In corporate networks or internet works on dominantly on IP protocol. IP protocols have two versions. Most popular default one is IPv4 and other next-generation by not so widespread version are IPv6. IPv6 have a lot of advantages against IPv4 but as you know changing and infrastructure through world wide is not so easy job. Now our question is what is Network Address Translation simply NAT.

NAT Example

In Local Area Networks (LAN) IP range of 192.168.0.0/24, 172.16.0.0/20 and 10.0.0.0/8 are used. These IP ranges are dedicated from IANA and do not use on the internet. Other IP addresses are used by the Internet. So the problem is what will happen when a host in the LAN wants to access the internet because LAN IP range cannot be used for internet? There must be an IP address used and reserved for the internet. The address will be used for internet-related network traffic. We will continue with the following IP address.

Host LAN IP Address:              192.168.1.10

Source Internet Address:           1.1.1.1

Destination Internet Address:      2.2.2.2

NAT Topology

To access destination IP address 2.2.2.2 LAN host 192.168.1.10 goes through firewall 1.1.1.1. The IP address 1.1.1.1 is used by 192.168.1.10 on the internet to identify itself. Packets arriving at the 2.2.2.2 have source address 1.1.1.1. We call this source address translation operation as NAT simply. Actually there is a different type of mechanisms in NAT.