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<book>

9
  <chapter id="ch01">
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  <title>Introduction </title>
  <para>The Internet Domain Name System (<acronym>DNS</acronym>) consists of the syntax
  to specify the names of entities in the Internet in a hierarchical
  manner, the rules used for delegating authority over names, and the
  system implementation that actually maps names to Internet
  addresses.  <acronym>DNS</acronym> data is maintained in a group of distributed
  hierarchical databases.</para>

  <sect1>
    <title>Scope of Document</title>

    <para>The Berkeley Internet Name Domain (<acronym>BIND</acronym>) implements an
    Internet nameserver for a number of operating systems. This
    document provides basic information about the installation and
    care of the Internet Software Consortium (<acronym>ISC</acronym>) <acronym>BIND</acronym> version 9
    software package for system administrators.</para>
  </sect1>
  <sect1><title>Organization of This Document</title>
    <para>In this document, <emphasis>Section 1</emphasis> introduces
    the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Section 2</emphasis>
    describes resource requirements for running <acronym>BIND</acronym> in various
    environments. Information in <emphasis>Section 3</emphasis> is
    <emphasis>task-oriented</emphasis> in its presentation and is
    organized functionally, to aid in the process of installing the
    <acronym>BIND</acronym> 9 software. The task-oriented section is followed by
    <emphasis>Section 4</emphasis>, which contains more advanced
    concepts that the system administrator may need for implementing
    certain options. Section 5 describes the <acronym>BIND</acronym> 9 lightweight
    resolver.  The contents of <emphasis>Section 6</emphasis> are
    organized as in a reference manual to aid in the ongoing
    maintenance of the software. <emphasis>Section 7
    </emphasis>addresses security considerations, and
    <emphasis>Section 8</emphasis> contains troubleshooting help. The
    main body of the document is followed by several
    <emphasis>Appendices</emphasis> which contain useful reference
    information, such as a <emphasis>Bibliography</emphasis> and
    historic information related to <acronym>BIND</acronym> and the Domain Name
    System.</para>
  </sect1>
  <sect1><title>Conventions Used in This Document</title>

    <para>In this document, we use the following general typographic
    conventions:</para>

<informaltable colsep = "0" frame = "all" rowsep = "0">
        <tgroup cols = "2" colsep = "0" rowsep = "0"
                tgroupstyle = "2Level-table">
          <colspec colname = "1" colnum = "1" colsep = "0"
                   colwidth = "3.000in"/>
          <colspec colname = "2" colnum = "2" colsep = "0"
                   colwidth = "2.625in"/>
          <tbody>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1">
<para><emphasis>To
describe:</emphasis></para></entry>
              <entry colname = "2" rowsep = "1">
<para><emphasis>We use the style:</emphasis></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1">
<para>a pathname, filename, URL, hostname,
mailing list name, or new term or concept</para></entry>
              <entry colname = "2" rowsep = "1"><para><filename>Italic</filename></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1"><para>literal user
input</para></entry>
              <entry colname = "2" rowsep = "1"><para><userinput>Fixed Width Bold</userinput></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1"><para>variable user
input</para></entry>
              <entry colname = "2" rowsep = "1"><para><optional>Fixed Width Italic</optional></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1"><para>program output</para></entry>
              <entry colname = "2"><para><computeroutput>Fixed Width Bold</computeroutput></para></entry>
            </row>
          </tbody>
        </tgroup>
</informaltable>

