Fortinet FortiGate 4000 User Manual

In a DHCP relay configuration, the FortiGate unit forwards DHCP requests from 
DHCP clients through the FortiGate unit to a DHCP server. The FortiGate unit also 
returns responses from the DHCP server to the DHCP clients. The DHCP server must 
have a route to the FortiGate unit that is configured as the DHCP relay so that the 
packets sent by the DHCP server to the DHCP client arrive at the FortiGate 
performing DHCP relay.

Go to System > Network > DHCP.

Select Service.

Select the interface to be the DHCP relay agent.

Select DHCP Relay Agent.

Enter the DHCP Server IP address.

Select Apply.

As a DHCP server, the FortiGate unit dynamically assigns IP addresses to hosts 
located on connected subnets. You can configure a DHCP server for any FortiGate 
interface. You can also configure a DHCP server for more than one FortiGate 
interface. For each DHCP server configuration you can add multiple scopes (also 
called address scopes) so that the DHCP server can assign IP addresses to 
computers on multiple subnets.

Use these procedures to configure an interface as a DHCP server:

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Go to System > Network > DHCP.

Select Service.

Select an interface.

Select DHCP Server.

Select Apply.

If you have configured an interface as a DHCP server, the interface requires at least 
one scope (also called an address scope). The scope designates the starting IP and 
ending IP for the range of addresses that the FortiGate unit assigns to DHCP clients.