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><DIV
CLASS="chapter"
><H1
><A
NAME="ch04"
>Chapter 4. Advanced DNS Features</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>4.1. <A
HREF="Bv9ARM.ch04.html#notify"
>Notify</A
></DT
><DT
>4.2. <A
HREF="Bv9ARM.ch04.html#dynamic_update"
>Dynamic Update</A
></DT
><DT
>4.3. <A
HREF="Bv9ARM.ch04.html#incremental_zone_transfers"
>Incremental Zone Transfers (IXFR)</A
></DT
><DT
>4.4. <A
HREF="Bv9ARM.ch04.html#AEN753"
>Split DNS</A
></DT
><DT
>4.5. <A
HREF="Bv9ARM.ch04.html#tsig"
>TSIG</A
></DT
><DT
>4.6. <A
HREF="Bv9ARM.ch04.html#AEN913"
>TKEY</A
></DT
><DT
>4.7. <A
HREF="Bv9ARM.ch04.html#AEN928"
>SIG(0)</A
></DT
><DT
>4.8. <A
HREF="Bv9ARM.ch04.html#DNSSEC"
>DNSSEC</A
></DT
><DT
>4.9. <A
HREF="Bv9ARM.ch04.html#AEN1015"
>IPv6 Support in <SPAN
CLASS="acronym"
>BIND</SPAN
> 9</A
></DT
></DL
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="notify"
>4.1. Notify</A
></H1
><P
><SPAN
CLASS="acronym"
>DNS</SPAN
> NOTIFY is a mechanism that allows master
servers to notify their slave servers of changes to a zone's data. In
response to a <B
CLASS="command"
>NOTIFY</B
> 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
><SPAN
CLASS="acronym"
>DNS</SPAN
>
For more information about
<B
CLASS="command"
>NOTIFY</B
>, see the description of the
<B
CLASS="command"
>notify</B
> option in <A
HREF="Bv9ARM.ch06.html#boolean_options"
>Section 6.2.14.1</A
> and
the description of the zone option <B
CLASS="command"
>also-notify</B
> in
<A
HREF="Bv9ARM.ch06.html#zone_transfers"
>Section 6.2.14.6</A
>. The <B
CLASS="command"
>NOTIFY</B
>
protocol is specified in RFC 1996.
</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="dynamic_update"
>4.2. Dynamic Update</A
></H1
><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 on a zone-by-zone basis, by
including an <B
CLASS="command"
>allow-update</B
> or
<B
CLASS="command"
>update-policy</B
> clause in the
<B
CLASS="command"
>zone</B
> statement.</P
><P
>Updating of secure zones (zones using DNSSEC) follows
RFC 3007: SIG and NXT 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="sect2"
><H2
CLASS="sect2"
><A
NAME="journal"
>4.2.1. The journal file</A
></H2
><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 when the first dynamic update takes place. The name of
the journal file is formed by appending the
extension <TT
CLASS="filename"
>.jnl</TT
> to the
name of the corresponding zone file. 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.</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 <B
CLASS="command"
>rndc stop</B
>.</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
<B
CLASS="command"
>rndc freeze <TT
CLASS="replaceable"
><I
>zone</I
></TT
></B
>.
This will also remove the zone's <TT
CLASS="filename"
>.jnl</TT
> file
and update the master file. Edit the zone file. Run
<B
CLASS="command"
>rndc unfreeze <TT
CLASS="replaceable"
><I
>zone</I
></TT
></B
>
to reload the changed zone and re-enable dynamic updates.</P
></DIV
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="incremental_zone_transfers"
>4.3. Incremental Zone Transfers (IXFR)</A
></H1
><P
>The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is specified in RFC
1995. See <A
HREF="Bv9ARM.ch09.html#proposed_standards"
>Proposed Standards</A
>.</P
><P
>When acting as a master, <SPAN
CLASS="acronym"
>BIND</SPAN
> 9
supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR. For manually maintained master
zones, and for slave zones obtained by performing a full zone
transfer (AXFR), IXFR is supported only if the option
<B
CLASS="command"
>ixfr-from-differences</B
> is set
to <TT
CLASS="userinput"
><B
>yes</B
></TT
>.
