Prova così: (file interfaces)

allow-hotplug eth0
iface eth0 inet static
address 192.168.1.10
netmask 255.255.255.0
gateway 192.168.1.25

allow-hotplug eth0:1
iface eth0 inet static
address 192.168.1.10
netmask 255.255.255.0
gateway 192.168.1.25