para um funcionamento imediato.. exemplo:
ifconfig eth1 192.168.1.10 netmask 255.255.255.0
route add -net 192.168.1.0 netmask 255.255.255.0 eth1

route add default eth1
route add default gw 192.168.1.1

mcedit /etc/resolv.conf
nameserver 8.8.8.8

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Fixar ip para quando startar levantar com o mesmo:

vim /etc/network/interfaces

auto lo
iface lo inet loopback

allow-hotplug eth0

allow-hotplug eth1

allow-hotplug eth2
iface eth2 inet static
address 192.168.254.254
netmask 255.255.255.0
network 192.168.254.0
broadcast 192.168.254.255
# dns-* options are implemented by the resolvconf package, if installed
dns-nameservers 127.0.0.1 200.165.132.147 8.8.8.8
dns-search debian.abratel

Para funcionamento permanente: