I have an ER706W. I have disabled the LAN/WAN1 port (SFP) and am using the WAN2 port, like so:

The WAN2 port is getting a dynamic IP address:

My device is on the LAN and can connect to the router, so client->router connection is good. But, my device on the LAN has no internet connectivity to the WAN; pings, DNS lookups, everything fails.

I know that it's not an issue with the upstream router that the WAN port is on, because if I connect this same WAN cable to my device directly, I have full public internet connectivity. I even tried cloning this (working) device's MAC on the router, but I still have no connectivity through the router to WAN.

My LAN configuration is pretty simple:

And the route table looks correct, it's correctly passing all outbound internet traffic through WAN2 to the next gateway.

What am I missing here? Why can the router get a WAN IP, but no traffic can get through the router from LAN to WAN, even when the WAN is verified working by direct-connecting it to a device with the same (cloned) MAC?