No WAN IP after power failure

[qarkhs]

This morning there was a one second blip in the power and every electronic device in the house went down. The cable modem and Opnsense box came back up but there's no Internet connection. I log into the OpnSense box and everything seems fine aside from the missing WAN address.  I reboot the cable modem (Arris SB2800) and then reboot the OpnSense box. No change. I swap the OpnSense box out for an Asus Router and I have an Internet connection.

This has happened several times before. The solution is always swap in the Asus box. Based on past experience, if I reconnect the OpnSense box in a couple of hours, everything will work fine. Any idea what's going ion here and how to fix it?

[coffeecup25]

Just a guess, but I think your cable modem lost the DHCP lease for the router and it won't renew. The ASUS resets it because the cable modem sees a different MAC address. Turning the  PC off and leaving it off long enough to let the capacitors drain might do it. Google might offer other solutions. Address Resolution Protocol is the issue. The ARP table in the modem is losing information and needs to be reset. Seeing a new MAC address causes the ARP table to wake up, more or less.

A small UPS for power blips would remove this problem completely. I use one to protect the network from brief power outages that only last a couple of seconds but are long enough to reboot everything.

Edit: See if the DHCP leases page on the router has a refresh button. Just in case the issue is on the OPNsense side.

Since OPNsense say you have no WAN IP when it drops, the problem more likely is on the Modem side. The refresh probably won't work but it's worth a try anyway.

[qarkhs]

Thanks. Next time this happens I will check this it out but, as you suggest, it may be worth getting a UPS.

This time it turned out to be more problematic than usual. I had the Asus sitting in for a couple of days and every few hours the WAN would disappear and then reappear after rebooting the Asus. Eventually I got round to swapping my OPNSense box back in and everything has been working as it was before.