span>(8)</a> for more information.)
</p>
<p>
<span class="command"><strong>named</strong></span> will periodically search the key directory
for keys matching the zone, and if the keys' metadata indicates
that any change should be made the zone, such as adding, removing,
or revoking a key, then that action will be carried out. By default,
the key directory is checked for changes every 60 minutes; this period
can be adjusted with the <code class="option">dnssec-loadkeys-interval</code>, up
to a maximum of 24 hours. The <span class="command"><strong>rndc loadkeys</strong></span> forces
<span class="command"><strong>named</strong></span> to check for key updates immediately.
</p>
<p>
If keys are present in the key directory the first time the zone
is loaded, the zone will be signed immediately, without waiting for an
<span class="command"><strong>rndc sign</strong></span> or <span class="command"><strong>rndc loadkeys</strong></span>
command. (Those commands can still be used when there are unscheduled
key changes, however.)
</p>
<p>
When new keys are added to a zone, the TTL is set to match that
of any existing DNSKEY RRset. If there is no existing DNSKEY RRset,
then the TTL will be set to the TTL specified when the key was
created (using the <span class="command"><strong>dnssec-keygen -L</strong></span> option), if
any, or to the SOA TTL.
</p>
<p>
If you wish the zone to be signed using NSEC3 instead of NSEC,
submit an NSEC3PARAM record via dynamic update prior to the
scheduled publication and activation of the keys. If you wish the
NSEC3 chain to have the OPTOUT bit set, set it in the flags field
of the NSEC3PARAM record. The NSEC3PARAM record will not appear in
the zone immediately, but it will be stored for later reference. When
the zone is signed and the NSEC3 chain is completed, the NSEC3PARAM
record will appear in the zone.
</p>
<p>Using the
<span class="command"><strong>auto-dnssec</strong></span> option requires the zone to be
configured to allow dynamic updates, by adding an
<span class="command"><strong>allow-update</strong></span> or
<span class="command"><strong>update-policy</strong></span> statement to the zone
configuration. If this has not been done, the configuration will
fail.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.24"></a>Private-type records</h3></div></div></div>
</div>
<p>The state of the signing process is signaled by
private-type records (with a default type value of 65534). When
signing is complete, these records will have a nonzero value for
the final octet (for those records which have a nonzero initial
octet).</p>
<p>The private type record format: If the first octet is
non-zero then the record indicates that the zone needs to be
signed with the key matching the record, or that all signatures
that match the record should be removed.</p>
<p>
</p>
<div class="literallayout"><p><br>
<br>
��algorithm�(octet�1)<br>
��key�id�in�network�order�(octet�2�and�3)<br>
��removal�flag�(octet�4)<br>
��complete�flag�(octet�5)<br>
</p></div>
<p>
</p>
<p>Only records flagged as "complete" can be removed via
dynamic update. Attempts to remove other private type records
will be silently ignored.</p>
<p>If the first octet is zero (this is a reserved algorithm
number that should never appear in a DNSKEY record) then the
record indicates changes to the NSEC3 chains are in progress. The
rest of the record contains an NSEC3PARAM record. The flag field
tells what operation to perform based on the flag bits.</p>
<p>
</p>
<div class="literallayout"><p><br>
<br>
��0x01�OPTOUT<br>
��0x80�CREATE<br>
��0x40�REMOVE<br>
��0x20�NONSEC<br>
</p></div>
<p>
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.31"></a>DNSKEY rollovers</h3></div></div></div>
</div>
<p>As with insecure-to-secure conversions, rolling DNSSEC
keys can be done in two ways: using a dynamic DNS update, or the
<span class="command"><strong>auto-dnssec</strong></span> zone option.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.33"></a>Dynamic DNS update method</h3></div></div></div>
</div>
<p> To perform key rollovers via dynamic update, you need to add
the <code class="filename">K*</code> files for the new keys so that
<span class="command"><strong>named</strong></span> can find them. You can then add the new
DNSKEY RRs via dynamic update.
<span class="command"><strong>named</strong></span> will then cause the zone to be signed
with the new keys. When the signing is complete the private type
records will be updated so that the last octet is non
zero.</p>
<p>If this is for a KSK you need to inform the parent and any
trust anchor repositories of the new KSK.</p>
<p>You should then wait for the maximum TTL in the zone before
removing the old DNSKEY. If it is a KSK that is being updated,
you also need to wait for the DS RRset in the parent to be
updated and its TTL to expire. This ensures that all clients will
be able to verify at least one signature when you remove the old
DNSKEY.</p>
<p>The old DNSKEY can be removed via UPDATE. Take care to
specify the correct key.
<span class="command"><strong>named</strong></span> will clean out any signatures generated
by the old key after the update completes.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.38"></a>Automatic key rollovers</h3></div></div></div>
</div>
<p>When a new key reaches its activation date (as set by
<span class="command"><strong>dnssec-keygen</strong></span> or <span class="command"><strong>dnssec-settime</strong></span>),
if the <span class="command"><strong>auto-dnssec</strong></span> zone option is set to
<code class="constant">maintain</code>, <span class="command"><strong>named</strong></span> will
automatically carry out the key rollover. If the key's algorithm
has not previously been used to sign the zone, then the zone will
be fully signed as quickly as possible. However, if the new key
is replacing an existing key of the same algorithm, then the
zone will be re-signed incrementally, with signatures from the
old key being replaced with signatures from the new key as their
signature validity periods expire. By default, this rollover
completes in 30 days, after which it will be safe to remove the
old key from the DNSKEY RRset.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.40"></a>NSEC3PARAM rollovers via UPDATE</h3></div></div></div>
</div>
<p>Add the new NSEC3PARAM record via dynamic update. When the
new NSEC3 chain has been generated, the NSEC3PARAM flag field
will be zero. At this point you can remove the old NSEC3PARAM
record. The old chain will be removed after the update request
completes.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.42"></a>Converting from NSEC to NSEC3</h3></div></div></div>
</div>
<p>To do this, you just need to add an NSEC3PARAM record. When
the conversion is complete, the NSEC chain will have been removed
and the NSEC3PARAM record will have a zero flag field. The NSEC3
chain will be generated before the NSEC chain is
destroyed.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.44"></a>Converting from NSEC3 to NSEC</h3></div></div></div>
</div>
<p>To do this, use <span class="command"><strong>nsupdate</strong></span> to
remove all NSEC3PARAM records with a zero flag
field. The NSEC chain will be generated before the NSEC3 chain is
removed.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.46"></a>Converting from secure to insecure</h3></div></div></div>
</div>
<p>To convert a signed zone to unsigned using dynamic DNS,
delete all the DNSKEY records from the zone apex using
<span class="command"><strong>nsupdate</strong></span>. All signatures, NSEC or NSEC3 chains,
and associated NSEC3PARAM records will be removed automatically.
