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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY mdash  "&#x2014;" >
]>

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

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

      <para>
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      It is recommended that the Kea DHCPv6 server be started and stopped
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      using <command>keactrl</command> (described in <xref linkend="keactrl"/>).
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      However, it is also possible to run the server directly: it accepts
      the following command-line switches:
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      </para>

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      <itemizedlist>
          <listitem>
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            <simpara>
            <command>-c <replaceable>file</replaceable></command> -
            specifies the configuration file. This is the only mandatory
            switch.</simpara>
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          </listitem>
          <listitem>
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            <simpara>
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            <command>-d</command> - specifies whether the server
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            logging should be switched to verbose mode. In verbose mode,
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            the logging severity and debuglevel specified in the configuration
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            file are ignored and "debug" severity and the maximum debuglevel
            (99) are assumed. The flag is convenient, for temporarily
            switching the server into maximum verbosity, e.g. when
            debugging.</simpara>
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          </listitem>
          <listitem>
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            <simpara>
            <command>-p <replaceable>port</replaceable></command> -
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            specifies UDP port on which the server will listen. This is only
            useful during testing, as a DHCPv6 server listening on
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            ports other than default DHCPv6 ports will not be able to
            handle regular DHCPv6 queries.</simpara>
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          </listitem>
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          <listitem>
            <simpara>
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              <command>-v</command> - prints out Kea version and exits.
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            </simpara>
          </listitem>
          <listitem>
            <simpara>
              <command>-V</command> - prints out Kea extended version with
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              additional parameters and exits.
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            </simpara>
          </listitem>
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          <listitem>
            <simpara>
              <command>-W</command> - prints out Kea configuration report
              and exits.
            </simpara>
          </listitem>
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      </itemizedlist>

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      <para>
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            The <command>-V</command> command returns the versions of the
            external libraries dynamically linked.
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      </para>

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      <para>
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            The <command>-W</command> command describes the environment used
            to build Kea.  This command displays a copy of the
            <filename>config.report</filename> file produced by
            <userinput>./configure</userinput> that is embedded in the
            executable binary.
      </para>

      <para>
            The <filename>config.report</filename> may also be accessed more
            directly.  The following command may be used to extract this
            information.  The binary <userinput>path</userinput> may be found
            in the install directory or in the <filename>.libs</filename>
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            subdirectory in the source treee. For example
            <filename>kea/src/bin/dhcp6/.libs/kea-dhcp6</filename>.

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<screen>
strings <userinput>path</userinput>/kea-dhcp6 | sed -n 's/;;;; //p'
</screen>
      </para>

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      <para>
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            When running in a console, the server can be shut down by
            pressing ctrl-c. It detects the key combination and shuts
            down gracefully.
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      </para>

      <para>
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        On start-up, the server will detect available network interfaces
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        and will attempt to open UDP sockets on all interfaces
        mentioned in the configuration file.
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      </para>

      <para>
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        Since the DHCPv6 server opens privileged ports, it requires root
        access. Make sure you run this daemon as root.
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      </para>

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      <para>
        During startup the server will attempt to create a PID file of the
        form: [localstatedir]/[conf name].kea-dhcp6.pid
        where:
        <itemizedlist>
            <listitem>
            <simpara><command>localstatedir</command>: The value as passed into the
            build configure script. It defaults defaults to "/usr/local/var".  Note
            that this value may be overridden at run time by setting the environment
            variable KEA_PIDFILE_DIR.  This is intended primarily for testing purposes.
            </simpara>
            </listitem>
            <listitem>
            <simpara><command>conf name</command>: The confguration file name
            used to start the server, minus all preceding path and file extension.
            For example, given a pathname of "/usr/local/etc/kea/myconf.txt", the
            portion used would be "myconf".
            </simpara>
            </listitem>
        </itemizedlist>
        If the file already exists and contains the PID of a live process,
        the server will issue a DHCP6_ALREADY_RUNNING log message and exit. It
        is possible, though unlikely, that the file is a remnant of a system crash
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        and the process to which the PID belongs is unrelated to Kea.  In such a
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        case it would be necessary to manually delete the PID file.
      </para>
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    </section>

