Service: Add DHCP relay

3 files changed, 169 insertions, 0 deletions

diff --git a/docs/ch11-services.rst b/docs/ch11-services.rst
index 35acb71d..52303b36 100644
--- a/docs/ch11-services.rst
+++ b/docs/ch11-services.rst
@@ -410,6 +410,175 @@ Commit the changes and show the configuration:
 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. See
+https://wiki.vyos.net/wiki/Network_address_setup.
+
+DHCP relay example
+^^^^^^^^^^^^^^^^^^
+
+.. figure:: images/service_dhcp-relay01.png
+   :scale: 80 %
+   :alt: DHCP relay example
+
+   DHCP relay example
+
+In this example the interfaces used for the DHCP relay are eth1 and eth2. The
+router receives DHCP client requests on eth1 and relays them through eth2 to
+the DHCP server at 10.0.1.4.
+
+Configuration
+^^^^^^^^^^^^^
+
+Enable DHCP relay for eth1 and eth2:
+
+.. code-block:: sh
+
+  set service dhcp-relay interface eth1
+  set service dhcp-relay interface eth2
+
+Set the IP address of the DHCP server:
+
+.. code-block:: sh
+
+  set service dhcp-relay server 10.0.1.4
+
+The router should discard DHCP packages already containing relay agent
+information to ensure that only requests from DHCP clients are forwarded:
+
+.. code-block:: sh
+
+  set service dhcp-relay relay-options relay-agents-packets discard
+
+Commit the changes and show the results:
+
+.. code-block:: sh
+
+  commit
+  show service dhcp-relay
+      interface eth1
+      interface eth2
+      server 10.0.1.4
+      relay-options {
+         relay-agents-packets discard
+      }
+
+The DHCP relay agent can be restarted with:
+
+.. code-block:: sh
+
+  restart dhcp relay-agent
+
+DHCPv6 relay example
+^^^^^^^^^^^^^^^^^^^^
+
+.. figure:: images/service_dhcpv6-relay01.png
+   :scale: 80 %
+   :alt: DHCPv6 relay example
+
+   DHCPv6 relay example
+
+In this example DHCPv6 requests are received by the router on eth1 (`listening
+interface`) and forwarded through eth2 (`upstream interface`) to the external
+DHCPv6 server at 2001:db8:100::4.
+
+Configuration
+*************
+
+Set eth1 to be the listening interface for the DHCPv6 relay:
+
+.. code-block:: sh
+
+  set service dhcpv6-relay listen-interface eth1
+
+Set eth2 to be the upstream interface and specify the IPv6 address of the DHCPv6 server:
+
+.. code-block:: sh
+
+  set service dhcpv6-relay upstream-interface eth2 address 2001:db8:100::4
+
+Commit the changes and show results:
+
+.. code-block:: sh
+
+  commit
+  show service dhcpv6-relay
+      listen-interface eth1 {
+      }
+      upstream-interface eth2 {
+         address 2001:db8:100::4
+      }
+
+Show the current status of the DHCPv6 relay agent:
+
+.. code-block:: sh
+
+  show dhcpv6 relay-agent status
+
+The DHCPv6 relay agent can be restarted with:
+
+.. code-block:: sh
+
+  restart dhcpv6 relay-agent
+
+Additional parameters
+^^^^^^^^^^^^^^^^^^^^^
+
+DHCP relay agent options
+************************
+
+Set the maximum hop count before packets are discarded. Range 0...255,
+default 10.
+
+* :code:`set service dhcp-relay relay-options hop-count 'count'`
+
+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.
+
+* :code:`set service dhcp-relay relay-options max-size 'size'`
+
+Set the port used to relay DHCP client messages. Range 1...65535, default 67.
+After setting a different port, requests are still accepted on port 67 but
+replies are forwarded to 255.255.255.255 port 0 instead of 68.
+
+* :code:`set service dhcp-relay relay-options port 'port'`
+
+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.
+
+* :code:`set service dhcp-relay relay-options relay-agents-packet 'policy'`
+
+DHCPv6 relay agent options
+**************************
+
+Set listening port for DHCPv6 requests. Default: 547.
+
+* :code:`set service dhcpv6-relay listen-port 'port'`
+
+Set maximum hop count before packets are discarded. Default: 10.
+
+* :code:`set service dhcpv6-relay max-hop-count 'count'`
+
+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.
+
+* :code:`set service dhcpv6-relay use-interface-id-option`
 
 DNS Forwarding
 --------------
diff --git a/docs/images/service_dhcp-relay01.png b/docs/images/service_dhcp-relay01.png
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diff --git a/docs/images/service_dhcpv6-relay01.png b/docs/images/service_dhcpv6-relay01.png
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