I wish to use the dual Wan with my 1+1gbps fibre broadband and at the same time have a 4g USB dongle as a failover. As the primary wan will be used for first 1gbps (eth0) and secondary wan used for second 1gbps (eth1) with load balancing enabled, I am not able to setup the 4g USB dongle (usb0) as a failover on the secondary wan. Therefore, I would like to write a script to check when primary and secondary wan are down, I will then assign secondary wan to the 4g USB dongle and restart secondary wan to activate 4g USB dongle. Then when wan 1 is up again, I will assign secondary wan back to the second 1gbps and restart secondary wan. Can I know if it is possible to write a script for it and can anyone point me to any documentation that allows me to do that, especially how I can switch secondary wan from eth1 to usb0?