    <section id="dhcp6-configuration">
      <title>DHCPv6 Server Configuration</title>
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<section>
  <title>Introduction</title>
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      <para>
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        This section explains how to configure the DHCPv6 server using the
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        Kea configuration backend. (Kea configuration using any other
        backends is outside of scope of this document.) Before DHCPv6
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        is started, its configuration file has to be created. The
        basic configuration looks as follows:
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<screen>
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{
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# DHCPv6 configuration starts on the next line
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"Dhcp6": {

# First we set up global values
    "renew-timer": 1000,
    "rebind-timer": 2000,
    "preferred-lifetime": 3000,
    "valid-lifetime": 4000,

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# Next we setup the interfaces to be used by the server.
    "interfaces-config": {
        "interfaces": [ "eth0" ]
    },

# And we specify the type of a lease database
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    "lease-database": {
        "type": "memfile",
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        "persist": true,
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        "name": "/var/kea/dhcp6.leases"
    },

# Finally, we list the subnets from which we will be leasing addresses.
    "subnet6": [
        {
            "subnet": "2001:db8:1::/64",
            "pools": [
                 {
                     "pool": "2001:db8:1::1-2001:db8:1::ffff"
                 }
             ]
        }
    ]
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# DHCPv6 configuration ends with the next line
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}

} </screen>
</para>

<para>The following paragraphs provide a brief overview of the parameters in
the above example and
their format. Subsequent sections of this chapter go into much greater detail
for these and other parameters.</para>

<para>The lines starting with a hash (#) are comments and are ignored by
the server; they do not impact its
operation in any way.</para>

<para>The configuration starts in the first line with the initial
opening curly bracket (or brace). Each configuration consists of
one or more objects. In this specific example, we have only one
object called Dhcp6. This is a simplified configuration, as usually
there will be additional objects, like <command>Logging</command> or
<command>DhcpDns</command>, but we omit them now for clarity. The Dhcp6
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configuration starts with the <command>"Dhcp6": {</command> line
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and ends with the corresponding closing brace (in the above example,
the brace after the last comment).  Everything defined between those
lines is considered to be the Dhcp6 configuration.</para>

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<para>In the general case, the order in which those parameters appear does not
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matter. There are two caveats here though. The first one is to remember that
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the configuration file must be well formed JSON. That means that parameters
for any given scope must be separated by a comma and there must not be a comma
after the last parameter. When reordering a configuration file, keep in mind that
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moving a parameter to or from the last position in a given scope may require
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moving the comma as well. The second caveat is that it is uncommon &mdash; although
legal JSON &mdash; to
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repeat the same parameter multiple times. If that happens, the last occurrence of a
given parameter in a given scope is used while all previous instances are
ignored. This is unlikely to cause any confusion as there are no real life
reasons to keep multiple copies of the same parameter in your configuration
file.</para>

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<para>Moving onto the DHCPv6 configuration elements, the very first few elements
define some global parameters. <command>valid-lifetime</command>
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defines for how long the addresses (leases) given out by the server are valid. If
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nothing changes, a client that got an address is allowed to use it for 4000
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seconds. (Note that integer numbers are specified as is, without any quotes
around them.) The address will become deprecated in 3000 seconds (clients are
allowed to keep old connections, but can't use this address for creating new
connections). <command>renew-timer</command> and <command>
rebind-timer</command> are values that define T1 and T2 timers that govern when
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the client will begin the renewal and rebind procedures.</para>
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<para>The <command>interfaces-config</command> map specifies the server
configuration concerning the network interfaces, on which the server should
listen to the DHCP messages. The <command>interfaces</command> parameter
specifies a list of network interfaces on which the server should listen.
Lists are opened and closed with square brackets, with elements separated
by commas. Had we wanted to listen on two interfaces, the
<command>interfaces-config</command> would look like this:
<screen>
"interfaces-config": {
    "interfaces": [ "eth0", "eth1" ]
},
</screen>
</para>

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<para>The next couple of lines define the lease database, the place where the server
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stores its lease information. This particular example tells the server to use
<command>memfile</command>, which is the simplest (and fastest) database
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backend. It uses an in-memory database and stores leases on disk in a CSV
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file. This is a very simple configuration. Usually, lease database configuration
is more extensive and contains additional parameters.  Note that
<command>lease-database</command>
is an object and opens up a new scope, using an opening brace.
Its parameters (just one in this example -- <command>type</command>)
follow. Had there been more than one, they would be separated by commas. This
scope is closed with a closing brace. As more parameters follow, a trailing
comma is present.</para>

