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  <chapter id="dhcp-ddns-server">
    <title>The DHCP-DDNS Server</title>
    <para>
    The DHCP-DDNS Server (kea-dhcp-ddns, known informally as D2) conducts the client side of
    the DDNS protocol (defined in RFC 2136) on behalf of the DHCPv4 and DHCPv6
    servers (kea-dhcp4 and kea-dhcp6 respectively). The DHCP servers construct
    DDNS update requests, known as NameChangeRequests (NCRs), based upon DHCP
    lease change events and then post these to D2. D2 attempts to match
    each such request to the appropriate DNS server(s) and carry out the
    necessary conversation with those servers to update the DNS data.
    </para>
    <para>
    In order to match a request to appropriate DNS servers, D2 must have a
    catalog of servers from which to select. In fact, D2 has two such catalogs,
    one for forward DNS and one for reverse DNS; these catalogs are referred
    to as DDNS Domain Lists.  Each list consists of one or more named DDNS
    Domains. Further, each DDNS Domain has a list of of one or more DNS
    servers that publish the DNS data for that domain.
    </para>
    <para>
    When conducting forward domain matching, D2 will compare the FQDN in
    the request against the name of each forward DDNS Domain. The domain
    whose name matches the longest portion of the FQDN is considered the
    best match.  For example, if the FQDN is "myhost.sample.example.com.",
    and there are two forward domains in the catalog: "sample.example.com."
    and "example.com.", the former is regarded as the best match.  In some
    cases, it may not be possible to find a suitable match. Given the same two
    forward domains there would be no match for the FQDN, "bogus.net", so the
    request would be rejected.   Finally, if there are no forward DDNS Domains
    defined, D2 will simply disregard the forward update portion of requests.
    </para>
    <para>
    When conducting reverse domain matching, D2 constructs a reverse
    FQDN from the lease address in the request and compare that against
    the name of each reverse DDNS Domain. Again, the domain whose name matches
    the longest portion of the FQDN is considered the best match. For instance,
    if the lease address is "172.16.1.40" and there are two reverse domains in
    the catalog: "1.16.172.in-addr.arpa." and "16.172.in-addr.arpa", the
    former is the best match.  As with forward matching, it is possible to not
    find a suitable match.  Given the same two domains, there would be no
    match for the lease address, "192.168.1.50", and the request would be
    rejected. Finally, if there are no reverse DDNS Domains defined, D2 will
    simply disregard the reverse update portion of requests.
    </para>
    <section id="dhcp-ddns-server-start-stop">
      <title>Starting and Stopping the DHCP-DDNS Server</title>
      <para>
      <command>kea-dhcp-ddns</command> is the BIND 10 DHCP-DDNS server and,
      like other parts of BIND 10, is configured through the
      <command>bindctl</command> program.
      </para>
      <para>
      After starting BIND 10 and entering bindctl, the first step in
      configuring the server is to add it to the list of running BIND 10
      services.
<screen>
&gt; <userinput>config add Init/components kea-dhcp-ddns</userinput>
&gt; <userinput>config set Init/components/kea-dhcp-ddns/kind dispensable</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </para>
      <para>
      To remove <command>kea-dhcp-ddns</command> from the set of running services,
      the <command>kea-dhcp-ddns</command> is removed from list of Init components:
<screen>
&gt; <userinput>config remove Init/components kea-dhcp-ddns</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </para>
      <para>
      Note that the server was only removed from the list, so it will not be
      automatically restarted, but the server itself is still running. Hence it
      is usually desired to stop it:
      </para>
<screen>
&gt; <userinput>DhcpDdns shutdown</userinput>
</screen>
      <para>
      Upon start up the module will load its configuration and begin listening
      for NCRs based on that configuration.
      </para>
    </section> <!-- end start-stop -->
    <section id="d2-configuration">
      <title>Configuring the DHCP-DDNS Server</title>
