Suddenly the WAN port on my Router no longer works.  This ethernet cable goes to my modem and if I plug that into my laptop instead (laptop to modem), laptop can access internet normally, through the modem.  But plugging the cable back into the router's WAN port, I only get an intermittant link connection on the modem and when it is connected, the modem reports 10mbps full duplex on that port.

I have a small switch and when I plug the WAN port from the router into my switch, I also get only an occasional link light.  Same cable from the modem, connected to the switch, I get link light on both sides and the modem reports 1000mbps full duplex on that port.  I have tried a couple of different cables, but with my laptop test, I am sure the cable is good.  I have tried connecting the router WAN to several ports on my modem, but that doesn't help.

All of the LAN ports on the router work normally, I can access the router directly with my laptop by plugging into LAN (or through Wifi).

I feel certain there is a physical plug or chip issue with that WAN port.  There is no dust in the port, the pins look fine, jiggling the plug around doesn't help.

Is there any way to repurpose a LAN port on this model to handle the external WAN ?