<para>Finally, we need to define a list of IPv6 subnets. This is the
most important DHCPv6 configuration structure as the server uses that
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information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
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specified with the <command>subnet6</command> parameter.  It is a list,
so it starts and ends with square brackets.  Each subnet definition in
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the list has several attributes associated with it, so it is a structure
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and is opened and closed with braces. At minimum, a subnet definition
has to have at least two parameters: <command>subnet</command> (that
defines the whole subnet) and <command>pool</command> (which is a list of
dynamically allocated pools that are governed by the DHCP server).</para>

<para>The example contains a single subnet. Had more than one been defined,
additional elements
in the <command>subnet6</command> parameter would be specified and
separated by commas. For example, to define two subnets, the following
syntax would be used:
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<screen>
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"subnet6": [
    {
        "pools": [
        {
            "pool": "2001:db8:1::/112"
        }
        ],
        "subnet": "2001:db8:1::/64"
    },
    {
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        "pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
        "subnet": "2001:db8:2::/64",
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        "interface": "eth0"
    }
]
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</screen>
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Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
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</para>
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<para>After all parameters are specified, we have two contexts open:
global and Dhcp6, hence we need two closing curly brackets to close them.
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In a real life configuration file there most likely would be additional
components defined such as Logging or DhcpDdns, so the closing brace would
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be followed by a comma and another object definition.</para>

</section>

<section>
  <title>Lease Storage</title>
  <para>All leases issued by the server are stored in the lease database.
  Currently there are three database backends available:
  memfile (which is the default backend), MySQL and PostgreSQL.</para>
<section>
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  <title>Memfile, Basic Storage for Leases</title>
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  <para>The server is able to store lease data in different repositories. Larger
  deployments may elect to store leases in a database. <xref
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  linkend="database-configuration6"/> describes this option. In typical
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  smaller deployments though, the server will use a CSV file rather than a database to
  store lease information. As well as requiring less administration, an
  advantage of using a file for storage is that it
  eliminates a dependency on third-party database software.</para>

  <para>The configuration of the file backend (Memfile) is controlled through
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  the Dhcp6/lease-database parameters. The <command>type</command> parameter
  is mandatory and it specifies which storage for leases the server should use.
  The value of <userinput>"memfile"</userinput> indicates that the file should
  be used as the storage. The following list presents the remaining, not mandatory
  parameters, which can be used to configure the Memfile backend.

  <itemizedlist>
    <listitem>
      <simpara><command>persist</command>: controls whether the new leases and
      updates to existing leases are written to the file. It is strongly
      recommended that the value of this parameter is set to
      <userinput>true</userinput> at all times, during the server's normal
      operation. Not writing leases to disk will mean that if a server is restarted
      (e.g. after a power failure), it will not know what addresses have been
      assigned.  As a result, it may hand out addresses to new clients that are
      already in use. The value of <userinput>false</userinput> is mostly useful
      for performance testing purposes. The default value of the
      <command>persist</command> parameter is <userinput>true</userinput>,
      which enables writing lease updates
      to the lease file.
      </simpara>
    </listitem>

    <listitem>
      <simpara><command>name</command>: specifies an absolute location of the lease
      file in which new leases and lease updates will be recorded. The default value
      for this parameter is <userinput>"[kea-install-dir]/var/kea/kea-leases6.csv"
      </userinput>.</simpara>
    </listitem>

    <listitem>
      <simpara><command>lfc-interval</command>: specifies the interval in seconds, at
      which the server (Memfile backend) will perform a lease file cleanup (LFC),
      which removes the redundant (historical) information from the lease file
      and effectively reduces the lease file size. The cleanup process is described
      in more detailed fashion further in this section. The default value of the
      <command>lfc-interval</command> is <userinput>0</userinput>, which disables
      the LFC.</simpara>
    </listitem>

