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  <chapter id="dhcp6">
    <title>The DHCPv6 Server</title>

    <section id="dhcp6-start-stop">
      <title>Starting and Stopping the DHCPv6 Server</title>

      <para>
        <command>kea-dhcp6</command> is the Kea DHCPv6 server and is configured
        through the <command>bindctl</command> program.
      </para>
      <para>
        After starting <command>bind10</command> and starting <command>bindctl</command>, the first step
        in configuring the server is to add <command>kea-dhcp6</command> to the list of running services.
<screen>
&gt; <userinput>config add Init/components kea-dhcp6</userinput>
&gt; <userinput>config set Init/components/kea-dhcp6/kind dispensable</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </para>
      <para>
         To remove <command>kea-dhcp6</command> from the set of running services,
         the <command>kea-dhcp6</command> is removed from list of Init components:
<screen>
&gt; <userinput>config remove Init/components kea-dhcp6</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </para>

      <para>
        Note that the server was only removed from the list, so BIND10 will not
        restart it, but the server itself is still running. Hence it is usually
        desired to stop it:
<screen>
&gt; <userinput>Dhcp6 shutdown</userinput>
</screen>
      </para>

      <para>
        During start-up the server will detect available network interfaces
        and will attempt to open UDP sockets on all interfaces that
        are up, running, are not loopback, are multicast-capable, and
        have IPv6 address assigned. It will then listen to incoming traffic.
      </para>


    </section>

    <section id="dhcp6-configuration">
      <title>DHCPv6 Server Configuration</title>
      <para>
        Once the server has been started, it can be configured. To view the
        current configuration, use the following command in <command>bindctl</command>:
        <screen>&gt; <userinput>config show Dhcp6</userinput></screen>
        When starting the Dhcp6 daemon for the first time, the default configuration
        will be available. It will look similar to this:
<screen>
&gt; <userinput>config show Dhcp6</userinput>
Dhcp6/hooks-libraries   []  list    (default)
Dhcp6/interfaces/   list    (default)
Dhcp6/renew-timer   1000    integer (default)
Dhcp6/rebind-timer  2000    integer (default)
Dhcp6/preferred-lifetime    3000    integer (default)
Dhcp6/valid-lifetime    4000    integer (default)
Dhcp6/option-def    []  list    (default)
Dhcp6/option-data   []  list    (default)
Dhcp6/lease-database/type   ""  string  (default)
Dhcp6/lease-database/name   ""  string  (default)
Dhcp6/lease-database/user   ""  string  (default)
Dhcp6/lease-database/host   ""  string  (default)
Dhcp6/lease-database/password   ""  string  (default)
Dhcp6/subnet6/  list
Dhcp6/dhcp-ddns/enable-updates  true    boolean
Dhcp6/dhcp-ddns/server-ip   "127.0.0.1" string
Dhcp6/dhcp-ddns/server-port 53001   integer
Dhcp6/dhcp-ddns/sender-ip	""	string
Dhcp6/dhcp-ddns/sender-port	0	integer
Dhcp6/dhcp-ddns/max-queue-size	1024  integer
Dhcp6/dhcp-ddns/ncr-protocol    "UDP"   string
Dhcp6/dhcp-ddns/ncr-format  "JSON"  string
Dhcp6/dhcp-ddns/always-include-fqdn false   boolean
Dhcp6/dhcp-ddns/override-no-update  false   boolean
Dhcp6/dhcp-ddns/override-client-update  false   boolean
Dhcp6/dhcp-ddns/replace-client-name false   boolean
Dhcp6/dhcp-ddns/generated-prefix    "myhost"    string
Dhcp6/dhcp-ddns/qualifying-suffix   "example.com"   string
</screen>
      </para>
      <para>
        To change one of the parameters, simply follow
        the usual <command>bindctl</command> procedure. For example, to make the
        leases longer, change their valid-lifetime parameter:
        <screen>
&gt; <userinput>config set Dhcp6/valid-lifetime 7200</userinput>
&gt; <userinput>config commit</userinput></screen>
        Most Dhcp6 parameters are of global scope
        and apply to all defined subnets, unless they are overridden on a
        per-subnet basis.
      </para>
      <note>
        <para>
          With this version of Kea, there are a number of known limitations
          and problems in the DHCPv6 server. See <xref linkend="dhcp6-limit"/>.
        </para>
      </note>

      <section>
      <title>Default storage for leases</title>
      <para>
        The server is able to store lease data in different repositories. Larger deployments
        may elect to store leases in a database.
        <xref linkend="database-configuration6"/> describes one way to do it.
        By default, the server will use a CSV file rather than a database to store
        lease information. One of the advantages of using a file is that it eliminates
        dependency on third party database software.
      </para>
      <para>
        The configuration of the file backend (Memfile)
        is controlled through the Dhcp6/lease-database parameters. When default
        parameters are left, the Memfile backend will write leases to a disk in the
        [bind10-install-dir]/var/bind10/kea-leases6.csv.
      </para>
      <para>
        It is possible to alter the default location of the lease file. The following
        configuration:
<screen>
&gt; <userinput>config set Dhcp4/lease-database/type "memfile"</userinput>
&gt; <userinput>config set Dhcp4/lease-database/persist true</userinput>
&gt; <userinput>config set Dhcp4/lease-database/leasefile "/tmp/kea-leases6.csv"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
        will change the default location of the lease file to /tmp/kea-leases6.csv.
      </para>
      <para>
        The "persist" parameter controls whether the leases are written to disk.
        It is strongly recommended that this parameter is set to "true" at all times
        during the normal operation of the server.
      </para>
      </section>

      <section id="database-configuration6">
      <title>Database Configuration</title>
      <para>
      All leases issued by the server are stored in the lease database. Currently
      there are 3 database backends available: MySQL, PostgreSQL and memfile.
      <footnote>
      <para>
      The server comes with an in-memory database ("memfile") configured as the default
      database. This is used for internal testing and is not supported.  In addition,
      it does not store lease information on disk: lease information will be lost if the
      server is restarted.
      </para>
      </footnote>, and so the server must be configured to
      access the correct database with the appropriate credentials.
      </para>
      <note>
        <para>
            Database access information must be configured for the DHCPv6 server, even if
            it has already been configured for the DHCPv4 server.  The servers store their
            information independently, so each server can use a separate
            database or both servers can use the same database.
          </para>
        </note>
      <para>
      Database configuration is controlled through the Dhcp6/lease-database parameters.
      The type of the database must be set to "mysql", "postgresql" or "memfile":
<screen>
&gt; <userinput>config set Dhcp6/lease-database/type "mysql"</userinput>
</screen>
      Next, the name of the database is to hold the leases must be set: this is the
      name used when the lease database was created (see <xref linkend="dhcp-mysql-database-create"/>
      or <xref linkend="dhcp-pgsql-database-create"/>).
<screen>
&gt; <userinput>config set Dhcp6/lease-database/name "<replaceable>database-name</replaceable>"</userinput>
</screen>
      If the database is located on a different system to the DHCPv6 server, the
      database host name must also be specified (although note that this configuration
      may have a severe impact on server performance):
<screen>
&gt; <userinput>config set Dhcp6/lease-database/host "<replaceable>remote-host-name</replaceable>"</userinput>
</screen>
      The usual state of affairs will be to have the database on the same machine as the
      DHCPv6 server.  In this case, set the value to the empty string (this is the default):
<screen>
&gt; <userinput>config set Dhcp6/lease-database/host ""</userinput>
</screen>
      </para>
      <para>
      Finally, the credentials of the account under which the server will access the database
      should be set:
<screen>
&gt; <userinput>config set Dhcp6/lease-database/user "<replaceable>user-name</replaceable>"</userinput>
&gt; <userinput>config set Dhcp6/lease-database/password "<replaceable>password</replaceable>"</userinput>
</screen>
      If there is no password to the account, set the password to the empty string "". (This is also the default.)
      </para>
      <note>
      <para>The password is echoed when entered and is stored in clear text in the configuration
      database.  Improved password security will be added in a future version of Kea.</para>
      </note>
      </section>

