auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 192.168.81.3
        netmask 255.255.255.248
        network 192.168.81.0
        broadcast 192.168.81.7
        gateway 192.168.81.1

iface eth1 inet static
        address 10.0.0.1
        netmask 255.255.255.0
        network 10.0.0.0
        broadcast 10.0.0.255

root@raspberrypi:~# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.81.1    0.0.0.0         UG    0      0        0 eth0
10.0.0.0        *               255.255.255.0   U     0      0        0 eth1
192.168.81.0    *               255.255.255.248 U     0      0        0 eth0

root@raspberrypi:~# route -C
Kernel IP routing cache
Source          Destination     Gateway         Flags Metric Ref    Use Iface