    <para>The following conventions are used in descriptions of the
<acronym>BIND</acronym> configuration file:<informaltable colsep = "0" frame = "all" rowsep = "0">
        <tgroup cols = "2" colsep = "0" rowsep = "0"
                tgroupstyle = "2Level-table">
          <colspec colname = "1" colnum = "1" colsep = "0" colwidth = "3.000in"/>
          <colspec colname = "2" colnum = "2" colsep = "0" colwidth = "2.625in"/>
          <tbody>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1"><para><emphasis>To
describe:</emphasis></para></entry>
              <entry colname = "2" rowsep = "1"><para><emphasis>We use the style:</emphasis></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1"><para>keywords</para></entry>
              <entry colname = "2" rowsep = "1"><para><literal>Sans Serif Bold</literal></para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1" colsep = "1" rowsep = "1"><para>variables</para></entry>
              <entry colname = "2" rowsep = "1"><para><varname>Sans Serif Italic</varname></para></entry>
            </row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>"meta-syntactic"
information (within brackets when optional)</para></entry>
<entry colname = "2" rowsep = "1"><para><optional>Fixed Width Italic</optional></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>Command line
input</para></entry>
<entry colname = "2" rowsep = "1"><para><userinput>Fixed Width Bold</userinput></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1" rowsep = "1"><para>Program output</para></entry>
                <entry colname = "2" rowsep = "1"><para><computeroutput>Fixed Width</computeroutput></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1" colsep = "1"><para>Optional input</para></entry>
                <entry colname = "2"><para><optional>Text is enclosed in square brackets</optional></para></entry>
</row>
</tbody>
</tgroup></informaltable></para></sect1>
<sect1><title>Discussion of Domain Name System (<acronym>DNS</acronym>) Basics and
<acronym>BIND</acronym></title>
<para>The purpose of this document is to explain the installation
and basic upkeep of the <acronym>BIND</acronym> software package, and we begin by reviewing
the fundamentals of the domain naming system as they relate to <acronym>BIND</acronym>.
<acronym>BIND</acronym> consists of a <emphasis>nameserver</emphasis> (or "daemon")
called <command>named</command> and a <command>resolver</command> library.
The <acronym>BIND</acronym> server runs in the background, servicing queries on a well
known network port. The standard port for the User Datagram Protocol
(UDP) and Transmission Control Protocol (TCP), usually port 53,
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is specified in <filename>/etc/services</filename>.
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The <emphasis>resolver</emphasis> is a set of routines residing
in a system library that provides the interface that programs can
use to access the domain name services.</para>
<sect2><title>Nameservers</title>
<para>A nameserver (NS) is a program that stores information about
named resources and responds to queries from programs called <emphasis>resolvers</emphasis> which
act as client processes. The basic function of an NS is to provide
information about network objects by answering queries.</para>
<para>With the nameserver, the network can be broken into a hierarchy
of domains. The name space is organized as a tree according to organizational
or administrative boundaries. Each node of the tree, called a domain,
is given a label. The name of the domain is the concatenation of
all the labels of the domains from the root to the current domain.
This is represented in written form as a string of labels listed
from right to left and separated by dots. A label need only be unique
within its domain. The whole name space is partitioned into areas
called <emphasis>zones</emphasis>, each starting at a domain and
extending down to the leaf domains or to domains where other zones
start. Zones usually represent administrative boundaries. For example,
a domain name for a host at the company <emphasis>Example, Inc.</emphasis> would
be:</para>
<para><systemitem class="systemname">ourhost.example.com</systemitem></para>
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<para>where <systemitem class="systemname">com</systemitem> is the top level domain to which
<systemitem class="systemname">ourhost.example.com</systemitem> belongs, 
<systemitem class="systemname">example</systemitem> is
a subdomain of <systemitem class="systemname">com</systemitem>, and
<systemitem class="systemname">ourhost</systemitem> is the
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name of the host.</para>
<para>The specifications for the domain nameserver are defined in
the RFC 1034, RFC 1035 and RFC 974. These documents can be found
in
<filename>/usr/src/etc/named/doc</filename> in 4.4BSD or are available
via File Transfer Protocol (FTP) from
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<ulink url="ftp://www.isi.edu/in-notes/">ftp://www.isi.edu/in-notes/</ulink>
or via the Web at <ulink url="http://www.ietf.org/rfc/">http://www.ietf.org/rfc/</ulink>.
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(See Appendix C for complete information on finding and retrieving
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RFCs.) It is also recommended that you read the related man pages:
<command>named</command> and <command>resolver</command>.</para></sect2>
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<sect2><title>Types of Zones</title>
<para>As we stated previously, a zone is a point of delegation in
the <acronym>DNS</acronym> tree. A zone consists of those contiguous parts of the domain
tree for which a domain server has complete information and over which
it has authority. It contains all domain names from a certain point
downward in the domain tree except those which are delegated to
other zones. A delegation point has one or more NS records in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.</para>
<para>To properly operate a nameserver, it is important to understand
the difference between a <emphasis>zone</emphasis> and a <emphasis>domain</emphasis>.</para>
<para>For instance, consider the <systemitem class="systemname">example.com</systemitem> domain
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which includes names such as <systemitem class="systemname">host.aaa.example.com</systemitem>
and <systemitem class="systemname">host.bbb.example.com</systemitem> even
though the <systemitem class="systemname">example.com</systemitem>
zone includes only delegations for the
<systemitem class="systemname">aaa.example.com</systemitem>
and <systemitem class="systemname">bbb.example.com</systemitem> zones.
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A zone can map exactly to a single domain, but could also include
only part of a domain, the rest of which could be delegated to other
nameservers. Every name in the <acronym>DNS</acronym> tree is a <emphasis>domain</emphasis>,
even if it is <emphasis>terminal</emphasis>, that is, has no <emphasis>subdomains</emphasis>.
Every subdomain is a domain and every domain except the root is
also a subdomain. The terminology is not intuitive and we suggest
that you read RFCs 1033, 1034 and 1035 to gain a complete understanding
of this difficult and subtle topic.</para>
<para>Though <acronym>BIND</acronym> is a Domain Nameserver, it deals primarily in
terms of zones. The master and slave declarations in the <filename>named.conf</filename> file
specify zones, not domains. When you ask some other site if it is willing
to be a slave server for your <emphasis>domain</emphasis>, you are
actually asking for slave service for some collection of zones.</para>
<para>Each zone will have one <emphasis>primary master</emphasis> (also
called <emphasis>primary</emphasis>) server which loads the zone
contents from some local file edited by humans or perhaps generated
mechanically from some other local file which is edited by humans.
There there will be some number of <emphasis>slave</emphasis> (also
called <emphasis>secondary) </emphasis>servers, which load the zone
contents using the <acronym>DNS</acronym> protocol (that is, the secondary servers
will contact the primary and fetch the zone data using TCP). This
set of servers &mdash; the primary and all of its secondaries &mdash; should be
listed in the NS records in the parent zone and will constitute a <emphasis>delegation</emphasis>.
This set of servers must also be listed in the zone file itself,
usually under the <command>@</command> name which indicates the <emphasis>top
level</emphasis> or <emphasis>root</emphasis> of the current zone.
You can list servers in the zone's top-level <command>@</command> NS
records that are not in the parent's NS delegation, but you cannot
list servers in the parent's delegation that are not present in
the zone's <command>@</command>.</para>
<para>Any servers listed in the NS records must be configured as <emphasis>authoritative</emphasis> for
the zone. A server is authoritative for a zone when it has been
configured to answer questions for that zone with authority, which
it does by setting the "authoritative answer" (AA) bit in reply
packets. A server may be authoritative for more than one zone. The
authoritative data for a zone is composed of all of the Resource
Records (RRs) &mdash; the data associated with names in a tree-structured
name space &mdash; attached to all of the nodes from the top node of the
zone down to leaf nodes or nodes above cuts around the bottom edge
of the zone.</para>
<para>Adding a zone as a type master or type slave will tell the
server to answer questions for the zone authoritatively. If the
server is able to load the zone into memory without any errors it
will set the AA bit when it replies to queries for the zone. See
RFCs 1034 and 1035 for more information about the AA bit.</para></sect2>
<sect2><title>Servers</title>
<para>A <acronym>DNS</acronym> server can be master for some zones and slave for others
or can be only a master, or only a slave, or can serve no zones
and just answer queries via its <emphasis>cache</emphasis>. Master
servers are often also called <emphasis>primaries</emphasis> and
slave servers are often also called <emphasis>secondaries</emphasis>.
Both master/primary and slave/secondary servers are authoritative
for a zone.</para>
<para>All servers keep data in their cache until the data expires,
based on a Time To Live (TTL) field which is maintained for all
resource records.</para>
<sect3><title>Master Server</title>
<para>The <emphasis>primary master server</emphasis> is the ultimate
source of information about a domain. The primary master is an authoritative
server configured to be the source of zone transfer for one or more
secondary servers. The primary master server obtains data for the
zone from a file on disk.</para></sect3>
<sect3><title>Slave Server </title>
<para>A <emphasis>slave server</emphasis>, also called a <emphasis>secondary
server</emphasis>, is an authoritative server that uses zone transfers from
the primary master server to retrieve the zone data. Optionally,
the slave server obtains zone data from a cache on disk. Slave servers
provide necessary redundancy. All secondary/slave servers are named
in the NS RRs for the zone.</para></sect3>
<sect3><title>Caching Only Server</title>
<para>Some servers are <emphasis>caching only servers</emphasis>.
This means that the server caches the information that it receives
and uses it until the data expires. A caching only server is a server
that is not authoritative for any zone. This server services queries
and asks other servers, who have the authority, for the information
it needs.</para></sect3>
<sect3><title>Forwarding Server</title>
<para>Instead of interacting with the nameservers for the root and
other domains, a <emphasis>forwarding server</emphasis> always forwards
queries it cannot satisfy from its authoritative data or cache to
a fixed list of other servers. The forwarded queries are also known
as <emphasis>recursive queries</emphasis>, the same type as a client would
send to a server. There may be one or more servers forwarded to,
and they are queried in turn until the list is exhausted or an answer
is found. A forwarding server is typically used when you do not
wish all the servers at a given site to interact with the rest of
the Internet servers. A typical scenario would involve a number
of internal <acronym>DNS</acronym> servers and an Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <acronym>DNS</acronym> servers
on the internal server's behalf. An added benefit of using the forwarding
feature is that the central machine develops a much more complete
cache of information that all the workstations can take advantage
of.</para>
<para>There is no prohibition against declaring a server to be a
forwarder even though it has master and/or slave zones as well;
the effect will still be that anything in the local server's cache
or zones will be answered, and anything else will be forwarded using
the forwarders list.</para></sect3>
<sect3><title>Stealth Server</title>
<para>A <emphasis>stealth server</emphasis> is a server that answers
authoritatively for a zone, but is not listed in that zone's NS
records. Stealth servers can be used as a way to centralize distribution
of a zone, without having to edit the zone on a remote nameserver.
Where the master file for a zone resides on a stealth server in
this way, it is often referred to as a "hidden primary" configuration.
Stealth servers can also be a way to keep a local copy of a zone
for rapid access to the zone's records, even if all "official" nameservers
for the zone are inaccessible.</para>
      </sect3>
    </sect2>
  </sect1>
  </chapter>

314
  <chapter id="ch02"><title><acronym>BIND</acronym> Resource Requirements</title>
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<sect1><title>Hardware requirements</title>
<para><acronym>DNS</acronym> hardware requirements have traditionally been quite modest.
For many installations, servers that have been pensioned off from
active duty have performed admirably as <acronym>DNS</acronym> servers.</para>
<para>The DNSSEC and IPv6 features of <acronym>BIND</acronym> 9 may prove to be quite
CPU intensive however, so organizations that make heavy use of these
features may wish to consider larger systems for these applications.
<acronym>BIND</acronym> 9 is now fully multithreaded, allowing full utilization of
multiprocessor systems for installations that need it.</para></sect1>
<sect1><title>CPU Requirements</title>
<para>CPU requirements for <acronym>BIND</acronym> 9 range from i486-class machines
for serving of static zones without caching, to enterprise-class
machines if you intend to process many dynamic updates and DNSSEC
signed zones, serving many thousands of queries per second.</para></sect1>
<sect1><title>Memory Requirements </title>
<para>The memory of the server has to be large enough to fit the
cache and zones loaded off disk. Future releases of <acronym>BIND</acronym> 9 will
provide methods to limit the amount of memory used by the cache,
at the expense of reducing cache hit rates and causing more <acronym>DNS</acronym>
traffic. It is still good practice to have enough memory to load
all zone and cache data into memory &mdash; unfortunately, the best way
to determine this for a given installation is to watch the nameserver
in operation. After a few weeks the server process should reach
a relatively stable size where entries are expiring from the cache as
fast as they are being inserted. Ideally, the resource limits should
be set higher than this stable size.</para></sect1>
<sect1><title>Nameserver Intensive Environment Issues</title>
<para>For nameserver intensive environments, there are two alternative
configurations that may be used. The first is where clients and
any second-level internal nameservers query a main nameserver, which
has enough memory to build a large cache. This approach minimizes
the bandwidth used by external name lookups. The second alternative
is to set up second-level internal nameservers to make queries independently.
In this configuration, none of the individual machines needs to
have as much memory or CPU power as in the first alternative, but
this has the disadvantage of making many more external queries,
as none of the nameservers share their cached data.</para></sect1>
<sect1><title>Supported Operating Systems</title>
<para>ISC <acronym>BIND</acronym> 9 compiles and runs on the following operating
systems:</para>
    <itemizedlist>
      <listitem>
        <simpara>IBM AIX 4.3</simpara>
      </listitem>
      <listitem>
        <simpara>Compaq Digital/Tru64 UNIX 4.0D</simpara>
      </listitem>
      <listitem>
        <simpara>HP HP-UX 11</simpara>
      </listitem>
      <listitem>
        <simpara>IRIX64 6.5</simpara>
      </listitem>
      <listitem>
        <simpara>Red Hat Linux 6.0, 6.1</simpara>
      </listitem>
      <listitem>
        <simpara>Sun Solaris 2.6, 7, 8 (beta)</simpara>
      </listitem>
      <listitem>
        <simpara>FreeBSD 3.4-STABLE</simpara>
      </listitem>
      <listitem>
        <simpara>NetBSD-current with "unproven" pthreads</simpara>
      </listitem>
    </itemizedlist>
  </sect1>
  </chapter>

