I've bought an Archer C6 as a replacement as it was on sale, that one works perfectly, I get full speed. It was indeed a faulty WAN port.

Thank you, I've done so, same story, WAN port shuts down as soon as I force 1000 Mbps. 100 Mbps works fine. I guess the router really is faulty then.

Hi all, I have a 500/50 connection. Directly from my modem I get full speed without issues. My Archer C80 shuts the WAN port down as soon as I set its negotiation speed to 1000 Mbps. Auto negotiaton...