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<HTML
><HEAD
><TITLE
>Advanced Concepts</TITLE
><META
NAME="GENERATOR"
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><BODY
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><TR
><TH
COLSPAN="3"
ALIGN="center"
>BIND 9 Administrator Reference Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="Bv9ARM.ch03.html"
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></TD
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WIDTH="80%"
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ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="chapter"
><H1
><A
NAME="ch04"
>Chapter 4. Advanced Concepts</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>4.1. <A
HREF="Bv9ARM.ch04.html#dynamic_update"
>Dynamic Update</A
></DT
><DT
>4.2. <A
HREF="Bv9ARM.ch04.html#incremental_zone_transfers"
>Incremental Zone Transfers (IXFR)</A
></DT
><DT
>4.3. <A
HREF="Bv9ARM.ch04.html#AEN727"
>Split DNS</A
></DT
><DT
>4.4. <A
HREF="Bv9ARM.ch04.html#tsig"
>TSIG</A
></DT
><DT
>4.5. <A
HREF="Bv9ARM.ch04.html#AEN887"
>TKEY</A
></DT
><DT
>4.6. <A
HREF="Bv9ARM.ch04.html#AEN902"
>SIG(0)</A
></DT
><DT
>4.7. <A
HREF="Bv9ARM.ch04.html#DNSSEC"
>DNSSEC</A
></DT
><DT
>4.8. <A
HREF="Bv9ARM.ch04.html#AEN987"
>IPv6 Support in <SPAN
CLASS="acronym"
>BIND</SPAN
> 9</A
></DT
></DL
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="dynamic_update"
>4.1. Dynamic Update</A
></H1
><P
>Dynamic update is the term used for the ability under
certain specified conditions to add, modify or delete records or
RRsets in the master zone files. Dynamic update is fully described
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"
>4.1.1. 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 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: Shut down
the server using <B
CLASS="command"
>rndc stop</B
> (sending a signal
or using <B
CLASS="command"
>rndc halt</B
> is <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>not</I
></SPAN
>
sufficient). Wait for the server to exit,
then <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>remove</I
></SPAN
> the zone's
<TT
CLASS="filename"
>.jnl</TT
> file, edit the zone file,
and restart the server. Removing the <TT
CLASS="filename"
>.jnl</TT
>
file is necessary because the manual edits will not be
present in the journal, rendering it inconsistent with the
contents of the zone file.</P
></DIV
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="incremental_zone_transfers"
>4.2. 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 documented 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, but not manually maintained master
zones nor slave zones obtained by performing a full zone transfer
(AXFR).</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="AEN727"
>4.3. Split DNS</A
></H1
><P
>Setting up different views, or visibility, of DNS space to
internal and external resolvers is usually referred to as a <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>Split
DNS</I
></SPAN
> setup. There are several reasons an organization
would want to set up its DNS this way.</P
><P
>One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.</P
><P
>Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.</P
><P
>Here is an example of a split DNS setup:</P
><P
>Let's say a company named <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>Example, Inc.</I
></SPAN
> (example.com)
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"
><I
CLASS="emphasis"
>Example, Inc.</I
></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 nameservers. 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
>,<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
> </I
></SPAN
><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 nameservers 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
nameservers 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"
><I
CLASS="emphasis"
>only</I
></SPAN
> the internal
nameservers 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"
><I
CLASS="emphasis"
>Example, Inc.</I
></SPAN
>'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 internals { 172.16.72.0/24; 192.168.1.0/24; };
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" {
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</PRE
><P
>External (bastion host) DNS server config:</P
><PRE
CLASS="programlisting"
> acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
allow-transfer { none; }; // sample allow-transfer (no one)
allow-query { 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"
>4.4. 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. Key-based
access control is far superior, see <A
HREF="Bv9ARM.ch09.html#proposed_standards"
>Proposed Standards</A
>. 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="AEN818"
>4.4.1. Generate Shared Keys for Each Pair of Hosts</A
></H2
><P
>A shared secret is generated to be shared between <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
> and <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host2</I
></SPAN
>.
