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-
- This Source Code Form is subject to the terms of the Mozilla Public
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<!-- Converted by db4-upgrade version 1.1 -->
<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="dhcp6">
<title>The DHCPv6 Server</title>
<section xml:id="dhcp6-start-stop">
<title>Starting and Stopping the DHCPv6 Server</title>
<para>
It is recommended that the Kea DHCPv6 server be started and stopped
using <command>keactrl</command> (described in <xref linkend="keactrl"/>).
However, it is also possible to run the server directly: it accepts
the following command-line switches:
</para>
<itemizedlist>
<listitem>
<simpara>
<command>-c <replaceable>file</replaceable></command> -
specifies the configuration file. This is the only mandatory
switch.</simpara>
</listitem>
<listitem>
<simpara>
<command>-d</command> - specifies whether the server
logging should be switched to verbose mode. In verbose mode,
the logging severity and debuglevel specified in the configuration
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>
</listitem>
<listitem>
<simpara>
<command>-p <replaceable>port</replaceable></command> -
specifies UDP port on which the server will listen. This is only
useful during testing, as a DHCPv6 server listening on
ports other than the standard ones will not be able to
handle regular DHCPv6 queries.</simpara>
</listitem>
<listitem>
<simpara>
<command>-t <replaceable>file</replaceable></command> -
specifies the configuration file to be tested. Kea-dhcp6
will attempt to load it, and will conduct sanity
checks. Note that certain checks are possible only while
running the actual server. The actual status is reported
with exit code (0 = configuration looks ok, 1 = error
encountered). Kea will print out log messages to standard
output and error to standard error when testing
configuration.</simpara>
</listitem>
<listitem>
<simpara>
<command>-v</command> - prints out the Kea version and exits.
</simpara>
</listitem>
<listitem>
<simpara>
<command>-V</command> - prints out the Kea extended version with
additional parameters and exits. The listing includes the versions
of the libraries dynamically linked to Kea.
</simpara>
</listitem>
<listitem>
<simpara>
<command>-W</command> - prints out the Kea configuration report
and exits. The report is a copy of the
<filename>config.report</filename> file produced by
<userinput>./configure</userinput>: it is embedded in the
executable binary.
</simpara>
</listitem>
</itemizedlist>
<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>
subdirectory in the source tree. For example
<filename>kea/src/bin/dhcp6/.libs/kea-dhcp6</filename>.
<screen>
strings <userinput>path</userinput>/kea-dhcp6 | sed -n 's/;;;; //p'
</screen>
</para>
<para>
On start-up, the server will detect available network interfaces
and will attempt to open UDP sockets on all interfaces
mentioned in the configuration file.
Since the DHCPv6 server opens privileged ports, it requires root
access. Make sure you run this daemon as root.
</para>
<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 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 configuration 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
and the process to which the PID belongs is unrelated to Kea. In such a
case it would be necessary to manually delete the PID file.
</para>
<para>
The server can be stopped using the <command>kill</command> command.
When running in a console, the server can be shut down by
pressing ctrl-c. It detects the key combination and shuts
down gracefully.
</para>
</section>
<section xml:id="dhcp6-configuration">
<title>DHCPv6 Server Configuration</title>
<section>
<title>Introduction</title>
<para>
This section explains how to configure the DHCPv6 server using a
configuration file. Before DHCPv6 is started, its configuration
file has to be created. The basic configuration is as follows:
<screen>
{
# DHCPv6 configuration starts on the next line
"Dhcp6": {
# First we set up global values
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"preferred-lifetime": 3000,
# Next we setup the interfaces to be used by the server.
"interfaces-config": {
"interfaces": [ "eth0" ]
},
# And we specify the type of lease database
"lease-database": {
"type": "memfile",
"persist": true,
"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"
}
]
}
]
# DHCPv6 configuration ends with the next line
}
} </screen>
</para>
<para>The following paragraphs provide a brief overview of the parameters in
the above example together with
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 must contain an
object specifying the configuration of the Kea module using it.
In the example above this object is called <command>Dhcp6</command>.
</para>
<note>
<para>In the current Kea release it is possible to specify configurations
of multiple modules within a single configuration file, but this is not
recommended and support for it will be removed in the future releases. The
only object, besides the one specifying module configuration, which can
(and usually is) included in the same file is <command>Logging</command>.
However, we don't include this object in the example above for clarity.
</para>
</note>
<para>The Dhcp6 configuration starts with the <command>"Dhcp6": {</command> line
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>
<para>In the general case, the order in which those parameters appear does not
matter. There are two caveats here though. The first one is to remember that
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
moving a parameter to or from the last position in a given scope may also require
moving the comma. The second caveat is that it is uncommon — although
legal JSON — to
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>
<para>Moving onto the DHCPv6 configuration elements, the very first few elements
define some global parameters. <command>valid-lifetime</command>
defines for how long the addresses (leases) given out by the server are valid. If
nothing changes, a client that got an address is allowed to use it for 4000
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 the client will begin the renewal and rebind procedures.</para>
<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>
<para>The next couple of lines define the lease database, the place where the server
stores its lease information. This particular example tells the server to use
<command>memfile</command>, which is the simplest (and fastest) database
backend. It uses an in-memory database and stores leases on disk in a CSV
file. This is a very simple configuration. Usually the 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 for the Dhcp6 definition
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
information to process clients' requests. It defines all subnets from
which the server is expected to receive DHCP requests. The subnets are
specified with the <command>subnet6</command> parameter. It is a list,
so it starts and ends with square brackets. Each subnet definition in
the list has several attributes associated with it, so it is a structure
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>pools</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:
<screen>
"subnet6": [
{
"pools": [ { "pool": "2001:db8:1::/112" } ],
"subnet": "2001:db8:1::/64"
},
{
"pools": [ { "pool": "2001:db8:2::1-2001:db8:2::ffff" } ],
"subnet": "2001:db8:2::/64"
}
]
</screen>
Note that indentation is optional and is used for aesthetic purposes only.
In some cases in may be preferable to use more compact notation.
</para>
<para>After all parameters are specified, we have two contexts open:
global and Dhcp6, hence we need two closing curly brackets to close them.
In a real life configuration file there most likely would be additional
components defined such as Logging, so the closing brace would 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 four database backends available: memfile (which is the
default backend), MySQL, PostgreSQL and Cassandra.</para>
<section>
<title>Memfile - Basic 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 this option. In typical
smaller deployments though, the server will store lease information in a CSV file rather
than a database. 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
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 gives additional, optional,
parameters that 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 will perform a lease file cleanup (LFC). This
removes 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>3600</userinput>. A value of 0
disables the LFC.</simpara>
</listitem>
</itemizedlist>
</para>
<para>An example configuration of the Memfile backend is presented below:
<screen>
"Dhcp6": {
"lease-database": {
<userinput>"type": "memfile"</userinput>,
<userinput>"persist": true</userinput>,
<userinput>"name": "/tmp/kea-leases6.csv"</userinput>,
<userinput>"lfc-interval": 1800</userinput>
}
}
</screen>
This configuration selects the <filename>/tmp/kea-leases6.csv</filename> as
the storage for lease information and enables persistence (writing lease updates
to this file). It also configures the backend perform the periodic cleanup
of the lease files, executed every 30 minutes.
</para>
<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
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 update the existing client's lease in the file, as it would
potentially require rewriting the entire file. Instead, it simply appends the new lease
information to the end of the 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 a larger number
of lease entries.
</para>
<para>Lease file cleanup (LFC) 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 the renewals, the smaller
the value of <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 it 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 the LFC to complete the cleanup before a
new cleanup is triggered.
</para>
<para>Lease file cleanup is performed by a separate process (in background) to avoid
a performance impact on the server process. In order to avoid the conflicts
between 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 in the Kea Administrator's Reference Manual:
<uri xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://jenkins.isc.org/job/Kea_doc/guide/kea-guide.html#kea-lfc">https://jenkins.isc.org/job/Kea_doc/guide/kea-guide.html#kea-lfc</uri>.
</para>
</section>
<section xml:id="database-configuration6">
<title>Lease Database Configuration</title>
<note>
<para>Lease 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>Lease database configuration is controlled through the
Dhcp6/lease-database parameters. The type of the database must be set to
"memfile", "mysql", "postgresql" or "cql", e.g.
<screen>
"Dhcp6": { "lease-database": { <userinput>"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 database was created
(see <xref linkend="mysql-database-create"/>,
<xref linkend="pgsql-database-create"/>
or <xref linkend="cql-database-create"/>).
<screen>
"Dhcp6": { "lease-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
</screen>
For Cassandra:
<screen>
"Dhcp6": { "lease-database": { <userinput>"keyspace": "<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. (It should be noted that this
configuration may have a severe impact on server performance.):
<screen>
"Dhcp6": { "lease-database": { <userinput>"host": "<replaceable>remote-host-name</replaceable>"</userinput>, ... }, ... }
</screen>
For Cassandra, multiple contact points can be provided:
<screen>
"Dhcp6": { "lease-database": { <userinput>"contact-points": "<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": { "lease-database": { <userinput>"host" : ""</userinput>, ... }, ... }
</screen>
For Cassandra:
<screen>
"Dhcp6": { "lease-database": { <userinput>"contact-points": ""</userinput>, ... }, ... }
</screen>
Should the database use a port different than default, it may be
specified as well:
<screen>
"Dhcp6": { "lease-database": { <userinput>"port" : 12345</userinput>, ... }, ... }
</screen>
Should the database be located on a different system, you may need to specify a longer interval
for the connection timeout:
<screen>
"Dhcp6": { "lease-database": { <userinput>"connect-timeout" : <replaceable>timeout-in-seconds</replaceable></userinput>, ... }, ... }
</screen>
The default value of five seconds should be more than adequate for local connections.
If a timeout is given though, it should be an integer greater than zero.
</para>
<para>
The maxiumum number of times the server will automatically attempt to reconnect to
the lease database after connectivity has been lost may be specified:
<screen>
"Dhcp6": { "lease-database": { <userinput>"max-reconnect-tries" : <replaceable>number-of-tries</replaceable></userinput>, ... }, ... }
</screen>
If the server is unable to reconnect to the database after making the maximum number
of attempts the server will exit. A value of zero (the default) disables automatic
recovery and the server will exit immediately upon detecting a loss of connectivity
(MySQL and Postgres only).
</para>
<para>
The number of milliseconds the server will wait in between attempts to reconnect to the
lease database after connectivity has been lost may also be specified:
<screen>
"Dhcp6": { "lease-database": { <userinput>"reconnect-wait-time" : <replaceable>number-of-milliseconds</replaceable></userinput>, ... }, ... }
</screen>
The default value for MySQL and Postgres is 0, which disables automatic recovery and
causes the server to exit immediately upon detecting the loss of connectivity.
The default value for Cassandra is 2000 ms.
</para>
<note>
<para>
Automatic reconnect to database backends is configured individually per backend.
This allows you to tailor the recovery parameters to the each backend you use.
We do suggest that you either enable it for all backends or no backends so you
have consistent behavior. Losing connectivity to a backend for which reconnect
is disabled will result in the server shutting itself down. This includes the
cases when lease database backend and hosts database backend is connected to
the same database instance.
</para>
</note>
<para>
Note that host parameter is used by MySQL and PostgreSQL
backends. Cassandra has a concept of contact points that could be
used to contact the cluster, instead of a single IP or
hostname. It takes a list of comma separated IP addresses. This may be specified as:
<screen>
"Dhcp6": { "lease-database": { <userinput>"contact-points" : "192.0.2.1,192.0.2.2"</userinput>, ... }, ... }
</screen>
</para>
<para>Finally, the credentials of the account under which the server will
access the database should be set:
<screen>
"Dhcp6": { "lease-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 xml:id="cassandra-database-configuration6">
<title>Cassandra specific parameters</title>
<para>The parameters are the same for DHCPv4 and DHCPv6. See <xref
linkend="cassandra-database-configuration4"/> for details.</para>
</section>
</section>
<section xml:id="hosts6-storage">
<title>Hosts Storage</title>
<para>Kea is also able to store information about host reservations in the
database. The hosts database configuration uses the same syntax as the lease
database. In fact, a Kea server opens independent connections for each
purpose, be it lease or hosts information. This arrangement gives the most
flexibility. Kea can be used to keep leases and host reservations
separately, but can also point to the same database. Currently the
supported hosts database types are MySQL and PostgreSQL. The Cassandra
backend does not support host reservations yet.</para>
<para>Please note that usage of hosts storage is optional. A user can define
all host reservations in the configuration file. That is the recommended way
if the number of reservations is small. However, when the number of
reservations grows it's more convenient to use host storage. Please note
that both storage methods (configuration file and one of the supported databases)
can be used together. If hosts are defined in both places, the definitions
from the configuration file are checked first and external storage is checked
later, if necessary.</para>
<para>Version 1.4 extends the host storage to multiple storages. Operations
are performed on host storages in the configuration order with a special
case for addition: read-only storages must be configured after a
required read-write storage, or host reservation addition will
always fail.</para>
<section xml:id="hosts-databases-configuration6">
<title>DHCPv6 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" or
"postgresql". Other hosts backends may be added in later version of Kea.
<screen>
"Dhcp6": { "hosts-database": { <userinput>"type": "mysql"</userinput>, ... }, ... }
</screen>
Next, the name of the database to hold the reservations must be set: this is the
name used when the database was created (see <xref linkend="supported-databases"/>
for instructions how to setup desired database type).
<screen>
"Dhcp6": { "hosts-database": { <userinput>"name": "<replaceable>database-name</replaceable>" </userinput>, ... }, ... }
</screen>
If the database is located on a different system than the DHCPv6 server, the
database host name must also be specified. (Again 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>
<screen>
"Dhcp6": { "hosts-database": { <userinput>"port" : 12345</userinput>, ... }, ... }
</screen>
</para>
<para>
The maxiumum number of times the server will automatically attempt to reconnect to
the host database after connectivity has been lost may be specified:
<screen>
"Dhcp6": { "host-database": { <userinput>"max-reconnect-tries" : <replaceable>number-of-tries</replaceable></userinput>, ... }, ... }
</screen>
If the server is unable to reconnect to the database after making the maximum number
of attempts the server will exit. A value of zero (the default) disables automatic
recovery and the server will exit immediately upon detecting a loss of connectivity
(MySQL and Postgres only).
</para>
<para>
The number of milliseconds the server will wait in between attempts to reconnect to the
host database after connectivity has been lost may also be specified:
<screen>
"Dhcp6": { "hosts-database": { <userinput>"reconnect-wait-time" : <replaceable>number-of-milliseconds</replaceable></userinput>, ... }, ... }
</screen>
The default value for MySQL and Postgres is 0, which disables automatic recovery and
causes the server to exit immediately upon detecting the loss of connectivity.
The default value for Cassandra is 2000 ms.
</para>
<note>
<para>
Automatic reconnect to database backends is configured individually per backend.
This allows you to tailor the recovery parameters to the each backend you use.
We do suggest that you either enable it for all backends or no backends so you
have consistent behavior. Losing connectivity to a backend for which reconnect
is disabled will result in the server shutting itself down. This includes the
cases when lease database backend and hosts database backend is connected to
the same database instance.
</para>
</note>
<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>
<para>The multiple storage extension uses a similar syntax: a configuration
is placed into a "hosts-databases" list instead of into a "hosts-database"
entry as in:
<screen>
"Dhcp6": { "hosts-databases": [ { <userinput>"type": "mysql"</userinput>, ... }, ... ], ... }
</screen>
</para>
<para>
For additional Cassandra specific parameters, see <xref
linkend="cassandra-database-configuration4" />.</para>
</section>
<section xml:id="read-only-database-configuration6">
<title>Using Read-Only Databases for Host Reservations</title>
<para>
In some deployments the database user whose name is specified in the database backend
configuration may not have write privileges to the database. This is often
required by the policy within a given network to secure the data from being
unintentionally modified. In many cases administrators have inventory databases
deployed, which contain substantially more information about the hosts than
static reservations assigned to them. The inventory database can be used to create
a view of a Kea hosts database and such view is often read only.
</para>
<para>
Kea host database backends operate with an implicit configuration to both
read from and write to the database. If the database user does not have
write access to the host database, the backend will fail to start and the
server will refuse to start (or reconfigure). However, if access to a read
only host database is required for retrieving reservations for clients
and/or assign specific addresses and options, it is possible to explicitly
configure Kea to start in "read-only" mode. This is controlled by the
<command>readonly</command> boolean parameter as follows:
<screen>
"Dhcp6": { "hosts-database": { <userinput>"readonly": true</userinput>, ... }, ... }
</screen>
Setting this parameter to <userinput>false</userinput> would configure the
database backend to operate in "read-write" mode, which is also a default
configuration if the parameter is not specified.
</para>
<note><para>The <command>readonly</command> parameter is currently only supported
for MySQL and PostgreSQL databases.</para></note>
</section>
</section>
<section xml:id="dhcp6-interface-selection">
<title>Interface Selection</title>
<para>The DHCPv6 server has to be configured to listen on specific network
interfaces. The simplest network interface configuration instructs the server to
listen on all available interfaces:
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"*"</userinput> ]
}
...
}
</screen>
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>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"eth1", "eth3"</userinput> ]
},
...
}
</screen>
</para>
<para>It is possible to use wildcard interface name (asterisk) concurrently
with the actual interface names:
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"eth1", "eth3", "*"</userinput> ]
},
...
}
</screen>
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>
<para>As for the DHCPv4 server binding to specific addresses and
disabling re-detection of interfaces are supported. But
<command>dhcp-socket-type</command> is not because DHCPv6 uses
UDP/IPv6 sockets only. The following example shows how to disable the
interface detection:
</para>
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"eth1", "eth3"</userinput> ],
"re-detect": <userinput>false</userinput>
},
...
}
</screen>
<para>The loopback interfaces (i.e. the "lo" or "lo0" interface)
are not configured by default, unles explicitely mentioned in
the configration. Note Kea requires a link-local address which does
not exist on all systems, or a specified unicast address as in:
</para>
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"lo/::1"</userinput> ]
},
...
}
</screen>
</section>
<section xml:id="ipv6-subnet-id">
<title>IPv6 Subnet Identifier</title>
<para>
The subnet identifier is a unique number associated with a particular subnet.
