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Implementations of NAT

Network Address and Port Translation (NAPT) / IP Masquerading

This is the most common for of NAT. It is often used in the situation where the network only one IP addresses has been assigned, such as a connection to an ISP.

In this instance, the private network, 192.168.1.0, is hiding behind the public address, 130.102.1.1. The NAT router having the addresses 130.102.1.1 and 192.168.1.1.

All requests originating from the private network (192.168.1.0) have their source IP address replaced with the NAT router's public IP address, 130.102.1.1. Only 1 IP address is visible from the public network. Note that the public network need not be the internet, it could be the company's network, with the private betwork being R & D or Finance, etc... Thus, the addresses space of the public network could be any valid IP.

Dynamic Network Address Translation

In dynamic NAT, only the address (not the port) is translated. usually, the number of externally visible IP addresses is less than the numebr being hidden behind the NAT router. Each time a request is made from a host on the private network, The NAT router chooses an external IP addresses that is currently unused, and then performs the translation. This type of situation is only possible when the number of concurrent requests to the external network are equal or less than the number of external Ip addresses on the NAT router.

Dynamic Network Address Translation with Port Translation

Although to my knowledge this is not implemented, is is conceivably possible to perform IP masquerading on each externally visible IP addresses. That way, you could increase the number of hosts making concurrent requests to the external network.

Static Network Address Translation

Static NAT is usually only implemented between private networks (although other possibilities also exist). Suppose there are 2 networks each having the same address space.

In this way, the upper network addresses the bottom network using the addresses 10.3.yy.zz and the bottom metwork addresses the top network using the addresses 10.2.ww.xx

Port Mapping and Redirection

Specific port on the external interface are re-mapped to services inside the private network. As only 130.102.1.1 is visible to the internet, but does not actually have any services (other than NAt off course) running on it, it is said to be a virtual server.

Here, requests made to 130.102.1.1:80 are re-mapped to the webserver on 192.168.1.2, an requests made to the vitual mail server are remapped to 192.168.1.3. In high load situations, it is possible for there to be several webservers on the private network, with the NAT router balancing the load between them. The same is also true for most services.