      <section id="dhcp6-interface-selection">
      <title>Interface selection</title>
      <para>
        When DHCPv6 server starts up, by default it will listen to the DHCP
        traffic and respond to it on all interfaces detected during startup.
        However, in many cases it is desired to configure the server to listen and
        respond on selected interfaces only. The sample commands in this section
        show how to make interface selection using bindctl.
      </para>
      <para>
        The default configuration can be presented with the following command:
        <screen>
&gt; <userinput>config show Dhcp6/interfaces</userinput>
<userinput>Dhcp6/interfaces[0] "*" string</userinput></screen>
        An asterisk sign plays a role of the wildcard and means "listen on all interfaces".
      </para>
      <para>
        In order to override the default configuration, the existing entry can be replaced
        with the actual interface name:
        <screen>
&gt; <userinput>config set Dhcp6/interfaces[0] eth1</userinput>
&gt; <userinput>config commit</userinput></screen>
        Other interface names can be added on one-by-one basis:
        <screen>
&gt; <userinput>config add Dhcp6/interfaces eth2</userinput>
&gt; <userinput>config commit</userinput></screen>
        Configuration will now contain two interfaces which can be presented as follows:
        <screen>
&gt; <userinput>config show Dhcp6/interfaces</userinput>
<userinput>Dhcp6/interfaces[0]	"eth1"	string</userinput>
<userinput>Dhcp6/interfaces[1]	"eth2"	string</userinput></screen>
        When configuration gets committed, the server will start to listen on
        eth1 and eth2 interfaces only.
      </para>
      <para>
        It is possible to use wildcard interface name (asterisk) concurrently with explicit
        interface names:
        <screen>
&gt; <userinput>config add Dhcp6/interfaces *</userinput>
&gt; <userinput>config commit</userinput></screen>
        This will result in the following configuration:
        <screen>
&gt; <userinput>config show Dhcp6/interfaces</userinput>
<userinput>Dhcp6/interfaces[0]	"eth1"	string</userinput>
<userinput>Dhcp6/interfaces[1]	"eth2"	string</userinput>
<userinput>Dhcp6/interfaces[2]	"*"	string</userinput></screen>
        The presence of the wildcard name implies that server will listen on all interfaces.
        In order to fall back to the previous configuration when server listens on eth1 and eth2:
        <screen>
&gt; <userinput>config remove Dhcp6/interfaces[2]</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>
    </section>

    <section id="ipv6-subnet-id">
      <title>IPv6 Subnet Identifier</title>
      <para>
        Subnet identifier is a unique number associated with a particular subnet.
        In principle, it is used to associate clients' leases with respective subnets.
        When subnet identifier is not specified for a subnet being configured, it will
        be automatically assigned by the configuration mechanism. The identifiers
        are assigned from 1 and are monotonically increased for each subsequent
        subnet: 1, 2, 3 ....
      </para>
      <para>
       If there are multiple subnets configured with auto-generated identifiers and
       one of them is removed, the subnet identifiers may be renumbered. For example:
       if there are 4 subnets and 3rd is removed the last subnet will be assigned
       identifier that the 3rd subnet had before removal. As a result, the leases
       stored in the lease database for subnet 3 are now associated with the
       subnet 4, which may have unexpected consequences. In the future it is planned
       to implement the mechanism to preserve auto-generated subnet ids upon removal
       of one of the subnets. Currently, the only remedy for this issue is to
       manually specify the unique subnet identifier for each subnet.
      </para>
      <para>
        The following configuration:
        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/id 1024</userinput>
&gt; <userinput>config commit</userinput>
        </screen>
        will assign the arbitrary subnet identifier to the newly configured subnet.
        This identifier will not change for this subnet until "id" parameter is
        removed or set to 0. The value of 0 forces auto-generation of subnet
        identifier.
      </para>
    </section>

    <section id="dhcp6-unicast">
      <title>Unicast traffic support</title>
      <para>
        When DHCPv6 server starts up, by default it listens to the DHCP traffic
        sent to multicast address ff02::1:2 on each interface that it is
        configured to listen on (see <xref linkend="dhcp6-interface-selection"/>).
        In some cases it is useful to configure a server to handle incoming
        traffic sent to the global unicast addresses as well. The most common
        reason for that is to have relays send their traffic to the server
        directly. To configure server to listen on specific unicast address, a
        notation to specify interfaces has been extended. Interface name can be
        optionally followed by a slash, followed by global unicast address that
        server should listen on. That will be done in addition to normal
        link-local binding + listening on ff02::1:2 address. The sample commands
        listed below show how to listen on 2001:db8::1 (a global address)
        configured on the eth1 interface.
      </para>
      <para>
        <screen>
&gt; <userinput>config set Dhcp6/interfaces[0] eth1/2001:db8::1</userinput>
&gt; <userinput>config commit</userinput></screen>
        When configuration gets committed, the server will start to listen on
        eth1 on link-local address, multicast group (ff02::1:2) and 2001:db8::1.
      </para>
      <para>
        It is possible to mix interface names, wildcards and interface name/addresses
        on the Dhcp6/interface list. It is not possible to specify more than one
        unicast address on a given interface.
      </para>
      <para>
        Care should be taken to specify proper unicast addresses. The server will
        attempt to bind to those addresses specified, without any additional checks.
        That approach is selected on purpose, so in the software can be used to
        communicate over uncommon addresses if the administrator desires so.
      </para>
    </section>

    <section id="dhcp6-address-config">
      <title>Subnet and Address Pool</title>
      <para>
        The essential role of a DHCPv6 server is address assignment. For this,
        the server has to be configured with at least one subnet and one pool of dynamic
        addresses to be managed. For example, assume that the server
        is connected to a network segment that uses the 2001:db8:1::/64
        prefix. The Administrator of that network has decided that addresses from range
        2001:db8:1::1 to 2001:db8:1::ffff are going to be managed by the Dhcp6
        server. Such a configuration can be achieved in the following way:
        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "2001:db8:1::0 - 2001:db8:1::ffff" ]</userinput>
&gt; <userinput>config commit</userinput></screen>
        Note that subnet is defined as a simple string, but the pool parameter
        is actually a list of pools: for this reason, the pool definition is
        enclosed in square brackets, even though only one range of addresses
        is specified.</para>
        <para>It is possible to define more than one pool in a
        subnet: continuing the previous example, further assume that
        2001:db8:1:0:5::/80 should be also be managed by the server. It could be written as
        2001:db8:1:0:5:: to 2001:db8:1::5:ffff:ffff:ffff, but typing so many 'f's
        is cumbersome. It can be expressed more simply as 2001:db8:1:0:5::/80. Both
        formats are supported by Dhcp6 and can be mixed in the pool list.
        For example, one could define the following pools:
        <screen>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "2001:db8:1::1 - 2001:db8:1::ffff", "2001:db8:1:0:5::/80" ]</userinput>
&gt; <userinput>config commit</userinput></screen>
        The number of pools is not limited, but for performance reasons it is recommended to
        use as few as possible.
      </para>
      <para>
         The server may be configured to serve more than one subnet. To add a second subnet,
         use a command similar to the following:
        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/subnet "2001:db8:beef::/48"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/pool [ "2001:db8:beef::/48" ]</userinput>
&gt; <userinput>config commit</userinput></screen>
        Arrays are counted from 0. subnet[0] refers to the subnet defined in the
        previous example.  The <command>config add Dhcp6/subnet6</command> command adds
        another (second) subnet. It can be referred to as
        <command>Dhcp6/subnet6[1]</command>. In this example, we allow server to
        dynamically assign all addresses available in the whole subnet. Although
        very wasteful, it is certainly a valid configuration to dedicate the
        whole /48 subnet for that purpose.
      </para>
      <para>
        When configuring a DHCPv6 server using prefix/length notation, please pay
        attention to the boundary values. When specifying that the server should use
        a given pool, it will be able to allocate also first (typically network
        address) address from that pool. For example for pool 2001:db8::/64 the
        2001:db8:: address may be assigned as well. If you want to avoid this,
        please use the "min-max" notation.
      </para>
    </section>