  </itemizedlist>
  </para>

  <para>The example configuration of the Memfile backend is presented below:
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<screen>
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"Dhcp6": {
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    "lease-database": {
        <userinput>"type": "memfile"</userinput>,
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        <userinput>"persist": true</userinput>,
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        <userinput>"name": "/tmp/kea-leases6.csv"</userinput>,
        <userinput>"lfc-interval": 1800</userinput>
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    }
}
</screen>
  </para>

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  <para>It is important to know how the lease file contents are organized
  to understand why the periodic lease file cleanup is needed. Every time when
  the server updates a lease or creates a new lease for the client, the new
  lease information must be recorded in the lease file. For performance reasons,
  the server does not supersede the existing client's lease, as it would require
  the lookup of the specific lease entry, but simply appends the new lease
  information at the end of the lease file. The previous lease entries for the
  client are not removed. When the server loads leases from the lease file, e.g.
  at the server startup, it assumes that the latest lease entry for the client
  is the valid one. The previous entries are discarded. This means that the
  server can re-construct the accurate information about the leases even though
  there may be many lease entries for each client. However, storing many entries
  for each client results in bloated lease file and impairs the performance of
  the server's startup and reconfiguration, as it needs to process larger number
  of lease entries.
  </para>

  <para>The lease file cleanup removes all previous entries for each client and
  leaves only the latest ones. The interval at which the cleanup is performed
  is configurable, and it should be selected according to the frequency of lease
  renewals initiated by the clients. The more frequent renewals are, the lesser
  value of the <command>lfc-interval</command> should be. Note however, that the
  LFC takes time and thus it is possible (although unlikely) that new cleanup
  is started while the previous cleanup instance is still running, if the
  <command>lfc-interval</command> is too short. The server would recover from
  this by skipping the new cleanup when it detects that the previous cleanup
  is still in progress. But, this implies that the actual cleanups will be
  triggered more rarely than configured. Moreover, triggering a new cleanup
  adds an overhead to the server, which will not be able to respond to new
  requests for a short period of time when the new cleanup process is spawned.
  Therefore, it is recommended that the <command>lfc-interval</command> value
  is selected in a way that would allow for completing the cleanup before the
  new cleanup is triggered.
  </para>

  <para>The LFC is performed by a separate process (in background) to avoid
  performance impact on the server process. In order to avoid the conflicts
  between the two processes both using the same lease files, the LFC process
  operates on the copy of the original lease file, rather than on the lease
  file used by the server to record lease updates. There are also other files
  being created as a side effect of the lease file cleanup. The detailed
  description of the LFC is located on the Kea wiki:
  <ulink url="http://kea.isc.org/wiki/LFCDesign"/>.
  </para>
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</section>

<section id="database-configuration6">
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  <title>Lease Database Configuration</title>
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  <note>
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    <para>Lease database access information must be configured for the DHCPv6 server,
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    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>

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  <para>Lease database configuration is controlled through the
  Dhcp6/lease-database parameters. The type of the database must be set to
  "memfile", "mysql" or "postgresql", e.g.
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<screen>
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"Dhcp6": { "lease-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
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</screen>
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  Next, the name of the database is to hold the leases must be set: this is the
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  name used when the lease database was created (see <xref linkend="mysql-database-create"/>
  or <xref linkend="pgsql-database-create"/>).
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<screen>
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"Dhcp6": { "lease-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
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</screen>
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  If the database is located on a different system than the DHCPv6 server, the
  database host name must also be specified (although it should be noted that this
  configuration may have a severe impact on server performance):
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<screen>
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"Dhcp6": { "lease-database": { <userinput>"host": <replaceable>remote-host-name</replaceable></userinput>, ... }, ... }
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</screen>
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  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:
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<screen>
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"Dhcp6": { "lease-database": { <userinput>"host" : ""</userinput>, ... }, ... }
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</screen>
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  </para>
  <para>Finally, the credentials of the account under which the server will
  access the database should be set:
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<screen>
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"Dhcp6": { "lease-database": { <userinput>"user": "<replaceable>user-name</replaceable>"</userinput>,
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                               <userinput>"password": "<replaceable>password</replaceable>"</userinput>,
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                              ... },
           ... }
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</screen>
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  If there is no password to the account, set the password to the empty string
  "". (This is also the default.)</para>
</section>
</section>
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<!-- Uncomment this once 4212 is merged. While the host storage for
     MySQL is there, it is able to store hosts, but not IPv6
     reservations. So technically we have host reservations for v6 in
     MySQL, but in practice it's kinda useless right now as it can't
     store addresses or prefixes. Let's keep it commented out until
     we implement that functionality -->

