This article illustrates the parameters to consider when setting up secondary WAN on FortiGate with DHCP or PPPoE setup.
Scope
FortiGate.
Solution
In this scenario, the admin wanted to set up a secondary WAN for backup purposes. Primary WAN is configured with static IP however, the admin wants to install DHCP for secondary WAN.
The routing table below shows the initial setup of the admin. No secondary WAN is connected yet.
When the secondary WAN is installed, users behind the firewall would probably lose connection to the internet. If checking the routing table, the secondary WAN takes the default route.
DHCP or PPPoE interface has a setting of distance that needs to be considered. The default distance configured on the interface is 5. When checking the routing as shown above, the same value of distance reflects on the routing table.
Below is the default distance setting of the interface:
Change the distance to a higher value than the distance configured on the primary WAN. In this case, the default static distance is 10. Change the distance to 15 and notice that the routing table below takes back port1 as the default route.
