Routing on Linux

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