Technical Tip: How to configure more than one DHCP relay IP on a FortiGate unit

[subramanis]

Description
This article explains how to specify more than one DHCP relay IP, to allow for the coverage of additional LAN subnets.
 
It is possible to set up to 8 IPs from the CLI. This option is also available on GUI since version 5.4.



Scope

Solution

For versions before V5.4:

To specify more than one IP for DHCP relay, run from CLI:

#config system interface
edit <REQUIRED_INTERFACE_HERE>
set dhcp-relay-ip <FIRST_IP> <SECOND_IP> ....<EIGHTH_IP>
end

Example:

#config system interface
edit dmz
set dhcp-relay-ip 1.1.1.1 2.2.2.2 3.3.3.3
end

Note: The WebUI will show only 1 IP. The rest of the configuration can be viewed only from CLI.

FGT# show system interface dmz
config system interface
edit "dmz"
set vdom "root"
set dhcp-relay-ip "1.1.1.1" "2.2.2.2" "3.3.3.3"
set type physical
next

For versions V5.4 and above:

In GUI:

Go to Network -> Interfaces -> Interface_NAME

Via CLI:

#FGT # config system interface
FGT (interface) # edit port2
FGT (port2) # set dhcp-relay-service enable
FGT (port2) # set dhcp-relay-ip 1.1.1.1 2.2.2.2 3.3.3.3

Note.

Fortinet will send the requests to all the DHCP servers configured in the relay settings and the client will accept an offer from the first DHCP server to reply.