This will take place after the update request completes.</p>
<p> This requires the
<span class="command"><strong>dnssec-secure-to-insecure</strong></span> option to be set to
<strong class="userinput"><code>yes</code></strong> in
<p>In addition, if the <span class="command"><strong>auto-dnssec maintain</strong></span>
zone statement is used, it should be removed or changed to
<span class="command"><strong>allow</strong></span> instead (or it will re-sign).
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.50"></a>Periodic re-signing</h3></div></div></div>
</div>
<p>In any secure zone which supports dynamic updates, <span class="command"><strong>named</strong></span>
will periodically re-sign RRsets which have not been re-signed as
a result of some update action. The signature lifetimes will be
adjusted so as to spread the re-sign load over time rather than
all at once.</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.10.52"></a>NSEC3 and OPTOUT</h3></div></div></div>
</div>
<p>
<span class="command"><strong>named</strong></span> only supports creating new NSEC3 chains
where all the NSEC3 records in the zone have the same OPTOUT
state.
<span class="command"><strong>named</strong></span> supports UPDATES to zones where the NSEC3
records in the chain have mixed OPTOUT state.
<span class="command"><strong>named</strong></span> does not support changing the OPTOUT
state of an individual NSEC3 record, the entire chain needs to be
changed if the OPTOUT state of an individual NSEC3 needs to be
changed.</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<p>
BIND is able to maintain DNSSEC trust anchors using RFC 5011 key
management. This feature allows <span class="command"><strong>named</strong></span> to keep track
of changes to critical DNSSEC keys without any need for the operator to
make changes to configuration files.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.11.3"></a>Validating Resolver</h3></div></div></div>
<p>To configure a validating resolver to use RFC 5011 to
maintain a trust anchor, configure the trust anchor using a
<span class="command"><strong>managed-keys</strong></span> statement. Information about
this can be found in
<a class="xref" href="Bv9ARM.ch06.html#managed-keys" title="managed-keys Statement Definition and Usage">the section called “<span class="command"><strong>managed-keys</strong></span> Statement Definition
and Usage”</a>.</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.11.4"></a>Authoritative Server</h3></div></div></div>
<p>To set up an authoritative zone for RFC 5011 trust anchor
maintenance, generate two (or more) key signing keys (KSKs) for
the zone. Sign the zone with one of them; this is the "active"
KSK. All KSKs which do not sign the zone are "stand-by"
keys.</p>
<p>Any validating resolver which is configured to use the
active KSK as an RFC 5011-managed trust anchor will take note
of the stand-by KSKs in the zone's DNSKEY RRset, and store them
for future reference. The resolver will recheck the zone
periodically, and after 30 days, if the new key is still there,
then the key will be accepted by the resolver as a valid trust
anchor for the zone. Any time after this 30-day acceptance
timer has completed, the active KSK can be revoked, and the
zone can be "rolled over" to the newly accepted key.</p>
<p>The easiest way to place a stand-by key in a zone is to
use the "smart signing" features of
<span class="command"><strong>dnssec-keygen</strong></span> and
<span class="command"><strong>dnssec-signzone</strong></span>. If a key with a publication
date in the past, but an activation date which is unset or in
the future, "
<span class="command"><strong>dnssec-signzone -S</strong></span>" will include the DNSKEY
record in the zone, but will not sign with it:</p>
<pre class="screen">
$ <strong class="userinput"><code>dnssec-keygen -K keys -f KSK -P now -A now+2y example.net</code></strong>
</pre>
<p>To revoke a key, the new command
<span class="command"><strong>dnssec-revoke</strong></span> has been added. This adds the
REVOKED bit to the key flags and re-generates the
<code class="filename">K*.key</code> and
<code class="filename">K*.private</code> files.</p>
<p>After revoking the active key, the zone must be signed
with both the revoked KSK and the new active KSK. (Smart
signing takes care of this automatically.)</p>
<p>Once a key has been revoked and used to sign the DNSKEY
RRset in which it appears, that key will never again be
accepted as a valid trust anchor by the resolver. However,
validation can proceed using the new active key (which had been
accepted by the resolver when it was a stand-by key).</p>
<p>See RFC 5011 for more details on key rollover
scenarios.</p>
<p>When a key has been revoked, its key ID changes,
increasing by 128, and wrapping around at 65535. So, for
<p>If two keys have IDs exactly 128 apart, and one is
revoked, then the two key IDs will collide, causing several
problems. To prevent this,
<span class="command"><strong>dnssec-keygen</strong></span> will not generate a new key if
another key is present which may collide. This checking will
only occur if the new keys are written to the same directory
which holds all other keys in use for that zone.</p>
<p>Older versions of BIND 9 did not have this precaution.
Exercise caution if using key revocation on keys that were
generated by previous releases, or if using keys stored in
multiple directories or on multiple machines.</p>
<p>It is expected that a future release of BIND 9 will
address this problem in a different way, by storing revoked
keys with their original unrevoked key IDs.</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="pkcs11"></a>PKCS#11 (Cryptoki) support</h2></div></div></div>
<p>
PKCS#11 (Public Key Cryptography Standard #11) defines a
platform-independent API for the control of hardware security
modules (HSMs) and other cryptographic support devices.
</p>
<p>
BIND 9 is known to work with three HSMs: The AEP Keyper, which has
been tested with Debian Linux, Solaris x86 and Windows Server 2003;
the Thales nShield, tested with Debian Linux; and the Sun SCA 6000
cryptographic acceleration board, tested with Solaris x86. In
addition, BIND can be used with all current versions of SoftHSM,
a software-based HSM simulator library produced by the OpenDNSSEC
project.
