Setting up a simple Gateway on a Linux Machine

Quite easy
1. Set "net.ipv4.ip_forward = 1" in /etc/sysctl.conf
2. Enter command "sysctl -p" as root.
3. Enter command "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE"
4. Enter command "/etc/init.d/iptables save" to make the settings permanent.
( only on Redhat,Fedora and alike ) Use some other means on different distros like rc.local file.