Zebra server was down yesterday due to Ubuntu 18.04 update installing a buggy kernel which caused my primary network card to stop working. After spending several hours trying to figure why I can’t get an IP from my ISP, I’ve decided to switch back to my previous kernel. This fixed the problem.
It seems Ubuntu’s 4.15.0-33 kernel has issues with Realtek NICs. Strangely my other two NICs (both based on the same chip as the main one) were not affected.

More downtime is to be expected as I will be moving the server’s root filesystem to an SSD, probably tonight.