      <para>
        Once the server is started, it can be configured. To view the
        current configuration, use the following command in <command>bindctl</command>:
        <screen>
&gt; <userinput>config show DhcpDdns</userinput></screen>
        When starting kea-dhcp-ddns module for the first time, the default
        configuration will be available. It will look similar to this:
<screen>
&gt; <userinput>config show DhcpDdns</userinput>
DhcpDdns/ip_address "127.0.0.1" string  (default)
DhcpDdns/port   53001   integer (default)
DhcpDdns/dns_server_timeout   100   integer (default)
DhcpDdns/ncr_protocol	"UDP"	string (default)
DhcpDdns/ncr_format	"JSON"	string (default)
DhcpDdns/tsig_keys  []  list    (default)
DhcpDdns/forward_ddns/ddns_domains  []  list    (default)
DhcpDdns/reverse_ddns/ddns_domains  []  list    (default)
</screen>
      <para>
      (While displayed, the parameter "interface" is not implemented, and
      will be removed in the near future.)
      </para>
      </para>
      <para>
      The configuration can be divided as follows, each of which is described
      in its own section:
      </para>
        <itemizedlist>
          <listitem>
            <simpara>
              <command>Global Server Parameters</command> &mdash;
              values which control connectivity and global server behavior
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>TSIG Key Info</command> &mdash;
              defines the TSIG keys used for secure traffic with DNS servers
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>Forward DDNS</command> &mdash;
              defines the catalog of Forward DDNS Domains
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>Reverse DDNS</command> &mdash;
              defines the catalog of Forward DDNS Domains
            </simpara>
          </listitem>
        </itemizedlist>
      <section id="d2-server-parameter-config">
        <title>Global Server Parameters</title>
      <orderedlist>
      <listitem><para>
      ip_address - IP address on which D2 listens for requests. The default is
      the local loopback interface at address 127.0.0.1. You may specify
      either an IPv4 or IPv6 address.
      </para></listitem>
      <listitem><para>
      port - Port on which D2 listens for requests.  The default value
      is 53001.
      </para></listitem>
      <listitem><para>
      ncr_format - Socket protocol to use when sending requests to D2.
      Currently only UDP is supported.  TCP may be available in an upcoming
      release.
      </para></listitem>
      <listitem><para>
      ncr_protocol - Packet format to use when sending requests to D2.
      Currently only JSON format is supported.  Other formats may be available
      in future releases.
      </para></listitem>
      <listitem><para>
      dns_server_timeout - The maximum amount of time in milliseconds, that
      D2 will wait for a response from a DNS server to a single DNS update
      message.
      </para></listitem>
      </orderedlist>
        <para>
        D2 must listen for change requests on a known address and port.  By
        default it listens at 127.0.0.1 on port 53001. The following example
        illustrates how to change D2's global parameters so it will listen
        at 192.168.1.10 port 900:
<screen>
&gt; <userinput>config set DhcpDdns/ip_address "192.168.1.10"</userinput>
&gt; <userinput>config set DhcpDdns/port 900</userinput>
&gt; <userinput>config commit</userinput>
</screen>
        </para>
        <warning>
          <simpara>
            When the DHCP-DDNS server is configured to listen at an address
            other than the loopback address (127.0.0.1 or ::1), it is possible
            for a malicious attacker to send bogus NameChangeRequests to it
            and change entries in the DNS. For this reason, addresses other
            than the IPv4 or IPv6 loopback addresses should only be used
            for testing purposes. A future version of Kea will implement
            authentication to guard against such attacks.
          </simpara>
        </warning>
<note>
<simpara>
If the ip_address and port are changed, it will be necessary to change the
corresponding values in the DHCP servers' "dhcp-ddns" configuration section.
</simpara>
</note>
      </section> <!-- "d2-server-parameter-config" -->