</P
><P
>When acting as a slave, <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 will
attempt to use IXFR unless
it is explicitly disabled. For more information about disabling
IXFR, see the description of the <B
CLASS="command"
>request-ixfr</B
> clause
of the <B
CLASS="command"
>server</B
> statement.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN753"
>4.4. Split DNS</A
></H1
><P
>Setting up different views, or visibility, of the DNS space to
internal and external resolvers is usually referred to as a <I
CLASS="emphasis"
>Split
DNS</I
> setup. There are several reasons an organization
would want to set up its DNS this way.</P
><P
>One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.</P
><P
>Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.</P
><P
>Here is an example of a split DNS setup:</P
><P
>Let's say a company named <I
CLASS="emphasis"
>Example, Inc.</I
>
(<TT
CLASS="literal"
>example.com</TT
>)
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
><I
CLASS="emphasis"
>Example, Inc.</I
> 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 <TT
CLASS="filename"
>site1.internal</TT
>, <TT
CLASS="filename"
>site2.internal</TT
>, <TT
CLASS="filename"
>site1.example.com</TT
>,
and <TT
CLASS="filename"
>site2.example.com</TT
>, to the servers in the
DMZ. These internal servers will have complete sets of information
for <TT
CLASS="filename"
>site1.example.com</TT
>, <TT
CLASS="filename"
>site2.example.com</TT
>,<I
CLASS="emphasis"
> </I
><TT
CLASS="filename"
>site1.internal</TT
>,
and <TT
CLASS="filename"
>site2.internal</TT
>.</P
><P
>To protect the <TT
CLASS="filename"
>site1.internal</TT
> and <TT
CLASS="filename"
>site2.internal</TT
> 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 <TT
CLASS="filename"
>site1</TT
> and <TT
CLASS="filename"
>site2.example.com</TT
> zones.
This could include things such as the host records for public servers
(<TT
CLASS="filename"
>www.example.com</TT
> and <TT
CLASS="filename"
>ftp.example.com</TT
>),
and mail exchange (MX) records (<TT
CLASS="filename"
>a.mx.example.com</TT
> and <TT
CLASS="filename"
>b.mx.example.com</TT
>).</P
><P
>In addition, the public <TT
CLASS="filename"
>site1</TT
> and <TT
CLASS="filename"
>site2.example.com</TT
> zones
should have special MX records that contain wildcard (`*') records
pointing to the bastion hosts. This is needed because external mail
servers do not have any other way of looking up how to deliver mail
to those internal hosts. With the wildcard records, the mail will
be delivered to the bastion host, which can then forward it on to
internal hosts.</P
><P
>Here's an example of a wildcard MX record:</P
><PRE
CLASS="programlisting"
><TT
CLASS="literal"
>* IN MX 10 external1.example.com.</TT
></PRE
><P
>Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers on
the bastion hosts will need to be configured to point to the internal
name servers for DNS resolution.</P
><P
>Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.</P
><P
>In order for all this to work properly, internal clients will
need to be configured to query <I
CLASS="emphasis"
>only</I
> 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, <I
CLASS="emphasis"
>Example, Inc.</I
>'s
internal clients will now be able to:</P
><P
></P
><UL
><LI
><P
>Look up any hostnames in the <TT
CLASS="literal"
>site1</TT
> and
<TT
CLASS="literal"
>site2.example.com</TT
> zones.</P
></LI
><LI
><P
>Look up any hostnames in the <TT
CLASS="literal"
>site1.internal</TT
> and
<TT
CLASS="literal"
>site2.internal</TT
> domains.</P
></LI
><LI
><P
>Look up any hostnames on the Internet.</P
></LI
><LI
><P
>Exchange mail with internal AND external people.</P
></LI
></UL
><P
>Hosts on the Internet will be able to:</P
><P
></P
><UL
><LI
><P
>Look up any hostnames in the <TT
CLASS="literal"
>site1</TT
> and
<TT
CLASS="literal"
>site2.example.com</TT
> zones.</P
></LI
><LI
><P
>Exchange mail with anyone in the <TT
CLASS="literal"
>site1</TT
> and
<TT
CLASS="literal"
>site2.example.com</TT
> zones.</P
></LI
></UL
><P
>Here is an example configuration for the setup we just
described above. Note that this is only configuration information;
for information on how to configure your zone files, see <A
HREF="Bv9ARM.ch03.html#sample_configuration"
>Section 3.1</A
></P
><P
>Internal DNS server config:</P
><PRE
CLASS="programlisting"
>
acl externals { <TT
CLASS="varname"
>bastion-ips-go-here</TT
>; };
options {
...