In principle, it is used to associate clients' leases with their respective subnets.
When a 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 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
subnet 4, something that may have unexpected consequences. It is planned
to implement a mechanism to preserve auto-generated subnet ids in a
future version of Kea. However, the only remedy for this issue
at present is to
manually specify a unique identifier for each subnet.
</para>
<note>
Subnet IDs must be greater than zero and less than 4294967295.
</note>
<para>
The following configuration will assign the specified subnet
identifier to the newly configured subnet:
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
<userinput>"id": 1024</userinput>,
...
}
]
}
</screen>
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.
</para>
<!-- @todo: describe whether database needs to be updated after changing
id -->
</section>
<section xml:id="dhcp6-unicast">
<title>Unicast Traffic Support</title>
<para>
When the DHCPv6 server starts, 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 this is to have relays send their traffic to the server
directly. To configure the server to listen on a specific unicast address,
nn interface name can be
optionally followed by a slash, followed by the global unicast address on which
the server should listen. The server listens to this address in addition to normal
link-local binding and listening on ff02::1:2 address. The sample configuration
below shows how to listen on 2001:db8::1 (a global address)
configured on the eth1 interface.
</para>
<para>
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ <userinput>"eth1/2001:db8::1"</userinput> ]
},
...
"option-data": [
{
"name": "unicast",
"data": "2001:db8::1"
} ],
...
}
</screen>
This configuration will cause the server to listen on
eth1 on the link-local address, the multicast group (ff02::1:2) and 2001:db8::1.
</para>
<para>
Usually unicast support is associated with a server unicast option
which allows clients to send unicast messages to the server.
The example above includes a server unicast option specification
which will cause the client to send messages to the specified
unicast address.
</para>
<para>
It is possible to mix interface names, wildcards and interface name/addresses
in the list of interfaces. It is not possible however 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 the addresses specified without any additional checks.
This approach has selected on purpose to allow the software to
communicate over uncommon addresses if so desired.
</para>
</section>
<section xml:id="dhcp6-address-config">
<title>Subnet and Address Pool</title>
<para>
The main 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>
"Dhcp6": {
<userinput>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
...
}
]</userinput>
}</screen>
Note that <command>subnet</command> is defined as a simple string, but
the <command>pools</command> 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>Each <command>pool</command> is a structure that contains the
parameters that describe a single pool. Currently there is only one
parameter, <command>pool</command>, which gives the range of addresses
in the pool. Additional parameters will be added in future releases of
Kea.</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 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>
"Dhcp6": {
<userinput>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" },
{ "pool": "2001:db8:1:05::/80" }
]</userinput>,
...
}
]
}</screen>
White space in pool definitions is ignored, so spaces before and after the hyphen are optional.
They can be used to improve readability.
</para>
<para>
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>
"Dhcp6": {
<userinput>"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{ "pool": "2001:db8:1::1-2001:db8:1::ffff" }
]
},
{
"subnet": "2001:db8:2::/64",
"pools": [
{ "pool": "2001:db8:2::/64" }
]
},
</userinput>
...
]
}</screen>
In this example, we allow the server to
dynamically assign all addresses available in the whole subnet. Although
rather wasteful, it is certainly a valid configuration to dedicate the
whole /64 subnet for that purpose. Note that the Kea server does not preallocate
the leases, so there is no danger in using gigantic address pools.
</para>
<para>
When configuring a DHCPv6 server using prefix/length notation, please pay
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
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.
</para>
</section>
<section>
<title>Subnet and Prefix Delegation Pools</title>
<para>
Subnets may also be configured to delegate prefixes, as defined in
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>,
section 6.3. A subnet may have one or more prefix delegation pools.
Each pool has a prefixed address, which is specified as a prefix
(<command>prefix</command>) and a prefix length
(<command>prefix-len</command>), as well as a delegated prefix length
(<command>delegated-len</command>). The delegated length must not be
shorter (that is it must be numerically greater or equal) than the
prefix length. If both the delegated and prefix lengths are equal, the
server will be able to delegate only one prefix. The delegated prefix
does not have to match the subnet prefix.
</para>
<para> Below is a sample subnet configuration which enables prefix
delegation for the subnet:
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:d8b:1::/64",
<userinput>"pd-pools": [
{
"prefix": "3000:1::",
"prefix-len": 64,
"delegated-len": 96
}
]</userinput>
}
],
...
}</screen>
</para>
</section>
<section xml:id="pd-exclude-option">
<title>Prefix Exclude Option</title>
<para>
For each delegated prefix the delegating router may choose to exclude
a single prefix out of the delegated prefix as specified in the
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6603"> RFC 6603</link>.
The requesting router must not assign the excluded prefix to any
of its downstream interfaces and it is intended to be used on a
link through which the delegating router exchanges DHCPv6 messages with
the requesting router. The configuration example below demonstrates how
to specify an excluded prefix within a prefix pool definition. The
excluded prefix "2001:db8:1:babe:cafe:80::/72" will be sent to a
requesting router which includes Prefix Exclude option in the ORO, and
which is delegated a prefix from this pool.
</para>
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pd-pools": [
{
"prefix": "2001:db8:1:8000::",
"prefix-len": 48,
"delegated-len": 64,
"excluded-prefix": "2001:db8:1:babe:cafe:80::",
"excluded-prefix-len": 72
}
]
}
]
}
</screen>
</section>
<section xml:id="dhcp6-std-options">
<title>Standard DHCPv6 Options</title>
<para>
One of the major features of a 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 requests them. The following example shows how to
configure DNS servers, one of the most frequently used
options. Options specified in this way are considered
global and apply to all configured subnets.
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8::cafe, 2001:db8::babe"</userinput>
},
...
]
}
</screen>
</para>
<para>
The <command>option-data</command> line creates a new entry in
the option-data table. This table contains
information on all global options that the server is supposed to configure
in all subnets. The <command>name</command> line specifies the option name.
(For a complete list
of currently supported names, see <xref linkend="dhcp6-std-options-list"/>.) The next line specifies the option code,
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,
including custom option spaces, see <xref linkend="dhcp6-option-spaces"/>. The following line specifies the format in
which the data will be entered: use of CSV (comma separated values) is
recommended. Finally, the <command>data</command> line gives the actual value to be sent to
clients. Data is specified as 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>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": false,
"data": "2001 0DB8 0001 0000 0000 0000 0000 CAFE
2001 0DB8 0001 0000 0000 0000 0000 BABE"</userinput>
},
...
]
}
</screen>
</para>
<note><para>
The value for the setting of the "data" element is split across two
lines in this example for clarity: when entering the command, the
whole string should be entered on the same line.
</para></note>
<para>
Care should be taken
to use proper encoding when using hexadecimal format as Kea's ability
to validate data correctness in hexadecimal is limited.
</para>
<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"/>. Only one
of name or code is required, so you don't need to specify
both. Space has a default value of "dhcp6", so you can skip
this as well if you define a regular (not encapsulated) DHCPv6
option. Finally, csv-format defaults to true, so it too can
be skipped, unless you want to specify the option value as
hexstring. Therefore the above example can be simplified to:
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe"</userinput>
},
...
]
}
</screen>
Defined options are added to response when the client requests them
at a few exceptions which are always added. To enforce the addition
of a particular option set the always-send flag to true as in:
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe",
"always-send": true</userinput>
},
...
]
}
</screen>
The effect is the same as if the client added the option code in the
Option Request Option (or its equivalent for vendor options) so in:
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "dns-servers",
"data": "2001:db8::cafe, 2001:db8::babe",
"always-send": true</userinput>
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"option-data": [
{
<userinput>"name": "dns-servers",
"data": "2001:db8:1::cafe, 2001:db8:1::babe"</userinput>
},
...
],
...
},
...
],
...
}
</screen>
The DNS Servers option is always added to responses
(the always-send is "sticky") but the value is the subnet one
when the client is localized in the subnet.
</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>
"Dhcp6": {
"subnet6": [
{
<userinput>"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:1::3"
},
...
]</userinput>,
...
},
...
],
...
}
</screen>
</para>
<para>
In some cases it is useful to associate some options with an
address or prefix pool from which a client is assigned a lease. Pool
specific option values override subnet specific and global option
values. If the client is assigned multiple leases from different
pools, the server will assign options from all pools from which the
leases have been obtained. However, if the particular option is specified
in multiple pools from which the client obtains the leases, only one
instance of this option will be handed out to the client. The server's
administrator must not try to prioritize assignment of pool specific
options by trying to order pools declarations in the server
configuration. Future Kea releases may change the order in which
options are assigned from the pools without any notice.
</para>
<para>
The following configuration snippet demonstrates how to specify the
DNS servers option, which will be assigned to a client only if the
client obtains an address from the given pool:
<screen>
"Dhcp6": {
"subnet6": [
{
"pools": [
{
"pool": "2001:db8:1::100-2001:db8:1::300",
<userinput>"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:1::10"
}
]</userinput>
}
]
},
...
],
...
}
</screen>
</para>
<para>
Options can be specified also in class of host reservation scope.
In Kea 1.4 options precedence order is (from most important):
host reservation, pool, subnet, shared network, class, global.
In Kea 1.5 order will be changed to:
host reservation, class, pool, subnet, shared network, global OR it will
be fully configurable.
</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>
<para>When a data field is a string, and that string contains
the comma (,; U+002C) character, the comma must be escaped with a
reverse solidus character (\; U+005C). This double escape is
required, because both the routine splitting CSV data into fields
and JSON use the same escape character: a single escape (\,) would
make the JSON invalid. For example, the string
"EST5EDT4,M3.2.0/02:00,M11.1.0/02:00" would be
represented as:
<screen>
"Dhcp6": {
"subnet6": [
{
"pools": [
{
<userinput>"option-data": [
{
"name": "new-posix-timezone",
"data": "EST5EDT4\,M3.2.0/02:00\,M11.1.0/02:00"
}
]</userinput>
},
...
],
...
},
...
],
...
}
</screen>
</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, allowing
clients to obtain the addresses of multiple DNS servers.
</para>
<!-- @todo: describe record types -->
<!-- @todo: describe array in 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 yes provide a definition. 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 the configuration mechanism would allow any option format as it has
no means to validate the format at the moment.
</para>
<para>
<table frame="all" xml:id="dhcp6-std-options-list">
<title>List of Standard 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>
<!-- Our engine uses those options on its own, admin must not configure them on his own
<row><entry>clientid</entry><entry>1</entry><entry>hex</entry><entry>false</entry></row>
<row><entry>serverid</entry><entry>2</entry><entry>hex</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>hex</entry><entry>false</entry></row>
<row><entry>auth</entry><entry>11</entry><entry>hex</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>hex</entry><entry>false</entry></row>
<row><entry>vendor-class</entry><entry>16</entry><entry>record</entry><entry>false</entry></row>
-->
<!-- Vendor-specific Information is configurable by the administrator -->
<row><entry>vendor-opts</entry><entry>17</entry><entry>uint32</entry><entry>false</entry></row>
<!--
<row><entry>interface-id</entry><entry>18</entry><entry>hex</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> -->
--&gt;
<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 (uint8, uint16, hex)</entry><entry>false</entry></row>
<row><entry>remote-id</entry><entry>37</entry><entry>record (uint32, hex)</entry><entry>false</entry></row>
<row><entry>subscriber-id</entry><entry>38</entry><entry>hex</entry><entry>false</entry></row>
<row><entry>client-fqdn</entry><entry>39</entry><entry>record (uint8, fqdn)</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 (1)</entry><entry>44</entry><entry>record (uint8, ipv6-address)</entry><entry>false</entry></row>
<row><entry>client-data (1)</entry><entry>45</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>clt-time (1)</entry><entry>46</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>lq-relay-data (1)</entry><entry>47</entry><entry>record (ipv6-address, hex)</entry><entry>false</entry></row>
<row><entry>lq-client-link (1)</entry><entry>48</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>v6-lost</entry><entry>51</entry><entry>fqdn</entry><entry>false</entry></row>
<row><entry>capwap-ac-v6</entry><entry>52</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>relay-id</entry><entry>53</entry><entry>hex</entry><entry>false</entry></row>
<row><entry>v6-access-domain</entry><entry>57</entry><entry>fqdn</entry><entry>false</entry></row>
<row><entry>sip-ua-cs-list</entry><entry>58</entry><entry>fqdn</entry><entry>true</entry></row>
<row><entry>bootfile-url</entry><entry>59</entry><entry>string</entry><entry>false</entry></row>
<row><entry>bootfile-param</entry><entry>60</entry><entry>tuple</entry><entry>true</entry></row>
<row><entry>client-arch-type</entry><entry>61</entry><entry>uint16</entry><entry>true</entry></row>
<row><entry>nii</entry><entry>62</entry><entry>record (uint8, uint8, uint8)</entry><entry>false</entry></row>
<row><entry>aftr-name</entry><entry>64</entry><entry>fqdn</entry><entry>false</entry></row>
<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>pd-exclude</entry><entry>67</entry><entry>hex</entry><entry>false</entry></row>
<row><entry>rdnss-selection</entry><entry>74</entry><entry>record (ipv6-address, uint8, fqdn)</entry><entry>true</entry></row>
<row><entry>client-linklayer-addr</entry><entry>79</entry><entry>hex</entry><entry>false</entry></row>
<row><entry>link-address</entry><entry>80</entry><entry>ipv6-address</entry><entry>false</entry></row>
<row><entry>solmax-rt</entry><entry>82</entry><entry>uint32</entry><entry>false</entry></row>
<row><entry>inf-max-rt</entry><entry>83</entry><entry>uint32</entry><entry>false</entry></row>
<!-- <row><entry>dhcpv4-message</entry><entry>87</entry><entry>hex</entry><entry>false</entry></row> -->
<row><entry>dhcp4o6-server-addr</entry><entry>88</entry><entry>ipv6-address</entry><entry>true</entry></row>
<row><entry>s46-rule</entry><entry>89</entry><entry>record (uint8, uint8, uint8, ipv4-address, ipv6-prefix)</entry><entry>false</entry></row>
<row><entry>s46-br</entry><entry>90</entry><entry>ipv6-address</entry><entry>false</entry></row>
<row><entry>s46-dmr</entry><entry>91</entry><entry>ipv6-prefix</entry><entry>false</entry></row>
<row><entry>s46-v4v6bind</entry><entry>92</entry><entry>record (ipv4-address, ipv6-prefix)</entry><entry>false</entry></row>
<row><entry>s46-portparams</entry><entry>93</entry><entry>record(uint8, psid)</entry><entry>false</entry></row>
<row><entry>s46-cont-mape</entry><entry>94</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>s46-cont-mapt</entry><entry>95</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>s46-cont-lw</entry><entry>96</entry><entry>empty</entry><entry>false</entry></row>
<row><entry>v6-captive-portal</entry><entry>103</entry><entry>string</entry><entry>false</entry></row>
<row><entry>ipv6-address-andsf</entry><entry>143</entry><entry>ipv6-address</entry><entry>true</entry></row>
</tbody>
</tgroup>
</table>
Options marked with (1) have option definitions, but the logic
behind them is not implemented. That means that technically Kea
knows how to parse them in incoming message or how to send them
if configured to do so, but not what to do with them. Since the
related RFCs require certain processing, the support for those
options is non-functional. However, it may be useful in some
limited lab testing, hence the definition formats are listed here.
</para>
</section>
<section id="s46-options">
<title>Common Softwire46 Options</title>
<para>
Softwire46 options are involved in IPv4 over IPv6 provisioning by
means of tunneling or translation as specified in the
<ulink url="http://tools.ietf.org/html/rfc7598">RFC 7598</ulink>.
The following sections provide configuration examples of these
options.
</para>
<section id="s46-containers">
<title>Softwire46 Container Options</title>
<para>
S46 container options group rules and optional port parameters
for a specified domain. There are three container options specified
in the "dhcp6" (top level) option space: MAP-E Container option,
MAP-T Container option and S46 Lightweight 4over6 Container option.
These options only contain encapsulated options specified below.
They do not include any data fields.
</para>
<para>
In order to configure the server to send specific container option
along with all encapsulated options, the container option must be
included in the server configuration as shown below:
<screen>
"Dhcp6": {
...
"option-data": [
{
"name": "s46-cont-mape"
} ],
...
}
</screen>
This configuration will cause the server to include MAP-E Container
option to the client. Use "s46-cont-mapt" or "s46-cont-lw" for the
MAP-T Container and S46 Lightweight 4over6 Container options
respectively.
</para>
<para>
All remaining softwire options described below are included in one
of the container options. Thus, they have to be included in appropriate
option spaces by selecting a "space" name, which specifies in which
option they are supposed to be included.
</para>
</section>
<section>
<title>S46 Rule Option</title>
<para>
The S46 Rule option is used for conveying the Basic Mapping Rule (BMR)
and Forwarding Mapping Rule (FMR).
<screen>
{
"space": "s46-cont-mape-options",
"name": "s46-rule",
"data": "128, 0, 24, 192.0.2.0, 2001:db8:1::/64"
}
</screen>
Other possible "space" value is "s46-cont-mapt-options".
</para>
<para>
The S46 Rule option conveys a number of parameters:
<itemizedlist>
<listitem>
<simpara><command>flags</command>, an unsigned 8 bits integer, with
currently only the most significant bit specified. It denotes whether
the rule can be used for forwarding (128) or not (0).
</simpara>
</listitem>
<listitem>
<simpara><command>ea-len</command>, an 8 bits long Embedded Address length. Allowed values
range from 0 to 48.</simpara>
</listitem>
<listitem>
<simpara><command>IPv4 prefix length</command>, 8 bits long; expresses the prefix length of the
Rule IPv4 prefix specified in the ipv4-prefix field. Allowed
values range from 0 to 32.</simpara>
</listitem>
<listitem>
<simpara><command>IPv4 prefix</command>, a fixed-length 32-bit field that specifies the IPv4
prefix for the S46 rule. The bits in the prefix after prefix4-len
number of bits are reserved and MUST be initialized to zero by the
sender and ignored by the receiver.</simpara>
</listitem>
<listitem>
<simpara><command>IPv6 prefix</command> in prefix/length notation that specifies the IPv6 domain
prefix for the S46 rule. The field is padded on the right with zero
bits up to the nearest octet boundary when prefix6-len is not evenly
divisible by 8.</simpara>
</listitem>
</itemizedlist>
</para>
</section>
<section>
<title>S46 BR Option</title>
<para>
The S46 BR option is used to convey the IPv6 address of the
Border Relay. This option is mandatory in the MAP-E
Container option and not permitted in the MAP-T and
S46 Lightweight 4over6 Container options.