    <section>
<!-- @todo: add real meat to the prefix delegation config this is just place holder stuff -->
      <title>Subnet and Prefix Delegation Pools</title>
      <para>
        Subnets may also be configured to delegate address prefixes....
        A subnet may have one or more prefix delegation pools.  Each pool has
        a prefixed address, which is specified as a prefix and a prefix length,
        as well as a delegated prefix length.  A sample configuration is shown
        below:
      <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config show Dhcp6/subnet6[0]</userinput>
&gt; <userinput>config add Dhcp6/subnet6[0]/pd-pools</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pd-pools[0]/prefix "2001:db8:1::"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pd-pools[0]/prefix-len 64</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pd-pools[0]/delegated-len 96</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>
    </section>

    <section id="dhcp6-std-options">
      <title>Standard DHCPv6 options</title>
      <para>
        One of the major features of DHCPv6 server is to provide configuration
        options to clients. Although there are several options that require
        special behavior, most options are sent by the server only if the client
        explicitly requested them.  The following example shows how to
        configure DNS servers, which is one of the most frequently used
        options. Numbers in the first column are added for easier reference and
        will not appear on screen. Options specified in this way are considered
        global and apply to all configured subnets.

        <screen>
1. &gt; <userinput>config add Dhcp6/option-data</userinput>
2. &gt; <userinput>config set Dhcp6/option-data[0]/name "dns-servers"</userinput>
3. &gt; <userinput>config set Dhcp6/option-data[0]/code 23</userinput>
4. &gt; <userinput>config set Dhcp6/option-data[0]/space "dhcp6"</userinput>
5. &gt; <userinput>config set Dhcp6/option-data[0]/csv-format true</userinput>
6. &gt; <userinput>config set Dhcp6/option-data[0]/data "2001:db8::cafe, 2001:db8::babe"</userinput>
7. &gt; <userinput>config commit</userinput>
</screen>
      </para>
    <para>
      The first line creates new entry in option-data table. It
      contains information on all global options that the server is
      supposed to configure in all subnets. The second line specifies
      option name. For a complete list of currently supported names,
      see <xref linkend="dhcp6-std-options-list"/>.
      The third line specifies option code, which must match one of the
      values from that
      list. Line 4 specifies option space, which must always
      be set to "dhcp6" as these are standard DHCPv6 options. For
      other name spaces, including custom option spaces, see <xref
      linkend="dhcp6-option-spaces"/>. The fifth line specifies the format in
      which the data will be entered: use of CSV (comma
      separated values) is recommended. The sixth line gives the actual value to
      be sent to clients. Data is specified as a normal text, with
      values separated by commas if more than one value is
      allowed.
    </para>

    <para>
      Options can also be configured as hexadecimal values. If csv-format is
      set to false, the option data must be specified as a string of hexadecimal
      numbers. The
      following commands configure the DNS-SERVERS option for all
      subnets with the following addresses: 2001:db8:1::cafe and
      2001:db8:1::babe.
      <screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/name "dns-servers"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/code 23</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/csv-format false</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/data "2001 0DB8 0001 0000 0000 0000</userinput>
        <userinput>0000 CAFE 2001 0DB8 0001 0000 0000 0000 0000 BABE"</userinput>
&gt; <userinput>config commit</userinput>
        </screen>
       (The value for the setting of the "data" element is split across two
        lines in this document for clarity: when entering the command, the
        whole string should be entered on the same line.)
      </para>

    <para>
      It is possible to override options on a per-subnet basis.  If
      clients connected to most of your subnets are expected to get the
      same values of a given option, you should use global options: you
      can then override specific values for a small number of subnets.
      On the other hand, if you use different values in each subnet,
      it does not make sense to specify global option values
      (Dhcp6/option-data), rather you should set only subnet-specific values
      (Dhcp6/subnet[X]/option-data[Y]).
     </para>
     <para>
      The following commands override the global
      DNS servers option for a particular subnet, setting a single DNS
      server with address 2001:db8:1::3.
      <screen>
&gt; <userinput>config add Dhcp6/subnet6[0]/option-data</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/option-data[0]/name "dns-servers"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/option-data[0]/code 23</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/option-data[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/option-data[0]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/option-data[0]/data "2001:db8:1::3"</userinput>
&gt; <userinput>config commit</userinput></screen>
    </para>

    <note>
      <para>
        In future versions of BIND 10 DHCP, it will not be necessary to specify
        option code, space and csv-format fields, as those fields will be set
        automatically.
      </para>
    </note>


    <para>
      The currently supported standard DHCPv6 options are
      listed in <xref linkend="dhcp6-std-options-list"/>.
      The "Name" and "Code"
      are the values that should be used as a name in the option-data
      structures. "Type" designates the format of the data: the meanings of
      the various types is given in <xref linkend="dhcp-types"/>.
    </para>
    <para>
      Some options are designated as arrays, which means that more than one
      value is allowed in such an option. For example the option dns-servers
      allows the specification of more than one IPv6 address, so allowing
      clients to obtain the the addresses of multiple DNS servers.
    </para>

<!-- @todo: describe record types -->

      <para>
        The <xref linkend="dhcp6-custom-options"/> describes the configuration
        syntax to create custom option definitions (formats). It is generally not
        allowed to create custom definitions for standard options, even if the
        definition being created matches the actual option format defined in the
        RFCs. There is an exception from this rule for standard options for which
        Kea does not provide a definition yet. In order to use such options,
        a server administrator must create a definition as described in
        <xref linkend="dhcp6-custom-options"/> in the 'dhcp6' option space. This
        definition should match the option format described in the relevant
        RFC but configuration mechanism would allow any option format as it has
        no means to validate it at the moment.
      </para>


    <para>
      <table frame="all" id="dhcp6-std-options-list">
        <title>List of standard DHCPv6 options</title>
        <tgroup cols='4'>
        <colspec colname='name'/>
        <colspec colname='code'/>
        <colspec colname='type'/>
        <colspec colname='array'/>
        <thead>
          <row><entry>Name</entry><entry>Code</entry><entry>Type</entry><entry>Array?</entry></row>
        </thead>
        <tbody>
<!-- Our engine uses those options on its own, admin must not configure them on his own
<row><entry>clientid</entry><entry>1</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>serverid</entry><entry>2</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>ia-na</entry><entry>3</entry><entry>record</entry><entry>false</entry></row>
<row><entry>ia-ta</entry><entry>4</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>iaaddr</entry><entry>5</entry><entry>record</entry><entry>false</entry></row>
<row><entry>oro</entry><entry>6</entry><entry>uint16</entry><entry>true</entry></row> -->
<row><entry>preference</entry><entry>7</entry><entry>uint8</entry><entry>false</entry></row>