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<section>
  <title>Hosts Storage</title>
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    <note>
      <para>This feature did not undergo the regular system level
      testing conducted by ISC. As such, please treat it as
      experimental.</para>
    </note>

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    <para>Kea is also able to store information about host reservations in the
    database. Hosts database configuration uses the same syntax as lease
    database. In fact, Kea server opens independent connections for each
    purpose, be it lease or hosts information. This gives the solution most
    flexibility. Kea can be used to keep leases and host reservations
    separately, but can also point to the same database. Currently the only
    supported hosts database type is MySQL.</para>

    <para>Please note that usage of hosts storage is optional. User can define
    all host reservations in the configuration file. That is the recommended way
    if the number of reservations is small. However, with the number of
    reservations growing it's more convenient to use host storage. Please note
    that both storages (configuration file and MySQL) can be used together. If
    hosts are defined in both places, the definitions from configuration file
    are checked first and external storage is checked later, if
    necessary.</para>

    <para>All hosts leases issued by the server are stored in the hosts
    database. Currently there is only one available backend: MySQL. Other host
    backends will become available in future Kea versions.</para>

<section id="hosts-database-configuration6">
  <title>IPv6 Hosts Database Configuration</title>

  <para>Hosts database configuration is controlled through the Dhcp6/hosts-database
  parameters. If enabled, the type of the database must be set to "mysql". Other
  hosts backends may be added in later Kea versions.
<screen>
"Dhcp6": { "hosts-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
</screen>
  Next, the name of the database to hold the leases must be set: this is the
  name used when the lease database was created (see <xref linkend="mysql-database-create"/>).
<screen>
"Dhcp6": { "hosts-database": { <userinput>"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 it should be noted that this
  configuration may have a severe impact on server performance):
<screen>
"Dhcp6": { "hosts-database": { <userinput>"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:
<screen>
"Dhcp6": { "hosts-database": { <userinput>"host" : ""</userinput>, ... }, ... }
</screen>
  </para>
  <para>Finally, the credentials of the account under which the server will
  access the database should be set:
<screen>
"Dhcp6": { "hosts-database": { <userinput>"user": "<replaceable>user-name</replaceable>"</userinput>,
                               <userinput>"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>
</section>
</section>
-->


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<section id="dhcp6-interface-selection">
  <title>Interface selection</title>
  <para>The DHCPv6 server has to be configured to listen on specific network
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  interfaces.  The simplest network interface configuration instructs the server to
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  listen on all available interfaces:
  <screen>
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"Dhcp6": {
    "interfaces-config": {
        "interfaces": [ <userinput>"*"</userinput> ]
    }
    ...
}
</screen>
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  The asterisk plays the role of a wildcard and means "listen on all interfaces".
  However, it is usually a good idea to explicitly specify interface names:
  <screen>
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"Dhcp6": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3"</userinput> ]
    },
    ...
}
  </screen>
</para>
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  <para>It is possible to use wildcard interface name (asterisk) concurrently
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  with the actual interface names:
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  <screen>
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"Dhcp6": {
    "interfaces-config": {
        "interfaces": [ <userinput>"eth1", "eth3", "*"</userinput> ]
    },
    ...
}
  </screen>
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It is anticipated that this will form of usage only be used where it is desired to
temporarily override a list of interface names and listen on all interfaces.
  </para>
</section>
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    <section id="ipv6-subnet-id">
      <title>IPv6 Subnet Identifier</title>
      <para>
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        The subnet identifier is a unique number associated with a particular subnet.
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        In principle, it is used to associate clients' leases with respective subnets.
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        When the subnet identifier is not specified for a subnet being configured, it will
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        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:
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       if there are four subnets and the third is removed the last subnet will be assigned
       the identifier that the third subnet had before removal. As a result, the leases
       stored in the lease database for subnet 3 are now associated with
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       subnet 4, which may have unexpected consequences. In the future it is planned
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       to implement a mechanism to preserve auto-generated subnet ids upon removal
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       of one of the subnets. Currently, the only remedy for this issue is to
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       manually specify a unique subnet identifier for each subnet.
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      </para>
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      <para>
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        The following configuration will assign the specified subnet
        identifier to the newly configured subnet:
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        <screen>
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"Dhcp6": {
    "subnet6": [
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        {
            "subnet": "2001:db8:1::/64",
            <userinput>"id": 1024</userinput>,
            ...
        }
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    ]
}
</screen>
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        This identifier will not change for this subnet unless the "id" parameter is
        removed or set to 0. The value of 0 forces auto-generation of the subnet
        identifier.
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      </para>
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      <!-- @todo: describe whether database needs to be updated after changing
      id -->
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    </section>