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="AEN823"
>4.4.1.1. 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"
>Key: La/E5CjG9O+os1jq0a2jdA==</PRE
><P
>The string "<TT
CLASS="literal"
>La/E5CjG9O+os1jq0a2jdA==</TT
>" can
be used as the shared secret.</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN834"
>4.4.1.2. 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="AEN839"
>4.4.2. 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="AEN842"
>4.4.3. Informing the Servers of the Key's Existence</A
></H2
><P
>Imagine <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
> and <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host 2</I
></SPAN
> 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;
secret "La/E5CjG9O+os1jq0a2jdA==";
};
</PRE
><P
>The algorithm, hmac-md5, is the only one supported by <SPAN
CLASS="acronym"
>BIND</SPAN
>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <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 succeeds, the response is signed by
the same key.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN854"
>4.4.4. 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 <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
>, if the IP address of <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host2</I
></SPAN
> is
10.1.2.3:</P
><PRE
CLASS="programlisting"
> server 10.1.2.3 {
keys { host1-host2. ;};
};
</PRE
><P
>Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a world-readable
file.</P
><P
>If <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
> sends a message that is a request
to that address, the message will be signed with the specified key. <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
> will
expect any responses to signed messages to be signed with the same
key.</P
><P
>A similar statement must be present in <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host2</I
></SPAN
>'s
configuration file (with <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
>'s address) for <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host2</I
></SPAN
> to
sign request messages to <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>host1</I
></SPAN
>.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN870"
>4.4.5. 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="AEN883"
>4.4.6. 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="AEN887"
>4.5. 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
> 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="AEN902"
>4.6. SIG(0)</A
></H1
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 partially supports DNSSEC SIG(0) transaction
signatures as specified in RFC 2535. SIG(0) uses public/private
keys to authenticate messages. Access control is performed in the
same manner as TSIG keys; privileges can be granted or denied
based on the key name.</P
><P
>When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
will not attempt to locate and/or validate the key.</P
><P
>SIG(0) signing of multiple-message TCP streams is not
supported.</P
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 does not ship with any tools that generate SIG(0)
signed messages.</P
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="DNSSEC"
>4.7. DNSSEC</A
></H1
><P
>Cryptographic authentication of DNS information is possible
through the DNS Security (<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>DNSSEC</I
></SPAN
>) 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, 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
the parent and/or child zone to transmit keys and signatures. A
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="AEN919"
>4.7.1. 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 (which is not yet supported in BIND 9.2)
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"
>Kchild.example.+003+12345.key</TT
> and
<TT
CLASS="filename"
>Kchild.example.+003+12345.private</TT
> (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 RSA, 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 with
<B
CLASS="command"
>$INCLUDE</B
> statements, including the
<TT
CLASS="filename"
>.key</TT
> files.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN939"
>4.7.2. 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
>dnssec-makekeyset -t 3600 -e +864000 Kchild.example.+003+12345 Kchild.example.+003+23456</B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>keyset-child.example.</TT
>. 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="AEN951"
>4.7.3. 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
>dnssec-signkey keyset-grand.child.example. Kchild.example.+003+12345 Kchild.example.+003+23456</B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>signedkey-grand.child.example.</TT
>. 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="AEN964"
>4.7.4. 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
>dnssec-signzone -o child.example zone.child.example</B
></TT
></P
><P
>One output file is produced:
<TT
CLASS="filename"
>zone.child.example.signed</TT
>. 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="AEN980"
>4.7.5. Configuring Servers</A
></H2
><P
>Unlike in <SPAN
CLASS="acronym"
>BIND</SPAN
> 8,
data is not verified on load in <SPAN
CLASS="acronym"
>BIND</SPAN
> 9,
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="AEN987"
>4.8. 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 A6 records has been moved
to experimental (RFC 3363) and should be treated as deprecated.</P
><P
>The use of "bitstring" labels for IPv6 has been moved to
experimental (RFC 3363) reverting to a nibble format. The
suffix for the IPv6 reverse lookups has also changed from
<TT
CLASS="literal"
>IP6.INT</TT
> to <TT
CLASS="literal"
>IP6.ARPA</TT
> (RFC
3152).</P
><P
><SPAN
CLASS="acronym"
>BIND</SPAN
> 9 now defaults to nibble
<TT
CLASS="literal"
>IP6.ARPA</TT
> format lookups.</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 bitstring labels, see <A
HREF="Bv9ARM.ch05.html"
>Chapter 5</A
>.</P
><P
>For an overview of the format and structure of IPv6 addresses,
see <A
HREF="Bv9ARM.ch09.html#ipv6addresses"
>Section A.3.1</A
>.</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1005"
>4.8.1. 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
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN1009"
>4.8.2. Address to Name Lookups Using Nibble Format</A
></H2
><P
>When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<TT
CLASS="literal"
>IP6.ARPA.</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.ARPA.
1.0.0.0.0.0.0.0.0.0.0.0.2.4.0.0 14400 IN PTR host.example.com.
</PRE
></DIV
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