384
  <chapter id="ch03">
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  <title>Nameserver Configuration</title>
<para>In this section we provide some suggested configurations along
with guidelines for their use. We also address the topic of reasonable
option setting.</para>
  <sect1 id="sample_configuration">
    <title>Sample Configurations</title>
    <sect2>
      <title>A Caching-only Nameserver</title>
      <para>The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation.  All queries
from outside clients are refused.</para>
      <programlisting>
// Two corporate subnets we wish to allow queries from.
acl "corpnets" { 192.168.4.0/24; 192.168.7.0/24; };
options {
     directory "/etc/namedb";		// Working directory
     pid-file "named.pid";		// Put pid file in working dir
     allow-query { "corpnets"; };
};
// Root server hints
zone "." { type hint; file "root.hint"; };
// Provide a reverse mapping for the loopback address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
     type master;
     file "localhost.rev";
     notify no;
};
</programlisting>
    </sect2>
    <sect2>
      <title>An Authoritative-only Nameserver</title>
      <para>This sample configuration is for an authoritative-only server
that is the master server for "<filename>example.com</filename>"
and a slave for the subdomain "<filename>eng.example.com</filename>".</para>
      <programlisting>
options {
     directory "/etc/namedb";		// Working directory
     pid-file "named.pid";		// Put pid file in working dir
     allow-query { any; };		// This is the default
     recursion no;			// Do not provide recursive service
};
// Root server hints
zone "." { type hint; file "root.hint"; };

// Provide a reverse mapping for the loopback address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
     type master;
     file "localhost.rev";
     notify no;
};
// We are the master server for example.com
zone "example.com" {
     type master;
     file "example.com.db";
     // IP addresses of slave servers allowed to transfer example.com
     allow-transfer {
          192.168.4.14;
          192.168.5.53;
     };
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
     type slave;
     file "eng.example.com.bk";
     // IP address of eng.example.com master server
     masters { 192.168.4.12; };
};
</programlisting>
    </sect2>
  </sect1>
  <sect1>
    <title>Load Balancing</title>
    <para>Primitive load balancing can be achieved in <acronym>DNS</acronym> using multiple
A records for one name.</para>
<para>For example, if you have three WWW servers with network addresses
of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a set of records such as the
following means that clients will connect to each machine one third
of the time:</para>
    <informaltable colsep = "0" rowsep = "0">
<tgroup cols = "5" colsep = "0" rowsep = "0"
    tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "0.875in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "0.500in"/>
<colspec colname = "3" colnum = "3" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "4" colnum = "4" colsep = "0" colwidth = "0.750in"/>
<colspec colname = "5" colnum = "5" colsep = "0" colwidth = "2.028in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para>Name</para></entry>
<entry colname = "2"><para>TTL</para></entry>
<entry colname = "3"><para>CLASS</para></entry>
<entry colname = "4"><para>TYPE</para></entry>
<entry colname = "5"><para>Resource Record (RR) Data</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><literal>www</literal></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.1</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.2</literal></para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para></para></entry>
<entry colname = "2"><para><literal>600</literal></para></entry>
<entry colname = "3"><para><literal>IN</literal></para></entry>
<entry colname = "4"><para><literal>A</literal></para></entry>
<entry colname = "5"><para><literal>10.0.0.3</literal></para></entry>
          </row>
        </tbody>
      </tgroup>
    </informaltable>
    <para>When a resolver queries for these records, <acronym>BIND</acronym> will rotate
    them and respond to the query with the records in a different
    order.  In the example above, clients will randomly receive
    records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
    will use the first record returned and discard the rest.</para>
    <para>For more detail on ordering responses, check the
    <command>rrset-order</command> substatement in the
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Andreas Gustafsson committed
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    <command>options</command> statement, see
    <xref endterm="rrset_ordering_title" linkend="rrset_ordering"/>.
    This substatement is not supported in
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    <acronym>BIND</acronym> 9, and only the ordering scheme described above is
    available.</para>

  </sect1>
  <sect1 id="notify">
    <title>Notify</title>

    <para><acronym>DNS</acronym> Notify is a mechanism that allows master nameservers to
    notify their slave servers of changes to a zone's data. In
    response to a <command>NOTIFY</command> 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 transfer.</para> <para><acronym>DNS</acronym>
    Notify is fully documented in RFC 1996. See also the description
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    of the zone option <command>also-notify</command>, see <xref
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    linkend="zone_transfers"/>. For more information about
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    <command>notify</command>, see <xref
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    linkend="boolean_options"/>.</para>