...
forward only;
forwarders { // forward to external servers
<TT
CLASS="varname"
>bastion-ips-go-here</TT
>;
};
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample master zone
type master;
file "m/site1.example.com";
forwarders { }; // do normal iterative
// resolution (do not forward)
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site2.example.com" { // sample slave zone
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</PRE
><P
>External (bastion host) DNS server config:</P
><PRE
CLASS="programlisting"
acl externals { bastion-ips-go-here; };
options {
...
...
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { internals; externals; }; // restrict query access
allow-recursion { internals; externals; }; // restrict recursion
...
...
};
zone "site1.example.com" { // sample slave zone
type master;
file "m/site1.foo.com";
allow-query { any; };
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-query { any; };
allow-transfer { internals; externals; }
};
</PRE
><P
>In the <TT
CLASS="filename"
>resolv.conf</TT
> (or equivalent) on
the bastion host(s):</P
><PRE
CLASS="programlisting"
> search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</PRE
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="tsig"
>4.5. TSIG</A
></H1
><P
>This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <SPAN
CLASS="acronym"
>BIND</SPAN
>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <SPAN
CLASS="acronym"
>BIND</SPAN
>.</P
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> primarily supports TSIG for server to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <SPAN
CLASS="acronym"
>BIND</SPAN
> 8 have limited support
for TSIG.</P
><P
>TSIG might be most useful for dynamic update. A primary
server for a dynamic zone should use access control to control
updates, but IP-based access control is insufficient.
The cryptographic access control provided by TSIG
is far superior. The <B
CLASS="command"
>nsupdate</B
>
program supports TSIG via the <TT
CLASS="option"
>-k</TT
> and
<TT
CLASS="option"
>-y</TT
> command line options.</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN844"
>4.5.1. Generate Shared Keys for Each Pair of Hosts</A
></H2
><P
>A shared secret is generated to be shared between <I
CLASS="emphasis"
>host1</I
> and <I
CLASS="emphasis"
>host2</I
>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.</P
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN849"
>4.5.1.1. Automatic Generation</A
></H3
><P
>The following command will generate a 128 bit (16 byte) HMAC-MD5
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is 512 bits;
keys longer than that will be digested with MD5 to produce a 128
bit key.</P
><P
><TT
CLASS="userinput"
><B
>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</B
></TT
></P
><P
>The key is in the file <TT
CLASS="filename"
>Khost1-host2.+157+00000.private</TT
>.
Nothing directly uses this file, but the base-64 encoded string
following "<TT
CLASS="literal"
>Key:</TT
>"
can be extracted from the file and used as a shared secret:</P
><PRE
CLASS="programlisting"
><P
>The string "<TT
CLASS="literal"
>" can
be used as the shared secret.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN860"
>4.5.1.2. Manual Generation</A
></H3
><P
>The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.</P
><P
>Also, a known string can be run through <B
CLASS="command"
>mmencode</B
> or
a similar program to generate base-64 encoded data.</P
></DIV
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN865"
>4.5.2. Copying the Shared Secret to Both Machines</A
></H2
><P
>This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN868"
>4.5.3. Informing the Servers of the Key's Existence</A
></H2
><P
>Imagine <I
CLASS="emphasis"
>host1</I
> and <I
CLASS="emphasis"
>host 2</I
> are
both servers. The following is added to each server's <TT
CLASS="filename"
>named.conf</TT
> file:</P
><PRE
CLASS="programlisting"
> key host1-host2. {
algorithm hmac-md5;
};
</PRE
><P
>The algorithm, hmac-md5, is the only one supported by <SPAN
CLASS="acronym"
>BIND</SPAN
>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <TT
CLASS="filename"
>named.conf</TT
> be non-world
readable, or the key directive be added to a non-world readable
file that is included by <TT
CLASS="filename"
>named.conf</TT
>.</P
><P
>At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature is successfully verified, the
response is signed by the same key.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN880"
>4.5.4. Instructing the Server to Use the Key</A
></H2
><P
>Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <TT
CLASS="filename"
>named.conf</TT
> file
for <I
CLASS="emphasis"
>host1</I
>, if the IP address of <I
CLASS="emphasis"
>host2</I
> is
10.1.2.3:</P
><PRE