</p>
<p>
PKCS#11 makes use of a "provider library": a dynamically loadable
library which provides a low-level PKCS#11 interface to drive the HSM
hardware. The PKCS#11 provider library comes from the HSM vendor, and
it is specific to the HSM to be controlled.
</p>
<p>
There are two available mechanisms for PKCS#11 support in BIND 9:
OpenSSL-based PKCS#11 and native PKCS#11. When using the first
mechanism, BIND uses a modified version of OpenSSL, which loads
the provider library and operates the HSM indirectly; any
cryptographic operations not supported by the HSM can be carried
out by OpenSSL instead. The second mechanism enables BIND to bypass
OpenSSL completely; BIND loads the provider library itself, and uses
the PKCS#11 API to drive the HSM directly.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.6"></a>Prerequisites</h3></div></div></div>
<p>
See the documentation provided by your HSM vendor for
information about installing, initializing, testing and
troubleshooting the HSM.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.7"></a>Native PKCS#11</h3></div></div></div>
<p>
Native PKCS#11 mode will only work with an HSM capable of carrying
out <span class="emphasis"><em>every</em></span> cryptographic operation BIND 9 may
need. The HSM's provider library must have a complete implementation
of the PKCS#11 API, so that all these functions are accessible. As of
this writing, only the Thales nShield HSM and SoftHSMv2 can be used
in this fashion. For other HSMs, including the AEP Keyper, Sun SCA
6000 and older versions of SoftHSM, use OpenSSL-based PKCS#11.
(Note: Eventually, when more HSMs become capable of supporting
native PKCS#11, it is expected that OpenSSL-based PKCS#11 will
be deprecated.)
</p>
<p>
To build BIND with native PKCS#11, configure as follows:
</p>
<pre class="screen">
$ <strong class="userinput"><code>cd bind9</code></strong>
--with-pkcs11=<em class="replaceable"><code>provider-library-path</code></em></code></strong>
</pre>
<p>
This will cause all BIND tools, including <span class="command"><strong>named</strong></span>
and the <span class="command"><strong>dnssec-*</strong></span> and <span class="command"><strong>pkcs11-*</strong></span>
tools, to use the PKCS#11 provider library specified in
<em class="replaceable"><code>provider-library-path</code></em> for cryptography.
(The provider library path can be overridden using the
<code class="option">-E</code> in <span class="command"><strong>named</strong></span> and the
<span class="command"><strong>dnssec-*</strong></span> tools, or the <code class="option">-m</code> in
the <span class="command"><strong>pkcs11-*</strong></span> tools.)
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.7.6"></a>Building SoftHSMv2</h4></div></div></div>
<p>
SoftHSMv2, the latest development version of SoftHSM, is available
from
</a>.
It is a software library developed by the OpenDNSSEC project
</a>)
which provides a PKCS#11 interface to a virtual HSM, implemented in
the form of a SQLite3 database on the local filesystem. It provides
less security than a true HSM, but it allows you to experiment with
native PKCS#11 when an HSM is not available. SoftHSMv2 can be
configured to use either OpenSSL or the Botan library to perform
cryptographic functions, but when using it for native PKCS#11 in
BIND, OpenSSL is required.
</p>
<p>
By default, the SoftHSMv2 configuration file is
<em class="replaceable"><code>prefix</code></em> is configured at compile time).
This location can be overridden by the SOFTHSM2_CONF environment
variable. The SoftHSMv2 cryptographic store must be installed and
initialized before using it with BIND.
</p>
<pre class="screen">
$ <strong class="userinput"><code> cd SoftHSMv2 </code></strong>
$ <strong class="userinput"><code> configure --with-crypto-backend=openssl --prefix=/opt/pkcs11/usr --enable-gost </code></strong>
$ <strong class="userinput"><code> make </code></strong>
$ <strong class="userinput"><code> make install </code></strong>
$ <strong class="userinput"><code> /opt/pkcs11/usr/bin/softhsm-util --init-token 0 --slot 0 --label softhsmv2 </code></strong>
</pre>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.8"></a>OpenSSL-based PKCS#11</h3></div></div></div>
<p>
OpenSSL-based PKCS#11 mode uses a modified version of the
OpenSSL library; stock OpenSSL does not fully support PKCS#11.
ISC provides a patch to OpenSSL to correct this. This patch is
based on work originally done by the OpenSolaris project; it has been
modified by ISC to provide new features such as PIN management and
key-by-reference.
</p>
<p>
There are two "flavors" of PKCS#11 support provided by
the patched OpenSSL, one of which must be chosen at
configuration time. The correct choice depends on the HSM
hardware:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Use 'crypto-accelerator' with HSMs that have hardware
cryptographic acceleration features, such as the SCA 6000
board. This causes OpenSSL to run all supported
cryptographic operations in the HSM.
</p>
</li>
<li class="listitem">
<p>
Use 'sign-only' with HSMs that are designed to
function primarily as secure key storage devices, but lack
hardware acceleration. These devices are highly secure, but
are not necessarily any faster at cryptography than the
system CPU — often, they are slower. It is therefore
most efficient to use them only for those cryptographic
functions that require access to the secured private key,
such as zone signing, and to use the system CPU for all
other computationally-intensive operations. The AEP Keyper
is an example of such a device.
</p>
</li>
</ul></div>
<p>
The modified OpenSSL code is included in the BIND 9 release,
in the form of a context diff against the latest versions of
OpenSSL. OpenSSL 0.9.8, 1.0.0, 1.0.1 and 1.0.2 are supported;
there are separate diffs for each version. In the examples to
follow, we use OpenSSL 0.9.8, but the same methods work with
OpenSSL 1.0.0 through 1.0.2.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The OpenSSL patches as of this writing (January 2016)
support versions 0.9.8zh, 1.0.0t, 1.0.1q and 1.0.2f.
ISC will provide updated patches as new versions of OpenSSL
are released. The version number in the following examples
is expected to change.