    <section id="dhcp6-unicast">
      <title>Unicast traffic support</title>
      <para>
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        When the DHCPv6 server starts, by default it listens to the DHCP traffic
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        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
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        directly. To configure the server to listen on a specific unicast address, the
        notation to specify interfaces has been extended.  An interface name can be
        optionally followed by a slash, followed by the global unicast address on which
        the server should listen. This will be done in addition to normal
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        link-local binding + listening on ff02::1:2 address. The sample configuration
        below shows how to listen on 2001:db8::1 (a global address)
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        configured on the eth1 interface.
      </para>
      <para>
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 <screen>
"Dhcp6": {
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    "interfaces-config": {
        "interfaces": [ <userinput>"eth1/2001:db8::1"</userinput> ]
    },
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    ...
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}
 </screen>
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        This configuration will cause the server to listen on
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        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
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        on the list of interfaces. It is not possible to specify more than one
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        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.
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        This approach is selected on purpose, so the software can be used to
        communicate over uncommon addresses if the administrator so desires.
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      </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>
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"Dhcp6": {
    <userinput>"subnet6": [
       {
           "subnet": "2001:db8:1::/64",
           "pools": [
               {
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                   "pool": "2001:db8:1::1-2001:db8:1::ffff"
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               }
           ],
           ...
       }
    ]</userinput>
}</screen>

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        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>
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        <para>Each <command>pool</command> is a structure that contains the
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        parameters that describe a single pool. Currently there is only one
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        parameter, <command>pool</command>, which gives the range of addresses
        in the pool. Additional parameters will be added in future releases of
        Kea.</para>

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        <para>It is possible to define more than one pool in a
        subnet: continuing the previous example, further assume that
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        2001:db8:1:0:5::/80 should also be managed by the server. It could be written as
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        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>
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"Dhcp6": {
    <userinput>"subnet6": [
    {
        "subnet": "2001:db8:1::/64",
        "pools": [
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            { "pool": "2001:db8:1::1-2001:db8:1::ffff" },
            { "pool": "2001:db8:1:05::/80" }
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        ]</userinput>,
        ...
    }
    ]
}</screen>
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        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>
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"Dhcp6": {
    <userinput>"subnet6": [
    {
        "subnet": "2001:db8:1::/64",
        "pools": [
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            { "pool": "2001:db8:1::1-2001:db8:1::ffff" }
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        ]
    },
    {
        "subnet": "2001:db8:2::/64",
        "pools": [
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            { "pool": "2001:db8:2::/64" }
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        ]
    },
</userinput>
        ...
    ]
}</screen>
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        In this example, we allow the server to
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        dynamically assign all addresses available in the whole subnet. Although
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        rather wasteful, it is certainly a valid configuration to dedicate the
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        whole /64 subnet for that purpose. Note that the Kea server does not preallocate
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        the leases, so there is no danger in using gigantic address pools.
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      </para>
      <para>
        When configuring a DHCPv6 server using prefix/length notation, please pay
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        attention to the boundary values. When specifying that the server can use
        a given pool, it will also be able to allocate the first (typically network
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        address) address from that pool. For example for pool 2001:db8:2::/64 the
        2001:db8:2:: address may be assigned as well. If you want to avoid this,
        use the "min-max" notation.
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      </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>
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        Subnets may also be configured to delegate prefixes, as defined in
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            <ulink url="http://tools.ietf.org/html/rfc3633">RFC 3633</ulink>.
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        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,
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        as well as a delegated prefix length. <command>delegated-len</command>
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            must not be shorter (that is it must be numerically greater or equal)
            than <command>prefix-len</command>.
            If both <command>delegated-len</command>
            and <command>prefix-len</command> are equal, the server will be able to
            delegate only one prefix. The delegated <command>prefix</command> does
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        not have to match the <command>subnet</command> prefix.
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      </para>
      <para> Below is a sample subnet configuration which enables prefix
      delegation for the subnet:
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      <screen>
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"Dhcp6": {
    "subnet6": [
        {
            "subnet": "2001:d8b:1::/64",
            <userinput>"pd-pools": [
                {
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                    "prefix": "3000:1::",
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                    "prefix-len": 64,
                    "delegated-len": 96
                }
            ]</userinput>
        }
    ],
    ...
}</screen>
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      </para>
    </section>