      <section id="d2-tsig-key-list-config">
        <title>TSIG Key List</title>
        <para>
        A DDNS protocol exchange can be conducted with or without TSIG
        (defined in <ulink url="http://tools.ietf/org/html/rfc2845">RFC
        2845</ulink>). This configuration section allows the administrator
        to define the set of TSIG keys that may be used in such
        exchanges.</para>

        <para>To use TSIG when updating entries in a DNS Domain,
        a key must be defined in the TSIG Key List and referenced by
        name in that domain's configuration entry.  When D2 matches a
        change request to a domain, it checks whether the domain has
        a TSIG key associated with it.  If so, D2 will use that key to
        sign DNS update messages sent to and verify responses received
        from the domain's DNS server(s). For each TSIG key required by
        the DNS servers that D2 will be working with there must be a
        corresponding TSIG key in the TSIG Key list.</para>

        <para>
        As one might gather from the name, the tsig_key section of the
        D2 configuration lists the TSIG keys.  Each entry describes a
        TSIG key used by one or more DNS servers to authenticate requests
        and sign responses.  Every entry in the list has three parameters:
        <itemizedlist>
          <listitem>
            <simpara>
              <command>name</command> &mdash;
              a unique text label used to identify this key within the
              list.  This value is used to specify which key (if any) should be
              used when updating a specific domain. So long as it is unique its
              content is arbitrary, although for clarity and ease of maintenance
              it is recommended that it match the name used on the DNS server(s).
              It cannot be blank.
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>algorithm</command> &mdash;
              specifies which hashing algorithm should be used with this
              key.  This value must specify the same algorithm used for the
              key on the DNS server(s). The supported algorithms are listed below:
              <itemizedlist>
                <listitem>
                   <command>HMAC-MD5</command>
                </listitem>
                <listitem>
                    <command>HMAC-SHA1</command>
                </listitem>
                <listitem>
                  <command>HMAC-SHA224</command>
              </listitem>
              <listitem>
                  <command>HMAC-SHA256</command>
              </listitem>
              <listitem>
                  <command>HMAC-SHA384</command>
                  </listitem>
              <listitem>
                  <command>HMAC-SHA512</command>
              </listitem>
              </itemizedlist>
              This value is not case sensitive.
            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>secret</command> &mdash;
              is used to specify the shared secret key code for this key.  This value is
              case sensitive and must exactly match the value specified on the DNS server(s).
              It is a base64-encoded text value.
            </simpara>
          </listitem>
        </itemizedlist>
        </para>
        <para>
        As an example, suppose that a domain D2 will be updating is
        maintained by a BIND9 DNS server which requires dynamic updates
        to be secured with TSIG.  Suppose further that the entry for
        the TSIG key in BIND9's named.conf file looks like this:
<screen>
   :
   key "key.four.example.com." {
       algorithm hmac-sha224;
       secret "bZEG7Ow8OgAUPfLWV3aAUQ==";
   };
   :
</screen>
        By default, the TSIG Key list is empty:
<screen>
<userinput>> config show DhcpDdns/tsig_keys</userinput>
DhcpDdns/tsig_keys  []  list  (default)
</screen>
        We must first create a new key in the list:
<screen>
<userinput>> config add DhcpDdns/tsig_keys</userinput>
</screen>
        Displaying the new element, reveals:
<screen>
<userinput>> config show DhcpDdns/tsig_keys[0]</userinput>
DhcpDdns/tsig_keys[0]/name  ""  string  (default)
DhcpDdns/tsig_keys[0]/algorithm "HMAC-MD5"  string  (modified)
DhcpDdns/tsig_keys[0]/secret  ""  string  (default)
</screen>
        Now set all three values to match BIND9's key:
<screen>
<userinput>> config set DhcpDdns/tsig_keys[0]/name "key.four.example.com"</userinput>
<userinput>> config set DhcpDdns/tsig_keys[0]/algorithm "HMAC-SHA224"</userinput>
<userinput>> config set DhcpDdns/tsig_keys[0]/secret "bZEG7Ow8OgAUPfLWV3aAUQ=="</userinput>
<userinput>> config commit</userinput>
</screen>
        </para>
        These steps would be repeated for each TSIG key needed.  Note that the same TSIG key
        can be used with more than one domain.
      </section> <!-- "d2-tsig-key-list-config" -->

