Network/Port Address Translation

Continuing from Perimeter Router, Firewall and Internal Routers, let review our knowledge of NAT (Network Address Translation) and PAT (Port Address Translation)!

Address Translation	Explaination of Usage
Network	Provides Many to Many IP translation. Works by mapping Internal Private IP to Internal Global IP (or IP provided by Service Providers.) Internal Private IPs are mapped to Global IPs temporary (Unless otherwise stated by configuring static NAT), and is mapped until no more traffic is using the IP, whereby the router will then unmap the IPs and assign the now vacant Global IP to another Private IP that is requesting for a connection.
Port	Provides Many to One IP translation. Works by mapping Internal Private IP to port of Global IP (or IP provided by Service Providers.) Internal Private IPs are mapped to Global IPs port, and is mapped until no more traffic is using the IP, whereby the router will then unmap the IPs and assign the now vacant Global IP to another Private IP that is requesting for a connection.

NAT and PAT are two of many solutions employed in easing the gradual decline of the amount of available IP that can be used. As such, NAT and PAT might be obselete when IPV6, a improved IP address scheme which is 128bits long, thus paving way for essentially, an unlimited amount of address, to the extend where one can say "Unless we find another thousand civilization out there, addresses can never run out!).

Source: http://papershakeinks.blogspot.com/2012_04_29_archive.html