Vladimir: If /etc/resolv.conf empty after upgrade from Oneiric and you get nameserver addresses via DHCP, run "sudo dpkg-reconfigure resolvconf" and reboot. After this, /etc/resolv.conf should be a symbolic link to "../run/resolvconf/resolv.conf" and resolv.conf should contain lines for the nameserver addresses received from the DHCP server.
Vladimir: If /etc/resolv.conf empty after upgrade from Oneiric and you get nameserver addresses via DHCP, run "sudo dpkg-reconfigure resolvconf" and reboot. After this, /etc/resolv.conf should be a symbolic link to "../run/ resolvconf/ resolv. conf" and resolv.conf should contain lines for the nameserver addresses received from the DHCP server.