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

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

    <para>
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      Options can also be configured as hexadecimal values.  If "csv-format" is
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      set to false, the option data must be specified as a string of hexadecimal
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      numbers.  The
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      following commands configure the DNS-SERVERS option for all
      subnets with the following addresses: 2001:db8:1::cafe and
      2001:db8:1::babe.
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        <screen>
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"Dhcp6": {
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    "option-data": [
        {
           <userinput>"name": "dns-servers",
           "code": 23,
           "space": "dhcp6",
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           "csv-format": false,
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           "data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
                    2001 0DB8 0001 0000 0000 0000 0000 BABE"</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
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       whole string should be entered on the same line.  Care should be taken
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       to use proper encoding when using hexadecimal format as Kea's ability
       to validate data correctness in hexadecimal is limited.
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      </para>

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      <para>
        Most of the parameters in the "option-data" structure are optional and
        can be omitted in some circumstances as discussed in the
        <xref linkend="dhcp6-option-data-defaults"/>.
      </para>


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    <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.
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<screen>
"Dhcp6": {
    "subnet6": [
        {
            <userinput>"option-data": [
                {
                    "name": "dns-servers",
                    "code": 23,
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Jeremy C. Reed committed
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                    "space": "dhcp6",
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                    "csv-format": true,
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                    "data": "2001:db8:1::3"
                },
                ...
            ]</userinput>,
            ...
        },
        ...
    ],
    ...
}
</screen>
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    </para>

    <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>
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    <para>
      Experimental options (like standard options but with a code
      which was not assigned by IANA) are listed in
      <xref linkend="dhcp6-exp-options-list"/>.
    </para>
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    <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
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      allows the specification of more than one IPv6 address, allowing
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      clients to obtain the addresses of multiple DNS servers.
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    </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
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        RFC but the configuration mechanism would allow any option format as it has
        no means to validate the format at the moment.
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      </para>


