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


set service dhcp-relay interface <interface>

Enable the DHCP relay service on the given interface.

set service dhcp-relay server <server>

Configure IP address of the DHCP <server> which will handle the relayed packets.


set service dhcp-relay relay-options hop-count <count>

Set the maximum hop <count> before packets are discarded. Range 0…255, default 10.

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.

set service dhcp-relay relay-options relay-agents-packets <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.


  • Listen for DHCP requests on interface eth1.

  • DHCP server is located at IPv4 address

  • Router receives DHCP client requests on eth1 and relays them to the server at

DHCP relay example

DHCP relay example

The generated configuration will look like:

show service dhcp-relay
    interface eth1
    interface eth2
    relay-options {
       relay-agents-packets discard


restart dhcp relay-agent

Restart DHCP relay service

IPv6 relay


set service dhcpv6-relay listen-interface <interface>

Set eth1 to be the listening interface for the DHCPv6 relay.

Multiple interfaces may be specified.

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.


set service dhcpv6-relay max-hop-count <count>

Set maximum hop count before packets are discarded, default: 10

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.


  • 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

DHCPv6 relay example

DHCPv6 relay example

The generated configuration will look like:

show service dhcpv6-relay
    listen-interface eth1 {
    upstream-interface eth2 {
       address 2001:db8::4


restart dhcpv6 relay-agent

Restart DHCPv6 relay agent immediately.