  </sect1>
  <sect1>
    <title>Nameserver Operations</title>
    <sect2>
      <title>Tools for Use With the Nameserver Daemon</title>
      <para>There are several indispensable diagnostic, administrative
and monitoring tools available to the system administrator for controlling
and debugging the nameserver daemon. We describe several in this
section </para>
      <sect3>
        <title>Diagnostic Tools</title>
        <variablelist>
          <varlistentry>
            <term><command>dig</command></term>
            <listitem>
              <para>The domain information groper (<command>dig</command>) is
a command line tool that can be used to gather information from
the Domain Name System servers. Dig has two modes: simple interactive
mode for a single query, and batch mode which executes a query for
each in a list of several query lines. All query options are accessible
from the command line.</para>
              <cmdsynopsis label="Usage">
                        <command>dig</command>
                        <arg>@<replaceable>server</replaceable></arg>
                        <arg choice="plain"><replaceable>domain</replaceable></arg>
                        <arg><replaceable>query-type</replaceable></arg>
                        <arg><replaceable>query-class</replaceable></arg>
                        <arg>+<replaceable>query-option</replaceable></arg>
                        <arg>-<replaceable>dig-option</replaceable></arg>
                        <arg>%<replaceable>comment</replaceable></arg>
                <!-- one of (SBR GROUP ARG COMMAND) -->
              </cmdsynopsis>
              <para>The usual simple use of dig will take the form</para>
              <simpara><command>dig @server domain query-type query-class</command></simpara>
              <para>For more information and a list of available commands and
options, see the <command>dig</command> man page.</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><command>host</command></term>
            <listitem>
              <para>The <command>host</command> utility
provides a simple <acronym>DNS</acronym> lookup using a command-line interface for
looking up Internet hostnames. By default, the utility converts
between host names and Internet addresses, but its functionality
can be extended with the use of options.</para>
              <cmdsynopsis label="Usage">
                <!-- one of (SBR GROUP ARG COMMAND) -->
                <command>host</command>
                <arg>-aCdlrTwv</arg>
                <arg>-c <replaceable>class</replaceable></arg>
                <arg>-N <replaceable>ndots</replaceable></arg>
                <arg>-t <replaceable>type</replaceable></arg>
                <arg>-W <replaceable>timeout</replaceable></arg>
                <arg>-R <replaceable>retries</replaceable></arg>
                <arg choice="plain"><replaceable>hostname</replaceable></arg>
                <arg><replaceable>server</replaceable></arg>
              </cmdsynopsis>
              <para>For more information and a list of available commands and
options, see the <command>host</command> man page.</para>
            </listitem>
          </varlistentry>
          <varlistentry>
            <term><command>nslookup</command></term>
            <listitem>
              <para><command>nslookup</command> is a program used to query Internet
domain nameservers. <command>nslookup</command> has two modes: interactive
and non-interactive. Interactive mode allows the user to query nameservers
for information about various hosts and domains or to print a list
of hosts in a domain. Non-interactive mode is used to print just
the name and requested information for a host or domain.</para>
              <cmdsynopsis label="Usage">
                <command>nslookup</command>
                <arg rep="repeat">-option</arg>
                <group>
                  <arg><replaceable>host-to-find</replaceable></arg>
                  <arg>- <arg>server</arg></arg>
                </group>
              </cmdsynopsis>
<para>Interactive mode is entered when no arguments are given (the
default nameserver will be used) or when the first argument is a
hyphen (`-') and the second argument is the host name or Internet address
of a nameserver.</para>
<para>Non-interactive mode is used when the name or Internet address
of the host to be looked up is given as the first argument. The
optional second argument specifies the host name or address of a nameserver.</para>
<para>Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of <command>nslookup</command>.
Use <command>dig</command> instead.</para>
            </listitem>
          </varlistentry>
        </variablelist>
      </sect3>
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      <sect3 id="admin_tools">
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        <title>Administrative Tools</title>
        <para>Administrative tools play an integral part in the management
of a server.</para>
        <variablelist>
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          <varlistentry id="rndc" xreflabel="Remote Name Daemon Control application">
            <term><command>rndc</command></term>
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            <listitem>
              <para>The remote name daemon control
              (<command>rndc</command>) program allows the system
              administrator to control the operation of a nameserver.
              If you run <command>rndc</command> without any options
              it will display a usage message as follows:</para>
              <cmdsynopsis label="Usage">
                <command>rndc</command>
                <arg>-c <replaceable>config</replaceable></arg>
                <arg>-s <replaceable>server</replaceable></arg>
                <arg>-p <replaceable>port</replaceable></arg>
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                <arg>-v <replaceable>view</replaceable></arg>
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                <arg>-y <replaceable>key</replaceable></arg>
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                <arg>-z <replaceable>zone</replaceable></arg>
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                <arg choice="plain"><replaceable>command</replaceable></arg>
                <arg rep="repeat"><replaceable>command</replaceable></arg>
              </cmdsynopsis>
              <para><command>command</command> is one of the following
              for <command>named</command>:</para>
              <informaltable colsep = "0" rowsep = "0">
                <tgroup cols = "2"
                        colsep = "0" rowsep = "0" tgroupstyle = "4Level-table">
                  <colspec colname = "1" colnum = "1"
                           colsep = "0" colwidth = "1.500in"/>
                  <colspec colname = "2" colnum = "2" colsep = "0"
                           colwidth = "3.000in"/>
                  <tbody>
                    <row rowsep = "0">
                      <entry colname = "1">
<para><userinput>status</userinput><footnote id="nyi1">
                            <para>not yet implemented</para>
                          </footnote></para></entry>
<entry colname = "2"><para>Display ps(1) status of named.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>dumpdb</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Dump database and cache to /var/tmp/named_dump.db.</para></entry>
</row>
<row rowsep = "0">
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<entry colname = "1"><para><userinput>refresh</userinput></para></entry>
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<entry colname = "2"><para>Force a refresh of specified zone.</para></entry>
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</row>
<row rowsep = "0">
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<entry colname = "1"><para><userinput>reload</userinput></para></entry>
<entry colname = "2"><para>Reload configuration file and zones.</para></entry>
</row>
<row rowsep = "0">
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<entry colname = "1"><para><userinput>stats</userinput></para></entry>
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<entry colname = "2"><para>Dump statistics to /var/tmp/named.stats.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><userinput>trace</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Increment debugging level by one.</para></entry>
</row>
<row rowsep = "0">
                      <entry colname = "1">
<para><userinput>notrace</userinput><footnoteref linkend="nyi1"/>
</para></entry>
<entry colname = "2"><para>Set debugging level to 0.</para></entry>
</row>
<row rowsep = "0">
                      <entry colname =
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                             "1"><para><userinput>querylog</userinput></para></entry>
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<entry colname = "2"><para>Toggle query logging.</para></entry>
</row>
<row rowsep = "0">
                      <entry colname =
                             "1"><para><userinput>stop</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Stop the server.</para></entry>
</row>
<row rowsep = "0">
                      <entry colname =
                             "1"><para><userinput>restart</userinput><footnoteref linkend="nyi1"/></para></entry>
<entry colname = "2"><para>Restart the server.</para></entry>
                    </row>
                  </tbody>
                </tgroup>
              </informaltable>
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              <para>As noted above, only a limited number of commands are
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              available in <acronym>BIND</acronym> 9.1. The other
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              commands, and more, are planned to be implemented for
              future releases.</para>

              <para>A configuration file is required, since all
              communication with the server is authenticated with
              digital signatures that rely on a shared secret, and
              there is no way to provide that secret other than with a
              configuration file.  The default location for the
              <command>rndc</command> configuration file is
              <filename>/etc/rndc.conf</filename>, but an alternate
              location can be specified with the <option>-c</option>
              option.</para>

              <para>The format of the configuration file is similar to
              that of <filename>named.conf</filename>, but limited to
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              only three statements, the <command>options</command>,
              <command>key</command> and <command>server</command>
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              statements.  These statements are what associate the
              secret keys to the servers with which they are meant to
              be shared.  The order of statements is not
              significant.</para>

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<para>The <command>options</command> statement has two clauses: <command>default-server</command> and <command>default-key</command>. <command>default-server</command> takes a
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host name or address argument  and represents the server that will
be contacted if no <option>-s</option>
option is provided on the command line.  <command>default-key</command> takes
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the name of key as its argument, as defined by a <command>key</command> statement.
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 In the future a <command>default-port</command> clause will be
added to specify the port to which <command>rndc</command> should
connect.</para>
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<para>The <command>key</command> statement names a key with its
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string argument. The string is required by the server to be a valid
domain name, though it need not actually be hierarchical; thus,
a string like "<userinput>rndc_key</userinput>" is a valid name.
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The <command>key</command> statement has two clauses: <command>algorithm</command> and <command>secret</command>.
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 While the configuration parser will accept any string as the argument
to algorithm, currently only the string "<userinput>hmac-md5</userinput>"
has any meaning.  The secret is a base-64 encoded string, typically
generated with either <command>dnssec-keygen</command> or <command>mmencode</command>.</para>
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<para>The <command>server</command> statement uses the key clause
to associate a <command>key</command>-defined key with a server.
 The argument to the <command>server</command> statement is a
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host name or address (addresses must be double quoted).  The argument
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to the key clause is the name of the key as defined by the <command>key</command> statement.
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 A <command>port</command> clause will be added to a future release
to specify the port to which <command>rndc</command> should connect
on the given server.</para>
<para>A sample minimal configuration file is as follows:</para>
              <programlisting>
key rndc_key {
     algorithm "hmac-md5";
     secret "c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
     default-server localhost;
     default-key    rndc_key;
};
</programlisting>
<para>This file, if installed as <filename>/etc/rndc.conf</filename>,
would allow the command:</para>
              <para><prompt>$ </prompt><userinput>rndc reload</userinput></para>
<para>to connect to 127.0.0.1 port 953 and cause the nameserver
to reload, if a nameserver on the local machine were running with
following controls statements:</para>
              <programlisting>
controls {
		inet 127.0.0.1 allow { localhost; } keys { rndc_key; };
};
</programlisting>
<para>and it had an identical key statement for
<literal>rndc_key</literal>.</para>
            </listitem>
          </varlistentry>
        </variablelist>

