Hi all. I have my Vigor 2762ac connected to a cable modem (WAN2), and also have a USB 4G dongle (WAN3) which is used as a backup should WAN2 fail. Under normal conditions where WAN2 is working, the 4G remains completely unused (no load balancing etc in place).

Yesterday we had an outage on WAN2, but the 4G did not take over as expected and we had no internet connectivity. 4G only kicked in when I either powered off the cable modem or physically disconnected it from the LAN port.

Can anyone suggest anything please?

Thank you.

Only a suggestion - try using Ping detect on WAN2 if you're not using it already.

Ive only got it to reliably work by changing the Wan detection option to ping detect then I use google dns 8.8.8.8 and 8.8.4.4 and the primary and secondary ping IP's
I use this on my 3220 for 3 WAN connections and it works faultlessly although I have to add that all 3 of mine are on all the time with load balance session based, but before I set to ping (I think default is ARP detect) it would keep them showing as up even when they were down.