      <section id="d2-forward-ddns-config">
        <title>Forward DDNS</title>
        <para>
        The Forward DDNS section is used to configure D2's forward update
        behavior. Currently it contains a single parameter, the catalog of
        forward DDNS Domains:
<screen>
<userinput>> config show DhcpDdns/forward_ddns/</userinput>
DhcpDdns/forward_ddns/ddns_domains  [] list  (default)
</screen>
        By default, this list is empty, which will cause the server to ignore
        the forward update portions of requests.
        </para>
        <section id="add-forward-ddns-domain">
          <title>Adding Forward DDNS Domains</title>
          <para>
          A forward DDNS Domain maps a forward DNS zone to a set of DNS servers
          which maintain the forward DNS data for that zone.  You will need one
          forward DDNS Domain for each zone you wish to service.  It may very
          well be that some or all of your zones are maintained by the same
          servers. You will still need one DDNS Domain per zone. Remember that
          matching a request to the appropriate server(s) is done by zone and
          a DDNS Domain only defines a single zone.
          </para>
          <para>
          The section describes how to add Forward DDNS Domains. Repeat these
          steps for each Forward DDNS Domain desired.  Each Forward DDNS Domain
          has the following parameters:
          <itemizedlist>
            <listitem>
              <simpara>
              <command>name</command> &mdash;
              The fully qualified domain name (or zone) that this DDNS Domain
              can update.  This is value used to compare against the request
              FQDN during forward matching.  It must be unique within the
              catalog.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>key_name</command> &mdash;
              If TSIG is used with this domain's servers, this
              value should be the name of the key from within the TSIG Key List
              to use.  If the value is blank (the default), TSIG will not be
              used in DDNS conversations with this domain's servers.  Currently
              TSIG has not been implemented, so this value is ignored.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>dns_servers</command> &mdash;
              A list of one or more DNS servers which can conduct the server
              side of the DDNS protocol for this domain.  The servers
              are used in a first to last preference. In other words, when D2
              begins to process a request for this domain it will pick the
              first server in this list and attempt to communicate with it.
              If that attempt fails, it will move to next one in the list and
              so on until the it achieves success or the list is exhausted.
              </simpara>
            </listitem>
          </itemizedlist>
        To create a new forward DDNS Domain, one must first add a new domain
        element:
<screen>
<userinput>> config add DhcpDdns/forward_ddns/ddns_domains</userinput>
</screen>
        Displaying the DDNS Domain reveals this:
<screen>
<userinput>> config show DhcpDdns/forward_ddns/ddns_domains[0]</userinput>
DhcpDdns/forward_ddns/ddns_domains[0]/name  ""  string  (default)
DhcpDdns/forward_ddns/ddns_domains[0]/key_name  ""  string  (default)
DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers   []  list    (default)
</screen>
        To set the domain's name to "other.example.com":
<screen>
<userinput>> config set DhcpDdns/forward_ddns/ddns_domains[1]/name "other.example.com"</userinput>
<userinput>> config commit</userinput>
</screen>
        It is permissible to add a domain without any servers. If that domain
        should be matched to a request, however, the request will fail.  In
        order to make the domain useful though, we must add at least one DNS
        server to it.
        </para>

        <section id="add-forward-dns-servers">
          <title>Adding Forward DNS Servers</title>
          <para>
          The section describes how to add DNS servers to a Forward DDNS Domain.
          Repeat them for as many servers as desired for a each domain.
          </para>
          <para>
          Forward DNS Server entries represent actual DNS servers which
          support the server side of the DDNS protocol. Each Forward DNS Server
          has the following parameters:
          <itemizedlist>
            <listitem>
              <simpara>
              <command>hostname</command> &mdash;
              The resolvable host name of the DNS server. This value is not
              yet implemented.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>ip_address</command> &mdash;
              The IP address at which the server listens for DDNS requests.
              This may be either an IPv4 or an IPv6 address.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>port</command> &mdash;
              The port on which the server listens for DDNS requests. It
              defaults to the standard DNS service port of 53.
              </simpara>
            </listitem>
          </itemizedlist>
          To create a new forward DNS Server, one must first add a new server
          element to the domain:
<screen>
<userinput>> config add DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers</userinput>
</screen>
         Displaying the DNS Server element should appear as follows:
<screen>
<userinput>> config show DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]</userinput>
DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]/hostname   ""  string  (default)
DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]/ip_address ""  string  (default)
DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]/port   53  integer(default)
</screen>
        As stated earlier, "hostname" is not yet supported so, the parameter
        "ip_address" must be set to the address of the DNS server. If for
        example the service is running at "172.88.99.10", then set it as
        follows:
<screen>
<userinput>> config set DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]/ip_address "172.88.99.10"</userinput>
<userinput>> config commit</userinput>
</screen>
          </para>
        </section> <!-- "add-forward-dns-servers" -->

