Comment 16 for bug 1586528

To debug this issue requires more information, the log messages from avahi itself are simply a "symptom" of the fact the network address was deleted.

For any affected system we need to know
 (1) How your network is setup, e.g. /etc/network/interfaces, Network-Manager, etc. Plus a copy of the relevant configuration file.
 (2) A full copy of the syslog file when the issue occurred including at least a few hours before the issue. There may be some other log items such as related to DHCP etc. If you reboot, the logs may get rotated to /var/log/syslog.1
 (3) It would be helpful to know that if you attempt to reconfigure the network, does it then work. e.g. if you do ifdown, then ifup. Or try a manual "dhclient eth0" (or whatever the interface name is)

I am imagining two main scenarios here, either
  (a) You are using DHCP and the DHCP lease fails for some reason causing it to be removed from the interface. Perhaps dhclient fails, or the DHCP server is temporarily unavailable. Hopefully syslog might have some info there.

  (b) The network card itself stops passing traffic due to a driver bug.. given everyone is reporting issues on realtek this doesn't seem unlikely. To narrow that down we really need someone to try re-configure the IP, try adding an IP manually/statically and then running tcpdump to see if any traffic is hitting the machine. You could also try perhaps remove the kernel module and insert it again.