I setup a headless Ubuntu 18.04 server on my home network some time ago (actually I run 2) and it's all been working beautifully up until a few days ago when I woke in the morning to find that my home network was down. After doing some troubleshooting and restarts with no success I started to do some isolation testing and found that whenever the server was connected to my router it would "kill" all the other ethernet ports (I run a basic TP-Link VR1600v with 4 gigabit ports). I normally run a mesh WiFi setup and have the WLAN on the router disabled but as this wasn't working, I tried enabling the WLAN on the router and WiFi connection to the internet would work but none of the ethernet connected devices would be available.
As it's a headless server, I haven't yet been able to login and look at any logs but, to be honest, I have no idea which log I would start with? I intend to pull the server out this weekend and have a look but hoping somebody can suggest what I should check.
The server has not skipped a beat since being built about a year ago. I run Docker on it and have a number of containers running and I don't recall changing anything to cause this, although I did install updates. Everything else on my network works fine when I unplug the ethernet cable for the server and then fails again as soon as I plug the cable back in??