      </section> <!-- "add-forward-ddns-domains" -->

      </section> <!-- "d2-forward-ddns-config" -->

      <section id="d2-reverse-ddns-config">
        <title>Reverse DDNS</title>
        <para>
        The Reverse DDNS section is used to configure D2's reverse update
        behavior, and the concepts are the same as for the forward DDNS
        section. Currently it contains a single parameter, the catalog of
        reverse DDNS Domains:
<screen>
<userinput>> config show DhcpDdns/reverse_ddns/</userinput>
DhcpDdns/reverse_ddns/ddns_domains  [] list  (default)
</screen>
        By default, this list is empty, which will cause the server to ignore
        the reverse update portions of requests.
        </para>
        <section id="add-reverse-ddns-domain">
          <title>Adding Reverse DDNS Domains</title>
          <para>
          A reverse DDNS Domain maps a reverse DNS zone to a set of DNS servers
          which maintain the reverse DNS data for that zone.  You will need one
          reverse DDNS Domain for each zone you wish to service.  It may very
          well be that some or all of your zones are maintained by the same
          servers; even then, you will still need one DDNS Domain entry for each
          zone. Remember that
          matching a request to the appropriate server(s) is done by zone and
          a DDNS Domain only defines a single zone.
          </para>
          <para>
          The section describes how to add Reverse DDNS Domains. Repeat these
          steps for each Reverse DDNS Domain desired.  Each Reverse DDNS Domain
          has the following parameters:
          <itemizedlist>
            <listitem>
              <simpara>
              <command>name</command> &mdash;
              The fully qualified reverse zone that this DDNS Domain
              can update.  This is the value used during reverse matching
              which will compare it with a reversed version of the request's
              lease address. The zone name should follow the appropriate
              standards: for example, to to support the IPv4 subnet 172.16.1,
              the name should be. "1.16.172.in-addr.arpa.".  Similarly,
              to support an IPv6 subent of 2001:db8:1, the name should be
              "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."
              Whatever the name, it must be unique within the catalog.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>key_name</command> &mdash;
              If TSIG should be used with this domain's servers, then this
              value should be the name of that key from the TSIG Key List.
              If the value is blank (the default), TSIG will not be
              used in DDNS conversations with this domain's servers.  Currently
              this value is not used as TSIG has not been implemented.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>dns_servers</command> &mdash;
              a list of one or more DNS servers which can conduct the server
              side of the DDNS protocol for this domain.  Currently the servers
              are used in a first to last preference. In other words, when D2
              begins to process a request for this domain it will pick the
              first server in this list and attempt to communicate with it.
              If that attempt fails, it will move to next one in the list and
              so on until the it achieves success or the list is exhausted.
              </simpara>
            </listitem>
          </itemizedlist>
        To create a new reverse DDNS Domain, one must first add a new domain
        element:
<screen>
<userinput>> config add DhcpDdns/reverse_ddns/ddns_domains</userinput>
</screen>
        Displaying the DDNS Domain reveals this:
<screen>
<userinput>> config show DhcpDdns/reverse_ddns/ddns_domains[0]</userinput>
DhcpDdns/reverse_ddns/ddns_domains[0]/name  ""  string  (default)
DhcpDdns/reverse_ddns/ddns_domains[0]/key_name  ""  string  (default)
DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers   []  list    (default)
</screen>
        For domain supporting the subnet 2001:db8:1::, we would set the
        domain's name as follows:
<screen>
<userinput>> config set DhcpDdns/reverse_ddns/ddns_domains[1]/name "1.0.0.0.8.B.D.0.1.0.0.2.ip6.arpa."</userinput>
<userinput>> config commit</userinput>
</screen>
        It is permissible to add a domain without any servers. If that domain
        should be matched to a request, however, the request will fail.  In
        order to make the domain useful though, we must add at least one DNS
        server to it.
        </para>

