Se:
em1 = ethernet
192.168.1.254 = IP address of router
192.168.0.120 = IP address of server
Teste este arquivo / etc / network / interfaces:
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto em1
iface em1 inet static
address 192.168.1.120
gateway 192.168.1.254
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255