<!-- Our engine uses those options on its own, admin must not configure them on his own
<row><entry>elapsed-time</entry><entry>8</entry><entry>uint16</entry><entry>false</entry></row>
<row><entry>relay-msg</entry><entry>9</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>auth</entry><entry>11</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>unicast</entry><entry>12</entry><entry>ipv6-address</entry><entry>false</entry></row>
<row><entry>status-code</entry><entry>13</entry><entry>record</entry><entry>false</entry></row>
<row><entry>rapid-commit</entry><entry>14</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>user-class</entry><entry>15</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>vendor-class</entry><entry>16</entry><entry>record</entry><entry>false</entry></row>
<row><entry>vendor-opts</entry><entry>17</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>interface-id</entry><entry>18</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>reconf-msg</entry><entry>19</entry><entry>uint8</entry><entry>false</entry></row>
<row><entry>reconf-accept</entry><entry>20</entry><entry>empty</entry><entry>false</entry></row> -->
<row><entry>sip-server-dns</entry><entry>21</entry><entry>fqdn</entry><entry>true</entry></row>
<row><entry>sip-server-addr</entry><entry>22</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>dns-servers</entry><entry>23</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>domain-search</entry><entry>24</entry><entry>fqdn</entry><entry>true</entry></row>
<!-- <row><entry>ia-pd</entry><entry>25</entry><entry>record</entry><entry>false</entry></row> -->
<!-- <row><entry>iaprefix</entry><entry>26</entry><entry>record</entry><entry>false</entry></row> -->
<row><entry>nis-servers</entry><entry>27</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>nisp-servers</entry><entry>28</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>nis-domain-name</entry><entry>29</entry><entry>fqdn</entry><entry>true</entry></row>
<row><entry>nisp-domain-name</entry><entry>30</entry><entry>fqdn</entry><entry>true</entry></row>
<row><entry>sntp-servers</entry><entry>31</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>information-refresh-time</entry><entry>32</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>bcmcs-server-dns</entry><entry>33</entry><entry>fqdn</entry><entry>true</entry></row>
<row><entry>bcmcs-server-addr</entry><entry>34</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>geoconf-civic</entry><entry>36</entry><entry>record</entry><entry>false</entry></row>
<row><entry>remote-id</entry><entry>37</entry><entry>record</entry><entry>false</entry></row>
<row><entry>subscriber-id</entry><entry>38</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>client-fqdn</entry><entry>39</entry><entry>record</entry><entry>false</entry></row>
<row><entry>pana-agent</entry><entry>40</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>new-posix-timezone</entry><entry>41</entry><entry>string</entry><entry>false</entry></row>
<row><entry>new-tzdb-timezone</entry><entry>42</entry><entry>string</entry><entry>false</entry></row>
<row><entry>ero</entry><entry>43</entry><entry>uint16</entry><entry>true</entry></row>
<row><entry>lq-query</entry><entry>44</entry><entry>record</entry><entry>false</entry></row>
<row><entry>client-data</entry><entry>45</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>clt-time</entry><entry>46</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>lq-relay-data</entry><entry>47</entry><entry>record</entry><entry>false</entry></row>
<row><entry>lq-client-link</entry><entry>48</entry><entry>ipv6-address</entry><entry>true</entry></row>
        </tbody>
        </tgroup>
      </table>
    </para>
    </section>

    <section id="dhcp6-custom-options">
      <title>Custom DHCPv6 options</title>
      <para>It is also possible to define options other than the standard ones.
      Assume that we want to define a new DHCPv6 option called "foo" which will have
      code 100 and will convey a single unsigned 32 bit integer value. We can define
      such an option by using the following commands:
      <screen>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/name "foo"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/code 100</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/type "uint32"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/record-types ""</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/encapsulate ""</userinput>
&gt; <userinput>config commit</userinput></screen>
      The "false" value of the "array" parameter determines that the option
      does NOT comprise an array of "uint32" values but rather a single value.
      Two other parameters have been left blank: "record-types" and "encapsulate".
      The former specifies the comma separated list of option data fields if the
      option comprises a record of data fields. The "record-fields" value should
      be non-empty if the "type" is set to "record". Otherwise it must be left
      blank. The latter parameter specifies the name of the option space being
      encapsulated by the particular option. If the particular option does not
      encapsulate any option space it should be left blank.
      Note that the above set of comments define the format of the new option and do not
      set its values.
      </para>
      <para>Once the new option format is defined, its value is set
      in the same way as for a standard option. For example the following
      commands set a global value that applies to all subnets.
        <screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/name "foo"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/code 100</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/data "12345"</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>

      <para>New options can take more complex forms than simple use of
      primitives (uint8, string, ipv6-address etc): it is possible to
      define an option comprising a number of existing primitives.
      </para>
      <para>
      Assume we want to define a new option that will consist of an IPv6
      address, followed by an unsigned 16 bit integer, followed by a
      boolean value, followed by a text string. Such an option could
      be defined in the following way:
<screen>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/name "bar"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/code 101</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/type "record"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/record-types "ipv6-address, uint16, boolean, string"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/encapsulate ""</userinput>
</screen>
      The "type" is set to "record" to indicate that the option contains
      multiple values of different types.  These types are given as a comma-separated
      list in the "record-types" field and should be those listed in <xref linkend="dhcp-types"/>.
      </para>
      <para>
      The values of the option are set as follows:
<screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/name "bar"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/code 101</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/data "2001:db8:1::10, 123, false, Hello World"</userinput>
&gt; <userinput>config commit</userinput></screen>
      "csv-format" is set "true" to indicate that the "data" field comprises a command-separated
      list of values.  The values in the "data" must correspond to the types set in
      the "record-types" field of the option definition.
      </para>
      <note>
        <para>
          It is recommended that boolean values are specified using "true" and "false"
          strings. This helps to prevent errors when typing multiple comma separated
          values, as it make it easier to identify the type of the value being typed,
          and compare it with the order of data fields. Nevertheless, it is possible
          to use integer values: "1" and "0", instead of "true" and "false"
          accordingly. If other integer value is specified, the configuration is
          rejected.
        </para>
      </note>
    </section>

    <section id="dhcp6-vendor-opts">
      <title>DHCPv6 vendor specific options</title>
      <para>
      Currently there are three option spaces defined: dhcp4 (to be used
      in DHCPv4 daemon) and dhcp6 (for the DHCPv6 daemon); there is also
      vendor-opts-space, which is empty by default, but options can be
      defined in it. Those options are called vendor-specific information
      options. The following examples show how to define an option "foo"
      with code 1 that consists of an IPv6 address, an unsigned 16 bit integer
      and a string. The "foo" option is conveyed in a vendor specific
      information option. This option comprises a single uint32 value
      that is set to "12345". The sub-option "foo" follows the data
      field holding this value.
      <screen>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/name "foo"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/code 1</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/space "vendor-opts-space"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/type "record"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/record-types "ipv6-address, uint16, string"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/encapsulates ""</userinput>
&gt; <userinput>config commit</userinput>
</screen>
     (Note that the option space is set to "vendor-opts-space".)
     Once the option format is defined, the next step is to define actual values
     for that option:
     <screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/name "foo"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/space "vendor-opts-space"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/code 1</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/data "2001:db8:1::10, 123, Hello World"</userinput>
&gt; <userinput>config commit</userinput></screen>
    We should also define values for the vendor-opts, that will convey our option foo.
     <screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/name "vendor-opts"</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/code 17</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/data "12345"</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>
    </section>