        <section id="add-reverse-dns-servers">
          <title>Adding Reverse DNS Servers</title>
          <para>
          The section describes how to add DNS servers to a Reverse DDNS Domain.
          Repeat them for as many servers as desired for a each domain.
          </para>
          <para>
          Reverse DNS Server entries represents a actual DNS servers which
          support the server side of the DDNS protocol. Each Reverse DNS Server
          has the following parameters:
          <itemizedlist>
            <listitem>
              <simpara>
              <command>hostname</command> &mdash;
              The resolvable host name of the DNS server. This value is
              currently ignored.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>ip_address</command> &mdash;
              The IP address at which the server listens for DDNS requests.
              </simpara>
            </listitem>
            <listitem>
              <simpara>
              <command>port</command> &mdash;
              The port on which the server listens for DDNS requests. It
              defaults to the standard DNS service port of 53.
              </simpara>
            </listitem>
          </itemizedlist>
          To create a new reverse DNS Server, one must first add a new server
          element to the domain:
<screen>
<userinput>> config add DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers</userinput>
</screen>
         Displaying the DNS Server element should appear as follows:
<screen>
<userinput>> config show DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]</userinput>
DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]/hostname   ""  string  (default)
DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]/ip_address ""  string  (default)
DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]/port   53  integer(default)
</screen>
        As stated earlier, "hostname" is not yet supported so, the parameter
        "ip_address" must be set to the address of the DNS server. If for
        example the service is running at "172.88.99.10", then set it as
        follows:
<screen>
<userinput>> config set DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]/ip_address "172.88.99.10"</userinput>
<userinput>> config commit</userinput>
</screen>
          </para>
        </section> <!-- "add-reverse-dns-servers" -->

      </section> <!-- "add-reverse-ddns-domains" -->

      </section> <!-- "d2-reverse-ddns-config" -->

      <section id="d2-exmaple-config">
        <title>Example DHCP-DDNS Server Configuration</title>
        <para>
        This section provides an example DHCP-DDNS server configuration based
        on a small example network.  Let's suppose our example network has
        three domains, each with their own subnet.

