auto lo eth0
iface lo inet loopback
auto eth0:0 eth0:1 eth0:2
allow-hotplug eth0
iface eth0 inet static
address 31.133.MMM.47
netmask 255.255.255.0
broadcast 31.133.MMM.255
network 31.133.MMM.0
post-up route add default gw 31.133.MMM.1 metric 1
pre-down route del default gw 31.133.MMM.1
iface eth0:0 inet static
address 31.133.NNN.254
netmask 255.255.255.128
broadcast 31.133.NNN.255
network 31.133.NNN.0
post-up route add default gw 31.133.NNN.129 metric 2
pre-down route del default gw 31.133.NNN.129
iface eth0:1 inet static
address 31.133.KKK.254
netmask 255.255.255.128
broadcast 31.133.KKK.255
network 31.133.KKK.0
post-up route add default gw 31.133.KKK.129 metric 3
pre-down route del default gw 31.133.KKK.129
iface eth0:2 inet static
address 31.133.LLL.229
netmask 255.255.255.0
broadcast 31.133.LLL.255
network 31.133.LLL.0
post-up route add default gw 31.133.LLL.1 metric 4
pre-down route del default gw 31.133.LLL.1
# Like so?
iface eth0:3 inet static
address 31.133.LLL.230
netmask 255.255.255.0
broadcast 31.133.LLL.255
network 31.133.LLL.0
post-up route add default gw 31.133.LLL.1 metric 4
pre-down route del default gw 31.133.LLL.1