NAT Network Address Translation

We know that home networks and other private networks are setup using private IP addresses. The private addresses that can use without any pre registration are given below,

Range	Total
10.0.0.0        to  10.255.255.255	2^24
172.16.0.0    to  172.31.255.255	2^20
192.168.0.0  to  192.168.255.255	2^16

The private addresses are used uniquely inside the organization but they are not unique globally. No router will forward a packet that has one of these addresses as the destination address. Here we use NAT to translate addresses. For example consider the following figure, that shows segment of a private organization network that have only one connection to the global Internet. NAT is placed between private network and Internet, all packets to and from are passed through it.

Network address translation

Network address translation (NAT) is the process of modifying IP address information in IP packet headers. All outgoing packets pass through the NAT router, which replaces the source address  with the global NAT address. All incoming packets also pass through the NAT router, which replaces the destination address in the packet with the specific private address.

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