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.. _dhcp-relay:
##########
DHCP Relay
##########
If you want your router to forward DHCP requests to an external DHCP server
you can configure the system to act as a DHCP relay agent. The DHCP relay
agent works with IPv4 and IPv6 addresses.
All interfaces used for the DHCP relay must be configured.
**********
IPv4 relay
**********
Configuration
=============
.. cfgcmd:: set service dhcp-relay interface <interface>
Enable the DHCP relay service on the given interface.
.. cfgcmd:: set service dhcp-relay server <server>
Configure IP address of the DHCP `<server>` which will handle the relayed
packets.
.. cfgcmd:: set service dhcp-relay relay-options relay-agents-packets discard
The router should discard DHCP packages already containing relay agent
information to ensure that only requests from DHCP clients are forwarded.
Options
-------
.. cfgcmd:: set service dhcp-relay relay-options hop-count <count>
Set the maximum hop `<count>` before packets are discarded. Range 0...255,
default 10.
.. cfgcmd:: set service dhcp-relay relay-options max-size <size>
Set maximum `<size>` of DHCP packets including relay agent information. If a
DHCP packet size surpasses this value it will be forwarded without appending
relay agent information. Range 64...1400, default 576.
.. cfgcmd:: set service dhcp-relay relay-options relay-agents-packet
<append | discard | forward | replace>
Four policies for reforwarding DHCP packets exist:
* **append:** The relay agent is allowed to append its own relay information
to a received DHCP packet, disregarding relay information already present
in the packet.
* **discard:** Received packets which already contain relay information will
be discarded.
* **forward:** All packets are forwarded, relay information already present
will be ignored.
* **replace:** Relay information already present in a packet is stripped and
replaced with the router's own relay information set.
Example
=======
* Listen for DHCP requests on interface ``eth1``.
* DHCP server is located at IPv4 address 10.0.1.4.
* Router receives DHCP client requests on ``eth1`` and relays them to the server
at 10.0.1.4.
.. figure:: /_static/images/service_dhcp-relay01.png
:scale: 80 %
:alt: DHCP relay example
DHCP relay example
The generated configuration will look like:
.. code-block:: none
show service dhcp-relay
interface eth1
server 10.0.1.4
relay-options {
relay-agents-packets discard
}
Operation
=========
.. opcmd:: restart dhcp relay-agent
Restart DHCP relay service
**********
IPv6 relay
**********
.. _dhcp-relay:ipv6_configuration:
Configuration
=============
.. cfgcmd:: set service dhcpv6-relay listen-interface <interface>
Set eth1 to be the listening interface for the DHCPv6 relay.
Multiple interfaces may be specified.
.. cfgcmd:: set service dhcpv6-relay upstream-interface <interface>
address <server>
Specifies an upstream network `<interface>` from which replies from
`<server>` and other relay agents will be accepted.
.. _dhcp-relay:ipv6_options:
Options
-------
.. cfgcmd:: set service dhcpv6-relay max-hop-count 'count'
Set maximum hop count before packets are discarded, default: 10
.. cfgcmd:: set service dhcpv6-relay use-interface-id-option
If this is set the relay agent will insert the interface ID. This option is
set automatically if more than one listening interfaces are in use.
.. _dhcp-relay:ipv6_example:
Example
=======
* DHCPv6 requests are received by the router on `listening interface` ``eth1``
* Requests are forwarded through ``eth2`` as the `upstream interface`
* External DHCPv6 server is at 2001:db8::4
.. figure:: /_static/images/service_dhcpv6-relay01.png
:scale: 80 %
:alt: DHCPv6 relay example
DHCPv6 relay example
The generated configuration will look like:
.. code-block:: none
commit
show service dhcpv6-relay
listen-interface eth1 {
}
upstream-interface eth2 {
address 2001:db8::4
}
.. _dhcp-relay:ipv6_op_cmd:
Operation
=========
.. opcmd:: restart dhcpv6 relay-agent
Restart DHCPv6 relay agent immediately.
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