Different Types of Network Address Translation

Three basic types of NAT 

Static mapping 

The network address translation has a pool of public IP addresses configured. Each private address is statically mapped to a specific public address. So computer A always receives the public address x, computer B always receives the public address y, and so on. This is generally used for servers that need to keep the same public address at all times.

Dynamic mapping 

The network address translation has a pool of IP addresses, but instead of statically mapping a public address to a specific private address, it works on a first-come, first-served basis. So if A needs to communicate over the Internet, his system makes a request to the NAT server. The NAT server takes the first IP on the list and maps it to A is private address. The balancing act is to estimate how many computers will most likely need to communicate outside the internal network at one time. This estimate is the number of public addresses the company purchases, instead of purchasing one public address for each computer.

Port Address Translation

Port Address Translation (PAT), is an extension to network address translation (NAT) that permits multiple devices on a local area network (LAN) to be mapped to a single public IP address. The goal of PAT is to conserve IP addresses.

Most home networks use PAT. In such a scenario, the Internet Service Provider (ISP) assigns a single IP address to the home network's router. When Computer X logs on the Internet, the router assigns the client a port number, which is appended to the internal IP address. This, in effect, gives Computer X a unique address. If Computer Z logs on the Internet at the same time, the router assigns it the same local IP address with a different port number. Although both computers are sharing the same public IP address and accessing the Internet at the same time, the router knows exactly which computer to send specific packets to because each computer has a unique internal address.

Port Address Translation is also called porting; port overloading, port-level multiplexed NAT and single address NAT.