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