</p>
</div>
<p>
Before building BIND 9 with PKCS#11 support, it will be
necessary to build OpenSSL with the patch in place, and configure
it with the path to your HSM's PKCS#11 provider library.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.8"></a>Patching OpenSSL</h4></div></div></div>
<pre class="screen">
$ <strong class="userinput"><code>wget <a class="link" href="" target="_top">http://www.openssl.org/source/openssl-0.9.8zc.tar.gz</a></code></strong>
</pre>
<p>Extract the tarball:</p>
<pre class="screen">
</pre>
<p>Apply the patch from the BIND 9 release:</p>
<pre class="screen">
$ <strong class="userinput"><code>patch -p1 -d openssl-0.9.8zc \
</pre>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
The patch file may not be compatible with the
"patch" utility on all operating systems. You may need to
install GNU patch.
</p>
</div>
<p>
When building OpenSSL, place it in a non-standard
location so that it does not interfere with OpenSSL libraries
elsewhere on the system. In the following examples, we choose
when we configure BIND 9.
</p>
<p>
Later, when building BIND 9, the location of the custom-built
OpenSSL library will need to be specified via configure.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.9"></a>Building OpenSSL for the AEP Keyper on Linux</h4></div></div></div>
<p>
The AEP Keyper is a highly secure key storage device,
but does not provide hardware cryptographic acceleration. It
can carry out cryptographic operations, but it is probably
slower than your system's CPU. Therefore, we choose the
'sign-only' flavor when building OpenSSL.
</p>
<p>
The Keyper-specific PKCS#11 provider library is
delivered with the Keyper software. In this example, we place
</p>
<pre class="screen">
$ <strong class="userinput"><code>cp pkcs11.GCC4.0.2.so.4.05 /opt/pkcs11/usr/lib/libpkcs11.so</code></strong>
</pre>
<p>
The Keyper library requires threads, so we
must specify -pthread.
</p>
<pre class="screen">
$ <strong class="userinput"><code>cd openssl-0.9.8zc</code></strong>
--pk11-flavor=sign-only \
</pre>
<p>
After configuring, run "<span class="command"><strong>make</strong></span>"
and "<span class="command"><strong>make test</strong></span>". If "<span class="command"><strong>make
test</strong></span>" fails with "pthread_atfork() not found", you forgot to
add the -pthread above.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.10"></a>Building OpenSSL for the SCA 6000 on Solaris</h4></div></div></div>
<p>
The SCA-6000 PKCS#11 provider is installed as a system
library, libpkcs11. It is a true crypto accelerator, up to 4
times faster than any CPU, so the flavor shall be
'crypto-accelerator'.
</p>
<p>
In this example, we are building on Solaris x86 on an
AMD64 system.
</p>
<pre class="screen">
$ <strong class="userinput"><code>cd openssl-0.9.8zc</code></strong>
--pk11-flavor=crypto-accelerator \
</pre>
<p>
</p>
<p>
After configuring, run
<span class="command"><strong>make</strong></span> and
<span class="command"><strong>make test</strong></span>.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.11"></a>Building OpenSSL for SoftHSM</h4></div></div></div>
<p>
SoftHSM (version 1) is a software library developed by the
OpenDNSSEC project
</a>)
which provides a
PKCS#11 interface to a virtual HSM, implemented in the form of
a SQLite3 database on the local filesystem. SoftHSM uses
the Botan library to perform cryptographic functions. Though
less secure than a true HSM, it can allow you to experiment
with PKCS#11 when an HSM is not available.
</p>
<p>
The SoftHSM cryptographic store must be installed and
initialized before using it with OpenSSL, and the SOFTHSM_CONF
environment variable must always point to the SoftHSM configuration
file:
</p>
<pre class="screen">
$ <strong class="userinput"><code> cd softhsm-1.3.7 </code></strong>
$ <strong class="userinput"><code> make </code></strong>
$ <strong class="userinput"><code> make install </code></strong>
$ <strong class="userinput"><code> echo "0:/opt/pkcs11/softhsm.db" > $SOFTHSM_CONF </code></strong>
$ <strong class="userinput"><code> /opt/pkcs11/usr/bin/softhsm --init-token 0 --slot 0 --label softhsm </code></strong>
</pre>
<p>
SoftHSM can perform all cryptographic operations, but
since it only uses your system CPU, there is no advantage to using
it for anything but signing. Therefore, we choose the 'sign-only'
flavor when building OpenSSL.
</p>
<pre class="screen">
$ <strong class="userinput"><code>cd openssl-0.9.8zc</code></strong>
--pk11-flavor=sign-only \
</pre>
<p>
After configuring, run "<span class="command"><strong>make</strong></span>"
and "<span class="command"><strong>make test</strong></span>".
</p>
</div>
<p>
Once you have built OpenSSL, run
that PKCS#11 support was compiled in correctly. The output
should be one of the following lines, depending on the flavor
selected:
</p>
<pre class="screen">
(pkcs11) PKCS #11 engine support (sign only)
</pre>
<p>Or:</p>
<pre class="screen">
(pkcs11) PKCS #11 engine support (crypto accelerator)
</pre>
<p>
Next, run
attempt to initialize the PKCS#11 engine. If it is able to
do so successfully, it will report
<span class="quote">“<span class="quote"><code class="literal">[ available ]</code></span>”</span>.
</p>
<p>
If the output is correct, run
"<span class="command"><strong>make install</strong></span>" which will install the
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.18"></a>Configuring BIND 9 for Linux with the AEP Keyper</h4></div></div></div>
<p>
To link with the PKCS#11 provider, threads must be
enabled in the BIND 9 build.
</p>
<pre class="screen">
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.19"></a>Configuring BIND 9 for Solaris with the SCA 6000</h4></div></div></div>
<p>
To link with the PKCS#11 provider, threads must be
enabled in the BIND 9 build.
</p>
<pre class="screen">
</pre>
<p>(For a 32-bit build, omit CC="cc -xarch=amd64".)</p>
<p>
If configure complains about OpenSSL not working, you
incorrectly specified the path to OpenSSL (it should be the
same as the --prefix argument to the OpenSSL
Configure).
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="id-1.5.12.8.20"></a>Configuring BIND 9 for SoftHSM</h4></div></div></div>
<pre class="screen">
</pre>
</div>
<p>
After configuring, run
"<span class="command"><strong>make</strong></span>",
"<span class="command"><strong>make test</strong></span>" and
"<span class="command"><strong>make install</strong></span>".