<screen>
{
"space": "s46-cont-mape-options",
"name": "s46-br",
"data": "2001:db8:cafe::1",
}
</screen>
Other possible "space" value is "s46-cont-lw-options".
</para>
</section>
<section>
<title>S46 DMR Option</title>
<para>
The S46 DMR option is used to convey values for the Default
Mapping Rule (DMR). This option is mandatory in the MAP-T
container option and not permitted in the MAP-E and S46
Lightweight 4over6 Container options.
<screen>
{
"space": "s46-cont-mapt-options",
"name": "s46-dmr",
"data": "2001:db8:cafe::/64",
}
</screen>
This option must not be included in other containers.
</para>
</section>
<section>
<title>S46 IPv4/IPv6 Address Binding option.</title>
<para>
The S46 IPv4/IPv6 Address Binding option may be used to specify
the full or shared IPv4 address of the Customer Edge (CE).
The IPv6 prefix field is used by the CE to identify the
correct prefix to use for the tunnel source.
<screen>
{
"space": "s46-cont-lw",
"name": "s46-v4v6bind",
"data": "192.0.2.3, 2001:db8:1:cafe::/64"
}
</screen>
This option must not be included in other containers.
</para>
</section>
<section>
<title>S46 Port Parameters</title>
<para>
The S46 Port Parameters option specifies optional port set
information that MAY be provided to CEs
<screen>
{
"space": "s46-rule-options",
"name": "s46-portparams",
"data": "2, 3/4",
}
</screen>
Other possible "space" value is "s46-v4v6bind" to include
this option in the S46 IPv4/IPv6 Address Binding option.
</para>
<para>
Note that the second value in the example above specifies the
PSID and PSID length fields in the format of PSID/PSID length.
This is equivalent to the values of PSID-len=4 and
PSID=12288 conveyed in the S46 Port Parameters option.
</para>
</section>
</section>
<section xml:id="dhcp6-custom-options">
<title>Custom DHCPv6 Options</title>
<para>It is possible to define options in addition to the standard ones.
Assume that we want to define a new DHCPv6 option called "foo" which will have
code 100 and which will convey a single unsigned 32 bit integer value. We can define
such an option by using the following commands:
<screen>
"Dhcp6": {
"option-def": [
{
<userinput>"name": "foo",
"code": 100,
"type": "uint32",
"array": false,
"record-types": "",
"space": "dhcp6",
"encapsulate": ""</userinput>
}, ...
],
...
}
</screen>
The "false" value of the <command>array</command> 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: <command>record-types</command> and
<command>encapsulate</command>.
The former specifies the comma separated list of option data fields if the
option comprises a record of data fields. The <command>record-types</command> value should
be non-empty if the <command>type</command> 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
example only defines the format of the new option, it does not set its
value(s).
</para>
<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
(i.e. ""). The default <command>space</command> is "dhcp6".
</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>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "foo",
"code": 100,
"space": "dhcp6",
"csv-format": true,
"data": "12345"</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>
For example, 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>
"Dhcp6": {
"option-def": [
{
<userinput>"name": "bar",
"code": 101,
"space": "dhcp6",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, boolean, string",
"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>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "bar",
"space": "dhcp6",
"code": 101,
"csv-format": true,
"data": "2001:db8:1::10, 123, false, Hello World"</userinput>
}
],
...
}</screen>
<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
the "record-types" field of the option definition.
</para>
<para>
When <command>array</command> is set to <command>true</command>
and <command>type</command> is set to "record", the last field
is an array, i.e., it can contain more than one value as in:
<screen>
"Dhcp6": {
"option-def": [
{
<userinput>"name": "bar",
"code": 101,
"space": "dhcp6",
"type": "record",
"array": true,
"record-types": "ipv6-address, uint16",
"encapsulate": ""</userinput>
}, ...
],
...
}
</screen>
The new option content is one IPv6 address followed by one or more 16
bit unsigned integers.
</para>
<note>
<para>In the general case, boolean values are specified as <command>true</command> or
<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 versions of Kea will accept all those values
for all boolean parameters.</para>
</note>
</section>
<section xml:id="dhcp6-vendor-opts">
<title>DHCPv6 Vendor-Specific Options</title>
<para>
Currently there are two option spaces defined for the DHCPv6
daemon: "dhcp6" (for top level DHCPv6 options) and "vendor-opts-space",
which is empty by default, but in which options can be defined.
Those options will be carried in the Vendor-Specific
Information option (code 17). 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>
"Dhcp6": {
"option-def": [
{
<userinput>"name": "foo",
"code": 1,
"space": "vendor-opts-space",
"type": "record",
"array": false,
"record-types": "ipv6-address, uint16, string",
"encapsulate": ""</userinput>
}
],
...
}</screen>
(Note that the option space is set to <command>vendor-opts-space</command>.)
Once the option format is defined, the next step is to define actual values
for that option:
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "foo",
"space": "vendor-opts-space",
"data": "2001:db8:1::10, 123, Hello World"</userinput>
},
...
],
...
}</screen>
We should also define a value (enterprise-number) for the
Vendor-specific Information option, that conveys our option "foo".
<screen>
"Dhcp6": {
"option-data": [
...,
{
<userinput>"name": "vendor-opts",
"data": "12345"</userinput>
}
],
...
}</screen>
Alternatively, the option can be specified using its code.
<screen>
"Dhcp6": {
"option-data": [
...,
{
<userinput>"code": 17,
"data": "12345"</userinput>
}
],
...
}</screen>
</para>
</section>
<section xml: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 their new option to
convey sub-options that use a 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 a new option space when
defining sub-options for a standard option because it is
created by default 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>
"Dhcp6": {
"option-def": [
{
<userinput>"name": "subopt1",
"code": 1,
"space": "isc",
"type": "ipv6-address",
"record-types": "",
"array": false,
"encapsulate": ""</userinput>
},
{
<userinput>"name": "subopt2",
"code": 2,
"space": "isc",
"type": "string",
"record-types": "",
"array": false
"encapsulate": ""</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>
"Dhcp6": {
"option-def": [
...,
{
<userinput>"name": "container",
"code": 102,
"space": "dhcp6",
"type": "empty",
"array": false,
"record-types": "",
"encapsulate": "isc"</userinput>
}
],
...
}</screen>
The name of the option space in which the sub-options are defined is set in
the <command>encapsulate</command> field. The <command>type</command> field
is set to <command>empty</command> which limits this option to only carrying
data in sub-options.
</para>
<para>
Finally, we can set values for the new options:
<screen>
"Dhcp6": {
"option-data": [
{
<userinput>"name": "subopt1",
"code": 1,
"space": "isc",
"data": "2001:db8::abcd"</userinput>
},
}
<userinput>"name": "subopt2",
"code": 2,
"space": "isc",
"data": "Hello world"</userinput>
},
{
<userinput>"name": "container",
"code": 102,
"space": "dhcp6"</userinput>
}
],
...
}
</screen>
</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 xml:id="dhcp6-option-data-defaults">
<title>Unspecified Parameters for DHCPv6 Option Configuration</title>
<para>In many cases it is not required to specify all parameters for
an option configuration and the default values can be used. However, it is
important to understand the implications of not specifying some of them
as it may result in configuration errors. The list below explains
the behavior of the server when a particular parameter is not explicitly
specified:
<itemizedlist>
<listitem>
<simpara><command>name</command> - the server requires an option name or
option code to identify an option. If this parameter is unspecified, the
option code must be specified.
</simpara>
</listitem>
<listitem>
<simpara><command>code</command> - the server requires an option name or
option code to identify an option. This parameter may be left unspecified if
the <command>name</command> parameter is specified. However, this also
requires that the particular option has its definition (it is either a
standard option or an administrator created a definition for the option
using an 'option-def' structure), as the option definition associates an
option with a particular name. It is possible to configure an option
for which there is no definition (unspecified option format).
Configuration of such options requires the use of option code.
</simpara>
</listitem>
<listitem>
<simpara><command>space</command> - if the option space is unspecified it
will default to 'dhcp6' which is an option space holding DHCPv6 standard
options.
</simpara>
</listitem>
<listitem>
<simpara><command>data</command> - if the option data is unspecified it
defaults to an empty value. The empty value is mostly used for the
options which have no payload (boolean options), but it is legal to specify
empty values for some options which carry variable length data and which
spec allows for the length of 0. For such options, the data parameter
may be omitted in the configuration.</simpara>
</listitem>
<listitem>
<simpara><command>csv-format</command> - if this value is not
specified the server will assume that the option data is specified as
a list of comma separated values to be assigned to individual fields
of the DHCP option. This behavior has changed in Kea 1.2. Older
versions used additional logic to determine whether the csv-format
should be true or false. That is no longer the case.
</simpara>
</listitem>
</itemizedlist>
</para>
</section>
<section xml: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 the server may have many subnet configurations defined, it must select
an appropriate subnet for a given request.
</para>
<para>
The server can not assume which of the configured subnets are local. In IPv4
it is possible as there is a 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: the DHCPv6 server must be able
to operate while only using link-local addresses. Therefore an optional
<command>interface</command> parameter is available within a subnet definition
to designate that a given subnet is local, i.e. reachable directly over
the specified interface. For example the server that is intended to serve
a local subnet over eth0 may be configured as follows:
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
<userinput>"interface": "eth0"</userinput>
}
],
...
}
</screen>
</para>
</section>
<section xml:id="dhcp6-rapid-commit">
<title>Rapid Commit</title>
<para>The Rapid Commit option, described in
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>, is supported
by the Kea DHCPv6 server. However, support is disabled by default for
all subnets. It can be enabled for a particular subnet using the
<command>rapid-commit</command> parameter as shown below:
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
<userinput>"rapid-commit": true</userinput>,
"pools": [
{
"pool": "2001:db8:beef::1-2001:db8:beef::10"
}
],
}
],
...
}
</screen>
</para>
<para>
This setting only affects the subnet for which the
<command>rapid-commit</command> is set to <command>true</command>.
For clients connected to other subnets, the server will ignore the
Rapid Commit option sent by the client and will follow the 4-way
exchange procedure, i.e. respond with an Advertise for a Solicit
containing a Rapid Commit option.
</para>
</section>
<section xml: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 a 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>
<command>interface</command> defines which local network interface can be used
to access a given subnet.
</simpara></listitem>
<listitem><simpara>
<command>interface-id</command> 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>
The following example configuration shows how to specify an interface-id with
a value of "vlan123".
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:beef::/48",
"pools": [
{
"pool": "2001:db8:beef::/48"
}
],
<userinput>"interface-id": "vlan123"</userinput>
}
],
...
}
</screen>
</para>
</section>
<section xml:id="dhcp6-rsoo">
<title>Relay-Supplied Options</title>
<para><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6422">RFC 6422</link>
defines a mechanism called Relay-Supplied DHCP Options. In certain cases relay
agents are the only entities that may have specific information. They can
insert options when relaying messages from the client to the server. The
server will then do certain checks and copy those options to the response
that will be sent to the client.</para>
<para>There are certain conditions that must be met for the option to be
included. First, the server must not provide the option itself. In
other words, if both relay and server provide an option, the server always
takes precedence. Second, the option must be RSOO-enabled. IANA maintains a
list of RSOO-enabled options <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-parameters.xhtml#options-relay-supplied">here</link>.
However, there may be cases when system administrators want to echo other
options. Kea can be instructed to treat other options as RSOO-enabled.
For example, to mark options 110, 120 and 130 as RSOO-enabled, the following
syntax should be used:
<screen>
"Dhcp6": {
<userinput>"relay-supplied-options": [ "110", "120", "130" ],</userinput>
...
}
</screen>
</para>
<para>As of March 2015, only option 65 is RSOO-enabled by IANA. This
option will always be treated as such and there's no need to explicitly
mark it. Also, when enabling standard options, it is possible to use their
names, rather than option code, e.g. (e.g. use
<command>dns-servers</command> instead of <command>23</command>). See
<xref linkend="dhcp6-std-options-list"/> for the names. In certain cases
it could also work for custom options, but due to the nature of the parser
code this may be unreliable and should be avoided.
</para>
</section>
<section xml:id="dhcp6-client-classifier">
<title>Client Classification in DHCPv6</title>
<para>
The DHCPv6 server includes support for client classification. For a deeper
discussion of the classification process see <xref linkend="classify"/>.
</para>
<para>In certain cases it is useful to configure the server to differentiate between
DHCP clients types and treat them accordingly. It is envisaged that client
classification will be used for modifying the behavior of almost any part of
the DHCP message processing. In the current release of Kea, there are three
mechanisms that take advantage of the client classification in DHCPv6: subnet
selection, address pool selection and DHCP options assignment.
</para>
<para>
In certain cases it is useful to differentiate between different types
of clients and treat them accordingly. It is envisaged that client
classification will be used for changing the behavior of almost any part of
the DHCP message processing. In the current release of the software however,
there are only some mechanisms that take advantage of client classification:
subnet selection, pool selection, and assignment of different options.
</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 is cable networks. Here, there are two
classes of devices: the cable modem itself, which should be handed a lease
from subnet A and all other devices behind the modem 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="classification-subnets"/>.
</para>
<para>
When subnets belong to a shared network the classification applies
to subnet selection but not to pools, e.g., a pool in a subnet
limited to a particular class can still be used by clients which do not
belong to the class if the pool they are expected to use is exhausted.
So the limit access based on class information is also available
at the address/prefix pool level, see <xref
linkend="classification-pools"/> within a subnet.
This is useful when to segregate clients belonging to the same subnet
into different address ranges.
</para>
<para>
In a similar way a pool can be constrained to serve only known
clients, i.e. clients which have a reservation, using the
built-in "KNOWN" or "UNKNOWN" classes. One can assign addresses
to registered clients without giving a different address per
reservations, for instance when there is not enough available
addresses. The determination whether there is a reservation
for a given client is made after a subnet is selected. As such, it
is not possible to use KNOWN/UNKNOWN classes to select a shared
network or a subnet.
</para>
<para>
The process of doing classification is conducted in five steps.
The first step is to assess an incoming packet and assign it to
zero or more classes.
The second step is to choose a subnet, possibly based on the
class information.
The next step is to evaluate class expressions depending on the
built-in "KNOWN"/"UNKNOWN" classes after host reservation lookup,
using them for pool/pd-pool selection and to assign classes from host
reservations.
After the list of required classes is built and each class of the list
has its expression evaluated: when it returns true the packet is added
as a member of the class.
The last step is to assign options again possibly based on the class
information.
More complete and detailed description is available in
<xref linkend="classify"/>.
</para>
<para>
There are two main methods of doing classification. The first is automatic and relies
on examining the values in the vendor class options or existence of a
host reservation. Information from these
options is extracted and a class name is constructed from it and added to
the class list for the packet. The second allows for specifying an expression
that is evaluated for each packet. If the result is true the packet is
a member of the class.
</para>
<note><para>
Care should be taken with client classification as it is easy for
clients that do not meet class criteria to be denied any service altogether.
</para></note>
<section>
<title>Defining and Using Custom Classes</title>
<para>
The following example shows how to configure a class using an expression
and a subnet making use of that class. This configuration defines the
class named "Client_enterprise". It is comprised
of all clients whose client identifiers start with the given hex string (which
would indicate a DUID based on an enterprise id of 0xAABBCCDD).
They will be given an address from 2001:db8:1::0 to 2001:db8:1::FFFF and
the addresses of their DNS servers set to 2001:db8:0::1 and 2001:db8:2::1.
<screen>
"Dhcp6": {
"client-classes": [
{<userinput>
"name": "Client_enterprise",
"test": "substring(option[1].hex,0,6) == 0x0002AABBCCDD'",
"option-data": [
{
"name": "dns-servers",
"code": 23,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:0::1, 2001:db8:2::1"
}
]</userinput>
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::ffff" } ],
<userinput>"client-class": "Client_enterprise"</userinput>
}
],
...
}</screen>
</para>
<para>
This example shows a configuration using an automatically generated
"VENDOR_CLASS_" class. The Administrator of the 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 and only clients belonging to the
eRouter1.0 client class are allowed to use that pool.
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff"
}
],
<userinput>"client-class": "VENDOR_CLASS_eRouter1.0"</userinput>
}
],
...
}
</screen>
</para>
</section>
<section id="dhcp6-required-class">
<title>Required classification</title>
<para>
In some cases it is useful to limit the scope of a class to
a shared-network, subnet or pool. There are two parameters
which are used to limit the scope of the class by instructing
the server to perform evaluation of test expressions when
required.
</para>
<para>
The first one is the per-class <command>only-if-required</command>
flag which is false by default. When it is set to
<command>true</command> the test expression of the class is not
evaluated at the reception of the incoming packet but later and
only if the class evaluation is required.
</para>
<para>
The second is the <command>require-client-classes</command> which
takes a list of class names and is valid in shared-network,
subnet and pool scope. Classes in these lists are marked as
required and evaluated after selection of this specific
shared-network/subnet/pool and before output option processing.
</para>
<para>
In this example, a class is assigned to the incoming packet
when the specified subnet is used.
<screen>
"Dhcp6": {
"client-classes": [
{<userinput>
"name": "Client_foo",
"test": "member('ALL')",
"only-if-required": true</userinput>
},
...
],
"subnet6": [
{
"subnet": "2001:db8:1::/64"
"pools": [
{
"pool": "2001:db8:1::-2001:db8:1::ffff"
}
],
<userinput>"require-client-classes": [ "Client_foo" ],</userinput>
...
},
...
],
...
}</screen>
</para>
<para>
Required evaluation can be used to express complex dependencies,
for example, subnet membership. It can also be used to reverse the
precedence: if you set an option-data in a subnet it takes
precedence over an option-data in a class. When you move the
option-data to a required class and require it in
the subnet, a class evaluated earlier may take precedence.