CLASS="programlisting"
> server 10.1.2.3 {
keys { host1-host2. ;};
};
</PRE
><P
>Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a world-readable
file.</P
><P
>If <I
CLASS="emphasis"
>host1</I
> sends a message that is a request
to that address, the message will be signed with the specified key. <I
CLASS="emphasis"
>host1</I
> will
expect any responses to signed messages to be signed with the same
key.</P
><P
>A similar statement must be present in <I
CLASS="emphasis"
>host2</I
>'s
configuration file (with <I
CLASS="emphasis"
>host1</I
>'s address) for <I
CLASS="emphasis"
>host2</I
> to
sign request messages to <I
CLASS="emphasis"
>host1</I
>.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN896"
>4.5.5. TSIG Key Based Access Control</A
></H2
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> allows IP addresses and ranges to be specified in ACL
definitions and
<B
CLASS="command"
>allow-{ query | transfer | update }</B
> directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <B
CLASS="command"
>key host1-host2.</B
></P
><P
>An example of an allow-update directive would be:</P
><PRE
CLASS="programlisting"
> allow-update { key host1-host2. ;};
</PRE
><P
>This allows dynamic updates to succeed only if the request
was signed by a key named
"<B
CLASS="command"
>host1-host2.</B
>".</P
><P
>You may want to read about the more
powerful <B
CLASS="command"
>update-policy</B
> statement in <A
HREF="Bv9ARM.ch06.html#dynamic_update_policies"
>Section 6.2.22.4</A
>.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN909"
>4.5.6. Errors</A
></H2
><P
>The processing of TSIG signed messages can result in
several errors. If a signed message is sent to a non-TSIG aware
server, a FORMERR will be returned, since the server will not
understand the record. This is a result of misconfiguration,
since the server must be explicitly configured to send a TSIG
signed message to a specific server.</P
><P
>If a TSIG aware server receives a message signed by an
unknown key, the response will be unsigned with the TSIG
extended error code set to BADKEY. If a TSIG aware server
receives a message with a signature that does not validate, the
response will be unsigned with the TSIG extended error code set
to BADSIG. If a TSIG aware server receives a message with a time
outside of the allowed range, the response will be signed with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified. In any of these cases, the message's rcode is set to
NOTAUTH.</P
></DIV
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN913"
>4.6. TKEY</A
></H1
><P
><B
CLASS="command"
>TKEY</B
> is a mechanism for automatically
generating a shared secret between two hosts. There are several
"modes" of <B
CLASS="command"
>TKEY</B
> that specify how the key is
generated or assigned. <SPAN
CLASS="acronym"
>BIND</SPAN
> 9
implements only one of these modes,
the Diffie-Hellman key exchange. Both hosts are required to have
a Diffie-Hellman KEY record (although this record is not required
to be present in a zone). The <B
CLASS="command"
>TKEY</B
> process
must use signed messages, signed either by TSIG or SIG(0). The
result of <B
CLASS="command"
>TKEY</B
> is a shared secret that can be
used to sign messages with TSIG. <B
CLASS="command"
>TKEY</B
> can also
be used to delete shared secrets that it had previously
generated.</P
><P
>The <B
CLASS="command"
>TKEY</B
> process is initiated by a client
or server by sending a signed <B
CLASS="command"
>TKEY</B
> query
(including any appropriate KEYs) to a TKEY-aware server. The
server response, if it indicates success, will contain a
<B
CLASS="command"
>TKEY</B
> record and any appropriate keys. After
this exchange, both participants have enough information to
determine the shared secret; the exact process depends on the
<B
CLASS="command"
>TKEY</B
> mode. When using the Diffie-Hellman
<B
CLASS="command"
>TKEY</B
> mode, Diffie-Hellman keys are exchanged,
and the shared secret is derived by both participants.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN928"
>4.7. SIG(0)</A
></H1
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC2931. SIG(0)
is performed in the same manner as TSIG keys; privileges can be
granted or denied based on the key name.</P
><P
>When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
><P
>SIG(0) signing of multiple-message TCP streams is not
supported.</P
><P
>The only tool shipped with <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 that
generates SIG(0) signed messages is <B
CLASS="command"
>nsupdate</B
>.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="DNSSEC"
>4.8. DNSSEC</A
></H1
><P
>Cryptographic authentication of DNS information is possible
through the DNS Security (<I
CLASS="emphasis"
>DNSSEC</I
>) extensions,