</p>
<p>
(Note: If "make test" fails in the "pkcs11" system test, you may
have forgotten to set the SOFTHSM_CONF environment variable.)
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.9"></a>PKCS#11 Tools</h3></div></div></div>
<p>
BIND 9 includes a minimal set of tools to operate the
HSM, including
<span class="command"><strong>pkcs11-keygen</strong></span> to generate a new key pair
within the HSM,
<span class="command"><strong>pkcs11-list</strong></span> to list objects currently
available,
<span class="command"><strong>pkcs11-destroy</strong></span> to remove objects, and
<span class="command"><strong>pkcs11-tokens</strong></span> to list available tokens.
</p>
<p>
9 is configured with the --with-pkcs11 option. (Note: If
--with-pkcs11 is set to "yes", rather than to the path of the
PKCS#11 provider, then the tools will be built but the
provider will be left undefined. Use the -m option or the
PKCS11_PROVIDER environment variable to specify the path to the
provider.)
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.10"></a>Using the HSM</h3></div></div></div>
<p>
For OpenSSL-based PKCS#11, we must first set up the runtime
environment so the OpenSSL and PKCS#11 libraries can be loaded:
</p>
<pre class="screen">
$ <strong class="userinput"><code>export LD_LIBRARY_PATH=/opt/pkcs11/usr/lib:${LD_LIBRARY_PATH}</code></strong>
</pre>
<p>
This causes <span class="command"><strong>named</strong></span> and other binaries to load
rather than from the default location. This step is not necessary
when using native PKCS#11.
</p>
<p>
Some HSMs require other environment variables to be set.
For example, when operating an AEP Keyper, it is necessary to
specify the location of the "machine" file, which stores
information about the Keyper for use by the provider
library. If the machine file is in
use:
</p>
<pre class="screen">
$ <strong class="userinput"><code>export KEYPER_LIBRARY_PATH=/opt/Keyper/PKCS11Provider</code></strong>
</pre>
<p>
Such environment variables must be set whenever running
any tool that uses the HSM, including
<span class="command"><strong>pkcs11-keygen</strong></span>,
<span class="command"><strong>pkcs11-list</strong></span>,
<span class="command"><strong>pkcs11-destroy</strong></span>,
<span class="command"><strong>dnssec-keyfromlabel</strong></span>,
<span class="command"><strong>dnssec-signzone</strong></span>,
<span class="command"><strong>dnssec-keygen</strong></span>, and
<span class="command"><strong>named</strong></span>.
</p>
<p>
We can now create and use keys in the HSM. In this case,
we will create a 2048 bit key and give it the label
"sample-ksk":
</p>
<pre class="screen">
$ <strong class="userinput"><code>pkcs11-keygen -b 2048 -l sample-ksk</code></strong>
</pre>
<p>To confirm that the key exists:</p>
<pre class="screen">
$ <strong class="userinput"><code>pkcs11-list</code></strong>
Enter PIN:
object[0]: handle 2147483658 class 3 label[8] 'sample-ksk' id[0]
object[1]: handle 2147483657 class 2 label[8] 'sample-ksk' id[0]
</pre>
<p>
Before using this key to sign a zone, we must create a
pair of BIND 9 key files. The "dnssec-keyfromlabel" utility
does this. In this case, we will be using the HSM key
"sample-ksk" as the key-signing key for "example.net":
</p>
<pre class="screen">
$ <strong class="userinput"><code>dnssec-keyfromlabel -l sample-ksk -f KSK example.net</code></strong>
</pre>
<p>
The resulting K*.key and K*.private files can now be used
to sign the zone. Unlike normal K* files, which contain both
public and private key data, these files will contain only the
public key data, plus an identifier for the private key which
remains stored within the HSM. Signing with the private key takes
place inside the HSM.
</p>
<p>
If you wish to generate a second key in the HSM for use
as a zone-signing key, follow the same procedure above, using a
different keylabel, a smaller key size, and omitting "-f KSK"
from the dnssec-keyfromlabel arguments:
</p>
<p>
(Note: When using OpenSSL-based PKCS#11 the label is an arbitrary
string which identifies the key. With native PKCS#11, the label is
a PKCS#11 URI string which may include other details about the key
and the HSM, including its PIN. See
<a class="xref" href="man.dnssec-keyfromlabel.html" title="dnssec-keyfromlabel"><span class="refentrytitle"><span class="application">dnssec-keyfromlabel</span></span>(8)</a> for details.)
</p>
<pre class="screen">
$ <strong class="userinput"><code>pkcs11-keygen -b 1024 -l sample-zsk</code></strong>
</pre>
<p>
Alternatively, you may prefer to generate a conventional
on-disk key, using dnssec-keygen:
</p>
<pre class="screen">
</pre>
<p>
This provides less security than an HSM key, but since
HSMs can be slow or cumbersome to use for security reasons, it
may be more efficient to reserve HSM keys for use in the less
frequent key-signing operation. The zone-signing key can be
rolled more frequently, if you wish, to compensate for a
reduction in key security. (Note: When using native PKCS#11,
there is no speed advantage to using on-disk keys, as cryptographic
operations will be done by the HSM regardless.)
</p>
<p>
Now you can sign the zone. (Note: If not using the -S
option to <span class="command"><strong>dnssec-signzone</strong></span>, it will be
necessary to add the contents of both <code class="filename">K*.key</code>
files to the zone master file before signing it.)
</p>
<pre class="screen">
Enter PIN:
Verifying the zone using the following algorithms:
NSEC3RSASHA1.
Zone signing complete:
Algorithm: NSEC3RSASHA1: ZSKs: 1, KSKs: 1 active, 0 revoked, 0 stand-by
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.11"></a>Specifying the engine on the command line</h3></div></div></div>
<p>
When using OpenSSL-based PKCS#11, the "engine" to be used by
OpenSSL can be specified in <span class="command"><strong>named</strong></span> and all of
the BIND <span class="command"><strong>dnssec-*</strong></span> tools by using the "-E
<engine>" command line option. If BIND 9 is built with
the --with-pkcs11 option, this option defaults to "pkcs11".