</para>
<para>
Required evaluation is also available at shared-network and
pool/pd-pool levels. The order in which required classes are
considered is: shared-network, subnet and (pd-)pool, i.e.
the opposite order option-data are processed.
</para>
</section>
</section>
<section xml:id="dhcp6-ddns-config">
<title>DDNS for DHCPv6</title>
<para>
As mentioned earlier, kea-dhcp6 can be configured to generate requests to
the DHCP-DDNS server (referred to here as "D2") 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 <command>dhcp-ddns</command> section of the kea-dhcp6
configuration. The mandatory parameters for the DHCP DDNS configuration
are <command>enable-updates</command> which is unconditionally
required, and <command>qualifying-suffix</command> which has no
default value and is required when <command>enable-updates</command>
is set to <command>true</command>.
The two (disabled and enabled) minimal DHCP DDNS configurations are:
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"enable-updates": false</userinput>
},
...
}
</screen>
and for example:
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"enable-updates": true,
"qualifying-suffix": "example."</userinput>
},
...
}
</screen>
The default values for the "dhcp-ddns" section are as follows:
<itemizedlist>
<listitem><simpara>
<command>"server-ip": "127.0.0.1"</command>
</simpara></listitem>
<listitem><simpara>
<command>"server-port": 53001</command>
</simpara></listitem>
<listitem><simpara>
<command>"sender-ip": ""</command>
</simpara></listitem>
<listitem><simpara>
<command>"sender-port": 0</command>
</simpara></listitem>
<listitem><simpara>
<command>"max-queue-size": 1024</command>
</simpara></listitem>
<listitem><simpara>
<command>"ncr-protocol": "UDP"</command>
</simpara></listitem>
<listitem><simpara>
<command>"ncr-format": "JSON"</command>
</simpara></listitem>
<listitem><simpara>
<command>"override-no-update": false</command>
</simpara></listitem>
<listitem><simpara>
<command>"override-client-update": false</command>
</simpara></listitem>
<listitem><simpara>
<command>"replace-client-name": "never"</command>
</simpara></listitem>
<listitem><simpara>
<command>"generated-prefix": "myhost"</command>
</simpara></listitem>
<listitem><simpara>
<command>"hostname-char-set": ""</command>
</simpara></listitem>
<listitem><simpara>
<command>"hostname-char-replacement": ""</command>
</simpara></listitem>
</itemizedlist>
</para>
<section xml: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 this communication:
<itemizedlist>
<listitem><simpara>
<command>enable-updates</command> - determines whether or not kea-dhcp6 will
generate NCRs. If missing, this value is assumed to be false hence DDNS updates
are disabled. To enable DDNS updates set this value to true:
</simpara></listitem>
<listitem><simpara>
<command>server-ip</command> - 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.
</simpara></listitem>
<listitem><simpara>
<command>server-port</command> - port on which D2 listens for requests. The default value
is 53001.
</simpara></listitem>
<listitem><simpara>
<command>sender-ip</command> - 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.
</simpara></listitem>
<listitem><simpara>
<command>sender-port</command> - port which kea-dhcp6 should use to send requests to D2. The
default value of 0 instructs kea-dhcp6 to select a suitable port.
</simpara></listitem>
<listitem><simpara>
<command>max-queue-size</command> - 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 to allow kea-dhcp6 to
continue lease operations. The default value is 1024.
</simpara></listitem>
<listitem><simpara>
<command>ncr-protocol</command> - socket protocol use when sending requests to D2. Currently
only UDP is supported. TCP may be available in an upcoming release.
</simpara></listitem>
<listitem><simpara>
<command>ncr-format</command> - packet format to use when sending requests to D2.
Currently only JSON format is supported. Other formats may be available
in future releases.
</simpara></listitem>
</itemizedlist>
By default, kea-dhcp-ddns 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 2001:db8::5 port 900, the following configuration
would be required:
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"server-ip": "2001:db8::5",
"server-port": 900</userinput>,
...
},
...
}
</screen>
</para>
</section>
<section xml:id="dhcpv6-d2-rules-config">
<title>When Does kea-dhcp6 Generate a DDNS Request?</title>
<para>kea-dhcp6 follows the behavior prescribed for DHCP servers in
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4704">RFC 4704</link>.
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 within the purview of D2 itself (<xref linkend="dhcp-ddns-server"/>).
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 <command>enable-updates</command> 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 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 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.
</para>
<para>
The decision making involved when granting a new lease the first case) is more
involved. When a new lease is granted, kea-dhcp6 will generate a DDNS
update request only if the 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 xml: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, <command>override-client-update</command>, 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
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4702">RFC 4702</link>. If such a
combination is received from the client, the packet will be dropped by kea-dhcp6.)
</para>
<para>
To override client delegation, set the following values in the configuration:
</para>
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"override-client-update": true</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, <command>override-no-update</command>,
can be used to instruct the server to disregard the client's wishes. When
this parameter is true, kea-dhcp6 will generate DDNS update requests to
kea-dhcp-ddns 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>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"override-no-update": true</userinput>,
...
},
...
}
</screen>
</section>
<section xml:id="dhcpv6-fqdn-name-generation">
<title>kea-dhcp6 Name Generation for DDNS Update Requests</title>
<para>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.</para>
<para>
The default rules for constructing the FQDN that will be used for DNS
entries are:
<orderedlist>
<listitem><para>
If the DHCPREQUEST contains the client FQDN option, the candidate name
is taken from there.
</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 provided is empty, generate an FQDN using a
configurable prefix and suffix.
</para></listitem>
<listitem><para>
If the client provided neither option, then no DNS action will be taken.
</para></listitem>
</orderedlist>
These rules can amended by setting the
<command>replace-client-name</command> parameter which provides the
following modes of behavior:
<itemizedlist>
<listitem><para>
<command>never</command> - Use the name the client sent. If the client
sent no name, do not generate one. This is the default mode.
</para></listitem>
<listitem><para>
<command>always</command> - Replace the name the client sent. If the
client sent no name, generate one for the client.
</para></listitem>
<listitem><para>
<command>when-present</command> - Replace the name the client sent.
If the client sent no name, do not generate one.
</para></listitem>
<listitem><para>
<command>when-not-present</command> - Use the name the client sent.
If the client sent no name, generate one for the client.
</para></listitem>
</itemizedlist>
<note>
Note that formerly, this parameter was a boolean and permitted only values
of <command>true</command> and <command>false</command>. Boolean values
have been deprecated and are no longer accepted. If you are currently using
booleans, you must replace them with the desired mode name. A value of
<command>true</command> maps to <command>"when-present"</command>, while
<command>false</command> maps to <command>"never"</command>.
</note>
For example, To instruct kea-dhcp6 to always generate the FQDN for a
client, set the parameter <command>replace-client-name</command> to
<command>always</command> as follows:
</para>
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"replace-client-name": "always"</userinput>,
...
},
...
}
</screen>
<para>
The prefix used in the generation of an FQDN is specified by the
<command>generated-prefix</command> parameter. The default value is "myhost". To alter
its value, simply set it to the desired string:
</para>
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"generated-prefix": "another.host"</userinput>,
...
},
...
}
</screen>
<para>
The suffix used when generating an FQDN or when qualifying a
partial name is specified by
the <command>qualifying-suffix</command> parameter. This
parameter has no default value, thus it is mandatory when
DDNS updates are enabled.
To set its value simply set it to the desired string:
</para>
<screen>
"Dhcp6": {
"dhcp-ddns": {
<userinput>"qualifying-suffix": "foo.example.org"</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
qualifying-suffix "example.com", the generated FQDN would be:
</para>
<para>
some-computer.example.com.
</para>
<para>
When generating 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,
the qualifying suffix "example.com", and the default value is used for
<command>generated-prefix</command>, the generated FQDN would be:
</para>
<para>
myhost-3001-1--70E.example.com.
</para>
<section xml:id="host-name-sanitization">
<title>Sanitizing Client FQDN Names</title>
It may be that some of your DHCP clients provide values in the name
component of the FQDN option (Option code 39), that contain undesirable
characters. It is possible to configure kea-dhcp5 to sanitize these
values. The most typical use case would be ensuring that only
characters that are permitted by RFC 1035 be included:
A-Z,a-z,0-9, and '-'. This may be accomplished with following two
parameters:
<itemizedlist>
<listitem><simpara>
<command>hostname-char-set</command> - a regular expression describing
the invalid character set. This can be any valid, regular expression
using POSIX extended expression syntax. For example, "[^A-Za-z0-9-]"
would replace any character other then the letters A through z, digits
0 through 9, and '-'. An empty string, the default value, disables
sanitization.
</simpara></listitem>
<listitem><simpara>
<command>hostname-char-replacement</command> - a string of zero or
more characters with which to replace each invalid character in the
client value. The default value is an empty string and will cause
invalid characters to be OMITTED rather than replaced.
</simpara></listitem>
</itemizedlist>
The following configuration, will replace anything other than a
letter, digit, hyphen, or dot with the letter 'x':
<screen>
"Dhcp4": {
"dhcp-ddns": {
"hostname-char-set": "[^A-Za-z0-9.-]",
"hostname-char-replacement": "x",
...
},
...
}
</screen>
Thus, a client supplied value of "myhost-$[123.org" would become
"myhost-xx123.org". Sanitizing is performed only on the portion of
the name supplied by the client and it is performed before applying
a qualifying suffix (if one is defined and needed).
<note>
The following are some considerations to keep in mind:
<para>
Name sanitizing is meant to catch the more common cases of invalid
characters through a relatively simple character replacement scheme.
It is difficult to devise a scheme that works well in all cases and
should you find you have clients that are using odd, corner cases of
character combinations that cannot be readily handled with this
mechanism, you should consider writing a hook that can carry out
sufficiently complex logic to address your needs.
</para>
<para>
You do not account for dots ins your hostname-char-set expression.
When scrubbing FQDNs, dots are treated as delimiters and used to
separate the option value into individual domain labels that are
scrubbed and then re-assembled.
</para>
<para>
If your clients are sending values that differ only by characters
considered as invalid by your hostname-char-set, be aware that scrubbing
them will yield identical values. In such cases, DDNS conflict rules
will permit only one of them from registering the name.
</para>
<para>
Finally, given the latitude clients have in the values they send, it is
virtually impossible to guarantee that a combination of these two
parameters will always yield a name that is valid for use in DNS. For
example, using an empty value for hostname-char-replacment could yield
an empty domain label within a name, if that label consists only of
invalid characters.
</para>
</note>
</section>
</section>
<section xml:id="dhcp6-dhcp4o6-config">
<title>DHCPv4-over-DHCPv6: DHCPv6 Side</title>
<para>
The support of DHCPv4-over-DHCPv6 transport is described in
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc7341">RFC 7341</link>
and is implemented using cooperating DHCPv4 and DHCPv6 servers.
This section is about the configuration of the DHCPv6 side
(the DHCPv4 side is described in <xref linkend="dhcp4-dhcp4o6-config"/>).
</para>
<note>
DHCPv4-over-DHCPv6 support is experimental and the details of
the inter-process communication can change: both the
DHCPv4 and DHCPv6 sides should be running the same version of Kea.
For instance the support of port relay (RFC 8357) introduced such
such incompatible change.
</note>
<para>
There is only one specific parameter for the DHCPv6 side:
<command>dhcp4o6-port</command> which specifies the first of the
two consecutive ports of the UDP sockets used for the communication
between the DHCPv6 and DHCPv4 servers (the DHCPv6 server is bound
to ::1 on <command>port</command> and connected to ::1 on
<command>port</command> + 1).
</para>
<para>
Two other configuration entries are in general required: unicast traffic
support (see <xref linkend="dhcp6-unicast"/>) and DHCP 4o6 server
address option (name "dhcp4o6-server-addr", code 88).
</para>
<para>
The following configuration was used during some tests:
<screen>
{
# DHCPv6 conf
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "eno33554984/2001:db8:1:1::1" ]
},
"lease-database": {
"type": "memfile",
"name": "leases6"
},
"preferred-lifetime": 3000,
"valid-lifetime": 4000,
"renew-timer": 1000,
"rebind-timer": 2000,
"subnet6": [ {
"subnet": "2001:db8:1:1::/64",
"interface": "eno33554984",
"pools": [ { "pool": "2001:db8:1:1::1:0/112" } ]
} ],
<userinput>"dhcp4o6-port": 6767,
"option-data": [ {
"name": "dhcp4o6-server-addr",
"code": 88,
"space": "dhcp6",
"csv-format": true,
"data": "2001:db8:1:1::1"
} ]
</userinput>
},
"Logging": {
"loggers": [ {
"name": "kea-dhcp6",
"output_options": [ {
"output": "/tmp/kea-dhcp6.log"
} ],
"severity": "DEBUG",
"debuglevel": 0
} ]
}
}
</screen>
</para>
<note>
Relayed DHCPv4-QUERY DHCPv6 messages are not yet supported.
</note>
</section>
<section xml:id="sanity-checks6">
<title>Sanity checks in DHCPv6</title>
<para>
An important aspect of a well running DHCP system is an assurance that
the data remains consisent. However, in some cases it may be convenient
to tolerate certain inconsistent data. For example, a network
administrator that temporarily removed a subnet from a configuration
wouldn't want all the leases associated with it disappear from the
lease database. Kea 1.5 introduced a mechanism to better control sanity
checks such as this. While currently the scope of configurable sanity
checks is limited and their default value is set low, it is expected
that over time the default settings will be set to more aggressive
values and more parameters of similar nature will be added in the
future.
</para>
<para>
Kea now supports a new configuration scope called
<command>sanity-checks</command>. It currently allows only a
single parameter called <command>lease-checks</command>. It
governs what sort of verification is done when a new lease is
being loaded from a lease file. With the introduction of
sanity checks mechanism, it is now possible to tell Kea to
try to correct inconsistent data.
</para>
<para>
Every subnet has a subnet-id value. This is how Kea internally
identifies subnets. Each lease has a subnet-id parameter as well, which
identifies which subnet it belongs to. However, if configuration has
changed, it is possible that a lease could exist with a subnet-id
without any subnet that matches it. Also, it may be possible that
subnets configuration has changed and the subnet-id now belongs to a
subnet that does not match the lease. Kea corrective algorithm first
checks if there is a subnet with subnet-id specified by the lease. If
there is, it checks whether the lease belongs to that subnet. If not,
depending on the lease-checks setting, the lease is discarded, a
warning is printed or a new subnet is selected for the lease that
matches it topologically.
</para>
<para>
Since delegated prefixes do not have to belong to a subnet in which
they're offered, there is no way to implement such a mechanism for IPv6
prefixes. As such, the mechanism works for IPv6 addresses only.
</para>
<para>
There are five levels which are supported:
</para>
<itemizedlist>
<listitem>
<simpara><command>none</command> - do no special checks, accept the
lease as is</simpara>
</listitem>
<listitem>
<simpara><command>warn</command> - if problems are detected, a
warning will be printed, but the lease data will be accepted
anyway. This is the default value. If not explicitly configured to
some other value, this level will be used.</simpara>
</listitem>
<listitem>
<simpara><command>fix</command> - If data inconsistency is
discovered, Kea will try to correct it. If the correction is
not successful, the data will be inserted anyway.</simpara>
</listitem>
<listitem>
<simpara><command>fix-del</command> - If data inconsistency is
discovered, Kea will try to correct it. If the correction is not
succesful, the lease will be rejected. This setting ensures the data
correctness, but some incorrect data may be lost. Use with
care.</simpara>
</listitem>
<listitem>
<simpara><command>del</command> - This is the strictest mode. If any
inconsistency is detected, the lease is rejected. Use with care.
</simpara>
</listitem>
</itemizedlist>
<para>This feature is currently implemented for memfile backend.</para>
<para>
An example configuration that sets this parameter looks as follows:
<screen>
"Dhcp6": {
"sanity-checks": {
// This parameter determines what to do when a new lease appears in the
// system (i.e. either is read from disk during memfile startup or is
// added via lease commands). There are five modes supported:
// none - do nothing, accept them as is
// warn - if subnet-id problems are detected, print a warning, but
// otherwise load the lease as is. This is the default value.
// fix - attempt to fix the lease by finding appropriate subnet-id value.
// if there is no suitable subnet, the lease is loaded as is.
// fix-del - attempt to fix the lease by findind appropriate subnet-id
// value. If there is no suitable subnet, the lease is deleted.
// del - delete leases that have incorrect subnet-id values.
<userinput>"lease-checks": "fix-del"</userinput>
},
...
}</screen>
</para>
</section>
</section>
<!-- Host reservation is a large topic. There will be many subsections,
so it should be a section on its own. -->
<section xml:id="host-reservation-v6">
<title>Host Reservation in DHCPv6</title>
<para>There are many cases where it is useful to provide a configuration on
a per host basis. The most obvious one is to reserve specific, static IPv6
address or/and prefix for exclusive use by a given client (host) ‐ returning
client will get the same address or/and prefix every time and other clients will
never get that address. Note that there may be cases when the
new reservation has been made for the client for the address or prefix being
currently in use by another client. We call this situation a "conflict". The
conflicts get resolved automatically over time as described in the subsequent
sections. Once conflict is resolved, the client will keep receiving the reserved
configuration when it renews.</para>
<para>Another example when the host reservations are applicable is when a host
has specific requirements, e.g. a printer that needs additional DHCP options
or a cable modem needs specific parameters. Yet another possible use case for
host reservation is to define unique names for hosts.</para>
<para>Hosts reservations are defined as parameters for each subnet. Each host
can be identified by either DUID or its hardware/MAC address. See
<xref linkend="mac-in-dhcpv6"/> for details. There is an optional
<command>reservations</command> array in the
<command>subnet6</command> structure. Each element in that array
is a structure, that holds information about a single host. In
particular, the structure has an identifier that
uniquely identifies a host. In the DHCPv6 context, such an identifier
is usually a DUID, but can also be a hardware or MAC address. Also,
either one or more addresses or prefixes may be specified. It is
possible to specify a hostname and DHCPv6 options for a given host.</para>
<para>The following example shows how to reserve addresses and prefixes
for specific hosts:
<screen>
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"pd-pools": [
{
"prefix": "2001:db8:1:8000::",
"prefix-len": 48,
"delegated-len": 64
}
],
<userinput>"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
},
{
"hw-address": "00:01:02:03:04:05",
"ip-addresses": [ "2001:db8:1::101", "2001:db8:1::102" ]
},
{
"duid": "01:02:03:04:05:06:07:08:09:0A",
"ip-addresses": [ "2001:db8:1::103" ],
"prefixes": [ "2001:db8:2:abcd::/64" ],
"hostname": "foo.example.com"
}
]</userinput>
}
]
</screen>
This example includes reservations for three different clients. The first reservation
is made for the address 2001:db8:1::100 for a client using DUID
01:02:03:04:05:0A:0B:0C:0D:0E. The second reservation is made for two addresses
2001:db8:1::101 and 2001:db8:1::102 for a client using MAC address
00:01:02:03:04:05. Lastly, address 2001:db8:1::103 and prefix 2001:db8:2:abcd::/64
are reserved for a client using DUID 01:02:03:04:05:06:07:08:09:0A. The
last reservation also assigns a hostname to this client.
