from one day to the next my trusty Zyxel NBG6617 decided to no longer give me internet access... I tried restarting it, and the fiber decoder (modem?), to no avail. All the routing tables seem good, there is an active IPv4 upstream lease, specifying an address and a gateway belonging to my ISP. Yet, even from the router itself, I cannot ping anything outside my network. Even pinging the gateway advertised by the DHCP lease results in 100% packet loss.
If you have any ideas what I could still try, I would be very grateful.
Note: My setup is really simple. Fiber goes into decoder, ethernet goes from decoder to router's WAN port, router provides WiFi and ethernet to LAN. Nothing special at all.
WAN IPs are in a /22 range confirmed to belong to my ISP. LAN IPs are 192.168.1.X/16.
The local network works just fine, with all devices able to ping each other.
ISP support suspects it might be an issue between their gateway and the fiber decoder, so maybe trying to fix the config is a worthless effort. I will update you when I hear back from them.