Configuring the GRE tunnel
The GRE tunnel runs between the virtual IPsec public interface on the FortiGate unit and the Cisco router. You must use the CLI to configure a GRE tunnel. In the example, you would enter:
config system gre-tunnel
edit gre1
set interface tocisco
set local-gw 172.20.120.141
set remote-gw 192.168.5.113
end
interface is the virtual IPsec interface, local-gw is the FortiGate unit public IP address, and remote-gw is the remote Cisco device public IP address