Specifying the engine will generally not be necessary unless
for some reason you wish to use a different OpenSSL
engine.
</p>
<p>
If you wish to disable use of the "pkcs11" engine —
for troubleshooting purposes, or because the HSM is unavailable
— set the engine to the empty string. For example:
</p>
<pre class="screen">
</pre>
<p>
This causes
<span class="command"><strong>dnssec-signzone</strong></span> to run as if it were compiled
without the --with-pkcs11 option.
</p>
<p>
When built with native PKCS#11 mode, the "engine" option has a
different meaning: it specifies the path to the PKCS#11 provider
library. This may be useful when testing a new provider library.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.12.12"></a>Running named with automatic zone re-signing</h3></div></div></div>
<p>
If you want <span class="command"><strong>named</strong></span> to dynamically re-sign zones
then <span class="command"><strong>named</strong></span> must have access to the HSM PIN. In OpenSSL-based PKCS#11,
this is accomplished by placing the PIN into the openssl.cnf file
(in the above examples,
</p>
<p>
The location of the openssl.cnf file can be overridden by
setting the OPENSSL_CONF environment variable before running
<span class="command"><strong>named</strong></span>.
</p>
<pre class="programlisting">
openssl_conf = openssl_def
[ openssl_def ]
engines = engine_section
[ engine_section ]
pkcs11 = pkcs11_section
[ pkcs11_section ]
PIN = <em class="replaceable"><code><PLACE PIN HERE></code></em>
</pre>
<p>
This will also allow the dnssec-* tools to access the HSM
without PIN entry. (The pkcs11-* tools access the HSM directly,
not via OpenSSL, so a PIN will still be required to use
them.)
</p>
<p>
In native PKCS#11 mode, the PIN can be provided in a file specified
as an attribute of the key's label. For example, if a key had the label
then the PIN would be read from the file
</p>
<div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Warning</h3>
<p>
Placing the HSM's PIN in a text file in this manner may reduce the
security advantage of using an HSM. Be sure this is what you want to
do before configuring the system in this way.
</p>
</div>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dlz-info"></a>DLZ (Dynamically Loadable Zones)</h2></div></div></div>
<p>
DLZ (Dynamically Loadable Zones) is an extension to BIND 9 that allows
zone data to be retrieved directly from an external database. There is
no required format or schema. DLZ drivers exist for several different
database backends including PostgreSQL, MySQL, and LDAP and can be
written for any other.
</p>
<p>
Historically, DLZ drivers had to be statically linked with the <span class="command"><strong>named</strong></span>
binary and were turned on via a configure option at compile time (for
example, <strong class="userinput"><code>"configure --with-dlz-ldap"</code></strong>).
Currently, the drivers provided in the BIND 9 tarball in
way.
</p>
<p>
In BIND 9.8 and higher, it is possible to link some DLZ modules
dynamically at runtime, via the DLZ "dlopen" driver, which acts as a
generic wrapper around a shared object implementing the DLZ API. The
"dlopen" driver is linked into <span class="command"><strong>named</strong></span> by default, so configure options
are no longer necessary when using these dynamically linkable drivers,
but are still needed for the older drivers in
</p>
<p>
When the DLZ module provides data to <span class="command"><strong>named</strong></span>, it does so in text format.
The response is converted to DNS wire format by <span class="command"><strong>named</strong></span>. This
conversion, and the lack of any internal caching, places significant
limits on the query performance of DLZ modules. Consequently, DLZ is
not recommended for use on high-volume servers. However, it can be
used in a hidden master configuration, with slaves retrieving zone
updates via AXFR. (Note, however, that DLZ has no built-in support for
DNS notify; slaves are not automatically informed of changes to the
zones in the database.)
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.13.6"></a>Configuring DLZ</h3></div></div></div>
<p>
A DLZ database is configured with a <span class="command"><strong>dlz</strong></span>
</p>
<pre class="screen">
dlz example {
search yes;
};
</pre>
<p>
This specifies a DLZ module to search when answering queries; the
loaded at runtime by the dlopen DLZ driver. Multiple
<span class="command"><strong>dlz</strong></span> statements can be specified; when
answering a query, all DLZ modules with <code class="option">search</code>
set to <code class="literal">yes</code> will be queried to find out if
they contain an answer for the query name; the best available
answer will be returned to the client.
</p>
<p>
The <code class="option">search</code> option in the above example can be
omitted, because <code class="literal">yes</code> is the default value.
</p>
<p>
If <code class="option">search</code> is set to <code class="literal">no</code>, then
this DLZ module is <span class="emphasis"><em>not</em></span> searched for the best
match when a query is received. Instead, zones in this DLZ must be
separately specified in a zone statement. This allows you to
configure a zone normally using standard zone option semantics,
but specify a different database back-end for storage of the
zone's data. For example, to implement NXDOMAIN redirection using
a DLZ module for back-end storage of redirection rules:
</p>
<pre class="screen">
dlz other {
search no;
};
zone "." {
type redirect;
dlz other;
};
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.13.7"></a>Sample DLZ Driver</h3></div></div></div>
<p>
For guidance in implementation of DLZ modules, the directory
dynamically-linkable DLZ module--i.e., one which can be
loaded at runtime by the "dlopen" DLZ driver.
The example sets up a single zone, whose name is passed
to the module as an argument in the <span class="command"><strong>dlz</strong></span>
statement:
</p>
<pre class="screen">
dlz other {
database "dlopen driver.so example.nil";
};
</pre>
<p>
In the above example, the module is configured to create a zone
"example.nil", which can answer queries and AXFR requests, and
accept DDNS updates. At runtime, prior to any updates, the zone
contains an SOA, NS, and a single A record at the apex:
</p>
<pre class="screen">
123 900 600 86400 3600
)
example.nil. 3600 IN NS example.nil.
example.nil. 1800 IN A 10.53.0.1
</pre>
<p>
The sample driver is capable of retrieving information about the
querying client, and altering its response on the basis of this
information. To demonstrate this feature, the example driver
responds to queries for "source-addr.<code class="option">zonename</code>>/TXT"
with the source address of the query. Note, however, that this
record will *not* be included in AXFR or ANY responses. Normally,
this feature would be used to alter responses in some other fashion,
e.g., by providing different address records for a particular name
depending on the network from which the query arrived.
