@Big_boss I assume he is referring to static DHCP binding on DHCP server (TO) for MAC address of Ubuntu server.
I got feeling this has something to do with port reconnecting issues:
- After router reboot - Switches need reboot too
- Swich ports offline if plugged during boot (seems to be recognized at should be fixed in next updates)
but I might be wrong as IPv6 works (but I’m not sure if @NCLI tested the IPv6 connectivity or there is just IPv6 address on Ubnutu)
EDIT: @NCLI do you have more clients connected to the TO with the same issue or you have only the Ubuntu server? Could you try to connect something else to check if it’s specific or system wide issue? I mean also try virtualmachine like @Big_boss suggest but also some separate HW on different cable/port in TO - notebook or so