</para>
<para>Note that DHCPv6 allows for a single client to lease multiple addresses
and multiple prefixes at the same time. Therefore <command>ip-addresses</command>
and <command>prefixes</command> are plural and are actually arrays.
When the client sends multiple IA options (IA_NA or IA_PD), each reserved
address or prefix is assigned to an individual IA of the appropriate type. If
the number of IAs of specific type is lower than the number of reservations
of that type, the number of reserved addresses or prefixes assigned to the
client is equal to the number of IA_NAs or IA_PDs sent by the client, i.e.
some reserved addresses or prefixes are not assigned. However,
they still remain reserved for this client and the server will not assign
them to any other client. If the number of IAs of specific type sent by the
client is greater than the number of reserved addresses or prefixes, the
server will try to assign all reserved addresses or prefixes to the individual
IAs and dynamically allocate addresses or prefixes to remaining IAs. If the
server cannot assign a reserved address or prefix because it is in use,
the server will select the next reserved address or prefix and try to assign it to
the client. If the server subsequently finds that there are no more reservations
that can be assigned to the client at the moment, the server will try to
assign leases dynamically.
</para>
<para>Making a reservation for a mobile host that may visit multiple subnets
requires a separate host definition in each subnet it is expected to visit.
It is not allowed to define multiple host definitions with the same hardware
address in a single subnet. Multiple host definitions with the same hardware
address are valid if each is in a different subnet. The reservation for a given host
should include only one identifier, either DUID or hardware address. Defining
both for the same host is considered a configuration error, but as of 1.1.0,
it is not rejected.
</para>
<para>Adding host reservation incurs a performance penalty. In principle,
when a server that does not support host reservation responds to a query,
it needs to check whether there is a lease for a given address being
considered for allocation or renewal. The server that also supports host
reservation, has to perform additional checks: not only if the address is
currently used (i.e. if there is a lease for it), but also whether the address
could be used by someone else (i.e. if there is a reservation for it). That
additional check incurs additional overhead.</para>
<section xml:id="reservation6-types">
<title>Address/Prefix Reservation Types</title>
<para>In a typical scenario there is an IPv6 subnet defined with a certain
part of it dedicated for dynamic address allocation by the DHCPv6
server. There may be an additional address space defined for prefix
delegation. Those dynamic parts are referred to as dynamic pools, address
and prefix pools or simply pools. In principle, the host reservation can
reserve any address or prefix that belongs to the subnet. The reservations
that specify an address that belongs to configured pools are called
"in-pool reservations". In contrast, those that do not
belong to dynamic pools are called "out-of-pool
reservations". There is no formal difference in the reservation
syntax and both reservation types are handled
uniformly. However, upcoming releases may offer improved performance if
there are only out-of-pool reservations as the server will be able to skip
reservation checks when dealing with existing leases. Therefore, system
administrators are encouraged to use out-of-pool reservations if
possible.</para>
<para>Beginning with Kea 1.5.0, there is now support for global
host reservations. These are reservations that are specified at the
global level within the configuration and that do not belong to any
specific subnet. Kea will still match inbound client packets to a
subnet as before, but when the subnet's reservation mode is set to
<command>"global"</command>, Kea will look for host reservations only
among the global reservations defined. Typcially, such reservations would
be used to reserve hostnames for clients which may move from one subnet
to another.
</para>
<note>You can reserve any ip-address or prefix in a global reservation.
Just keep in mind that Kea will not do any sanity checking on the address
or prefix and that for Kea 1.5.0, support for global reservations should
be considered experimental.
</note>
</section>
<section xml:id="reservation6-conflict">
<title>Conflicts in DHCPv6 Reservations</title>
<para>As reservations and lease information are stored separately,
conflicts may arise. Consider the following series of events. The server
has configured the dynamic pool of addresses from the range of 2001:db8::10
to 2001:db8::20. Host A requests an address and gets 2001:db8::10. Now the
system administrator decides to reserve address 2001:db8::10 for Host B.
In general, reserving an address
that is currently assigned to someone else is not recommended, but there
are valid use cases where such an operation is warranted.</para>
<para>The server now has a conflict to resolve. Let's analyze the
situation here. If Host B boots up and request an address, the server is
not able to assign the reserved address 2001:db8::10. A naive approach
would to be immediately remove the lease for Host A and create a new one
for Host B. That would not solve the problem, though, because as soon as
Host B get the address, it will detect that the address is already in use
by someone else (Host A) and would send a Decline message. Therefore in this
situation, the server has to temporarily assign a different address from the
dynamic pool (not matching what has been reserved) to Host B.</para>
<para>When Host A renews its address, the server will discover that
the address being renewed is now reserved for someone else (Host
B). Therefore the server will remove the lease for 2001:db8::10, select
a new address and create a new lease for it. It will send two
addresses in its response: the old address with lifetime set to 0 to
explicitly indicate that it is no longer valid and the new address with a
non-zero lifetime. When Host B renews its temporarily assigned
address, the server will detect that the existing lease does not match
reservation, so it will release the current address Host B has and will
create a new lease matching the reservation. Similar as before, the server
will send two addresses: the temporarily assigned one with zeroed
lifetimes, and the new one that matches reservation with proper lifetimes
set.</para>
<para>This recovery will succeed, even if other hosts will attempt to get
the reserved address. Had Host C requested address 2001:db8::10 after
the reservation was made, the server will propose a different address.</para>
<para>This recovery mechanism allows the server to fully recover from a
case where reservations conflict with existing leases. This procedure
takes time and will roughly take as long as renew-timer value specified.
The best way to avoid such recovery is to not define new reservations that
conflict with existing leases. Another recommendation is to use
out-of-pool reservations. If the reserved address does not belong to a
pool, there is no way that other clients could get this address.
</para>
<note>
<para>The conflict resolution mechanism does not work for global
reservations. As of Kea 1.5.0, it is generally recommended to not use
global reservations for addresses or prefixes. If you want to use it
anyway, you have to manually ensure that the reserved values are not
in the dynamic pools.</para>
</note>
</section>
<section xml:id="reservation6-hostname">
<title>Reserving a Hostname</title>
<para>When the reservation for the client includes the <command>hostname</command>,
the server will assign this hostname to the client and send
it back in the Client FQDN, if the client sent the FQDN option to the
server. The reserved hostname always takes precedence over the hostname
supplied by the client (via the FQDN option) or the autogenerated
(from the IPv6 address) hostname.</para>
<para>The server qualifies the reserved hostname with the value
of the <command>qualifying-suffix</command> parameter. For example, the
following subnet configuration:
<screen>
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "alice-laptop"
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
"qualifying-suffix": "example.isc.org."
}
</screen>
will result in assigning the "alice-laptop.example.isc.org." hostname to the
client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E". If the <command>qualifying-suffix
</command> is not specified, the default (empty) value will be used, and
in this case the value specified as a <command>hostname</command> will
be treated as fully qualified name. Thus, by leaving the
<command>qualifying-suffix</command> empty it is possible to qualify
hostnames for the different clients with different domain names:
<screen>
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::/80" } ],
"reservations": [
{
"duid": "01:02:03:04:05:0A:0B:0C:0D:0E",
"ip-addresses": [ "2001:db8:1::100" ]
"hostname": "mark-desktop.example.org."
}
]
}
],
"dhcp-ddns": {
"enable-updates": true,
}
</screen>
The above example results in the assignment of the "mark-desktop.example.org." hostname to the
client using the DUID "01:02:03:04:05:0A:0B:0C:0D:0E".
</para>
</section>
<section xml:id="reservation6-options">
<title>Including Specific DHCPv6 Options in Reservations</title>
<para>Kea 1.1.0 introduced the ability to specify options on a
per host basis. The options follow the same rules as any other
options. These can be standard options (see <xref linkend="dhcp6-std-options"/>), custom options (see <xref linkend="dhcp6-custom-options"/>) or vendor specific options
(see <xref linkend="dhcp6-vendor-opts"/>). The following
example demonstrates how standard options can be defined.</para>
<screen>
"reservations": [
{
"duid": "01:02:03:05:06:07:08",
"ip-addresses": [ "2001:db8:1::2" ],
<userinput>"option-data": [
{
"option-data": [ {
"name": "dns-servers",
"data": "3000:1::234"
},
{
"name": "nis-servers",
"data": "3000:1::234"
}
} ]</userinput>
} ]</screen>
<para>Vendor specific options can be reserved in a similar manner:</para>
<screen>
"reservations": [
{
"duid": "aa:bb:cc:dd:ee:ff",
"ip-addresses": [ "2001:db8::1" ],
<userinput>"option-data": [
{
"name": "vendor-opts",
"data": 4491
},
{
"name": "tftp-servers",
"space": "vendor-4491",
"data": "3000:1::234"
} ]</userinput>
} ]</screen>
<para>
Options defined at host level have the highest priority. In other words,
if there are options defined with the same type on global, subnet, class and
host level, the host specific values will be used.
</para>
</section>
<section xml:id="reservation6-client-classes">
<title>Reserving Client Classes in DHCPv6</title>
<para>The <xref linkend="classification-using-expressions"/> explains how
to configure the server to assign classes to a client based on the content
of the options that this client sends to the server. Host reservations
mechanisms also allow for the static assignment of classes to clients.
The definitions of these classes are placed in the Kea
configuration. The following configuration snippet shows how to specify
that the client belongs to classes <command>reserved-class1</command>
and <command>reserved-class2</command>. Those classes are associated with
specific options being sent to the clients which belong to them.
</para>
<screen>
{
"client-classes": [
{
"name": "reserved-class1",
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:1::50"
}
]
},
{
"name": "reserved-class2",
"option-data": [
{
"name": "nis-servers",
"data": "2001:db8:1::100"
}
]
}
],
"subnet6": [
{ "pools": [ { "pool": "2001:db8:1::/64" } ],
"subnet": "2001:db8:1::/48",
"reservations": [
{
"duid": "01:02:03:04:05:06:07:08",
<userinput>
"client-classes": [ "reserved-class1", "reserved-class2" ]
</userinput>
} ]
} ]
}
</screen>
<para>Static class assignments, as shown above, can be used in conjunction
with classification using expressions. The "KNOWN" or "UNKNOWN" builtin
class is added to the packet and any class depending on it directly or
indirectly and not only-if-required is evaluated.
</para>
<note>
<para>If you want to force the evaluation of a class expression after
the host reservation lookup, for instance because of a dependency on
"reserved-class1" from the previous example, you should add a
"member('KNOWN')" in the expression.</para>
</note>
</section>
<section id="reservations6-mysql-pgsql-cql">
<title>Storing Host Reservations in MySQL, PostgreSQL or Cassandra</title>
<para>
It is possible to store host reservations in MySQL, PostgreSQL or Cassandra. See
<xref linkend="hosts6-storage" /> for information on how to configure Kea to use
reservations stored in MySQL, PostgreSQL or Cassandra. Kea provides dedicated hook for
managing reservations in a database, section <xref linkend="host-cmds" /> provide
detailed information. The Kea wiki <uri
xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:href="https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management">https://gitlab.isc.org/isc-projects/kea/wikis/designs/commands#23-host-reservations-hr-management</uri>
provides some examples how to conduct some common operations
on host reservations.
</para>
<note><simpara>In Kea maximum length of an option specified per host is
arbitrarily set to 4096 bytes.</simpara></note>
</section>
<section xml:id="reservations6-tuning">
<title>Fine Tuning DHCPv6 Host Reservation</title>
<para>The host reservation capability introduces additional restrictions for the
allocation engine (the component of Kea that selects an address for a client)
during lease selection and renewal. In particular, three
major checks are necessary. First, when selecting a new lease, it is not
sufficient for a candidate lease to not be used by another DHCP client. It
also must not be reserved for another client. Second, when renewing a lease,
additional check must be performed whether the address being renewed is not
reserved for another client. Finally, when a host renews an address or a
prefix, the server has to check whether there is a reservation for this host,
so the existing (dynamically allocated) address should be revoked and the
reserved one be used instead.</para>
<para>Some of those checks may be unnecessary in certain deployments and not
performing them may improve performance. The Kea server provides the
<command>reservation-mode</command> configuration parameter to select the
types of reservations allowed for the particular subnet. Each reservation
type has different constraints for the checks to be performed by the
server when allocating or renewing a lease for the client.
Allowed values are:
<itemizedlist>
<listitem><simpara> <command>all</command> - enables both in-pool
and out-of-pool host reservation types. This is the default value. This
setting is the safest and the most flexible. As all checks are conducted,
it is also the slowest. This does not check against global reservations.
</simpara></listitem>
<listitem><simpara> <command>out-of-pool</command> - allows only out of
pool host reservations. With this setting in place, the server may assume
that all host reservations are for addresses that do not belong to the
dynamic pool. Therefore it can skip the reservation checks when dealing
with in-pool addresses, thus improving performance. Do not use this mode
if any of your reservations use in-pool address. Caution is advised when
using this setting. Kea does not sanity check the reservations against
<command>reservation-mode</command> and misconfiguration may cause
problems.
</simpara></listitem>
<listitem><simpara> <command>global</command> - allows only global
host reservations. With this setting in place, the server searches for
reservations for a client only among the defined global reservations.
If an address is specified, the server will skip the reservation checks
done when dealing in other modes, thus improving performance.
Caution is advised when using this setting: Kea does not sanity check
the reservations when <command>global</command> and
misconfiguration may cause problems.
</simpara></listitem>
<listitem><simpara>
<command>disabled</command> - host reservation support is disabled. As there
are no reservations, the server will skip all checks. Any reservations defined
will be completely ignored. As the checks are skipped, the server may
operate faster in this mode.
</simpara></listitem>
</itemizedlist>
The parameter can be specified at global, subnet and shared network
levels.
</para>
<para>
An example configuration that disables reservation looks like follows:
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
<userinput>"reservation-mode": "disabled"</userinput>,
...
}
]
}
</screen>
</para>
<para>
An example configuration using global reservations is shown below:
<screen>
"Dhcp6": {
<userinput>
"reservation-mode": "global",
"reservations": [
{
"duid": "00:03:00:01:11:22:33:44:55:66",
"hostname": "host-one"
},
{
"duid": "00:03:00:01:99:88:77:66:55:44",
"hostname": "host-two"
}
],
</userinput>
"subnet6": [
{
"subnet": "2001:db8:1::/64",
...
}
]
}
</screen>
For more details regarding global reservations, see
<xref linkend="global-reservations6"/>.
</para>
<para>Another aspect of the host reservations are different types of
identifiers. Kea 1.1.0 supports two types of identifiers
in DHCPv6: hw-address and duid, but more identifier types
are likely to be added in the future. This is beneficial from a
usability perspective. However, there is a drawback. For each incoming
packet Kea has to to extract each identifier type and then query the
database to see if there is a reservation done by this particular
identifier. If nothing is found, the next identifier is extracted and next
query is issued. This process continues until either a reservation is
found or all identifier types have been checked. Over time with an increasing
number of supported identifier types, Kea would become slower and
slower.</para>
<para>To address this problem, a parameter called
<command>host-reservation-identifiers</command> has been introduced. It
takes a list of identifier types as a parameter. Kea will check only those
identifier types enumerated in host-reservation-identifiers. From a
performance perspective the number of identifier types should be kept to
minimum, ideally limited to one. If your deployment uses several
reservation types, please enumerate them from most to least frequently
used as this increases the chances of Kea finding the reservation using the
fewest number of queries. An example of host reservation identifiers looks
as follows:
<screen>
<userinput>"host-reservation-identifiers": [ "duid", "hw-address" ],</userinput>
"subnet6": [
{
"subnet": "2001:db8:1::/64",
...
}
]</screen>
</para>
<para>
If not specified, the default value is:
<screen>
<userinput>"host-reservation-identifiers": [ "hw-address", "duid" ]</userinput>
</screen>
</para>
</section>
<section id="global-reservations6">
<title>Global reservations in DHCPv6</title>
<para>In some deployments, such as mobile, clients can roam within the
network and there is a desire to specify certain parameters regardless of
the client's current location. To facilitate such a need, a global
reservation mechanism has been implemented. The idea behind it is that
regular host reservations are tied to specific subnets, by using specific
subnet-id. Kea 1.5.0 introduced a new capability to specify global
reservation that can be used in every subnet that has global reservations
enabled.</para>
<para>This feature can be used to assign certain parameters, such as
hostname or other dedicated, host-specific options. It can also be used to
assign addresses or prefixes. However, global reservations that assign
either of these bypass the whole topology determination provided by DHCP
logic implemented in Kea. It is very easy to misuse this feature and get
configuration that is inconsistent. To give a specific example, imagine a
global reservation for an address 2001:db8:1111::1 and two subnets
2001:db8:1111::/48 and 2001:db8:ffff::/48. If global reservations are used
in both subnets and a device matching global host reservations visits part
of the network that is covered by 2001:db8:ffff::/48, it will get an IP
address 2001:db8:ffff::1, which will be outside of the prefix announced
by its local router using Router Advertisements. Such a configuration
would be unsuable or at the very least ridden with issues, such as the
downlink traffic not reaching the device.</para>
<para>
To use global host reservations a configuration similar to the following
can be used:
<screen>
"Dhcp6:" {
// This specifies global reservations. They will apply to all subnets that
// have global reservations enabled.