    <para>
      <table frame="all" id="dhcp6-std-options-list">
        <title>List of standard DHCPv6 options</title>
        <tgroup cols='4'>
        <colspec colname='name'/>
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        <colspec colname='code' align='center'/>
        <colspec colname='type' align='center'/>
        <colspec colname='array' align='center'/>
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        <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>
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-->
<!-- Vendor-specific Information is configurable by the administrator -->
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<row><entry>vendor-opts</entry><entry>17</entry><entry>uint32</entry><entry>false</entry></row>
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<!--
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<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> -->
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-->
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<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>
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<row><entry>geoconf-civic</entry><entry>36</entry><entry>record (uint8, uint16, binary)</entry><entry>false</entry></row>
<row><entry>remote-id</entry><entry>37</entry><entry>record (uint32, binary)</entry><entry>false</entry></row>
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<row><entry>subscriber-id</entry><entry>38</entry><entry>binary</entry><entry>false</entry></row>
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<row><entry>client-fqdn</entry><entry>39</entry><entry>record (uint8, fqdn)</entry><entry>false</entry></row>
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<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>
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<row><entry>lq-query</entry><entry>44</entry><entry>record (uint8, ipv6-address)</entry><entry>false</entry></row>
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<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>
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<row><entry>lq-relay-data</entry><entry>47</entry><entry>record (ipv6-address, binary)</entry><entry>false</entry></row>
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<row><entry>lq-client-link</entry><entry>48</entry><entry>ipv6-address</entry><entry>true</entry></row>
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<row><entry>bootfile-url</entry><entry>59</entry><entry>string</entry><entry>false</entry></row>
<row><entry>bootfile-param</entry><entry>60</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>client-arch-type</entry><entry>61</entry><entry>uint16</entry><entry>true</entry></row>
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<row><entry>nii</entry><entry>62</entry><entry>record (uint8, uint8, uint8)</entry><entry>false</entry></row>
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<row><entry>erp-local-domain-name</entry><entry>65</entry><entry>fqdn</entry><entry>false</entry></row>
<row><entry>rsoo</entry><entry>66</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>client-linklayer-addr</entry><entry>79</entry><entry>binary</entry><entry>false</entry></row>
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<!-- <row><entry>dhcpv4-message</entry><entry>87</entry><entry>binary</entry><entry>false</entry></row> -->
<row><entry>dhcp4o6-server-addr</entry><entry>88</entry><entry>ipv6-address</entry><entry>true</entry></row>
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        </tbody>
        </tgroup>
      </table>
    </para>
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    <para>
      <table frame="all" id="dhcp6-exp-options-list">
        <title>List of experimental DHCPv6 options</title>
        <tgroup cols='4'>
        <colspec colname='name'/>
        <colspec colname='code' align='center'/>
        <colspec colname='type' align='center'/>
        <colspec colname='array' align='center'/>
        <thead>
          <row><entry>Name</entry><entry>Code</entry><entry>Type</entry><entry>Array?</entry></row>
        </thead>
        <tbody>
<row><entry>public-key</entry><entry>701</entry><entry>binary</entry><entry>false</entry></row>
<row><entry>certificate</entry><entry>702</entry><entry>binary</entry><entry>false</entry></row>
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<row><entry>signature</entry><entry>703</entry><entry>record (uint8, uint8, binary)</entry><entry>false</entry></row>
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<row><entry>timestamp</entry><entry>704</entry><entry>binary</entry><entry>false</entry></row>
        </tbody>
        </tgroup>
      </table>
    </para>
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    </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:
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<screen>
"Dhcp6": {
    "option-def": [
        {
            <userinput>"name": "foo",
            "code": 100,
            "type": "uint32",
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            "array": false,
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            "record-types": "",
            "space": "dhcp6",
            "encapsulate": ""</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".
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      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
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      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.
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      </para>
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      <para>The <command>name</command>, <command>code</command> and
      <command>type</command> parameters are required, all others are
      optional. The <command>array</command> default value is
      <command>false</command>. The <command>record-types</command>
      and <command>encapsulate</command> default values are blank
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      (i.e. ""). The default <command>space</command> is "dhcp6".
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      </para>

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      <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.
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<screen>
"Dhcp6": {
    "option-data": [
        {
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            <userinput>"name": "foo",
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            "code": 100,
            "space": "dhcp6",
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            "csv-format": true,
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            "data": "12345"</userinput>
        }, ...
    ],
    ...
}
</screen>
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      </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>
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"Dhcp6": {
    "option-def": [
        {
            <userinput>"name": "bar",
            "code": 101,
            "space": "dhcp6",
            "type": "record",
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            "array": false,
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            "record-types": "ipv6-address, uint16, boolean, string",
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            "encapsulate": ""</userinput>
        }, ...
    ],
    ...
}
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</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>
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"Dhcp6": {
    "option-data": [
        {
            <userinput>"name": "bar",
            "space": "dhcp6",
            "code": 101,
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            "csv-format": true,
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            "data": "2001:db8:1::10, 123, false, Hello World"</userinput>
        }
    ],
    ...
}</screen>
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      <command>csv-format</command> is set <command>true</command> to indicate
      that the <command>data</command> field comprises a command-separated list
      of values.  The values in the "data" must correspond to the types set in
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      the "record-types" field of the option definition.
      </para>
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      <note>
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       <para>In the general case, boolean values are specified as <command>true</command> or
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       <command>false</command>, without quotes. Some specific boolean parameters may
       accept also <command>"true"</command>, <command>"false"</command>,
       <command>0</command>, <command>1</command>, <command>"0"</command> and
       <command>"1"</command>. Future Kea versions will accept all those values
       for all boolean parameters.</para>
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      </note>