defined in RFC 2535. This section describes the creation and use
of DNSSEC signed zones.</P
><P
>In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 ships
with several tools
that are used in this process, which are explained in more detail
below. In all cases, the <TT
CLASS="option"
>-h</TT
> option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset and signedkey files to be in the working directory or the
directory specified by the <TT
CLASS="option"
>-h</TT
> option, and
that the tools shipped with BIND 9.0.x are not fully compatible
with the current ones.</P
><P
>There must also be communication with the administrators of
zone's security status must be indicated by the parent zone for a
DNSSEC capable resolver to trust its data.</P
><P
>For other servers to trust data in this zone, they must
either be statically configured with this zone's zone key or the
zone key of another zone above this one in the DNS tree.</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN947"
>4.8.1. Generating Keys</A
></H2
><P
>The <B
CLASS="command"
>dnssec-keygen</B
> 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
<B
CLASS="command"
>ZONE</B
>, 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
these are RSASHA1 and DSA.</P
><P
>The following command will generate a 768 bit DSA key for
the <TT
CLASS="filename"
>child.example</TT
> zone:</P
><P
><TT
CLASS="userinput"
><B
>dnssec-keygen -a DSA -b 768 -n ZONE child.example.</B
></TT
></P
><P
>Two output files will be produced:
<TT
CLASS="filename"
> and
<TT
CLASS="filename"
> (where
12345 is an example of a key tag). The key file names contain
the key name (<TT
CLASS="filename"
>child.example.</TT
>), algorithm (3
is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in this case).
The private key (in the <TT
CLASS="filename"
>.private</TT
> file) is
used to generate signatures, and the public key (in the
<TT
CLASS="filename"
>.key</TT
> file) is used for signature
verification.</P
><P
>To generate another key with the same properties (but with
a different key tag), repeat the above command.</P
><P
>The public keys should be inserted into the zone file by
including the <TT
CLASS="filename"
>.key</TT
> files using
<B
CLASS="command"
>$INCLUDE</B
> statements.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN967"
>4.8.2. Creating a Keyset</A
></H2
><P
>The <B
CLASS="command"
>dnssec-makekeyset</B
> program is used
to create a key set from one or more keys.</P
><P
>Once the zone keys have been generated, a key set must be
built for transmission to the administrator of the parent zone,
so that the parent zone can sign the keys with its own zone key
and correctly indicate the security status of this zone. When
building a key set, the list of keys to be included and the TTL
of the set must be specified, and the desired signature validity
period of the parent's signature may also be specified.</P
><P
>The list of keys to be inserted into the key set may also
included non-zone keys present at the top of the zone.
<B
CLASS="command"
>dnssec-makekeyset</B
> may also be used at other
names in the zone.</P
><P
>The following command generates a key set containing the
above key and another key similarly generated, with a TTL of
3600 and a signature validity period of 10 days starting from
now.</P
><P
><TT
CLASS="userinput"
><B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>. This file should be
transmitted to the parent to be signed. It includes the keys,
as well as signatures over the key set generated by the zone
keys themselves, which are used to prove ownership of the
private keys and encode the desired validity period.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN979"
>4.8.3. Signing the Child's Keyset</A
></H2
><P
>The <B
CLASS="command"
>dnssec-signkey</B
> program is used to
sign one child's keyset.</P
><P
>If the <TT
CLASS="filename"
>child.example</TT
> zone has any
delegations which are secure, for example,
<TT
CLASS="filename"
>grand.child.example</TT
>, the
<TT
CLASS="filename"
>child.example</TT
> administrator should receive
keyset files for each secure subzone. These keys must be signed
by this zone's zone keys.</P
><P
>The following command signs the child's key set with the
zone keys:</P
><P
><TT
CLASS="userinput"
><B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>. This file
should be both transmitted back to the child and retained. It
includes all keys (the child's keys) from the keyset file and
signatures generated by this zone's zone keys.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN992"
>4.8.4. Signing the Zone</A
></H2
><P
>The <B
CLASS="command"
>dnssec-signzone</B
> program is used to
sign a zone.</P
><P
>Any <TT
CLASS="filename"
>signedkey</TT
> files corresponding to
