I have a 8169 chipset network card (my blog) and i hate it when in this bizarre mode.
Recently it has been playing up, so i decided to disable some restarts of daemons and firewall operations. The thing still disconnected while the router was happy with another connection, so its been restarting the router to get the connection back so restarting the wrong thing to get the right thing ‘up’.
In the end i regenerate my dnssec and it appears to stay up. Layers but I really hate that ethernet network card for being awful.
I then explore wol adding a ‘p’ to ug settings (seen with ethtool).
ethtool -s eth1 wol ugp
Supports Wake-on: pumbg
And that appears to still not fix my drop out problem. I have no damm idea why the card now needs a p setting to retain connection, while other things connected to the router are still working and its debian stable.