    <section id="dhcp6-option-spaces">
      <title>Nested DHCPv6 options (custom option spaces)</title>
      <para>It is sometimes useful to define completely new option
      spaces.  This is useful if the user wants his new option to
      convey sub-options that use separate numbering scheme, for
      example sub-options with codes 1 and 2. Those option codes
      conflict with standard DHCPv6 options, so a separate option
      space must be defined.
      </para>
      <para>Note that it is not required to create new option space when
      defining sub-options for a standard option because it is by
      default created if the standard option is meant to convey
      any sub-options (see <xref linkend="dhcp6-vendor-opts"/>).
      </para>
      <para>
      Assume that we want to have a DHCPv6 option called "container"
      with code 102 that conveys two sub-options with codes 1 and 2.
      First we need to define the new sub-options:
<screen>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/name "subopt1"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/code 1</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/space "isc"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/type "ipv6-address"</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/record-types ""</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[0]/encapsulate ""</userinput>
&gt; <userinput>config commit</userinput>
&gt; <userinput></userinput>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/name "subopt2"</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/code 2</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/space "isc"</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/type "string"</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/record-types ""</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[1]/encapsulate ""</userinput>
&gt; <userinput>config commit</userinput>
</screen>
    Note that we have defined the options to belong to a new option space
    (in this case, "isc").
    </para>
    <para>
The next step is to define a regular DHCPv6 option and specify that it
should include options from the isc option space:
<screen>
&gt; <userinput>config add Dhcp6/option-def</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/name "container"</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/code 102</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/type "empty"</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/array false</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/record-types ""</userinput>
&gt; <userinput>config set Dhcp6/option-def[2]/encapsulate "isc"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
    The name of the option space in which the sub-options are defined
    is set in the "encapsulate" field. The "type" field is set to "empty"
    which imposes that this option does not carry any data other than
    sub-options.
    </para>
    <para>
    Finally, we can set values for the new options:
<screen>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/name "subopt1"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/space "isc"</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/code 1</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[0]/data "2001:db8::abcd"</userinput>
&gt; <userinput>config commit</userinput>
&gt; <userinput></userinput>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/name "subopt2"</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/space "isc"</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/code 2</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[1]/data "Hello world"</userinput>
&gt; <userinput>config commit</userinput>
&gt; <userinput></userinput>
&gt; <userinput>config add Dhcp6/option-data</userinput>
&gt; <userinput>config set Dhcp6/option-data[2]/name "container"</userinput>
&gt; <userinput>config set Dhcp6/option-data[2]/space "dhcp6"</userinput>
&gt; <userinput>config set Dhcp6/option-data[2]/code 102</userinput>
&gt; <userinput>config set Dhcp6/option-data[2]/csv-format true</userinput>
&gt; <userinput>config set Dhcp6/option-data[2]/data ""</userinput>
&gt; <userinput>config commit</userinput>
</screen>
    Even though the "container" option does not carry any data except
    sub-options, the "data" field must be explicitly set to an empty value.
    This is required because in the current version of BIND 10 DHCP, the
    default configuration values are not propagated to the configuration parsers:
    if the "data" is not set the parser will assume that this
    parameter is not specified and an error will be reported.
    </para>
    <para>Note that it is possible to create an option which carries some data
    in addition to the sub-options defined in the encapsulated option space.  For example,
    if the "container" option from the previous example was required to carry an uint16
    value as well as the sub-options, the "type" value would have to be set to "uint16" in
    the option definition. (Such an option would then have the following
    data structure: DHCP header, uint16 value, sub-options.) The value specified
    with the "data" parameter - which should be a valid integer enclosed in quotes,
    e.g. "123" - would then be assigned to the uint16 field in the "container" option.
    </para>
    </section>

      <section id="dhcp6-config-subnets">
        <title>IPv6 Subnet Selection</title>
          <para>
          The DHCPv6 server may receive requests from local (connected to the
          same subnet as the server) and remote (connecting via relays) clients.
          As server may have many subnet configurations defined, it must select
          appropriate subnet for a given request.
          </para>
          <para>
          The server can not assume which of configured subnets are local. It is
          possible in IPv4, where there is reasonable expectation that the
          server will have a (global) IPv4 address configured on the interface,
          and can use that information to detect whether a subnet is local or
          not. That assumption is not true in IPv6, as the DHCPv6 must be able
          to operate with having link-local addresses only. Therefore an optional
          &quot;interface&quot; parameter is available within a subnet definition
          to designate that a given subnet is local, i.e. reachable directly over
          specified interface. For example the server that is intended to serve
          a local subnet over eth0 may be configured as follows:
<screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/subnet "2001:db8:beef::/48"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/pool [ "2001:db8:beef::/48" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/interface "eth0"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
        </para>
      </section>

      <section id="dhcp6-relays">
        <title>DHCPv6 Relays</title>
        <para>
          A DHCPv6 server with multiple subnets defined must select the
          appropriate subnet when it receives a request from client.  For clients
          connected via relays, two mechanisms are used:
        </para>
        <para>
          The first uses the linkaddr field in the RELAY_FORW message. The name
          of this field is somewhat misleading in that it does not contain a link-layer
          address: instead, it holds an address (typically a global address) that is
          used to identify a link. The DHCPv6 server checks if the address belongs
          to a defined subnet and, if it does, that subnet is selected for the client's
          request.
        </para>
        <para>
          The second mechanism is based on interface-id options. While forwarding a client's
          message, relays may insert an interface-id option into the message that
          identifies the interface on the relay that received the message. (Some
          relays allow configuration of that parameter, but it is sometimes
          hardcoded and may range from the very simple (e.g. "vlan100") to the very cryptic:
          one example seen on real hardware was "ISAM144|299|ipv6|nt:vp:1:110"). The
          server can use this information to select the appropriate subnet.
          The information is also returned to the relay which then knows the
          interface to use to transmit the response to the client. In order for
          this to work successfully, the relay interface IDs must be unique within
          the network and the server configuration must match those values.
        </para>
        <para>
          When configuring the DHCPv6 server, it should be noted that two
          similarly-named parameters can be configured for a subnet:
          <itemizedlist>
            <listitem><simpara>
              "interface" defines which local network interface can be used
              to access a given subnet.
            </simpara></listitem>
            <listitem><simpara>
              "interface-id" specifies the content of the interface-id option
              used by relays to identify the interface on the relay to which
              the response packet is sent.
            </simpara></listitem>
          </itemizedlist>
          The two are mutually exclusive: a subnet cannot be both reachable locally
          (direct traffic) and via relays (remote traffic). Specifying both is a
          configuration error and the DHCPv6 server will refuse such a configuration.
        </para>

        <para>
          To specify interface-id with value "vlan123", the following commands can
          be used:
          <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:beef::/48"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "2001:db8:beef::/48" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/interface-id "vland123"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
        </para>
      </section>