      </sect3>
    </sect2>
    <sect2>
      <title>Signals</title>
<para>Certain UNIX signals cause the name server to take specific
actions, as described in the following table.  These signals can
be sent using the <command>kill</command> command.</para>
<informaltable colsep = "0" rowsep = "0"><tgroup cols = "2"
    colsep = "0" rowsep = "0" tgroupstyle = "3Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.125in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "4.000in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><command>SIGHUP</command></para></entry>
<entry colname = "2"><para>Causes the server to read <filename>named.conf</filename> and
reload the database. </para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><command>SIGTERM</command></para></entry>
<entry colname = "2"><para>Causes the server to clean up and exit.</para></entry>
            </row>
            <row rowsep = "0">
              <entry colname = "1">
<para><command>SIGINT</command></para>
</entry>
              <entry colname = "2"><para>Causes the server to clean up and exit.</para></entry>
            </row>
          </tbody>
        </tgroup>
      </informaltable>
    </sect2>
  </sect1>
  </chapter>

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  <chapter id="ch04">
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  <title>Advanced Concepts</title>
  <sect1 id="dynamic_update">
    <title>Dynamic Update</title>

    <para>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.</para>

    <para>Dynamic update is enabled on a zone-by-zone basis, by
    including an <command>allow-update</command> or
    <command>update-policy</command> clause in the
    <command>zone</command> statement.</para>

    <para>Updating of secure zones (zones using DNSSEC) is modelled
    after the <emphasis>simple-secure-update</emphasis> proposal, a
    work in progress in the DNS Extensions working group of the IETF.
    (See <ulink
    url="http://www.ietf.org/html.charters/dnsext-charter.html">http://www.ietf.org/html.charters/dnsext-charter.html</ulink>
    for information about the DNS Extensions working group.) 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.</para>

    <para>The zone files of dynamic zones must not be edited by hand.
    The zone file on disk at any given time may not contain the latest
    changes performed by dynamic update. The zone file is written to
    disk only periodically, and changes that have occurred since the
    zone file was last written to disk are stored only in the zone's
    journal (<filename>.jnl</filename>) file. <acronym>BIND</acronym> 9 currently does
    not update the zone file when it exits as <acronym>BIND</acronym> 8 does, so editing
    the zone file manually is unsafe even when the server has been
    shut down. </para>
  </sect1>
  <sect1 id="incremental_zone_transfers">
    <title>Incremental Zone Transfers (IXFR)</title>

    <para>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
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    1995. See <xref linkend="proposed_standards"/></para>
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<para>When acting as a master, <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, but not manually maintained master
zones nor slave zones obtained by performing a full zone transfer
(AXFR).</para>
<para>When acting as a slave, <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 <command>request-ixfr</command> clause
of the <command>server</command> statement.</para></sect1>
<sect1><title>Split DNS</title>
<para>Setting up different views, or visibility, of DNS space to
internal and external resolvers is usually referred to as a <emphasis>Split
DNS</emphasis> setup. There are several reasons an organization
would want to set up its DNS this way.</para>
<para>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.</para>
<para>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.</para>
<para>Here is an example of a split DNS setup:</para>
<para>Let's say a company named <emphasis>Example, Inc.</emphasis> (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.</para>
<para><emphasis>Example, Inc.</emphasis> 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.</para>
<para>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.</para>
<para>The internal servers will be configured to forward all queries,
except queries for <filename>site1.internal</filename>, <filename>site2.internal</filename>, <filename>site1.example.com</filename>,
and <filename>site2.example.com</filename>, to the servers in the
DMZ. These internal servers will have complete sets of information
for <filename>site1.example.com</filename>, <filename>site2.example.com</filename>,<emphasis> </emphasis><filename>site1.internal</filename>,
and <filename>site2.internal</filename>.</para>
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<para>To protect the <filename>site1.internal</filename> and <filename>site2.internal</filename> domains,
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the internal nameservers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.</para>
<para>The external servers, which are on the bastion hosts, will
be configured to serve the "public" version of the <filename>site1</filename> and <filename>site2.example.com</filename> zones.
This could include things such as the host records for public servers
(<filename>www.example.com</filename> and <filename>ftp.example.com</filename>),
and mail exchange (MX)  records (<filename>a.mx.example.com</filename> and <filename>b.mx.example.com</filename>).</para>
<para>In addition, the public <filename>site1</filename> and <filename>site2.example.com</filename> 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.</para>
<para>Here's an example of a wildcard MX record:</para>
<programlisting><literal>*   IN MX 10 external1.example.com.</literal></programlisting>
<para>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.</para>
<para>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.</para>
<para>In order for all this to work properly, internal clients will
need to be configured to query <emphasis>only</emphasis> the internal
nameservers for DNS queries. This could also be enforced via selective
filtering on the network.</para>
<para>If everything has been set properly, <emphasis>Example, Inc.</emphasis>'s
internal clients will now be able to:</para>
<itemizedlist><listitem>
        <simpara>Look up any hostnames in the <systemitem class="systemname">site1</systemitem> and 
<systemitem class="systemname">site2.example.com</systemitem> zones.</simpara></listitem>
<listitem>
        <simpara>Look up any hostnames in the <systemitem class="systemname">site1.internal</systemitem> and 
<systemitem class="systemname">site2.internal</systemitem> domains.</simpara></listitem>
<listitem>
        <simpara>Look up any hostnames on the Internet.</simpara></listitem>
<listitem>
        <simpara>Exchange mail with internal AND external people.</simpara></listitem></itemizedlist>
<para>Hosts on the Internet will be able to:</para>
<itemizedlist><listitem>
        <simpara>Look up any hostnames in the <systemitem class="systemname">site1</systemitem> and 
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<systemitem class="systemname">site2.example.com</systemitem> zones.</simpara></listitem>
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<listitem>
        <simpara>Exchange mail with anyone in the <systemitem class="systemname">site1</systemitem> and 
<systemitem class="systemname">site2.example.com</systemitem> zones.</simpara></listitem></itemizedlist>

    <para>Here is an example configuration for the setup we just
    described above. Note that this is only configuration information;
961
    for information on how to configure your zone files, see <xref
962 963 964 965
    linkend="sample_configuration"/></para>

<para>Internal DNS server config:</para>
<programlisting>
966 967 968

acl internals { 172.16.72.0/24; 192.168.1.0/24; };

969
acl externals { <varname>bastion-ips-go-here</varname>; };
970

971 972 973 974
options {
    ...
    ...
    forward only;
975 976 977 978 979 980
    forwarders { 				// forward to external servers
    	<varname>bastion-ips-go-here</varname>; 
    };
    allow-transfer { none; };			// sample allow-transfer (no one)
    allow-query { internals; externals; };	// restrict query access
    allow-recursion { internals; };		// restrict recursion
981 982 983
    ...
    ...
};
984 985

zone "site1.example.com" { 			// sample slave zone
986 987
  type master;
  file "m/site1.example.com";
988 989
  forwarders { }; 				// do normal iterative
						// resolution (do not forward)
990 991 992
  allow-query { internals; externals; };
  allow-transfer { internals; };
};
993

994 995 996 997 998 999 1000 1001
zone "site2.example.com" {
  type slave;
  file "s/site2.example.com";
  masters { 172.16.72.3; };
  forwarders { };
  allow-query { internals; externals; };
  allow-transfer { internals; };
};
1002

1003 1004 1005 1006 1007 1008 1009
zone "site1.internal" {
  type master;
  file "m/site1.internal";
  forwarders { };
  allow-query { internals; };
  allow-transfer { internals; }
};
1010

1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021
zone "site2.internal" {
  type slave;
  file "s/site2.internal";
  masters { 172.16.72.3; };
  forwarders { };
  allow-query { internals };
  allow-transfer { internals; }
};
</programlisting>
    <para>External (bastion host) DNS server config:</para>
<programlisting>
1022 1023
acl internals { 172.16.72.0/24; 192.168.1.0/24; };

1024
acl externals { bastion-ips-go-here; };
1025

1026 1027 1028
options {
  ...
  ...
1029 1030 1031
  allow-transfer { none; };			// sample allow-transfer (no one)
  allow-query { internals; externals; };	// restrict query access
  allow-recursion { internals; externals; };	// restrict recursion
1032 1033 1034
  ...
  ...
};
1035 1036

zone "site1.example.com" {			// sample slave zone
1037 1038 1039 1040 1041
  type master;
  file "m/site1.foo.com";
  allow-query { any; };
  allow-transfer { internals; externals; };
};
1042