<userinput>
"reservations": [
{
"hw-address": "aa:bb:cc:dd:ee:ff",
"hostname": "hw-host-dynamic"
},
{
"hw-address": "01:02:03:04:05:06",
"hostname": "hw-host-fixed",
// Use of IP address is global reservation is risky. If used outside of
// matching subnet, such as 3001::/64, it will result in a broken
// configuration being handled to the client.
"ip-address": "2001:db8:ff::77"
},
{
"duid": "01:02:03:04:05",
"hostname": "duid-host"
}
]</userinput>,
"valid-lifetime": 600,
"subnet4": [ {
"subnet": "2001:db8:1::/64",
<userinput>"reservation-mode": "global",</userinput>
"pools": [ { "pool": "2001:db8:1::-2001:db8:1::100" } ]
} ]
}
</screen>
</para>
<para>When using database backends, the global host reservations are
distinguished from regular reservations by using subnet-id value of
zero.</para>
<!-- see CfgHostOperations::createConfig6() in
src/lib/dhcpsrv/cfg_host_operations.cc -->
</section>
<!-- @todo: add support for per IA reservation (that specifies IAID in
the ip-addresses and prefixes) -->
</section>
<!-- end of host reservations section -->
<!-- shared networks starts here -->
<section id="shared-network6">
<title>Shared networks in DHCPv6</title>
<para>DHCP servers use subnet information in two ways. First, it is used
to determine the point of attachment, or simply put, where the client is
connected to the network. Second, the subnet information is used to group
information pertaining to specific location in the network. This approach
works well in general case, but the are scenarios where the boundaries are
blurred. Sometimes it is useful to have more than one logical IP subnet
being deployed on the same physical link. The need to understand
that two or more subnets are used on the same link requires additional logic
in the DHCP server. This capability has been added in Kea 1.3.0. It is
called "shared networks" in Kea and ISC DHCP projects. It is sometimes also
called "shared subnets". In Microsoft's nomenclature it is called "multinet".
</para>
<para>There are many use cases where the feature is useful. The most common
example in the IPv4 case is when the server is running out of available
addresses in a subnet. This is less common in IPv6, but the shared networks
are still useful in IPv6. One of the use cases is an exhaustion of IPv6
delegated prefixes within a subnet. Another IPv6 specific example
is an experiment with addressing scheme. With the advent of IPv6 deployment
and vast address space, many organizations split the address space into
subnets, then deploy it and after a while discover that they want to split it
differently. In the transition period they want both old and new addressing
to be available. Thus the need for more than one subnet on the same physical
link.</para>
<para>Finally, the case of cable networks is directly applicable in
IPv6. There are two types of devices in cable networks: cable modems and the
end user devices behind them. It is a common practice to use different
subnet for cable modems to prevent users from tinkering with their cable
modems. In this case, the distinction is based on the type of device, rather
than coming out of running out address space.</para>
<para>A client connected to a shared network may be assigned a lease (address
or prefix) from any of the pools defined within the subnets belonging to the
shared network. Internally, the server selects one of the subnets belonging to the
shared network and tries to allocate a lease from this subnet. If the
server is unable to allocate a lease from the selected subnet (e.g. due
to pools exhaustion) it will use another subnet from the same shared
network and try to allocate a lease from this subnet etc. Therefore, in the
typical case, the server will allocate all leases available in a given
subnet before it starts allocating leases from other subnets belonging to
the same shared network. However, in certain situations the client can be
allocated a lease from the other subnets before the pools in the first
subnet get exhausted, e.g. when the client provides a hint that belongs
to another subnet or the client has reservations in a different than
default subnet.
</para>
<note>
<para>It is strongly discouraged for the Kea deployments to assume that the
server doesn't allocate leases from other subnets until it uses all
the leases from the first subnet in the shared network. Apart from the
fact that hints, host reservations and client classification affect subnet
selection, it is also foreseen that we will enhance allocation strategies
for shared networks in the future versions of Kea, so as the selection
of subnets within a shared network is equally probable (unpredictable).</para>
</note>
<para>In order to define a shared network an additional configuration scope
is introduced:
<screen>
{
"Dhcp6": {
<userinput>"shared-networks": [
{
// Name of the shared network. It may be an arbitrary string
// and it must be unique among all shared networks.
"name": "ipv6-lab-1",
// Subnet selector can be specifed on the shared network level.
// Subnets from this shared network will be selected for clients
// communicating via relay agent having the specified IP address.
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
// This starts a list of subnets in this shared network.
// There are two subnets in this example.
"subnet6": [
{
"subnet": "2001:db8::/48",
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ]
},
{
"subnet": "3ffe:ffe::/64",
"pools": [ { "pool": "3ffe:ffe::/64" } ]
}
]
} ]</userinput>, // end of shared-networks
// It is likely that in your network you'll have a mix of regular,
// "plain" subnets and shared networks. It is perfectly valid to mix
// them in the same config file.
//
// This is regular subnet. It's not part of any shared-network.
"subnet6": [
{
"subnet": "2001:db9::/48",
"pools": [ { "pool": "2001:db9::/64" } ],
"relay": {
"ip-addresses": [ "2001:db8:1:2::1" ]
}
}
]
} // end of Dhcp6
}
</screen>
</para>
<para>As you see in the example, it is possible to mix shared and regular
("plain") subnets. Each shared network must have a unique name. This is a
similar concept to ID for subnets, but it offers more flexibility. This is used
for logging, but also internally for identifying shared networks.</para>
<para>In principle it makes sense to define only shared networks that
consist of two or more subnets. However, for testing purposes it is allowed
to define a shared network with just one subnet or even an empty one. This
is not a recommended practice in production networks, as the shared network
logic requires additional processing and thus lowers server's performance.
To avoid unnecessary performance degradation the shared subnets should only
be defined when required by the deployment.
</para>
<para>Shared networks provide an ability to specify many parameters in
the shared network scope that will apply to all subnets within it. If
necessary, you can specify a parameter in the shared network scope and then
override its value on the subnet scope. For example:
<screen>
"shared-networks": [
{
"name": "lab-network3",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
// This applies to all subnets in this shared network, unless
// values are overridden on subnet scope.
<userinput>"valid-lifetime": 600</userinput>,
// This option is made available to all subnets in this shared
// network.
<userinput>"option-data": [ {
"name": "dns-servers",
"data": "2001:db8::8888"
} ]</userinput>,
"subnet6": [
{
"subnet": "2001:db8:1::/48",
"pools": [ { "pool": "2001:db8:1::1 - 2001:db8:1::ffff" } ],
// This particular subnet uses different values.
<userinput>"valid-lifetime": 1200,
"option-data": [
{
"name": "dns-servers",
"data": "2001:db8::1:2"
},
{
"name": "unicast",
"data": "2001:abcd::1"
} ]</userinput>
},
{
"subnet": "2001:db8:2::/48",
"pools": [ { "pool": "2001:db8:2::1 - 2001:db8:2::ffff" } ],
// This subnet does not specify its own valid-lifetime value,
// so it is inherited from shared network scope.
<userinput>"option-data": [
{
"name": "dns-servers",
"data": "2001:db8:cafe::1"
} ]</userinput>
}
],
} ]</screen>
In this example, there is a dns-servers option defined that is available to
clients in both subnets in this shared network. Also, a valid lifetime is
set to 10 minutes (600s). However, the first subnet overrides some of the values
(valid lifetime is 20 minutes, different IP address for dns-servers), but
also adds its own option (unicast address). Assuming a client asking for a
server unicast and dns servers options is assigned a lease from this subnet,
he will get a lease for 20 minutes and dns-servers and be allowed to use
server unicast at address 2001:abcd::1. If the same client is assigned to
the second subnet, he will get a 10 minutes long lease, dns-servers value of
2001:db8:cafe::1 and no server unicast.
</para>
<para>Some parameters must be the same in all subnets in the same shared
network. This restriction applies to <command>interface</command> and
<command>rapid-commit</command> settings. The most convenient way is to
define them on shared network scope, but you may specify them for each
subnet. However, care should be taken for each subnet to have the same
value.</para>
<section>
<title>Local and relayed traffic in shared networks</title>
<para>It is possible to specify interface name in the shared network scope to
tell the server that this specific shared network is reachable directly (not
via relays) using local network interface. It is sufficient to specify
it once at the shared network level. As all subnets in a shared network are
expected to be used on the same physical link, it is a configuration error
to attempt to make a shared network out of subnets that are reachable over
different interfaces. It is allowed to specify interface parameter on each
subnet, although its value must be the same for each subnet. Thus it's
usually more convenient to specify it once at the shared network level.
<screen>
"shared-networks": [
{
"name": "office-floor-2",
// This tells Kea that the whole shared networks is reachable over
// local interface. This applies to all subnets in this network.
<userinput>"interface": "eth0"</userinput>,
"subnet6": [
{
"subnet": "2001:db8::/64",
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ],
<userinput>"interface": "eth0"</userinput>
},
{
"subnet": "3ffe:abcd::/64",
"pools": [ { "pool": "3ffe:abcd::1 - 3ffe:abcd::ffff" } ]
// Specifying a different interface name is configuration
// error:
// "interface": "eth1"
}
],
} ]
</screen>
</para>
<para>Somewhat similar to interface names, also relay IP addresses can be
specified for the whole shared network. However, depending on your relay
configuration, it may use different IP addresses depending on which subnet
is being used. Thus there is no requirement to use the same IP relay address
for each subnet. Here's an example:
<screen>
"shared-networks": [
{
"name": "kakapo",
<userinput>"relay": {
"ip-addresses": [ "2001:db8::abcd" ]
}</userinput>,
"subnet6": [
{
"subnet": "2001:db8::/64",
<userinput>"relay": {
"ip-addresses": [ "2001:db8::1234" ]
}</userinput>,
"pools": [ { "pool": "2001:db8::1 - 2001:db8::ffff" } ]
},
{
"subnet": "3ffe:abcd::/64",
"pools": [ { "pool": "3ffe:abcd::1 - 3ffe:abcd::ffff" } ],
<userinput>"relay": {
"ip-addresses": [ "3ffe:abcd::cafe" ]
}</userinput>
}
]
}
]</screen>
In this particular case the relay IP address specified at network level doesn't
have much sense, as it is overridden in both subnets, but it was left there
as an example of how one could be defined at network level. Note that the
relay agent IP address typically belongs to the subnet it relays packets from,
but this is not a strict requirement. Therefore Kea accepts any value here
as long as it is valid IPv6 address.</para>
</section>
<section>
<title>Client classification in shared networks</title>
<para>Sometimes it is desired to segregate clients into specific subnets
based on some properties. This mechanism is called client classification
and is described in <xref linkend="classify"/>. Client classification
can be applied to subnets belonging to shared networks in the same way
as it is used for subnets specified outside of shared networks.
It is important to understand how the server selects subnets for
the clients when client classification is in use, to assure that the
desired subnet is selected for a given client type.</para>
<para>If a subnet is associated with a class, only the clients
belonging to this class can use this subnet. If there are no
classes specified for a subnet, any client connected to a given shared
network can use this subnet. A common mistake is to assume that the
subnet including a client class is preferred over subnets without
client classes. Consider the following example:
<screen>
{
"client-classes": [
{
"name": "b-devices",
"test": "option[1234].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"relay": {
"ip-address": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
},
{
"subnet": "2001:db8:3::/64",
"pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
<userinput>"client-class": "b-devices"</userinput>
}
]
}
]
}
</screen>
If the client belongs to "b-devices" class (because it includes option
1234 with a value of 0x0002) it doesn't guarantee that the subnet 2001:db8:3::/64
will be used (or preferred) for this client. The server can use any of
the two subnets because the subnet 2001:db8:1::/64 is also allowed for
this client. The client classification used in this case should be pereceived
as a way to restrict access to certain subnets, rather than a way to express
subnet preference. For example, if the client doesn't belong to the
"b-devices" class it may only use the subnet 2001:db8:1::/64 and will
never use the subnet 2001:db8:3::/64.
</para>
<para>A typical use case for client classification is in the cable network,
where cable modems should use one subnet and other devices should use
another subnet within the same shared network. In this case it is required
to apply classification on all subnets. The following example defines two
classes of devices. The subnet selection is made based on option 1234 values.
<screen>
{
"client-classes": [
{
"name": "a-devices",
"test": "option[1234].hex == 0x0001"
},
{
"name": "b-devices",
"test": "option[1234].hex == 0x0002"
}
],
"shared-networks": [
{
"name": "galah",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [ { "pool": "2001:db8:1::20 - 2001:db8:1::ff" } ],
<userinput>"client-class": "a-devices"</userinput>
},
{
"subnet": "2001:db8:3::/64",
"pools": [ { "pool": "2001:db8:3::20 - 2001:db8:3::ff" } ],
<userinput>"client-class": "b-devices"</userinput>
}
]
}
]
}
</screen>
In this example each class has its own restriction. Only clients that belong to
class a-devices will be able to use subnet 2001:db8:1::/64 and only clients
belonging to b-devices will be able to use subnet 2001:db8:3::/64. Care should
be taken to not define too restrictive classification rules, as clients that are
unable to use any subnets will be refused service. Although, this may be
desired outcome if one desires to service only clients of known properties
(e.g. only VoIP phones allowed on a given link).</para>
<para>
Note that it is possible to achieve similar effect as presented in this
section without the use of shared networks. If the subnets are placed in
the global subnets scope, rather than in the shared network, the server
will still use classification rules to pick the right subnet for a given
class of devices. The major benefit of placing subnets within the
shared network is that common parameters for the logically grouped
subnets can be specified once, in the shared network scope, e.g.
"interface" or "relay" parameter. All subnets belonging to this shared
network will inherit those parameters.
</para>
</section>
<section>
<title>Host reservations in shared networks</title>
<para>
Subnets being part of a shared network allow host reservations, similar to
regular subnets:
<screen>
{
"shared-networks": [
{
"name": "frog",
"relay": {
"ip-addresses": [ "2001:db8:2:34::1" ]
},
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"id": 100,
"pools": [ { "2001:db8:1::1 - 2001:db8:1::64" } ],
<userinput>"reservations": [
{
"duid": "00:03:00:01:11:22:33:44:55:66",
"ip-addresses": [ "2001:db8:1::28" ]
}
]</userinput>
},
{
"subnet": "2001:db8:3::/64",
"id": 101,
"pools": [ { "pool": "2001:db8:3::1 - 2001:db8:3::64" } ],
<userinput>"reservations": [
{
"duid": "00:03:00:01:aa:bb:cc:dd:ee:ff",
"ip-addresses": [ "2001:db8:2::28" ]
}
]</userinput>
}
]
}
]
}
</screen>
</para>
<para>It is worth noting that Kea conducts additional checks when processing a
packet if shared networks are defined. First, instead of simply checking if
there's a reservation for a given client in his initially selected subnet, it
goes through all subnets in a shared network looking for a reservation. This is
one of the reasons why defining a shared network may impact performance. If
there is a reservation for a client in any subnet, that particular subnet will
be picked for the client. Although it's technically not an error, it is
considered a bad practice to define reservations for the same host in multiple
subnets belonging to the same shared network.</para>
<para>While not strictly mandatory, it is strongly recommended to use explicit
"id" values for subnets if you plan to use database storage for host
reservations. If ID is not specified, the values for it be autogenerated,
i.e. it will assign increasing integer values starting from 1. Thus, the
autogenerated IDs are not stable across configuration changes.
</para>
</section>
</section>
<!-- end of shared networks -->
<section xml: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.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>
defines four DUID types: DUID-LLT, DUID-EN, DUID-LL and DUID-UUID.
Future specifications may introduce new DUID types.</para>
<para>The Kea DHCPv6 server generates a server identifier once, upon
the first startup, and stores it in a file. This identifier isn't
modified across restarts of the server and so is a stable identifier.</para>
<para>Kea follows recommendation from
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>
to use DUID-LLT as the default server identifier. However, we have
received reports that some deployments require different DUID
types, and there is a need to administratively select both DUID
type and/or its contents.</para>
<para>The server identifier can be configured using parameters
within the <command>server-id</command> map element in the global
scope of the Kea configuration file. The following example
demonstrates how to select DUID-EN as a server identifier:
<screen>
"Dhcp6": {
"server-id": {
"type": "EN"
},
...
}
</screen>
</para>
<para>Currently supported values for <command>type</command>
parameter are: "LLT", "EN" and "LL", for DUID-LLT, DUID-EN and
DUID-LL respectively.</para>
<para>When a new DUID type is selected the server will generate its
value and replace any existing DUID in the file. The server will then
use the new server identifier in all future interactions with the
clients.</para>
<note><para>If the new server identifier is created after some clients
have obtained their leases, the clients using the old identifier will not
be able to renew the leases: the server will ignore messages
containing the old server identifier. Clients will continue sending
Renew until they transition to the rebinding state. In this state they
will start sending Rebind messages to multicast address without
a server identifier. The server will respond to the Rebind messages
with a new server identifier and the clients will associate the
new server identifier with their leases. Although the clients will
be able to keep their leases and will eventually learn the new server
identifier, this will be at the cost of increased number of renewals
and multicast traffic due to a need to rebind. Therefore it is
recommended that modification of the server identifier type
and value is avoided if the server has already assigned leases and these
leases are still valid.</para></note>
<para>There are cases when an administrator needs to explicitly
specify a DUID value rather than allow the server to generate it.
The following example demonstrates how to explicitly set all
components of a DUID-LLT.
<screen>
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 8,
"identifier": "A65DC7410F05",
"time": 2518920166
},
...
}
</screen>
where:
<itemizedlist>
<listitem><simpara><command>htype</command> is a 16-bit unsigned value
specifying hardware type,</simpara></listitem>
<listitem><simpara><command>identifier</command> is a link layer
address, specified as a string of hexadecimal digits,</simpara>
</listitem>
<listitem><simpara><command>time</command> is a 32-bit unsigned
time value.</simpara></listitem>
</itemizedlist>
</para>
<para>The hexadecimal representation of the DUID generated as a result
of the configuration specified above will be:
<screen>
00:01:00:08:96:23:AB:E6:A6:5D:C7:41:0F:05
|type |htype| time | identifier |
</screen>
</para>
<para>It is allowed to use special value of 0 for "htype" and "time",
which indicates that the server should use ANY value for these
components. If the server already uses a DUID-LLT it will use the
values from this DUID. If the server uses a DUID of a different type
or doesn't use any DUID yet, it will generate these values.
