Why Does My Linux System Keep Losing Connection with the Router?

When I had similar issues, I noticed dropped packets during ping tests sporadically. Sometimes putting my computer on "suspend" and waking it back up helped fix the connection temporarily. Just thinking it through, if you’ve already tested with another good cable, it might be more of a software or motherboard issue.

It sounds like this shouldn't be happening at all. Since your cables are built into the walls, you might want to consider hiring a professional to check the quality of the cables themselves. There are really two main places where errors can occur: in the physical cable or from the external internet connection. Most routers will have a menu option showing the connection quality which could help you diagnose the issue. If you're still having problems, maybe try using Wi-Fi just for testing purposes—if the issue persists, then the problem might lie elsewhere in the external signal.

I’ve had problems with some poorly designed Wi-Fi cards where they go into sleep mode unexpectedly. It might be worth looking into your ethernet controller to see if there's a DKMS driver available for it. Also, check if there are any sleep settings that you can adjust.

When your connection drops, what exactly happens? Have you checked your logs like journal or dmesg? There might be a conflict between NetworkManager or systemd-networkd—I've encountered that before and it was a pain to nail down.