1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073
zone "site2.example.com" {
  type slave;
  file "s/site2.foo.com";
  masters { another_bastion_host_maybe; };
  allow-query { any; };
  allow-transfer { internals; externals; }
};
</programlisting>
<para>In the <filename>resolv.conf</filename> (or equivalent) on
the bastion host(s):</para>
<programlisting>
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</programlisting>
</sect1>
<sect1 id="tsig"><title>TSIG</title>
<para>This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym>BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym>BIND</acronym>.</para>
<para><acronym>BIND</acronym> primarily supports TSIG for server to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym>BIND</acronym> 8 have limited support
for TSIG.</para>

    <para>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
1074
    access control is far superior, see <xref
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    linkend="proposed_standards"/>. The <command>nsupdate</command>
    program supports TSIG via the <option>-k</option> and
    <option>-y</option> command line options.</para>

<sect2><title>Generate Shared Keys for Each Pair of Hosts</title>
<para>A shared secret is generated to be shared between <emphasis>host1</emphasis> and <emphasis>host2</emphasis>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.</para>
<sect3><title>Automatic Generation</title>
<para>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.</para>
        <para><userinput>dnssec-keygen -a hmac-md5 -b 128 -n HOST host1-host2.</userinput></para>
<para>The key is in the file <filename>Khost1-host2.+157+00000.private</filename>.
Nothing directly uses this file, but the base-64 encoded string
following "<literal>Key:</literal>"
can be extracted from the file and used as a shared secret:</para>
<programlisting>Key: La/E5CjG9O+os1jq0a2jdA==</programlisting>
<para>The string "<literal>La/E5CjG9O+os1jq0a2jdA==</literal>" can
be used as the shared secret.</para></sect3>
<sect3><title>Manual Generation</title>
<para>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.</para>
<para>Also, a known string can be run through <command>mmencode</command> or
a similar program to generate base-64 encoded data.</para></sect3></sect2>
<sect2><title>Copying the Shared Secret to Both Machines</title>
<para>This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.</para></sect2>
<sect2><title>Informing the Servers of the Key's Existence</title>
<para>Imagine <emphasis>host1</emphasis> and <emphasis>host 2</emphasis> are
both servers. The following is added to each server's <filename>named.conf</filename> file:</para>
<programlisting>
key host1-host2. {
  algorithm hmac-md5;
  secret "La/E5CjG9O+os1jq0a2jdA==";
};
</programlisting>
<para>The algorithm, hmac-md5, is the only one supported by <acronym>BIND</acronym>.
The secret is the one generated above. Since this is a secret, it
is recommended that either <filename>named.conf</filename> be non-world
readable, or the key directive be added to a non-world readable
file that is included by <filename>named.conf</filename>.</para>
<para>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.</para></sect2>
<sect2><title>Instructing the Server to Use the Key</title>
<para>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 <filename>named.conf</filename> file
for <emphasis>host1</emphasis>, if the IP address of <emphasis>host2</emphasis> is
10.1.2.3:</para>
<programlisting>
server 10.1.2.3 {
  keys { host1-host2. ;};
};
</programlisting>
<para>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.</para>
1138
<para>If <emphasis>host1</emphasis> sends a message that is a request
1139 1140 1141 1142 1143
to that address, the message will be signed with the specified key. <emphasis>host1</emphasis> will
expect any responses to signed messages to be signed with the same
key.</para>
<para>A similar statement must be present in <emphasis>host2</emphasis>'s
configuration file (with <emphasis>host1</emphasis>'s address) for <emphasis>host2</emphasis> to
1144
sign request messages to <emphasis>host1</emphasis>.</para></sect2>
1145 1146 1147
<sect2><title>TSIG Key Based Access Control</title>
<para><acronym>BIND</acronym> allows IP addresses and ranges to be specified in ACL
definitions and
1148
<command>allow-{ query | transfer | update }</command> directives.
1149 1150 1151 1152 1153 1154 1155 1156 1157
This has been extended to allow TSIG keys also. The above key would
be denoted <command>key host1-host2.</command></para>
<para>An example of an allow-update directive would be:</para>
<programlisting>
allow-update { key host1-host2. ;};
</programlisting>

      <para>This allows dynamic updates to succeed only if the request
      was signed by a key named
1158 1159
      "<command>host1-host2.</command>".</para> <para>You may want to read about the more
      powerful <command>update-policy</command> statement in <xref
1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240
      linkend="dynamic_update_policies"/>.</para>

    </sect2>
    <sect2>
      <title>Errors</title>

      <para>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.</para>

      <para>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.</para>

    </sect2>
  </sect1>
  <sect1>
    <title>TKEY</title>

    <para><command>TKEY</command> is a mechanism for automatically
    generating a shared secret between two hosts.  There are several
    "modes" of <command>TKEY</command> that specify how the key is
    generated or assigned.  <acronym>BIND</acronym> 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 <command>TKEY</command> process
    must use signed messages, signed either by TSIG or SIG(0).  The
    result of <command>TKEY</command> is a shared secret that can be
    used to sign messages with TSIG.  <command>TKEY</command> can also
    be used to delete shared secrets that it had previously
    generated.</para>

    <para>The <command>TKEY</command> process is initiated by a client
    or server by sending a signed <command>TKEY</command> query
    (including any appropriate KEYs) to a TKEY-aware server.  The
    server response, if it indicates success, will contain a
    <command>TKEY</command> record and any appropriate keys.  After
    this exchange, both participants have enough information to
    determine the shared secret; the exact process depends on the
    <command>TKEY</command> mode.  When using the Diffie-Hellman
    <command>TKEY</command> mode, Diffie-Hellman keys are exchanged,
    and the shared secret is derived by both participants.</para>
  
  </sect1>
  <sect1>
    <title>SIG(0)</title>

    <para><acronym>BIND</acronym> 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.</para>

    <para>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.</para>

    <para><acronym>BIND</acronym> 9 does not ship with any tools that generate SIG(0)
    signed messages.</para>

  </sect1>
  <sect1 id="DNSSEC">
    <title>DNSSEC</title>

    <para>Cryptographic authentication of DNS information is possible
    through the DNS Security (<emphasis>DNSSEC</emphasis>) extensions,
    defined in RFC 2535. This section describes the creation and use
    of DNSSEC signed zones.</para>

    <para>In order to set up a DNSSEC secure zone, there are a series
1241 1242
    of steps which must be followed.  <acronym>BIND</acronym> 9 ships
    with several tools
1243 1244
    that are used in this process, which are explained in more detail
    below.  In all cases, the "<option>-h</option>" option prints a
1245
    full list of parameters.  Note that the DNSSEC tools require the
1246 1247 1248
    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.</para>
1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294

    <para>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.</para>

    <para>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.</para>

    <sect2>
      <title>Generating Keys</title>

      <para>The <command>dnssec-keygen</command> program is used to
      generate keys.</para>

      <para>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
      <command>ZONE</command>, and must be usable for authentication.
      It is recommended that zone keys be mandatory to implement a
      cryptographic algorithm; currently the only key mandatory to
      implement an algorithm is DSA.</para>

      <para>The following command will generate a 768 bit DSA key for
      the <filename>child.example</filename> zone:</para>

      <para><userinput>dnssec-keygen -a DSA -b 768 -n ZONE child.example.</userinput></para>

      <para>Two output files will be produced:
      <filename>Kchild.example.+003+12345.key</filename> and
      <filename>Kchild.example.+003+12345.private</filename> (where
      12345 is an example of a key tag).  The key file names contain
      the key name (<filename>child.example.</filename>), algorithm (3
      is DSA, 1 is RSA, etc.), and the key tag (12345 in this case).
      The private key (in the <filename>.private</filename> file) is
      used to generate signatures, and the public key (in the
      <filename>.key</filename> file) is used for signature
      verification.</para>

      <para>To generate another key with the same properties (but with
      a different key tag), repeat the above command.</para>

      <para>The public keys should be inserted into the zone file with
      <command>$INCLUDE</command> statements, including the
1295
      <filename>.key</filename> files.</para>
1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321

    </sect2>
    <sect2>
      <title>Creating a Keyset</title>

      <para>The <command>dnssec-makekeyset</command> program is used
      to create a key set from one or more keys.</para>

      <para>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.</para>

      <para>The list of keys to be inserted into the key set may also
      included non-zone keys present at the top of the zone.
      <command>dnssec-makekeyset</command> may also be used at other
      names in the zone.</para>

      <para>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.</para>

1322
<para><userinput>dnssec-makekeyset -t 3600 -e +864000 Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>
1323 1324