</p>
<p>
Documentation of the DLZ module API can be found in
defines the API and should be included by any dynamically-linkable
DLZ module.
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dyndb-info"></a>DynDB (Dynamic Database)</h2></div></div></div>
<p>
DynDB is an extension to BIND 9 which, like DLZ
(see <a class="xref" href="Bv9ARM.ch04.html#dlz-info" title="DLZ (Dynamically Loadable Zones)">the section called “DLZ (Dynamically Loadable Zones)”</a>), allows zone data to be
retrieved from an external database. Unlike DLZ, a DynDB module
provides a full-featured BIND zone database interface. Where
DLZ translates DNS queries into real-time database lookups,
resulting in relatively poor query performance, and is unable
to handle DNSSEC-signed data due to its limited API, a DynDB
module can pre-load an in-memory database from the external
data source, providing the same performance and functionality
as zones served natively by BIND.
</p>
<p>
A DynDB module supporting LDAP has been created by Red Hat
and is available from
<a class="link" href="https://fedorahosted.org/bind-dyndb-ldap/" target="_top">https://fedorahosted.org/bind-dyndb-ldap/</a>.
</p>
<p>
A sample DynDB module for testing and developer guidance
is included with the BIND source code, in the directory
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.14.5"></a>Configuring DynDB</h3></div></div></div>
<p>
A DynDB database is configured with a <span class="command"><strong>dyndb</strong></span>
</p>
<pre class="screen">
dyndb example "driver.so" {
<em class="replaceable"><code>parameters</code></em>
};
</pre>
<p>
implements the full DNS database API. Multiple
<span class="command"><strong>dyndb</strong></span> statements can be specified, to load
different drivers or multiple instances of the same driver.
Zones provided by a DynDB module are added to the view's zone
table, and are treated as normal authoritative zones when BIND
is responding to queries. Zone configuration is handled internally
by the DynDB module.
</p>
<p>
The <em class="replaceable"><code>parameters</code></em> are passed as an opaque
string to the DynDB module's initialization routine. Configuration
syntax will differ depending on the driver.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.14.6"></a>Sample DynDB Module</h3></div></div></div>
<p>
For guidance in implementation of DynDB modules, the directory
contains a basic DynDB module.
The example sets up two zones, whose names are passed
to the module as arguments in the <span class="command"><strong>dyndb</strong></span>
statement:
</p>
<pre class="screen">
dyndb sample "sample.so" { example.nil. arpa. };
</pre>
<p>
In the above example, the module is configured to create a zone
"example.nil", which can answer queries and AXFR requests, and
accept DDNS updates. At runtime, prior to any updates, the zone
contains an SOA, NS, and a single A record at the apex:
</p>
<pre class="screen">
0 28800 7200 604800 86400
)
example.nil. 86400 IN NS example.nil.
example.nil. 86400 IN A 127.0.0.1
</pre>
<p>
When the zone is updated dynamically, the DynDB module will determine
whether the updated RR is an address (i.e., type A or AAAA) and if
so, it will automatically update the corresponding PTR record in a
reverse zone. (Updates are not stored permanently; all updates are
lost when the server is restarted.)
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="catz-info"></a>Catalog Zones</h2></div></div></div>
<p>
A "catalog zone" is a special DNS zone that contains a list of
other zones to be served, along with their configuration parameters.
Zones listed in a catalog zone are called "member zones".
When a catalog zone is loaded or transferred to a slave server
which supports this functionality, the slave server will create
the member zones automatically. When the catalog zone is updated
(for example, to add or delete member zones, or change
their configuration parameters) those changes are immediately put
into effect. Because the catalog zone is a normal DNS zone, these
zone transfer mechanism.
</p>
<p>
Catalog zones' format and behavior are specified as an internet draft
for interoperability among DNS implementations. As of this release, the
latest revision of the DNS catalog zones draft can be found here:
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.15.4"></a>Principle of Operation</h3></div></div></div>
<p>
Normally, if a zone is to be served by a slave server, the
zone, or the zone must be added using <span class="command"><strong>rndc addzone</strong></span>.
the zones being served are changing frequently, the overhead involved
in maintaining consistent zone configuration on all the slave
servers can be significant.
</p>
<p>
A catalog zone is a way to ease this administrative burden. It is a
DNS zone that lists member zones that should be served by slave servers.
When a slave server receives an update to the catalog zone, it adds,
removes, or reconfigures member zones based on the data received.
</p>
<p>
To use a catalog zone, it must first be set up as a normal zone on
the master and the on slave servers that will be configured to use
it. It must also be added to a <code class="option">catalog-zones</code> list
in the <code class="option">options</code> or <code class="option">view</code> statement
a policy zone is configured as a normal zone and also listed in
a <code class="option">response-policy</code> statement.)
</p>
<p>
To use the catalog zone feature to serve a new member zone:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Set up the the member zone to be served on the master as normal.
or by running <span class="command"><strong>rndc addzone</strong></span>.
</p>
</li>
<li class="listitem">
<p>
Add an entry to the catalog zone for the new member zone.
This could be done by editing the catalog zone's master file
and running <span class="command"><strong>rndc reload</strong></span>, or by updating
the zone using <span class="command"><strong>nsupdate</strong></span>.
</p>
</li>
</ul></div>
<p>
The change to the catalog zone will be propagated from the master to all
update to the catalog zone, it will detect the entry for the new member
zone, create an instance of of that zone on the slave server, and point
that instance to the <code class="option">masters</code> specified in the catalog
zone data. The newly created member zone is a normal slave zone, so
BIND will immediately initiate a transfer of zone contents from the
master. Once complete, the slave will start serving the member zone.
</p>
<p>
Removing a member zone from a slave server requires nothing more than
deleting the member zone's entry in the catalog zone. The change to the
transfer mechanism. The slave server, on processing the update, will
notice that the member zone has been removed. It will stop serving the
zone and remove it from its list of configured zones. (Removing the
member zone from the master server has to be done in the normal way,
by editing the configuration file or running
<span class="command"><strong>rndc delzone</strong></span>.)
