Network-address-translation (NAT) on a Linux system with Iptables
rules so that the system can act as a gateway and provide Internet
access to multiple hosts on a local network using a single public IP
address. This is achieved by rewriting the source and/or destination
addresses of IP packets as they pass through the NAT system.

Minimum Requirements are any Linux OS, Iptables and Two Network
interface card.

1. Configure eth0 for Internet with a Public IP


2. Configure eth1 for LAN with a Private IP (Internal private network)


3. DNS Configuration


4. NAT configuration with IP Tables.....Read On¹

You may also want to look at ^{NAT Setup in Ubuntu Server}

^{1Source:NAT configuration with iptables in Ubuntu}