      <para>One output file is produced:
1325
      <filename>keyset-child.example.</filename>.  This file should be
1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347
      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.</para>

    </sect2>
    <sect2>
      <title>Signing the Child's Keyset</title>

      <para>The <command>dnssec-signkey</command> program is used to
      sign one child's keyset.</para>

      <para>If the <filename>child.example</filename> zone has any
      delegations which are secure, for example,
      <filename>grand.child.example</filename>, the
      <filename>child.example</filename> administrator should receive
      keyset files for each secure subzone.  These keys must be signed
      by this zone's zone keys.</para>

      <para>The following command signs the child's key set with the
      zone keys:</para>

1348
<para><userinput>dnssec-signkey keyset-grand.child.example. Kchild.example.+003+12345 Kchild.example.+003+23456</userinput></para>
1349 1350

      <para>One output file is produced:
1351
      <filename>signedkey-grand.child.example.</filename>.  This file
1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405
      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.</para>

    </sect2>
    <sect2>
      <title>Signing the Zone</title>

      <para>The <command>dnssec-signzone</command> program is used to
      sign a zone.</para>

      <para>Any <filename>signedkey</filename> files corresponding to
      secure subzones should be present, as well as a
      <filename>signedkey</filename> file for this zone generated by
      the parent (if there is one). The zone signer will generate
      <literal>NXT</literal> and <literal>SIG</literal> records for
      the zone, as well as incorporate the zone key signature from the
      parent and indicate the security status at all delegation
      points.</para>

      <para>The following command signs the zone, assuming it is in a
      file called <filename>zone.child.example</filename>.  By
      default, all zone keys which have an available private key are
      used to generate signatures.</para>

<para><userinput>dnssec-signzone -o child.example zone.child.example</userinput></para>

      <para>One output file is produced:
      <filename>zone.child.example.signed</filename>.  This file
      should be referenced by <filename>named.conf</filename> as the
      input file for the zone.</para>

    </sect2>
    <sect2><title>Configuring Servers</title>

      <para>Unlike in <acronym>BIND</acronym> 8, data is not verified on load in <acronym>BIND</acronym> 9,
      so zone keys for authoritative zones do not need to be specified
      in the configuration file.</para>

      <para>The public key for any security root must be present in
      the configuration file's <command>trusted-keys</command>
      statement, as described later in this document. </para>

    </sect2>
  </sect1>
  <sect1>
    <title>IPv6 Support in <acronym>BIND</acronym> 9</title>

    <para><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.</para>

    <para>For forward lookups, <acronym>BIND</acronym> 9 supports both A6 and AAAA
1406
    records.  The use of AAAA records is deprecated, but it is still
1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419
    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.</para>

    <para>For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports the new
    "bitstring" format used in the <emphasis>ip6.arpa</emphasis>
    domain, as well as the older, deprecated "nibble" format used in
    the <emphasis>ip6.int</emphasis> domain.</para>

    <para><acronym>BIND</acronym> 9 includes a new lightweight resolver library and
    resolver daemon which new applications may choose to use to avoid
1420
    the complexities of A6 chain following and bitstring labels, see <xref
1421
    linkend="ch05"/>.</para>
1422 1423 1424 1425 1426 1427 1428 1429 1430 1431

    <sect2>
      <title>Address Lookups Using AAAA Records</title>

      <para>The AAAA record is a parallel to the IPv4 A record.  It
      specifies the entire address in a single record.  For
      example,</para>

<programlisting>
$ORIGIN example.com.
1432
host		3600	IN	AAAA	3ffe:8050:201:1860:42::1
1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451
</programlisting>

      <para>While their use is deprecated, they are useful to support
      older IPv6 applications.  They should not be added where they
      are not absolutely necessary.</para>

    </sect2>
    <sect2>
      <title>Address Lookups Using A6 Records</title>

      <para>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:</para>

<programlisting>
$ORIGIN example.com.
1452
host		3600	IN	A6	0 3ffe:8050:201:1860:42::1
1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467
</programlisting>
      <sect3>
        <title>A6 Chains</title>

        <para>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.</para>

        <para>In the company's address space:</para>

<programlisting>
$ORIGIN	example.com.
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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.
1470 1471 1472 1473 1474 1475
</programlisting>

        <para>ISP1 will use:</para>

<programlisting>
$ORIGIN example1.net.
1476
company		3600	IN	A6	0 3ffe:8050:201:1860::
1477 1478 1479 1480 1481 1482
</programlisting>

<para>ISP2 will use:</para>

<programlisting>
$ORIGIN example2.net.
1483
company		3600	IN	A6	0 1234:5678:90ab:fffa::
1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501
</programlisting>

        <para>When <systemitem
        class="systemname">host.example.com</systemitem> 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.</para>

      </sect3>
      <sect3>
        <title>A6 Records for DNS Servers</title>

        <para>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:</para>

<programlisting>
$ORIGIN example.com.
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@		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
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</programlisting>

        <para>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 <literal>::ffff:192.168.42.1</literal> as the
        address.</para>

      </sect3>
    </sect2>
    <sect2>
      <title>Address to Name Lookups Using Nibble Format</title>

      <para>While the use of nibble format to look up names is
      deprecated, it is supported for backwards compatiblity with
      existing IPv6 applications.</para>

      <para>When looking up an address in nibble format, the address
      components are simply reversed, just as in IPv4, and
      <literal>ip6.int.</literal> is appended to the resulting name.
      For example, the following would provide reverse name lookup for
      a host with address
      <literal>3ffe:8050:201:1860:42::1</literal>.</para>

<programlisting>
$ORIGIN 0.6.8.1.1.0.2.0.0.5.0.8.e.f.f.3.ip6.int.
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1.0.0.0.0.0.0.0.0.0.0.0.2.4.0.0	  14400 IN 	PTR	host.example.com.
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</programlisting>
    </sect2>
    <sect2>
      <title>Address to Name Lookups Using Bitstring Format</title>

      <para>Bitstring 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 <emphasis>ip6.arpa</emphasis> rather than
      <emphasis>ip6.int</emphasis>.</para>

      <para>To replicate the previous example using bitstrings:</para>

<programlisting>
$ORIGIN \[x3ffe805002011860/64].ip6.arpa.
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\[x0042000000000001/64] 	14400 	IN 	PTR	host.example.com.
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</programlisting>
    </sect2>
    <sect2>
      <title>Using DNAME for Delegation of IPv6 Reverse Addresses</title>

      <para>In IPV6, the same host may have many addresses from many
      network providers.  Since the trailing portion of the address
      usually remains constant, <command>DNAME</command> can help
      reduce the number of zone files used for reverse mapping that
      need to be maintained.</para>

      <para>For example, consider a host which has two providers
      (<systemitem class="systemname">example.net</systemitem> and
      <systemitem class="systemname">example2.net</systemitem>) 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:</para>

<programlisting>
$ORIGIN example.com.
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host			A6	64	::1234:5678:1212:5675 cust1.example.net.
			A6	64	::1234:5678:1212:5675 subnet5.example2.net.
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$ORIGIN example.net.
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cust1			A6	48	0:0:0:dddd:: ipv6net.example.net.
ipv6net			A6	0	aa:bb:cccc::
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$ORIGIN example2.net.
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subnet5			A6	48	0:0:0:1:: ipv6net2.example2.net.
ipv6net2		A6	0	6666:5555:4::
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</programlisting>

<para>This sets up forward lookups.  To handle the reverse lookups,
the provider <systemitem class="systemname">example.net</systemitem>
would have:</para>

<programlisting>
$ORIGIN \[x00aa00bbcccc/48].ip6.arpa.
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\[xdddd/16]		DNAME		ipv6-rev.example.com.
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</programlisting>

      <para>and <systemitem
      class="systemname">example2.net</systemitem> would have:</para>

<programlisting>
$ORIGIN \[x666655550004/48].ip6.arpa.
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\[x0001/16]		DNAME		ipv6-rev.example.com.
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</programlisting>

      <para><systemitem class="systemname">example.com</systemitem>
      needs only one zone file to handle both of these reverse
      mappings:</para>

<programlisting>
$ORIGIN ipv6-rev.example.com.
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\[x1234567812125675/64]	PTR		host.example.com. 
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</programlisting>
    </sect2>
  </sect1>
  </chapter>

