NAT Router on Linux

1- Enable Packet forwarding for IPv4 via /etc/sysctl.conf, by uncommenting the following line:

net.ipv4.ip_forward=1

2- Add the following lines to the bottom of /etc/rc.local:

/sbin/iptables -P FORWARD ACCEPT
/sbin/iptables --table nat -A POSTROUTING -o eth0 -j MASQUERADE

Taking into consideration that eth0 is the interface connected to the internet.