One way to get IP addresses for the computers on the trusted or optional networks is to use a DHCP server on a different network. You can use DHCP relay to get IP addresses for the computers on the trusted or optional network. With this feature, the XTM device sends DHCP requests to a server on a different network.
If the DHCP server you want to use is not on a network protected by your XTM device, you must set up a branch office VPN tunnel between your XTM device and the network where the DHCP server is for this feature to operate correctly.
To configure DHCP relay:
Configure IPv4 DHCP in Mixed Routing Mode