        <table>
          <title>Our example network</title>
          <tgroup cols='4' align='left'>
          <colspec colname='domain'/>
          <colspec colname='subnet'/>
          <colspec colname='fservers'/>
          <colspec colname='rservers'/>
          <thead>
            <row>
              <entry>Domain</entry>
              <entry>Subnet</entry>
              <entry>Forward DNS Servers</entry>
              <entry>Reverse DNS Servers</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>four.example.com</entry>
              <entry>192.0.2.0/24</entry>
              <entry>172.16.1.5, 172.16.2.5</entry>
              <entry>172.16.1.5, 172.16.2.5</entry>
            </row>
            <row>
              <entry>six.example.com</entry>
              <entry>2001:db8:1::/64</entry>
              <entry>3001:1::50</entry>
              <entry>3001:1::51</entry>
            </row>
            <row>
              <entry>example.com</entry>
              <entry>192.0.0.0/16</entry>
              <entry>172.16.2.5</entry>
              <entry>172.16.2.5</entry>
            </row>
          </tbody>
          </tgroup>
        </table>
        </para>
        <para>
        We need to construct three forward DDNS Domains:
        <table>
          <title>Forward DDNS Domains Needed</title>
          <tgroup cols='3' align='left'>
          <colspec colname='num'/>
          <colspec colname='name'/>
          <colspec colname='servers'/>
          <thead>
            <row>
              <entry>#</entry>
              <entry>DDNS Domain Name</entry>
              <entry>DNS Servers</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>1.</entry>
              <entry>four.example.com.</entry>
              <entry>172.16.1.5, 172.16.2.5</entry>
            </row>
            <row>
              <entry>2.</entry>
              <entry>six.example.com.</entry>
              <entry>3001:1::50</entry>
            </row>
            <row>
              <entry>3.</entry>
              <entry>example.com.</entry>
              <entry>172.16.2.5</entry>
            </row>
          </tbody>
          </tgroup>
        </table>
        As discussed earlier, FQDN to domain matching is based on the longest
        match. The FQDN, "myhost.four.example.com.", will match the first
        domain ("four.example.com") while "admin.example.com." will match the
        third domain ("example.com"). The
        FQDN, "other.example.net." will fail to match any domain and would
        be rejected.
        </para>
        <para>
        The following series of commands in bindctl will create the Forward
        DDNS Domains.
<screen>
<userinput>
> config add DhcpDdns/forward_ddns/ddns_domains
> config set DhcpDdns/forward_ddns/ddns_domains[0]/name "four.example.com."
> config add DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers
> config set DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[0]/ip_address "172.16.1.5"
> config add DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers
> config set DhcpDdns/forward_ddns/ddns_domains[0]/dns_servers[1]/ip_address "172.16.2.5"
>
> config add DhcpDdns/forward_ddns/ddns_domains
> config set DhcpDdns/forward_ddns/ddns_domains[1]/name "six.example.com."
> config add DhcpDdns/forward_ddns/ddns_domains[1]/dns_servers
> config set DhcpDdns/forward_ddns/ddns_domains[1]/dns_servers[0]/ip_address "3001:1::50:"
>
> config add DhcpDdns/forward_ddns/ddns_domains
> config set DhcpDdns/forward_ddns/ddns_domains[2]/name "example.com."
> config add DhcpDdns/forward_ddns/ddns_domains[2]/dns_servers
> config set DhcpDdns/forward_ddns/ddns_domains[2]/dns_servers[0]/ip_address "172.16.2.5"
>
> config commit
</userinput>
</screen>
        </para>
        <para>
        Similarly, we need to construct the three reverse DDNS Domains:
        <table>
          <title>Reverse DDNS Domains Needed</title>
          <tgroup cols='3' align='left'>
          <colspec colname='num'/>
          <colspec colname='DDNS Domain name'/>
          <colspec colname='DDNS Domain DNS Servers'/>
          <thead>
            <row>
              <entry>#</entry>
              <entry>DDNS Domain Name</entry>
              <entry>DNS Servers</entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>1.</entry>
              <entry>2.0.192.in-addr.arpa.</entry>
              <entry>172.16.1.5, 172.16.2.5</entry>
            </row>
            <row>
              <entry>2.</entry>
              <entry>1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa.</entry>
              <entry>3001:1::50</entry>
            </row>
            <row>
              <entry>3.</entry>
              <entry>0.182.in-addr.arpa.</entry>
              <entry>172.16.2.5</entry>
            </row>
          </tbody>
          </tgroup>
        </table>
        An address of "192.0.2.150" will match the first domain,
        "2001:db8:1::10" will match the second domain, and "192.0.50.77"
        the third domain.
        </para>
        <para>
        The following series of commands in bindctl will create our Reverse
        DDNS Domains.
<screen>
<userinput>
> config add DhcpDdns/reverse_ddns/ddns_domains
> config set DhcpDdns/reverse_ddns/ddns_domains[0]/name "2.0.192.in-addr.arpa."
> config add DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers
> config set DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[0]/ip_address "172.16.1.5"
> config add DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers
> config set DhcpDdns/reverse_ddns/ddns_domains[0]/dns_servers[1]/ip_address "172.16.2.5"
>
> config add DhcpDdns/reverse_ddns/ddns_domains
> config set DhcpDdns/reverse_ddns/ddns_domains[1]/name "1.0.0.0.8.d.b.0.1.0.0.2.ip6.arpa."
> config add DhcpDdns/reverse_ddns/ddns_domains[1]/dns_servers
> config set DhcpDdns/reverse_ddns/ddns_domains[1]/dns_servers[0]/ip_address "3001:1::50:"
>
> config add DhcpDdns/reverse_ddns/ddns_domains
> config set DhcpDdns/reverse_ddns/ddns_domains[2]/name "0.192.in-addr.arpa."
> config add DhcpDdns/reverse_ddns/ddns_domains[2]/dns_servers
> config set DhcpDdns/reverse_ddns/ddns_domains[2]/dns_servers[0]/ip_address "172.16.2.5"
>
> config commit
</userinput>
</screen>
        </para>
        </section> <!-- end of "d2-example" -->
    </section> <!-- end of section "d2-configuration" -->
    <section>
      <title>DHCP-DDNS Server Limitations</title>
      <para>The following are the current limitations of the DHCP-DDNS Server.</para>
      <itemizedlist>
        <listitem>
          <simpara>
            Requests received from the DHCP servers are placed in a
            queue until they are processed.  Currently all queued requests
            are lost when the server shuts down.
          </simpara>
        </listitem>
        <listitem>
          <simpara>
            TSIG Authentication (<ulink
            url="http://tools.ietf.org/html/rfc2845">RFC 2845</ulink>)
            is not supported yet.
          </simpara>
        </listitem>
      </itemizedlist>
    </section>
  </chapter> <!-- DHCP-DDNS Server -->