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.15.5"></a>Configuring Catalog Zones</h3></div></div></div>
<p>
Catalog zones are configured with a <span class="command"><strong>catalog-zones</strong></span>
statement in the <code class="literal">options</code> or <code class="literal">view</code>
</p>
<pre class="screen">
catalog-zones {
zone "catalog.example"
default-masters { 10.53.0.1; }
in-memory no
zone-directory "catzones"
min-update-interval 10;
};
</pre>
<p>
This statement specifies that the zone
properly configured in the same view. In most configurations, it would
be a slave zone.
</p>
<p>
The options following the zone name are not required, and may be
specified in any order:
</p>
<p>
The <code class="option">default-masters</code> option defines the default masters
for member zones listed in a catalog zone. This can be overridden by
options within a catalog zone. If no such options are included, then
member zones will transfer their contents from the servers listed in
this option.
</p>
<p>
The <code class="option">in-memory</code> option, if set to <code class="literal">yes</code>,
causes member zones to be stored only in memory. This is functionally
equivalent to configuring a slave zone without a <code class="option">file</code>.
option. The default is <code class="literal">no</code>; member zones' content
will be stored locally in a file whose name is automatically generated
from the view name, catalog zone name, and member zone name.
</p>
<p>
The <code class="option">zone-directory</code> option causes local copies of
member zones' master files (if <code class="option">in-memory</code> is not set
to <code class="literal">yes</code>) to be stored in the specified directory.
The default is to store zone files in the server's working directory.
A non-absolute pathname in <code class="option">zone-directory</code> is
assumed to be relative to the working directory.
</p>
<p>
The <code class="option">min-update-interval</code> option sets the minimum
interval between processing of updates to catalog zones, in seconds.
If an update to a catalog zone (for example, via IXFR) happens less
than <code class="option">min-update-interval</code> seconds after the most
recent update, then the changes will not be carried out until this
interval has elapsed. The default is <code class="literal">5</code> seconds.
</p>
<p>
Catalog zones are defined on a per-view basis. Configuring a non-empty
<code class="option">catalog-zones</code> statement in a view will automatically
turn on <code class="option">allow-new-zones</code> for that view. (Note: this
means <span class="command"><strong>rndc addzone</strong></span> and <span class="command"><strong>rndc delzone</strong></span>
will also work in any view that supports catalog zones.)
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.15.6"></a>Catalog Zone format</h3></div></div></div>
<p>
A catalog zone is a regular DNS zone; therefore, it has to have a
single <code class="literal">SOA</code> and at least one <code class="literal">NS</code>
record.
</p>
<p>
A record stating the version of the catalog zone format is
also required. If the version number listed is not supported by
the server, then a catalog zone may not be used by that server.
</p>
<pre class="screen">
catalog.example. IN SOA . . 2016022901 900 600 86400 1
catalog.example. IN NS nsexample.
version.catalog.example. IN TXT "1"
</pre>
<p>
Note that this record must have the domain name
version.<em class="replaceable"><code>catalog-zone-name</code></em>. This illustrates
how the meaning of data stored in a catalog zone is indicated by the
the domain name label immediately before the catalog zone domain.
</p>
<p>
Catalog zone options can be set either globally for the whole catalog
zone or for a single member zone. Global options override the settings
in the configuration file and member zone options override global
options.
</p>
<p>
Global options are set at the apex of the catalog zone, e.g.:
</p>
<pre class="screen">
masters.catalog.example. IN AAAA 2001:db8::1
</pre>
<p>BIND currently supports the following options:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>A simple <code class="option">masters</code> definition:</p>
<pre class="screen">
masters.catalog.example. IN A 192.0.2.1
</pre>
<p>
This option defines a master server for the member zones - it
can be either an A or AAAA record. If multiple masters are set the
order in which they are used is random.
</p>
</li>
<li class="listitem">
<p>A <code class="option">masters</code> with a TSIG key defined:</p>
<pre class="screen">
label.masters.catalog.example. IN A 192.0.2.2
label.masters.catalog.example. IN TXT "tsig_key_name"
</pre>
<p>
This option defines a master server for the member zone with a TSIG
key set. The TSIG key must be configured in the configuration file.
<code class="option">label</code> can be any valid DNS label.
</p>
</li>
<li class="listitem">
<p><code class="option">allow-query</code> and
<code class="option">allow-transfer</code> ACLs:</p>
<pre class="screen">
</pre>
<p>
These options are the equivalents of <code class="option">allow-query</code>
and <code class="option">allow-transfer</code> in a zone declaration in the
processed in order - if there's no match to any rule the default
policy is to deny access. For the syntax of the APL RR see RFC
3123
</p>
</li>
</ul></div>
<p>
A member zone is added by including a <code class="literal">PTR</code>
resource record in the <code class="literal">zones</code> sub-domain of the
catalog zone. The record label is a <code class="literal">SHA-1</code> hash
of the member zone name in wire format. The target of the PTR
record is the member zone name. For example, to add the member
</p>
<pre class="screen">
</pre>
<p>
The hash is necessary to identify options for a specific member
zone. The member zone-specific options are defined the same way as
global options, but in the member zone subdomain:
</p>
<pre class="screen">
label.masters.5960775ba382e7a4e09263fc06e7c00569b6a05c.zones.catalog.example. IN AAAA 2001:db8::2
</pre>
<p>
As would be expected, options defined for a specific zone override
the global options defined in the catalog zone. These in turn override
the global options defined in the <code class="literal">catalog-zones</code>
statement in the configuration file.
</p>
<p>
(Note that none of the global records an option will be inherited if
any records are defined for that option for the specific zone. For
example, if the zone had a <code class="literal">masters</code> record of type
A but not AAAA, then it would <span class="emphasis"><em>not</em></span> inherit the
type AAAA record from the global option.)
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="ipv6"></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
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 class="xref" href="Bv9ARM.ch11.html#ipv6addresses" title="IPv6 addresses (AAAA)">the section called “IPv6 addresses (AAAA)”</a>.
</p>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.16.6"></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="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="id-1.5.16.7"></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
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">
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
</pre>
</div>
</div>
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