</simpara>
</listitem>
</itemizedlist>
-
+
<para>This feature is currently implemented for memfile backend.</para>
<para>
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 resrvations 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">
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">
Allowed values are:
<itemizedlist>
- <listitem><simpara> <command>all</command> - enables all host reservation
- types. This is the default value. This setting is the safest and the most
- flexible. It allows in-pool and out-of-pool reservations. As all checks
- are conducted, it is also the slowest.
+ <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
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.
+ <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>
}
]
}
-</screen>
+ </screen>
</para>
+ <para>
+ An example configuration using global reservations is shown below:
+<screen>
+"Dhcp6": {
+
+ <userinput>
+ "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",
+ <userinput>"reservation-mode": "global"</userinput>,
+ ...
+ },
+ {
+ "subnet": "2001:db8:2::/64",
+ <userinput>"reservation-mode": "global"</userinput>,
+ ...
+ }
+ ]
+}
+</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
</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::/64 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::/48, 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 2001:db8:1::/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 -->
projects / thirdparty / kea.git / commitdiff