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  <chapter id="ch05"><title>The <acronym>BIND</acronym> 9 Lightweight Resolver</title>
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<sect1><title>The Lightweight Resolver Library</title>
<para>Traditionally applications have been linked with a stub resolver
library that sends recursive DNS queries to a local caching name
server.</para>
<para>IPv6 introduces new complexity into the resolution process,
such as following A6 chains and DNAME records, and simultaneous
lookup of IPv4 and IPv6 addresses.  These are hard or impossible
to implement in a traditional stub resolver.</para>
<para>Instead, <acronym>BIND</acronym> 9 provides resolution services to local clients
using a combination of a lightweight resolver library and a resolver
daemon process running on the local host.  These communicate using
a simple UDP-based protocol, the "lightweight resolver protocol"
that is distinct from and simpler than the full DNS protocol.</para></sect1>
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<sect1 id="lwresd"><title>Running a Resolver Daemon</title>
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<para>To use the lightweight resolver interface, the system must
run the resolver daemon <command>lwresd</command>.</para>
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<para>By default, applications using the lightweight resolver library will make
UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.  The
address can be overriden by <command>lwserver</command> lines in
<filename>/etc/resolv.conf</filename>.
The daemon will try to find the answer to the questions "what are the
addresses for host
<systemitem class="systemname">foo.example.com</systemitem>?" and "what are
the names for IPv4 address 10.1.2.3?"</para>
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<para>The daemon currently only looks in the DNS, but in the future
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it may use other sources such as <filename>/etc/hosts</filename>,
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NIS, etc.</para>
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<para>The <command>lwresd</command> daemon is essentially a
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caching-only name server that answers requests using the lightweight
resolver protocol rather than the DNS protocol.  Because it needs
to run on each host, it is designed to require no or minimal configuration.
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Unless configured otherwise, it uses the name servers listed on
<command>nameserver</command> lines in <filename>/etc/resolv.conf</filename>
as forwarders, but is also capable of doing the resolution autonomously if
none are specified.</para>
<para>The <command>lwresd</command> daemon may also be configured with a
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<filename>named.conf</filename> style configuration file, in
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<filename>/etc/lwresd.conf</filename> by default.  A name server may also
be configured to act as a lightweight resolver daemon using the
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<command>lwres</command> statement in <filename>named.conf</filename>.</para>
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</sect1></chapter>
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<chapter id="ch06"><title><acronym>BIND</acronym> 9 Configuration Reference</title>
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<para><acronym>BIND</acronym> 9 configuration is broadly similar to <acronym>BIND</acronym> 8.x; however,
there are a few new areas of configuration, such as views. <acronym>BIND</acronym>
8.x configuration files should work with few alterations in <acronym>BIND</acronym>
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in <acronym>BIND</acronym> 9.</para>
<para><acronym>BIND</acronym> 4 configuration files can be converted to the new format
using the shell script
<filename>contrib/named-bootconf/named-bootconf.sh</filename>.</para>
<sect1 id="configuration_file_elements"><title>Configuration File Elements</title>
<para>Following is a list of elements used throughout the <acronym>BIND</acronym> configuration
file documentation:</para>
<informaltable colsep = "0"  rowsep = "0"><tgroup cols = "2"
    colsep = "0" rowsep = "0" tgroupstyle = "2Level-table">
<colspec colname = "1" colnum = "1" colsep = "0" colwidth = "1.855in"/>
<colspec colname = "2" colnum = "2" colsep = "0" colwidth = "3.770in"/>
<tbody>
<row rowsep = "0">
<entry colname = "1"><para><varname>acl_name</varname></para></entry>
<entry colname = "2"><para>The name of an <varname>address_match_list</varname> as
defined by the <command>acl</command> statement.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>address_match_list</varname></para></entry>
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<entry colname = "2"><para>A list of one or more <varname>ip_addr</varname>, <varname>ip_prefix</varname>, <varname>key_id</varname>, or <varname>acl_name</varname> elements, see
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<xref linkend="address_match_lists"/>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>domain_name</varname></para></entry>
<entry colname = "2"><para>A quoted string which will be used as
a DNS name, for example "<systemitem class="systemname">my.test.domain</systemitem>".</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>dotted_decimal</varname></para></entry>
<entry colname = "2"><para>One or more integers valued 0 through
255 separated only by dots (`.'), such as <command>123</command>, <command>45.67</command> or <command>89.123.45.67</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip4_addr</varname></para></entry>
<entry colname = "2"><para>An IPv4 address with exactly four elements
in <varname>dotted_decimal</varname> notation.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip6_addr</varname></para></entry>
<entry colname = "2"><para>An IPv6 address, such as <command>fe80::200:f8ff:fe01:9742</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_addr</varname></para></entry>
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<entry colname = "2"><para>An <varname>ip4_addr</varname> or <varname>ip6_addr</varname>.</para></entry>
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</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_port</varname></para></entry>
<entry colname = "2"><para>An IP port <varname>number</varname>.
 <varname>number</varname> is limited to 0 through 65535, with values
below 1024 typically restricted to root-owned processes. In some
cases an asterisk (`*') character can be used as a placeholder to
select a random high-numbered port.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>ip_prefix</varname></para></entry>
<entry colname = "2"><para>An IP network specified as an <varname>ip_addr</varname>,
followed by a slash (`/') and then the number of bits in the netmask.
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Trailing zeros in a <varname>ip_addr</varname> may omitted.
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For example, <command>127/8</command> is the network <command>127.0.0.0</command> with
netmask <command>255.0.0.0</command> and <command>1.2.3.0/28</command> is
network <command>1.2.3.0</command> with netmask <command>255.255.255.240</command>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>key_id</varname></para></entry>
<entry colname = "2"><para>A <varname>domain_name</varname> representing
the name of a shared key, to be used for transaction security.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>key_list</varname></para></entry>
<entry colname = "2"><para>A list of one or more <varname>key_id</varname>s,
separated by semicolons and ending with a semicolon.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>number</varname></para></entry>
<entry colname = "2"><para>A non-negative integer with an entire
range limited by the range of a C language signed integer (2,147,483,647
on a machine with 32 bit integers). Its acceptable value might further
be limited by the context in which it is used.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>path_name</varname></para></entry>
<entry colname = "2"><para>A quoted string which will be used as
a pathname, such as <filename>zones/master/my.test.domain</filename>.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>size_spec</varname></para></entry>
<entry colname = "2"><para>A number, the word <userinput>unlimited</userinput>,
or the word <userinput>default</userinput>.</para><para>The maximum
value of <varname>size_spec</varname> is that of unsigned long integers
on the machine. An <varname>unlimited</varname> <varname>size_spec</varname> requests unlimited
use, or the maximum available amount. A <varname>default size_spec</varname> uses
the limit that was in force when the server was started.</para><para>A <varname>number</varname> can
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optionally be followed by a scaling factor: <userinput>K</userinput> or <userinput>k</userinput> for
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kilobytes, <userinput>M</userinput> or <userinput>m</userinput> for
megabytes, and <userinput>G</userinput> or <userinput>g</userinput> for gigabytes,
which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.</para><para>Integer
storage overflow is currently silently ignored during conversion
of scaled values, resulting in values less than intended, possibly
even negative. Using <varname>unlimited</varname> is the best way
to safely set a really large number.</para></entry>
</row>
<row rowsep = "0">
<entry colname = "1"><para><varname>yes_or_no</varname></para></entry>
<entry colname = "2"><para>Either <userinput>yes</userinput> or <userinput>no</userinput>.
The words <userinput>true</userinput> and <userinput>false</userinput> are
also accepted, as are the numbers <userinput>1</userinput> and <userinput>0</userinput>.</para></entry>
</row>
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<row rowsep = "0">
<entry colname = "1"><para><varname>dialup_option</varname></para></entry>
<entry colname = "2"><para>One of <userinput>yes</userinput>,
<userinput>no</userinput>, <userinput>notify</userinput>,
<userinput>notify-passive</userinput>, <userinput>refresh</userinput> or
<userinput>passive</userinput>.
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When used in a zone, <userinput>notify-passive</userinput>,
<userinput>refresh</userinput>, and <userinput>passive</userinput>
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are restricted to slave and stub zones.</para></entry>
</row>
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