Network Address Translation (NAT)

Network address translation (NAT) is a method of remapping one IP address space into another by modifying network address information in Internet Protocol (IP) datagram packet headers while they are in transit across a traffic routing device.[1] The technique was originally used for ease of rerouting traffic in IP networks without readdressing every host. It has become a popular and essential tool in conserving global address space allocations in face of IPv4 address exhaustion by sharing one Internet-routable IP address of a NAT gateway for an entire private network.

The original use of network address translation consisted of mapping every address of one address space to a corresponding address in another space, such as when an enterprise changed Internet service providers without having a facility to announce a public route to the network.

The method enables communication through the router only when the conversation originates in the masqueraded network since this establishes the translation tables. For example, a web browser in the masqueraded network can browse a website outside, but a web browser outside could not browse a website hosted within the masqueraded network.

Because of the popularity of this technique to conserve IPv4 address space, the term NAT has become virtually synonymous with the method of IP masquerading.

• Basic NAT or One-to-one NAT
• One-to-many NAT