    <section id="dhcp6-client-classifier">
      <title>Client Classification in DHCPv6</title>
      <note>
      <para>
        DHCPv6 server has been extended to support limited client classification.
        Although the current capability is modest, it is expected to be expanded
        in the future. It is envisaged that the majority of client classification
        extensions will be using hooks extensions.
      </para>
      </note>
      <para>In certain cases it is useful to differentiate between different types
      of clients and treat them differently. The process of doing classification
      is conducted in two steps. The first step is to assess incoming packet and
      assign it to zero or more classes. This classification is currently simple,
      but is expected to grow in capability soon. Currently the server checks whether
      incoming packet has vendor class option (16). If it has, content
      of that option is prepended with &quot;VENDOR_CLASS_&quot; interpreted as a
      class. For example, modern cable modems will send this option with value
      &quot;docsis3.0&quot; and as a result the packet will belong to class
      &quot;VENDOR_CLASS_docsis3.0&quot;.
      </para>

      <para>It is envisaged that the client classification will be used for changing
      behavior of almost any part of the DHCP engine processing, including assigning
      leases from different pools, assigning different option (or different values of
      the same options) etc. For now, there is only one mechanism that is taking
      advantage of client classification: subnet selection.</para>

      <para>
        Kea can be instructed to limit access to given subnets based on class information.
        This is particularly useful for cases where two types of devices share the
        same link and are expected to be served from two different subnets. The
        primary use case for such a scenario are cable networks. There are two
        classes of devices: cable modem itself, which should be handled a lease
        from subnet A and all other devices behind modems that should get a lease
        from subnet B. That segregation is essential to prevent overly curious
        users from playing with their cable modems. For details on how to set up
        class restrictions on subnets, see <xref linkend="dhcp6-subnet-class"/>.
      </para>

    </section>

    <section id="dhcp6-subnet-class">
      <title>Limiting access to IPv6 subnet to certain classes</title>
      <para>
        In certain cases it beneficial to restrict access to certain subnets
        only to clients that belong to a given subnet. For details on client
        classes, see <xref linkend="dhcp6-client-classifier"/>. This is an
        extension of a previous example from <xref linkend="dhcp6-address-config"/>.

        Let's assume that the server is connected to a network segment that uses
        the 2001:db8:1::/64 prefix. The Administrator of that network has
        decided that addresses from range 2001:db8:1::1 to 2001:db8:1::ffff are
        going to be managed by the Dhcp6 server. Only clients belonging to the
        eRouter1.0 client class are allowed to use that pool. Such a
        configuration can be achieved in the following way:

        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "2001:db8:1::0 - 2001:db8:1::ffff" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/client-class "eRouter1.0"</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>

      <para>
        Care should be taken with client classification as it is easy to prevent
        clients that do not meet class criteria to be denied any service altogether.
      </para>
    </section>


