What is Port Address Translation (PAT), or “NAT overloading”?
Also called Port Address Translation (PAT) or port-level multiplexed NAT, NAT “overload” is used to translate all “internal” (local) private addresses to a single “outside” (global – usually registered) IP address. Unique port numbers on each translation are used to distinguish between the conversations. With NAT overload, a translation entry containing full address and port information is created. A port translation may be created if another translation is using that port number with that outside/global address. This is necessary in order to eliminate any ambiguity about which translation needs to be applied to each packet traversing the router.