Similarly, if the "identifier" is assigned an empty string, the
value of the identifier will be generated. Omitting any of these
parameters is equivalent to setting them to those special values.
</para>
<para>For example, the following configuration:
<screen>
"Dhcp6": {
"server-id": {
"type": "LLT",
"htype": 0,
"identifier": "",
"time": 2518920166
},
...
}
</screen>
indicates that the server should use ANY link layer address and
hardware type. If the server is already using DUID-LLT it will
use the link layer address and hardware type from the existing DUID.
If the server is not using any DUID yet, it will use link layer
address and hardware type from one of the available network
interfaces. The server will use an explicit value of time. If it
is different than a time value present in the currently used
DUID, that value will be replaced, effectively causing
modification of the current server identifier.
</para>
<para>
The following example demonstrates an explicit configuration of
a DUID-EN:
<screen>
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545"
},
...
}
</screen>
where:
<itemizedlist>
<listitem><simpara><command>enterprise-id</command> is a 32-bit
unsigned value holding enterprise number,</simpara></listitem>
<listitem><simpara><command>identifier</command> is a variable
length identifier within DUID-EN.</simpara></listitem>
</itemizedlist>
</para>
<para>
The hexadecimal representation of the DUID-EN created according to
the configuration above is:
<screen>
00:02:00:00:09:BF:87:AB:EF:7A:5B:B5:45
|type | ent-id | identifier |
</screen>
</para>
<para>As in the case of the DUID-LLT, special values can be used for the
configuration of the DUID-EN. If <command>enterprise-id</command> is 0, the server
will use a value from the existing DUID-EN. If the server is not using
any DUID or the existing DUID has a different type, the ISC enterprise
id will be used. When an empty string is used for <command>identifier</command>, the
identifier from the existing DUID-EN will be used. If the server is
not using any DUID-EN the new 6-bytes long identifier will be generated.
</para>
<para>DUID-LL is configured in the same way as DUID-LLT with an exception
that the <command>time</command> parameter has no effect for DUID-LL,
because this DUID type only comprises a hardware type and link layer
address. The following example demonstrates how to configure DUID-LL:
<screen>
"Dhcp6": {
"server-id": {
"type": "LL",
"htype": 8,
"identifier": "A65DC7410F05"
},
...
}
</screen>
</para>
<para>
which will result in the following server identifier:
<screen>
00:03:00:08:A6:5D:C7:41:0F:05
|type |htype| identifier |
</screen>
</para>
<para>The server stores the generated server identifier in the following
location: [kea-install-dir]/var/kea/kea-dhcp6-serverid.
</para>
<para>In some uncommon deployments where no stable storage is
available, the server should be configured not to try to
store the server identifier. This choice is controlled
by the value of <command>persist</command> boolean parameter:
<screen>
"Dhcp6": {
"server-id": {
"type": "EN",
"enterprise-id": 2495,
"identifier": "87ABEF7A5BB545",
"persist": false
},
...
}
</screen>
</para>
<para>The default value of the "persist" parameter is
<command>true</command> which configures the server to store the
server identifier on a disk.</para>
<para>In the example above, the server is configured to not store
the generated server identifier on a disk. But, if the server
identifier is not modified in the configuration the same value
will be used after server restart, because entire server
identifier is explicitly specified in the configuration.</para>
</section>
<section xml:id="stateless-dhcp6">
<title>Stateless DHCPv6 (Information-Request Message)</title>
<para>Typically DHCPv6 is used to assign both addresses and options. These
assignments (leases) have state that changes over time, hence
their name, stateful. DHCPv6 also supports a stateless mode,
where clients request configuration options only. This mode is
considered lightweight from the server perspective as it does not require
any state tracking; hence its name.</para>
<para>The Kea server supports stateless mode. Clients can send
Information-Request messages and the server will send back
answers with the requested options (providing the options are
available in the server configuration). The server will attempt to
use per-subnet options first. If that fails - for whatever reason - it
will then try to provide options defined in the global scope.</para>
<para>Stateless and stateful mode can be used together. No special
configuration directives are required to handle this. Simply use the
configuration for stateful clients and the stateless clients will get
just options they requested.</para>
<para>This usage of global options allows for an interesting case.
It is possible to run a server that provides just options and no
addresses or prefixes. If the options have the same value in each
subnet, the configuration can define required options in the global
scope and skip subnet definitions altogether. Here's a simple example of
such a configuration:
<screen>
"Dhcp6": {
"interfaces-config": {
"interfaces": [ "ethX" ]
},
<userinput>"option-data": [ {
"name": "dns-servers",
"data": "2001:db8::1, 2001:db8::2"
} ]</userinput>,
"lease-database": { "type": "memfile" }
}
</screen>
This very simple configuration will provide DNS server information
to all clients in the network, regardless of their location. Note the
specification of the memfile lease database: this is needed as
Kea requires a lease database to be specified
even if it is not used.</para>
</section>
<section xml:id="dhcp6-rfc7550">
<title>Support for RFC 7550 (being now part of RFC 8415)</title>
<para>The <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc7550">RFC 7550</link>
introduced some changes to the previous DHCPv6 specifications,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc3315">RFC 3315</link>
and <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc3633">RFC 3633</link>,
to resolve a few issues with the coexistence of multiple stateful
options in the messages sent between the clients and servers. Those
changes were later included in the most recent DHCPv6 protocol specification,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>,
which obsoleted <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc7550">RFC 7550</link>.
Kea supports <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>
along with these protocol changes, which are briefly described below.
</para>
<para>When a client, such as a requesting router, requests an allocation
of both addresses and prefixes during the 4-way (SARR) exchange with the
server, and the server is not configured to allocate any prefixes but it
can allocate some addresses, it will respond with the IA_NA(s) containing
allocated addresses and the IA_PD(s) containing the NoPrefixAvail status code.
According to the updated specifications, if the client can operate without
prefixes it should accept allocated addresses and transition to
the 'bound' state. When the client subsequently sends Renew/Rebind messages
to the server, according to the T1 and T2 times, to extend the lifetimes of
the allocated addresses, if the client is still interested in obtaining
prefixes from the server, it may also include an IA_PD in the Renew/Rebind
to request allocation of the prefixes. If the server still cannot
allocate the prefixes it will respond with the IA_PD(s) containing
NoPrefixAvail status code. However, if the server can allocate the
prefixes it will allocate and send them in the IA_PD(s) to the client.
Similar situation occurs when the server is unable to allocate addresses
for the client but can delegate prefixes. The client may request allocation
of the addresses while renewing the delegated prefixes. Allocating leases for
other IA types while renewing existing leases is by default supported by
the Kea DHCPv6 server, and the server provides no configuration mechanisms
to disable this behavior.</para>
<para>
The following are the other behaviors first introduced in the
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc7550">RFC 7550</link>
(now being part of the
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>)
and supported by the Kea DHCPv6 server:
<itemizedlist>
<listitem><simpara>Set T1/T2 timers to the same value for all
stateful (IA_NA and IA_PD) options to facilitate renewal of all
client's leases at the same time (in a single message exchange),
</simpara></listitem>
<listitem><simpara>NoAddrsAvail and NoPrefixAvail status codes
are placed in the IA_NA and IA_PD options in the Advertise message,
rather than as the top level options.</simpara></listitem>
</itemizedlist>
</para>
</section>
<section xml: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 the interface that belongs to the subnet from which
the server will assign addresses. In the typical case, the
server is able to use the IPv6 address inserted by the relay (in the link-addr
field in RELAY-FORW message) to select the 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. The 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 a 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 with an address in 2001:db8:1::/64 subnet.
It will also select that subnet for a relay with address 3000::1.
<screen>
"Dhcp6": {
"subnet6": [
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
<userinput>"relay": {
"ip-addresses": [ "3000::1" ]
}</userinput>
}
]
}
</screen>
</para>
<para>If "relay" is specified, the "ip-addresses" parameter within
it is mandatory.</para>
<note>
<para>
As of Kea 1.4, the "ip-address" parameter in "relay" has been deprecated
in favor of "ip-addresses" which supports specifying a list of addresses.
Configuration parsing, will honor the singular form for now but users are
encouraged to migrate.
</para>
</note>
</section>
<section xml: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="classify"/>.
One specific example is a 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>
"Dhcp6": {
"subnet6": [
{
"subnet": "3000::/64",
"pools": [
{ "pool": "3000::2 - 3000::ffff" }
],
<userinput>"client-class": "VENDOR_CLASS_docsis3.0",
"relay": {
"ip-addresses": [ "3000::1" ]
}</userinput>
},
{
"subnet": "2001:db8:1::/64",
"pools": [
{
"pool": "2001:db8:1::1-2001:db8:1::ffff"
}
],
<userinput>"relay": {
"ip-addresses": [ "3000::1" ]
}</userinput>
}
]
}
</screen>
</para>
</section>
<section xml:id="mac-in-dhcpv6">
<title>MAC/Hardware Addresses in DHCPv6</title>
<para>MAC/hardware addresses are available in DHCPv4 messages
from the clients and administrators
frequently use that information to perform certain tasks, like per host
configuration, address reservation for specific MAC addresses and other.
Unfortunately, the DHCPv6 protocol does not provide any completely reliable way
to retrieve that information. To mitigate that issue a number of mechanisms
have been implemented in Kea that attempt to gather it. Each
of those mechanisms works in certain cases, but may fail in other cases.
Whether the mechanism works or not in the particular deployment is
somewhat dependent on the network topology and the technologies used.</para>
<para>Kea allows configuration of which of the supported methods should be
used and in what order. This configuration may be considered a fine tuning
of the DHCP deployment. In a typical deployment the default
value of <command>"any"</command> is sufficient and there is no
need to select specific methods. Changing the value of this parameter
is the most useful in cases when an administrator wants to disable
certain method, e.g. if the administrator trusts the network infrastructure
more than the information provided by the clients themselves, the
administrator may prefer information provided by the relays over that
provided by the clients.
</para>
<para>
The configuration is controlled by the <command>mac-sources</command>
parameter as follows:
<screen>
"Dhcp6": {
<userinput>"mac-sources": [ "method1", "method2", "method3", ... ]</userinput>,
"subnet6": [ ... ],
...
}
</screen>
When not specified, a special value of "any" is used, which
instructs the server to attempt to use all the methods in sequence and use
value returned by the first one that succeeds. If specified, it
has to have at least one value.</para>
<para>Supported methods are:
<itemizedlist>
<listitem>
<simpara><command>any</command> - Not an actual method, just a keyword that
instructs Kea to try all other methods and use the first one that succeeds.
This is the default operation if no <command>mac-sources</command> are defined.
</simpara>
</listitem>
<listitem>
<simpara><command>raw</command> - In principle, a DHCPv6 server could use raw
sockets to receive incoming traffic and extract MAC/hardware address
information. This is currently not implemented for DHCPv6 and this value has
no effect.
</simpara>
</listitem>
<listitem>
<simpara><command>duid</command> - DHCPv6 uses DUID identifiers instead of
MAC addresses. There are currently four DUID types defined, with two of them
(DUID-LLT, which is the default one and DUID-LL) convey MAC address information.
Although <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="" utl="http://tools.ietf.org/html/rfc8415">RFC 8415</link> forbids
it, it is possible to parse those DUIDs and extract
necessary information from them. This method is not completely reliable, as
clients may use other DUID types, namely DUID-EN or DUID-UUID.
</simpara>
</listitem>
<listitem>
<simpara><command>ipv6-link-local</command> - Another possible acquisition
method comes from the source IPv6 address. In typical usage, clients are
sending their packets from IPv6 link-local addresses. There is a good chance
that those addresses are based on EUI-64, which contains MAC address. This
method is not completely reliable, as clients may use other link-local address
types. In particular, privacy extensions, defined in
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4941">RFC 4941</link>, do not use
MAC addresses. Also note that successful extraction requires that the
address's u-bit must be set to 1 and its g-bit set to 0, indicating that it
is an interface identifier as per
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc2373#section-2.5.1">
RFC 2373, section 2.5.1</link>.
</simpara>
</listitem>
<listitem>
<simpara><command>client-link-addr-option</command> - One extension defined
to alleviate missing MAC issues is client link-layer address option, defined
in <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6939">RFC 6939</link>. This is
an option that is inserted by a relay and contains information about client's
MAC address. This method requires a relay agent that supports the option and
is configured to insert it. This method is useless for directly connected
clients. This parameter can also be specified as <command>rfc6939</command>,
which is an alias for <command>client-link-addr-option</command>.
</simpara>
</listitem>
<listitem>
<simpara><command>remote-id</command> -
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4649">RFC 4649</link>
defines a remote-id option that is inserted by a relay agent. Depending
on the relay agent configuration, the inserted option may convey the client's
MAC address information. This parameter can also be specified as
<command>rfc4649</command>, which is an alias for <command>remote-id</command>.
</simpara>
</listitem>
<listitem>
<simpara><command>subscriber-id</command> - Another option
that is somewhat similar to the previous one is subscriber-id,
defined in <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4580">RFC
4580</link>. It is, too, inserted by a relay agent that is
configured to insert it. This parameter can also be specified
as <command>rfc4580</command>, which is an alias for
<command>subscriber-id</command>. This method is currently not
implemented.
</simpara>
</listitem>
<listitem>
<simpara><command>docsis-cmts</command> - Yet another possible source of MAC
address information are the DOCSIS options inserted by a CMTS that acts
as a DHCPv6 relay agent in cable networks. This method attempts to extract
MAC address information from suboption 1026 (cm mac) of the vendor specific option
with vendor-id=4491. This vendor option is extracted from the relay-forward message,
not the original client's message.
</simpara>
</listitem>
<listitem>
<simpara><command>docsis-modem</command> - Yet another possible source of MAC
address information are the DOCSIS options inserted by the cable modem itself.
This method attempts to extract MAC address information from suboption 36 (device id)
of the vendor specific option with vendor-id=4491. This vendor option is extracted from
the original client's message, not from any relay options.
</simpara>
</listitem>
</itemizedlist>
</para>
<para>Empty mac-sources is not allowed. If you do not want to specify it,
either simply omit mac-sources definition or specify it with the "any" value
which is the default.</para>
</section>
<section xml:id="dhcp6-decline">
<title>Duplicate Addresses (DECLINE Support)</title>
<para>The DHCPv6 server is configured with a certain pool of
addresses that it is expected to hand out to the DHCPv6 clients.
It is assumed that the server is authoritative and has complete
jurisdiction over those addresses. However, due to various
reasons, such as misconfiguration or a faulty client implementation
that retains its address beyond the valid lifetime, there may be
devices connected that use those addresses without the server's
approval or knowledge.</para>
<para>Such an unwelcome event can be detected
by legitimate clients (using Duplicate Address Detection) and
reported to the DHCPv6 server using a DECLINE message. The server
will do a sanity check (if the client declining an address really
was supposed to use it), then will conduct a clean up operation
and confirm it by sending back a REPLY message. Any DNS entries
related to that address will be removed, the fact will be logged
and hooks will be triggered. After that is done, the address
will be marked as declined (which indicates that it is used by
an unknown entity and thus not available for assignment to
anyone) and a probation time will be set on it. Unless otherwise
configured, the probation period lasts 24 hours. After that
period, the server will recover the lease (i.e. put it back into
the available state) and the address will be available for assignment
again. It should be noted that if the underlying issue of a
misconfigured device is not resolved, the duplicate address
scenario will repeat. On the other hand, it provides an
opportunity to recover from such an event automatically, without
any sysadmin intervention.</para>
<para>To configure the decline probation period to a value other
than the default, the following syntax can be used:
<screen>
"Dhcp6": {
<userinput>"decline-probation-period": 3600</userinput>,
"subnet6": [ ... ],
...
}
</screen>
The parameter is expressed in seconds, so the example above will instruct
the server to recycle declined leases after an hour.</para>
<para>There are several statistics and hook points associated with the
Decline handling procedure. The lease6_decline hook is triggered after the
incoming Decline message has been sanitized and the server is about to decline
the lease. The declined-addresses statistic is increased after the
hook returns (both global and subnet specific variants). (See
<xref linkend="dhcp4-stats"/> and <xref linkend="hooks-libraries"/> for more details
on DHCPv4 statistics and Kea hook points.)</para>
<para>Once the probation time elapses, the declined lease is recovered
using the standard expired lease reclamation procedure, with several
additional steps. In particular, both declined-addresses statistics
(global and subnet specific) are decreased. At the same time,
reclaimed-declined-addresses statistics (again in two variants, global and
subnet specific) are increased.</para>
<para>Note about statistics: The server does not decrease the
assigned-addresses statistics when a DECLINE message is received and
processed successfully. While technically a declined address is no longer
assigned, the primary usage of the assigned-addresses statistic is to
monitor pool utilization. Most people would forget to include
declined-addresses in the calculation, and simply do
assigned-addresses/total-addresses. This would have a bias towards
under-representing pool utilization. As this has a potential for major
issues, we decided not to decrease assigned addresses immediately after
receiving Decline, but to do it later when we recover the address back to
the available pool.</para>
</section>
<section xml:id="dhcp6-stats">
<title>Statistics in the DHCPv6 Server</title>
<note>
<para>This section describes DHCPv6-specific statistics. For a general
overview and usage of statistics, see <xref linkend="stats"/>.</para>
</note>
<para>
The DHCPv6 server supports the following statistics:
</para>
<table frame="all" xml:id="dhcp6-statistics">
<title>DHCPv6 Statistics</title>
<tgroup cols="3">
<colspec colname="statistic" align="center"/>
<colspec colname="type" align="center"/>
<colspec colname="description" align="left"/>
<thead>
<row>
<entry>Statistic</entry>
<entry>Data Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>pkt6-received</entry>
<entry>integer</entry>
<entry>Number of DHCPv6 packets received. This includes all packets:
valid, bogus, corrupted, rejected etc. This statistic is expected
to grow rapidly.</entry>
</row>
<row>
<entry>pkt6-receive-drop</entry>
<entry>integer</entry>
<entry>Number of incoming packets that were dropped. The exact reason
for dropping packets is logged, but the most common reasons may
be: an unacceptable or not supported packet type, direct responses
are forbidden, the server-id sent by the client does not match the
server's server-id or the packet is malformed.</entry>
</row>
<row>
<entry>pkt6-parse-failed</entry>
<entry>integer</entry>
<entry>Number of incoming packets that could not be parsed.
