First we have to enable port forwarding
root@server1:~# apt-get install iproute
root@server1:~# vim /etc/sysctl.conf
net.ipv4.ip_forward=1
root@server1:~# sysctl -p
net.ipv4.ip_forward=1
Now, we will add ip address and a static route.
root@server1:~# vim /etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
allow-hotplug eth0
iface eth0 inet static
address 202.94.76.71
netmask 255.255.252.0
auto eth1
allow-hotplug eth1
iface eth0 inet static
address 172.16.0.254
netmask 255.255.0.0
auto eth2
allow-hotplug eth2
iface eth2 inet static
address 192.168.1.1
netmask 255.255.255.0
### add default gateway
up route add default gw 202.94.76.65
### ip route add (remote_network) via (remote_connecting_gatway) dev (local_outgoing_interface)
up ip route add 192.168.55.0/24 via 192.168.1.254 dev eth1
down ip route del 192.168.55.0/24 via 192.168.1.254 dev eth1
root@server1:~# /etc/init.d/networking restart