    <section id="dhcp6-ddns-config">
      <title>Configuring DHCPv6 for DDNS</title>
      <para>
      As mentioned earlier, kea-dhcp6 can be configured to generate requests to
      the DHCP-DDNS server (referred to here as the "D2" server) to update
      DNS entries.  These requests are known as NameChangeRequests or NCRs.
      Each NCR contains the following information:
      <orderedlist>
      <listitem><para>
      Whether it is a request to add (update) or remove DNS entries
      </para></listitem>
      <listitem><para>
      Whether the change requests forward DNS updates (AAAA records), reverse
      DNS updates (PTR records), or both.
      </para></listitem>
      <listitem><para>
      The FQDN, lease address, and DHCID
      </para></listitem>
      </orderedlist>
      The parameters controlling the generation of NCRs for submission to D2
      are contained in the "dhcp-ddns" section of kea-dhcp6
      configuration. The default values for this section appears as follows:
<screen>
&gt; <userinput>config show Dhcp6/dhcp-ddns</userinput>
Dhcp6/dhcp-ddns/enable-updates	true	boolean
Dhcp6/dhcp-ddns/server-ip	"127.0.0.1"	string
Dhcp6/dhcp-ddns/server-port	53001	integer
Dhcp6/dhcp-ddns/sender-ip	""	string
Dhcp6/dhcp-ddns/sender-port	0	integer
Dhcp6/dhcp-ddns/max-queue-size	1024 integer
Dhcp6/dhcp-ddns/ncr-protocol	"UDP"	string
Dhcp6/dhcp-ddns/ncr-format	"JSON"	string
Dhcp6/dhcp-ddns/override-no-update	false	boolean
Dhcp6/dhcp-ddns/override-client-update	false	boolean
Dhcp6/dhcp-ddns/replace-client-name	false	boolean
Dhcp6/dhcp-ddns/generated-prefix	"myhost"	string
Dhcp6/dhcp-ddns/qualifying-suffix	"example.com"	string
</screen>
      </para>
      <para>
      The "enable-updates" parameter determines whether or not kea-dhcp6 will
      generate NCRs.  By default, this value is false hence DDNS updates are
      disabled.  To enable DDNS updates set this value to true as follows:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/enable-updates true</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      <section id="dhcpv6-d2-io-config">
      <title>DHCP-DDNS Server Connectivity</title>
      <para>
      In order for NCRs to reach the D2 server, kea-dhcp6 must be able
      to communicate with it.  kea-dhcp6 uses the following configuration
      parameters to control how it communications with D2:
      <orderedlist>
      <listitem><para>
      server-ip - 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>
      server-port - port on which D2 listens for requests.  The default value
      is 53001.
      </para></listitem>
      <listitem><para>
      sender-ip - IP address which kea-dhcp6 should use to send requests to D2.
      The default value is blank which instructs kea-dhcp6 to select a suitable
      address.
      </para></listitem>
      <listitem><para>
      sender-port - port which kea-dhcp6 should use to send requests to D2. The
      default value of 0 instructs kea-dhcp6 to select suitable port.
      </para></listitem>
      <listitem><para>
      ncr-format - Socket protocol 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>
      max-queue-size - maximum number of requests allowed to queue waiting to
      be sent to D2. This value guards against requests accumulating
      uncontrollably if they are being generated faster than they can be
      delivered.  If the number of requests queued for transmission reaches
      this value, DDNS updating will be turned off until the queue backlog has
      been sufficiently reduced.  The intent is allow kea-dhcp6 to
      continue lease operations.  The default value is 1024.
      </para></listitem>
      </orderedlist>
      By default, D2 is assumed to running on the same machine as kea-dhcp6, and
      all of the default values mentioned above should be sufficient.
      If, however, D2 has been configured to listen on a different address or
      port, these values must altered accordingly. For example, if D2 has been
      configured to listen on 3001::5 port 900, the following commands
      would be required:
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/server-ip "3001::5"</userinput>
&gt; <userinput>config set Dhcp6/dhcp-ddns/server-port 900</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </para>
      </section>
      <section id="dhcpv6-d2-rules-config">
      <title>When does kea-dhcp6 generate DDNS request</title>
      kea-dhcp6 follows the behavior prescribed for DHCP servers in RFC 4704.
      It is important to keep in mind that kea-dhcp6 provides the initial decision
      making of when and what to update and forwards that information to D2 in
      the form of NCRs. Carrying out the actual DNS updates and dealing with
      such things as conflict resolution are the purview of D2 (<xref linkend="dhcp-ddns-server"/>).
      <para>
      This section describes when kea-dhcp6 will generate NCRs and the
      configuration parameters that can be used to influence this decision.
      It assumes that the "enable-updates" parameter is true.
      </para>
      <note>
        <para>
        Currently the interface between kea-dhcp6 and D2 only supports requests
        which update DNS entries for a single IP address.  If a lease grants
        more than one address, kea-dhcp6 will create the DDNS update request for
        only the first of these addresses.  Support for multiple address
        mappings may be provided in a future release.
        </para>
      </note>
      <para>
      In general, kea-dhcp6 will generate DDNS update requests when:
      <orderedlist>
      <listitem><para>
      A new lease is granted in response to a DHCP REQUEST
      </para></listitem>
      <listitem><para>
      An existing lease is renewed but the FQDN associated with it has
      changed.
      </para></listitem>
      <listitem><para>
      An existing lease is released in response to a DHCP RELEASE
      </para></listitem>
      </orderedlist>
      In the second case, lease renewal, two  DDNS requests will be issued: one
      request to remove entries for the previous FQDN and a second request to
      add entries for the new FQDN.  In the last case, a lease release, a
      single DDNS request to remove its entries will be made.  The decision
      making involved when granting a new lease is more involved and is
      discussed next.
      </para>
      <para>
      kea-dhcp6 will generate a DDNS update request only if the DHCP REQUEST
      contains the FQDN option (code 39). By default kea-dhcp6 will
      respect the FQDN N and S flags specified by the client as shown in the
      following table:
      </para>
        <table id="dhcp6-fqdn-flag-table">
          <title>Default FQDN Flag Behavior</title>
          <tgroup cols='4' align='left'>
          <colspec colname='cflags'/>
          <colspec colname='meaning'/>
          <colspec colname='response'/>
          <colspec colname='sflags'/>
          <thead>
              <row>
                <entry>Client Flags:N-S</entry>
                <entry>Client Intent</entry>
                <entry>Server Response</entry>
                <entry>Server Flags:N-S-O</entry>
              </row>
          </thead>
          <tbody>
            <row>
                <entry>0-0</entry>
                <entry>
                Client wants to do forward updates, server should do reverse updates
                </entry>
                <entry>Server generates reverse-only request</entry>
                <entry>1-0-0</entry>
            </row>
            <row>
                <entry>0-1</entry>
                <entry>Server should do both forward and reverse updates</entry>
                <entry>Server generates request to update both directions</entry>
                <entry>0-1-0</entry>
            </row>
            <row>
                <entry>1-0</entry>
                <entry>Client wants no updates done</entry>
                <entry>Server does not generate a request</entry>
                <entry>1-0-0</entry>
            </row>
          </tbody>
          </tgroup>
        </table>
      <para>
      The first row in the table above represents "client delegation". Here
      the DHCP client states that it intends to do the forward DNS updates and
      the server should do the reverse updates.  By default, kea-dhcp6 will honor
      the client's wishes and generate a DDNS request to D2 to update only
      reverse DNS data.  The parameter, "override-client-update", can be used
      to instruct the server to override client delegation requests.  When
      this parameter is true, kea-dhcp6 will disregard requests for client
      delegation and generate a DDNS request to update both forward and
      reverse DNS data.  In this case, the N-S-O flags in the server's
      response to the client will be 0-1-1 respectively.
      </para>
      <para>
      (Note that the flag combination N=1, S=1 is prohibited according to
      RFC 4702. If such a combination is received from the client, the packet
      will be dropped by kea-dhcp6.)
      </para>
      <para>
      To override client delegation, issue the following commands:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/override-client-update true</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      <para>
      The third row in the table above describes the case in which the client
      requests that no DNS updates be done. The parameter, "override-no-update",
      can be used to instruct the server to disregard the client's wishes. When
      this parameter is true, kea-dhcp6 will generate DDNS update request to D2
      even if the client requests no updates be done.  The N-S-O flags in the
      server's response to the client will be 0-1-1.
      </para>
      <para>
      To override client delegation, issue the following commands:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/override-no-update true</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </section>
      <section id="dhcpv6-fqdn-name-generation">
      <title>kea-dhcp6 name generation for DDNS update requests</title>
      Each NameChangeRequest must of course include the fully qualified domain
      name whose DNS entries are to be affected.  kea-dhcp6 can be configured to
      supply a portion or all of that name based upon what it receives from
      the client in the DHCP REQUEST.
      <para>
      The rules for determining the FQDN option are as follows:
      <orderedlist>
      <listitem><para>
      If configured to do so ignore the REQUEST contents and generate a
      FQDN using a configurable prefix and suffix.
      </para></listitem>
      <listitem><para>
      Otherwise, using is the domain name value from the client FQDN option as
      the candidate name:
      <orderedlist>
      <listitem><para>
      If the candidate name is a fully qualified domain name then use it.
      </para></listitem>
      <listitem><para>
      If the candidate name is a partial (i.e. unqualified) name then
      add a configurable suffix to the name and use the result as the FQDN.
      </para></listitem>
      <listitem><para>
      If the candidate name is a empty then generate a FQDN using a
      configurable prefix and suffix.
      </para></listitem>
      </orderedlist>
      </para></listitem>
      </orderedlist>
      To instruct kea-dhcp6 to always generate a FQDN, set the parameter
      "replace-client-name" to true:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/replace-client-name true</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      <para>
      The prefix used when generating a FQDN is specified by the
      "generated-prefix" parameter.  The default value is "myhost".  To alter
      its value, simply set it to the desired string:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/generated-prefix "another.host"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      <para>
      The suffix used when generating a FQDN or when qualifying a partial
      name is specified by the "qualifying-suffix" parameter.  The default
      value is "example.com".  To alter its value simply set it to the desired
      string:
      </para>
<screen>
&gt; <userinput>config set Dhcp6/dhcp-ddns/generated-prefix "our.net"</userinput>
&gt; <userinput>config commit</userinput>
</screen>
      </section>
      <para>
      When qualifying a partial name, kea-dhcp6 will construct a name with the
      format:
      </para>
      <para>
        [candidate-name].[qualifying-suffix].
      </para>
      <para>
      where candidate-name is the partial name supplied in the REQUEST.
      For example, if FQDN domain name value was "some-computer" and assuming
      the default value for qualifying-suffix, the generated FQDN would be:
      </para>
      <para>
        some-computer.example.com.
      </para>
      <para>
      When generating a the entire name, kea-dhcp6 will construct name of the
      format:
      </para>
      <para>
        [generated-prefix]-[address-text].[qualifying-suffix].
      </para>
      <para>
      where address-text is simply the lease IP address converted to a
      hyphenated string.  For example, if lease address is 3001:1::70E and
      assuming default values for generated-prefix and qualifying-suffix, the
      generated FQDN would be:
      </para>
      <para>
        myhost-3001-1--70E.example.com.
      </para>
    </section>

   </section>

    <section id="dhcp6-serverid">
      <title>Server Identifier in DHCPv6</title>
      <para>The DHCPv6 protocol uses a "server identifier" (also known
      as a DUID) for clients to be able to discriminate between several
      servers present on the same link.  There are several types of
      DUIDs defined, but <ulink url="http://tools.ietf.org/html/rfc3315">RFC 3315</ulink> instructs servers to use DUID-LLT if
      possible. This format consists of a link-layer (MAC) address and a
      timestamp. When started for the first time, the DHCPv6 server will
      automatically generate such a DUID and store the chosen value to
      a file.  That file is read by the server
      and the contained value used whenever the server is subsequently started.
      </para>
      <para>
        It is unlikely that this parameter should ever need to be changed.
        However, if such a need arises, stop the server, edit the file and restart
        the server. (The file is named kea-dhcp6-serverid and by default is
        stored in the "var" subdirectory of the directory in which BIND 10 is installed.
        This can be changed when BIND 10 is built by using "--localstatedir"
        on the "configure" command line.)  The file is a text file that contains
        double digit hexadecimal values
        separated by colons. This format is similar to typical MAC address
        format. Spaces are ignored. No extra characters are allowed in this
        file.
      </para>

    </section>

    <section id="dhcp6-relay-override">
      <title>Using specific relay agent for a subnet</title>
      <para>
        The relay has to have an interface connected to the link on which
        the clients are being configured. Typically the relay has a global IPv6
        address configured on that interface that belongs to the subnet that
        the server will assign addresses from. In such typical case, the
        server is able to use IPv6 address inserted by the relay (in link-addr
        field in RELAY-FORW message) to select appropriate subnet.
      </para>
      <para>
        However, that is not always the case. The relay
        address may not match the subnet in certain deployments. This
        usually means that there is more than one subnet allocated for a given
        link. Two most common examples where this is the case are long lasting
        network renumbering (where both old and new address space is still being
        used) and a cable network. In a cable network both cable modems and the
        devices behind them are physically connected to the same link, yet
        they use distinct addressing. In such case, the DHCPv6 server needs
        additional information (like the value of interface-id option or IPv6
        address inserted in the link-addr field in RELAY-FORW message) to
        properly select an appropriate subnet.
      </para>
      <para>
        The following example assumes that there is a subnet 2001:db8:1::/64
        that is accessible via relay that uses 3000::1 as its IPv6 address.
        The server will be able to select this subnet for any incoming packets
        that came from a relay that has an address in 2001:db8:1::/64 subnet.
        It will also select that subnet for a relay with address 3000::1.
        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "2001:db8:1::2 - 2001:db8:1::ffff" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/relay/ip-address "3000::1"</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>

    </section>

      <section id="dhcp6-client-class-relay">
        <title>Segregating IPv6 clients in a cable network</title>
        <para>
          In certain cases, it is useful to mix relay address information,
          introduced in <xref linkend="dhcp6-relay-override"/> with client
          classification, explained in <xref linkend="dhcp6-subnet-class"/>.
          One specific example is cable network, where typically modems
          get addresses from a different subnet than all devices connected
          behind them.
        </para>
        <para>
          Let's assume that there is one CMTS (Cable Modem Termination System)
          with one CM MAC (a physical link that modems are connected to).
          We want the modems to get addresses from the 3000::/64 subnet,
          while everything connected behind modems should get addresses from
          another subnet (2001:db8:1::/64). The CMTS that acts as a relay
          an uses address 3000::1. The following configuration can serve
          that configuration:
        <screen>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/subnet "3000::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/pool [ "3000::2 - 3000::ffff" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/client-class "docsis3.0"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[0]/relay/ip-address "3000::1"</userinput>
&gt; <userinput>config add Dhcp6/subnet6</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/subnet "2001:db8:1::/64"</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/pool [ "2001:db8:1::1 - 2001:db8:1::ffff" ]</userinput>
&gt; <userinput>config set Dhcp6/subnet6[1]/relay/ip-address "3000::1"</userinput>
&gt; <userinput>config commit</userinput></screen>
      </para>
      </section>


    <section id="dhcp6-std">
      <title>Supported Standards</title>
      <para>The following standards and draft standards are currently
      supported:</para>
      <itemizedlist>
          <listitem>
            <simpara><ulink url="http://tools.ietf.org/html/rfc3315">RFC 3315</ulink>: Supported messages are SOLICIT,
            ADVERTISE, REQUEST, RELEASE, RENEW, REBIND, CONFIRM and REPLY.</simpara>
          </listitem>
          <listitem>
            <simpara><ulink url="http://tools.ietf.org/html/rfc3633">RFC 3633</ulink>: Supported options are IA_PD and
            IA_PREFIX. Also supported is the status code NoPrefixAvail.</simpara>
          </listitem>
          <listitem>
            <simpara><ulink url="http://tools.ietf.org/html/rfc3646">RFC 3646</ulink>: Supported option is DNS_SERVERS.</simpara>
          </listitem>
          <listitem>
            <simpara><ulink url="http://tools.ietf.org/html/rfc4704">RFC 4704</ulink>: Supported option is CLIENT_FQDN.</simpara>
          </listitem>
      </itemizedlist>
    </section>

    <section id="dhcp6-limit">
      <title>DHCPv6 Server Limitations</title>
      <para> These are the current limitations and known problems
      with the DHCPv6 server
      software. Most of them are reflections of the early stage of
      development and should be treated as <quote>not implemented
      yet</quote>, rather than actual limitations.</para>
      <itemizedlist>
          <listitem> <!-- see tickets #3234, #3281 -->
            <para>
              On-line configuration has some limitations. Adding new subnets or
              modifying existing ones work, as is removing the last subnet from
              the list. However, removing non-last (e.g. removing subnet 1,2 or 3 if
              there are 4 subnets configured) will cause issues. The problem is
              caused by simplistic subnet-id assignment. The subnets are always
              numbered, starting from 1. That subnet-id is then used in leases
              that are stored in the lease database. Removing non-last subnet will
              cause the configuration information to mismatch data in the lease
              database. It is possible to manually update subnet-id fields in
              MySQL or PostgreSQL database, but it is awkward and error prone
              process. A better reconfiguration support is planned.
            </para>
          </listitem>

        <listitem>
          <para>
            On startup, the DHCPv6 server does not get the full configuration from
            BIND 10.  To remedy this, after starting BIND 10, modify any parameter
            and commit the changes, e.g.
            <screen>
&gt; <userinput>config show Dhcp6/renew-timer</userinput>
Dhcp6/renew-timer	1000	integer	(default)
&gt; <userinput>config set Dhcp6/renew-timer 1001</userinput>
&gt; <userinput>config commit</userinput></screen>
          </para>
        </listitem>
        <listitem>
          <simpara>Temporary addresses are not supported.</simpara>
        </listitem>
        <listitem>
          <simpara>
            The server will allocate, renew or rebind a maximum of one lease
            for a particular IA option (IA_NA or IA_PD) sent by a client.
            <ulink url="http://tools.ietf.org/html/rfc3315">RFC 3315</ulink> and
            <ulink url="http://tools.ietf.org/html/rfc3633">RFC 3633</ulink> allow
            for multiple addresses or prefixes to be allocated for a single IA.
          </simpara>
        </listitem>
        <listitem>
          <simpara>Temporary addresses are not supported.</simpara>
        </listitem>
        <listitem>
          <simpara>
            Duplication report (DECLINE), stateless configuration
            (INFORMATION-REQUEST) and client reconfiguration (RECONFIGURE) are
            not yet supported.
          </simpara>
        </listitem>
          <listitem>
            <simpara>
              The server doesn't act upon expired leases. In particular,
              when a lease expires, the server doesn't request removal of
              the DNS records associated with it.
            </simpara>
          </listitem>
      </itemizedlist>
    </section>

    <!--
    <section id="dhcp6-srv-examples">
      <title>Kea DHCPv6 server examples</title>

      <para>
        This section provides easy to use example. Each example can be read
        separately. It is not intended to be read sequentially as there will
        be many repetitions between examples. They are expected to serve as
        easy to use copy-paste solutions to many common deployments.
      </para>

      @todo: add simple configuration for direct clients
      @todo: add configuration for relayed clients
      @todo: add client classification example

    </section> -->

  </chapter>
