Technical Tip: How to enable automatic routing adjustment for an ECMP failover, when using a wireless modem with a PPPoE assigned dynamic IP address

Description

This article describes that when using the ECMP routing failover feature with a wireless modem as the secondary interface, the routing to the modem interface will not get enabled automatically, even when the primary interface is down, and the modem interface is up.

This would happen because when a dynamic interface comes up, the routing table will not be updated automatically.

 
Scope

FortiOS version 4.00 MR3.

FortiOS version 5.0.x.

Solution

For this to work, it is necessary to enable a 'dynamic-gateway' option on the modem interface route:

config router static 
edit <seq_no> 
dynamic-gateway enable 
next 
end

Once that is done, routing entries will be updated properly when a PPPoE dynamic interface comes up.

Related article:

Technical Tip: How to check PPPoE IP address using FortiGate CLI