Routers can be very strange at times. Last night, my router decided to not talk to my notebook. I still have no idea what the problem was.

Symptom : Notebook receives no DHCP IPv4 address, nor establishes a valid routable IPv6 address. Issue is present on WiFi, ethernet via Thunderbolt monitor, and via a separate ethernet dongle.

Booting another machine on the network works fine. Restarting the notebook doesn't fix the issue. Rebooting the notebook into recovery mode (so a completely different isolated OS) doesn't fix the problem.

Rebooting the router, and connectivity came back. My best guess is some weird DHCP issue, though I didn't try a static IP assignment to fully verify. The notebook never fell back to a self assigned IPv4 address, even after 10 minutes.

I'm still boggled by tahir's problem as much as I was with mine last night.