Wired network drops off in Ubuntu 16.04 where to start looking for the cause?

Question

linux

Hello! I use Ubuntu 16.04 x64 Unity
Recently, the Internet connection on the desktop that is connected to the router via a LAN cable has begun to fall off, before that this has never happened here on you. Falls off about once every 3 hours. At the same time, the Internet via Wi-Fi from the same router works properly on a smartphone, i.e. The reason is not in the provider and not in the router. Also, the connection break is not shown, which is also extremely strange in principle, earlier when there was a break due to the provider, the icon immediately became like: "no connection", but now it does not change. There is no connection to the router at 192.168.1.1 either. The connection is restored by simply reconnecting.
What to do? What logs to look to find the culprit? Where do you even start? I've never experienced this before, so I don't know where to start.

Answer 1

Does dmesg give something useful?