A non-zero value of this statistic indicates that the server
received a malformed or truncated packet. This may indicate problems
in your network, faulty clients, faulty relay agents or a bug in the
server.</entry>
</row>
<row>
<entry>pkt6-solicit-received</entry>
<entry>integer</entry>
<entry>
Number of SOLICIT packets received. This statistic is expected
to grow. Its increase means that clients that just booted
started their configuration process and their initial packets
reached your server.
</entry>
</row>
<row>
<entry>pkt6-advertise-received</entry>
<entry>integer</entry>
<entry>
Number of ADVERTISE packets received. Advertise packets are sent
by the server and the server is never expected to receive them. A non-zero
value of this statistic indicates an error occurring in the network.
One likely cause would be a misbehaving relay agent that incorrectly
forwards ADVERTISE messages towards the server rather back to the
clients.
</entry>
</row>
<row>
<entry>pkt6-request-received</entry>
<entry>integer</entry>
<entry>Number of REQUEST packets received. This statistic
is expected to grow. Its increase means that clients that just booted
received the server's response (ADVERTISE), accepted it and are now
requesting an address (REQUEST).
</entry>
</row>
<row>
<entry>pkt6-reply-received</entry>
<entry>integer</entry>
<entry>Number of REPLY packets received. This statistic is
expected to remain zero at all times, as REPLY packets are sent by
the server and the server is never expected to receive
them. A non-zero value indicates an error. One likely cause would be
a misbehaving relay agent that incorrectly forwards REPLY messages
towards the server, rather back to the clients.
</entry>
</row>
<row>
<entry>pkt6-renew-received</entry>
<entry>integer</entry>
<entry>Number of RENEW packets received. This statistic
is expected to grow. Its increase means that clients received their
addresses and prefixes and are trying to renew them.
</entry>
</row>
<row>
<entry>pkt6-rebind-received</entry>
<entry>integer</entry>
<entry>Number of REBIND packets received. A non-zero value
indicates that clients didn't receive responses to their RENEW messages
(regular lease renewal mechanism) and are attempting to find any server
that is able to take over their leases. It may mean that some server's
REPLY messages never reached the clients.
</entry>
</row>
<row>
<entry>pkt6-release-received</entry>
<entry>integer</entry>
<entry>Number of RELEASE packets received. This statistic is expected
to grow when a device is being shut down in the network. It
indicates that the address or prefix assigned is reported as no longer
needed. Note that many devices, especially wireless, do not send RELEASE
packets either because of design choice or due to the client moving out
of range.
</entry>
</row>
<row>
<entry>pkt6-decline-received</entry>
<entry>integer</entry>
<entry>
Number of DECLINE packets received. This statistic is expected to
remain close to zero. Its increase means that a client leased an
address, but discovered that the address is currently used by an
unknown device in your network. If this statistic is growing, it
may indicate a misconfigured server or devices that have statically
assigned conflicting addresses.
</entry>
</row>
<row>
<entry>pkt6-infrequest-received</entry>
<entry>integer</entry>
<entry>
Number of INFORMATION-REQUEST packets received. This statistic
is expected to grow if there are devices that are using
stateless DHCPv6. INFORMATION-REQUEST messages are used by
clients that request stateless configuration, i.e. options
and parameters other than addresses or prefixes.
</entry>
</row>
<row>
<entry>pkt6-dhcpv4-query-received</entry>
<entry>integer</entry>
<entry>
Number of DHCPv4-QUERY packets received. This
statistic is expected to grow if there are devices
that are using DHCPv4-over-DHCPv6. DHCPv4-QUERY
messages are used by DHCPv4 clients on an IPv6 only
line which encapsulates the requests over DHCPv6.
</entry>
</row>
<row>
<entry>pkt6-dhcpv4-response-received</entry>
<entry>integer</entry>
<entry>
Number of DHCPv4-RESPONSE packets received. This
statistic is expected to remain zero at all times, as
DHCPv4-RESPONSE packets are sent by the server and the
server is never expected to receive them. A non-zero
value indicates an error. One likely cause would be a
misbehaving relay agent that incorrectly forwards
DHCPv4-RESPONSE message towards the server rather
back to the clients.
</entry>
</row>
<row>
<entry>pkt6-unknown-received</entry>
<entry>integer</entry>
<entry>Number of packets received of an unknown type. A non-zero
value of this statistic indicates that the server received a
packet that it wasn't able to recognize: either it had an unsupported
type or was possibly malformed.</entry>
</row>
<row>
<entry>pkt6-sent</entry>
<entry>integer</entry>
<entry>Number of DHCPv6 packets sent. This statistic is expected
to grow every time the server transmits a packet. In general, it
should roughly match pkt6-received, as most incoming packets cause
the server to respond. There are exceptions (e.g. server receiving a
REQUEST with server-id matching other server), so do not worry, if
it is lesser than pkt6-received.</entry>
</row>
<row>
<entry>pkt6-advertise-sent</entry>
<entry>integer</entry>
<entry>Number of ADVERTISE packets sent. This statistic is
expected to grow in most cases after a SOLICIT is processed. There
are certain uncommon, but valid cases where incoming SOLICIT is
dropped, but in general this statistic is expected to be close to
pkt6-solicit-received.</entry>
</row>
<row>
<entry>pkt6-reply-sent</entry>
<entry>integer</entry>
<entry>Number of REPLY packets sent. This statistic is expected to
grow in most cases after a SOLICIT (with rapid-commit), REQUEST,
RENEW, REBIND, RELEASE, DECLINE or INFORMATION-REQUEST is
processed. There are certain cases where there is no response.
</entry>
</row>
<row>
<entry>pkt6-dhcpv4-response-sent</entry>
<entry>integer</entry>
<entry>Number of DHCPv4-RESPONSE packets sent. This
statistic is expected to grow in most cases after a
DHCPv4-QUERY is processed. There are certain cases where
there is no response.
</entry>
</row>
<row>
<entry>subnet[id].total-nas</entry>
<entry>integer</entry>
<entry>
This statistic shows the total number of NA addresses available for
DHCPv6 management for a given subnet. In other words, this is the sum
of all addresses in all configured pools. This statistic changes only
during configuration changes. Note that it does not take into account any
addresses that may be reserved due to host reservation. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately and is
reset during a reconfiguration event.
</entry>
</row>
<row>
<entry>subnet[id].assigned-nas</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of NA addresses in a given subnet that
are assigned. This statistic increases every time a new lease is allocated
(as a result of receiving a REQUEST message) and is decreased every time a
lease is released (a RELEASE message is received) or expires. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately and is
reset during a reconfiguration event.
</entry>
</row>
<row>
<entry>subnet[id].total-pds</entry>
<entry>integer</entry>
<entry>
This statistic shows the total number of PD prefixes available for
DHCPv6 management for a given subnet. In other words, this is the sum
of all prefixes in all configured pools. This statistic changes only
during configuration changes. Note it does not take into account any
prefixes that may be reserved due to host reservation. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately and is
reset during a reconfiguration event.
</entry>
</row>
<row>
<entry>subnet[id].assigned-pds</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of PD prefixes in a given subnet that
are assigned. This statistic increases every time a new lease is allocated
(as a result of receiving a REQUEST message) and is decreased every time a
lease is released (a RELEASE message is received) or expires. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This statistic
is exposed for each subnet separately and is reset during a
reconfiguration event.
</entry>
</row>
<row>
<entry>reclaimed-leases</entry>
<entry>integer</entry>
<entry> This statistic is the number of expired leases that have been
reclaimed since server startup. It is incremented each time an expired
lease is reclaimed (it counts both NA and PD reclamations) and is reset
when the server is reconfigured.
</entry>
</row>
<row>
<entry>subnet[id].reclaimed-leases</entry>
<entry>integer</entry>
<entry>This statistic is the number of expired leases associated with
a given subnet (<emphasis>"id"</emphasis> is the subnet-id) that have
been reclaimed since server startup. It is incremented each time an expired
lease is reclaimed (it counts both NA and PD reclamations) and is reset
when the server is reconfigured.
</entry>
</row>
<row>
<entry>declined-addresses</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of IPv6 addresses that are
currently declined and so counts the number of leases
currently unavailable. Once a lease is recovered, this
statistic will be decreased. Ideally, this statistic should be
zero. If this statistic is non-zero (or worse, increasing),
the network administrator should investigate if there is
a misbehaving device in the network. This is a global statistic
that covers all subnets.
</entry>
</row>
<row>
<entry>subnet[id].declined-addresses</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of IPv6 addresses that are
currently declined in a given subnet. This statistic counts the
number of leases currently unavailable. Once a lease is
recovered, this statistic will be decreased. Ideally, this
statistic should be zero. If this statistic is
non-zero (or worse, increasing), a network administrator should
investigate if there is a misbehaving device in the network. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</entry>
</row>
<row>
<entry>reclaimed-declined-addresses</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of IPv6 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. This is a global statistic that
covers all subnets.
</entry>
</row>
<row>
<entry>subnet[id].reclaimed-declined-addresses</entry>
<entry>integer</entry>
<entry>
This statistic shows the number of IPv6 addresses that were
declined, but have now been recovered. Unlike
declined-addresses, this statistic never decreases. It can be used
as a long term indicator of how many actual valid Declines were
processed and recovered from. The
<emphasis>id</emphasis> is the subnet-id of a given subnet. This
statistic is exposed for each subnet separately.
</entry>
</row>
</tbody>
</tgroup>
</table>
</section>
<section xml:id="dhcp6-ctrl-channel">
<title>Management API for the DHCPv6 Server</title>
<para>
The management API allows the issuing of specific
management commands, such as statistics retrieval, reconfiguration or shutdown.
For more details, see <xref linkend="ctrl-channel"/>. Currently the only
supported communication channel type is UNIX stream socket. By default there
are no sockets open. To instruct Kea to open a socket, the following entry
in the configuration file can be used:
<screen>
"Dhcp6": {
"control-socket": {
"socket-type": "unix",
"socket-name": <userinput>"/path/to/the/unix/socket"</userinput>
},
"subnet6": [
...
],
...
}
</screen>
</para>
<para>
The length of the path specified by the <command>socket-name</command>
parameter is restricted by the maximum length for the unix socket name
on your operating system, i.e. the size of the <command>sun_path</command>
field in the <command>sockaddr_un</command> structure, decreased by 1.
This value varies on different operating systems between 91 and 107
characters. Typical values are 107 on Linux and 103 on FreeBSD.
</para>
<para>
Communication over control channel is conducted using JSON structures.
See the Control Channel section in the Kea Developer's Guide for more details.
</para>
<para>The DHCPv6 server supports the following operational commands:
<itemizedlist>
<listitem>build-report</listitem>
<listitem>config-get</listitem>
<listitem>config-reload</listitem>
<listitem>config-set</listitem>
<listitem>config-test</listitem>
<listitem>config-write</listitem>
<listitem>dhcp-disable</listitem>
<listitem>dhcp-enable</listitem>
<listitem>leases-reclaim</listitem>
<listitem>list-commands</listitem>
<listitem>shutdown</listitem>
<listitem>version-get</listitem>
</itemizedlist>
as described in <xref linkend="commands-common"/>. In addition,
it supports the following statistics related commands:
<itemizedlist>
<listitem>statistic-get</listitem>
<listitem>statistic-reset</listitem>
<listitem>statistic-remove</listitem>
<listitem>statistic-get-all</listitem>
<listitem>statistic-reset-all</listitem>
<listitem>statistic-remove-all</listitem>
</itemizedlist>
as described here <xref linkend="command-stats"/>.
</para>
</section>
<section id="dhcp6-user-contexts">
<title>User contexts in IPv6</title>
<para>
Kea allows loading hook libraries that sometimes could benefit from
additional parameters. If such a parameter is specific to the whole
library, it is typically defined as a parameter for the hook library.
However, sometimes there is a need to specify parameters that are
different for each pool.
</para>
<para>
User contexts can store arbitrary data as long as it is valid JSON
syntax and its top level element is a map (i.e. the data must be
enclosed in curly brackets). Some hook libraries may expect specific
formatting, though. Please consult specific hook library
documentation for details.
</para>
<para>
User contexts can be specified at either global scope,
shared network, subnet, pool, client class, option data or
definition level, and host reservation. One other useful
usage is the ability to store comments or descriptions.
</para>
<para>
Let's consider a lightweight 4over6 deployment as an example. It is an
IPv6 transition technology that allows mapping IPv6 prefix into full
or parts of IPv4 addresses. In DHCP context, these are certain
parameters that are supposed to be delivered to clients in form of
additional options. Values of those options are correlated to
delegated prefixes, so it is reasonable to keep those parameters
together with the PD pool. On the other hand, lightweight 4over6 is
not a commonly used feature, so it is not a part of the base Kea
code. The solution to this problem is to use user context. For each PD
pool that is expected to be used for lightweight 4over6, user context
with extra parameters is defined. Those extra parameters will be used
by hook library that would be loaded only when dynamic calculation of
the lightweight 4over6 option is actually needed. An example
configuration looks as follows:
<screen>
"Dhcp6": {
"subnet6": [ {
"pd-pools": [
{
"prefix": "2001:db8::",
"prefix-len": 56,
"delegated-len": 64,
// This is a pool specific context.
<userinput>"user-context": {
"threshold-percent": 85,
"v4-network": "192.168.0.0/16",
"v4-overflow": "10.0.0.0/16",
"lw4over6-sharing-ratio": 64,
"lw4over6-v4-pool": "192.0.2.0/24",
"lw4over6-sysports-exclude": true,
"lw4over6-bind-prefix-len": 56
}</userinput>
} ],
"subnet": "2001:db8::/32",
// This is a subnet specific context. You can put any type of
// information here as long as it is a valid JSON.
<userinput>"user-context": {
"comment": "Those v4-v6 migration technologies are tricky.",
"experimental": true,
"billing-department": 42,
"contact-points": [ "Alice", "Bob" ]
}</userinput>
} ],
...
}</screen>
</para>
<para>
Kea does not interpret or use the content of the user context:
it just stores it, making it available to the hook
libraries. It is up to each hook library to extract the information
and make use of it.
The parser translates a "comment" entry into a user-context
with the entry, this allows to attach a comment inside the
configuration itself.
</para>
<para>
For more background information, see <xref linkend="user-context"/>.
</para>
</section>
<section xml:id="dhcp6-std">
<title>Supported DHCPv6 Standards</title>
<para>The following standards are currently
supported:</para>
<itemizedlist>
<listitem>
<simpara><emphasis>Dynamic Host Configuration Protocol for IPv6</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc3315">RFC 3315</link>:
Supported messages are SOLICIT,
ADVERTISE, REQUEST, RELEASE, RENEW, REBIND, INFORMATION-REQUEST,
CONFIRM and REPLY.</simpara>
</listitem>
<listitem>
<simpara><emphasis>IPv6 Prefix Options for
Dynamic Host Configuration Protocol (DHCP) version 6</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc3633">RFC 3633</link>:
Supported options are IA_PD and
IA_PREFIX. Also supported is the status code NoPrefixAvail.</simpara>
</listitem>
<listitem>
<simpara><emphasis>DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc3646">RFC 3646</link>:
Supported option is DNS_SERVERS.</simpara>
</listitem>
<listitem>
<simpara><emphasis>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Relay Agent Remote-ID Option</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4649">RFC 4649</link>:
REMOTE-ID option is supported.</simpara>
</listitem>
<listitem>
<simpara><emphasis>The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Client
Fully Qualified Domain Name (FQDN) Option</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc4704">RFC 4704</link>:
Supported option is CLIENT_FQDN.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
Option for Dual-Stack Lite</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6334">RFC 6334</link>:
the AFTR-Name DHCPv6 Option is supported.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Relay-Supplied DHCP Options</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6422">RFC 6422</link>:
Full functionality is supported: OPTION_RSOO, ability of the server
to echo back the options, checks whether an option is RSOO-enabled,
ability to mark additional options as RSOO-enabled.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Prefix Exclude Option for DHCPv6-based Prefix
Delegation</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6603">RFC
6603</link>: Prefix Exclude option is supported.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Client Link-Layer Address Option in
DHCPv6</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc6939">RFC
6939</link>: Supported option is client link-layer
address option.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Issues and Recommendations with Multiple
Stateful DHCPv6 Options</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc7550">RFC
7550</link>: All recommendations related to the DHCPv6 server
operation are supported.</simpara>
</listitem>
<listitem>
<simpara><emphasis>DHCPv6 Options for Configuration of Softwire
Address and Port-Mapped Clients</emphasis>,
<ulink url="http://tools.ietf.org/html/rfc7598">RFC
7598</ulink>: All options specified in this specification are
supported by the DHCPv6 server.</simpara>
</listitem>
<listitem>
<simpara><emphasis>Dynamic Host Configuration Protocol for IPv6 (DHCPv6)</emphasis>,
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>:
New DHCPv6 protocol specification which obsoletes RFC 3315, RFC 3633, RFC 3736, RFC 4242, RFC 7083,
RFC 7283 and RFC 7550</simpara>
</listitem>
</itemizedlist>
</section>
<section xml:id="dhcp6-limit">
<title>DHCPv6 Server Limitations</title>
<para> These are the current limitations of 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>
<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.
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://tools.ietf.org/html/rfc8415">RFC 8415</link>
allows 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>
Client reconfiguration (RECONFIGURE) is not yet supported.
</simpara>
</listitem>
</itemizedlist>
</section>
<section id="dhcp6-srv-examples">
<title>Kea DHCPv6 server examples</title>
<para>
A collection of simple to use examples for DHCPv6 component of Kea is
available with the sources. It is located in doc/examples/kea6
directory. At the time of writing this text there were 18 examples,
but the number is growing slowly with each release.
</para>
</section>
</chapter>
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