secure subzones should be present, as well as a
<TT
CLASS="filename"
>signedkey</TT
> file for this zone generated by
the parent (if there is one). The zone signer will generate
<TT
CLASS="literal"
>NXT</TT
> and <TT
CLASS="literal"
>SIG</TT
> records for
the zone, as well as incorporate the zone key signature from the
parent and indicate the security status at all delegation
points.</P
><P
>The following command signs the zone, assuming it is in a
file called <TT
CLASS="filename"
>zone.child.example</TT
>. By
default, all zone keys which have an available private key are
used to generate signatures.</P
><P
><TT
CLASS="userinput"
><B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>. This file
should be referenced by <TT
CLASS="filename"
>named.conf</TT
> as the
input file for the zone.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1008"
>4.8.5. Configuring Servers</A
></H2
><P
>Unlike <SPAN
CLASS="acronym"
>BIND</SPAN
> 8,
<SPAN
CLASS="acronym"
>BIND</SPAN
> 9 does not verify signatures on load,
so zone keys for authoritative zones do not need to be specified
in the configuration file.</P
><P
>The public key for any security root must be present in
the configuration file's <B
CLASS="command"
>trusted-keys</B
>
statement, as described later in this document. </P
></DIV
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN1015"
>4.9. IPv6 Support in <SPAN
CLASS="acronym"
>BIND</SPAN
> 9</A
></H1
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 fully supports all currently defined forms of IPv6
name to address and address to name lookups. It will also use
IPv6 addresses to make queries when running on an IPv6 capable
system.</P
><P
>For forward lookups, <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 supports both A6 and AAAA
records. The use of AAAA records is deprecated, but it is still
useful for hosts to have both AAAA and A6 records to maintain
backward compatibility with installations where AAAA records are
still used. In fact, the stub resolvers currently shipped with
most operating system support only AAAA lookups, because following
A6 chains is much harder than doing A or AAAA lookups.</P
><P
>For IPv6 reverse lookups, <SPAN
CLASS="acronym"
>BIND</SPAN
> 9 supports the new
"binary label" (also known as "bitstring")
format used in the <I
CLASS="emphasis"
>ip6.arpa</I
>
domain, as well as the older, deprecated "nibble" format used in
the <I
CLASS="emphasis"
>ip6.int</I
> domain.</P
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 includes a new lightweight resolver library and
resolver daemon which new applications may choose to use to avoid
the complexities of A6 chain following and binary labels, see <A
HREF="Bv9ARM.ch05.html"
>Chapter 5</A
>. Alternatively, applications can link with a stub
resolver that supports A and AAAA records only and rely on the server to
synthesize AAAA recorsd from A6 chains (<A
HREF="Bv9ARM.ch06.html#synthesis"
>Section 6.2.14.13</A
>).
</P
><P
>For an overview of the format and structure of IPv6 addresses,
see <A
HREF="Bv9ARM.ch09.html#ipv6addresses"
>Section A.2.1</A
>.</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1032"
>4.9.1. Address Lookups Using AAAA Records</A
></H2
><P
>The AAAA record is a parallel to the IPv4 A record. It
specifies the entire address in a single record. For
example,</P
><PRE
CLASS="programlisting"
> $ORIGIN example.com.
host 3600 IN AAAA 3ffe:8050:201:1860:42::1
</PRE
><P
>While their use is deprecated, they are useful to support
older IPv6 applications. They should not be added where they
are not absolutely necessary.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1037"
>4.9.2. Address Lookups Using A6 Records</A
></H2
><P
>The A6 record is more flexible than the AAAA record, and
is therefore more complicated. The A6 record can be used to
form a chain of A6 records, each specifying part of the IPv6
address. It can also be used to specify the entire record as
well. For example, this record supplies the same data as the
AAAA record in the previous example:</P
><PRE
CLASS="programlisting"
> $ORIGIN example.com.
host 3600 IN A6 0 3ffe:8050:201:1860:42::1
</PRE
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN1041"
>4.9.2.1. A6 Chains</A
></H3
><P
>A6 records are designed to allow network
renumbering. This works when an A6 record only specifies the
part of the address space the domain owner controls. For
example, a host may be at a company named "company." It has
two ISPs which provide IPv6 address space for it. These two
ISPs fully specify the IPv6 prefix they supply.</P
><P
>In the company's address space:</P
><PRE
CLASS="programlisting"
> $ORIGIN example.com.
host 3600 IN A6 64 0:0:0:0:42::1 company.example1.net.
host 3600 IN A6 64 0:0:0:0:42::1 company.example2.net.
