Network Address Translation

Have you ever wondered how the request originating from your PC or laptop returns back only to you via your corporate office firewall, reason being for the external world outside of your firewall the client IP address of all the machines are same in your LAN?

The answer lies in the NAT - Network Address Translation

NAT is often used in conjunction with a firewall. NAT, also known as network masquerading or IP masquerading, is a technique where the source and/or destination addresses on packets are rewritten as they pass through a firewall. This allows many computers on a private network to access the internet using a single public IP address.

• The firewall translates each private network address to the public IP address when the packet leaves the private network.
• The internet destination for the packet processes the request and responds to the public IP address
• The request is sent back to the firewall which recognises that the packet is intended for a machine on the private network
• The firewall rewrites the destination address of the packet for the private network and sends it on
• The iptables mechanism works well with NAT.