</PRE
><P
>ISP1 will use:</P
><PRE
CLASS="programlisting"
> $ORIGIN example1.net.
company 3600 IN A6 0 3ffe:8050:201:1860::
</PRE
><P
>ISP2 will use:</P
><PRE
CLASS="programlisting"
> $ORIGIN example2.net.
company 3600 IN A6 0 1234:5678:90ab:fffa::
</PRE
><P
>When <TT
CLASS="literal"
>host.example.com</TT
> is looked up,
the resolver (in the resolver daemon or caching name server)
will find two partial A6 records, and will use the additional
name to find the remainder of the data.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN1052"
>4.9.2.2. A6 Records for DNS Servers</A
></H3
><P
>When an A6 record specifies the address of a name
server, it should use the full address rather than specifying
a partial address. For example:</P
><PRE
CLASS="programlisting"
> $ORIGIN example.com.
@ 14400 IN NS ns0
14400 IN NS ns1
ns0 14400 IN A6 0 3ffe:8050:201:1860:42::1
ns1 14400 IN A 192.168.42.1
</PRE
><P
>It is recommended that IPv4-in-IPv6 mapped addresses not
be used. If a host has an IPv4 address, use an A record, not
an A6, with <TT
CLASS="literal"
>::ffff:192.168.42.1</TT
> as the
address.</P
></DIV
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1058"
>4.9.3. Address to Name Lookups Using Nibble Format</A
></H2
><P
>While the use of nibble format to look up names is
deprecated, it is supported for backwards compatibility with
existing IPv6 applications.</P
><P
>When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<TT
CLASS="literal"
>ip6.int.</TT
> is appended to the resulting name.
For example, the following would provide reverse name lookup for
a host with address
<TT
CLASS="literal"
>3ffe:8050:201:1860:42::1</TT
>.</P
><PRE
CLASS="programlisting"
> $ORIGIN 0.6.8.1.1.0.2.0.0.5.0.8.e.f.f.3.ip6.int.
1.0.0.0.0.0.0.0.0.0.0.0.2.4.0.0 14400 IN PTR host.example.com.
</PRE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1065"
>4.9.4. Address to Name Lookups Using Binary Label Format</A
></H2
><P
>Binary labels can start and end on any bit boundary,
rather than on a multiple of 4 bits as in the nibble
format. They also use <I
CLASS="emphasis"
>ip6.arpa</I
> rather than
<I
CLASS="emphasis"
>ip6.int</I
>.</P
><P
>To replicate the previous example using binary labels:</P
><PRE
CLASS="programlisting"
</PRE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1072"
>4.9.5. Using DNAME for Delegation of IPv6 Reverse Addresses</A
></H2
><P
>In IPv6, the same host may have many addresses from many
network providers. Since the trailing portion of the address
usually remains constant, <B
CLASS="command"
>DNAME</B
> can help
reduce the number of zone files used for reverse mapping that
need to be maintained.</P
><P
>For example, consider a host which has two providers
(<TT
CLASS="literal"
>example.net</TT
> and
<TT
CLASS="literal"
>example2.net</TT
>) and
therefore two IPv6 addresses. Since the host chooses its own 64
bit host address portion, the provider address is the only part
that changes:</P
><PRE
CLASS="programlisting"
> $ORIGIN example.com.
host IN A6 64 ::1234:5678:1212:5675 cust1.example.net.
IN A6 64 ::1234:5678:1212:5675 subnet5.example2.net.
$ORIGIN example.net.
cust1 IN A6 48 0:0:0:dddd:: ipv6net.example.net.
ipv6net IN A6 0 aa:bb:cccc::
$ORIGIN example2.net.
subnet5 IN A6 48 0:0:0:1:: ipv6net2.example2.net.
ipv6net2 IN A6 0 6666:5555:4::
</PRE
><P
>This sets up forward lookups. To handle the reverse lookups,
the provider <TT
CLASS="literal"
>example.net</TT
>
would have:</P
><PRE
CLASS="programlisting"
</PRE
><P
>and <TT
CLASS="literal"
>example2.net</TT
> would have:</P
><PRE
CLASS="programlisting"
</PRE
><P
><TT
CLASS="literal"
>example.com</TT
>
needs only one zone file to handle both of these reverse
mappings:</P
><PRE
CLASS="programlisting"
> $ORIGIN ipv6-rev.example.com.
</PRE
></DIV
></DIV
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