The goal of NAT is to provide functionality as if the private network had globally unique addresses and the NAT device was not present. Basic NAT allows a one-to-one mapping between one private address and one public address. In its simplest configuration, the Network Address Translator (NAT) operates on a router connecting two networks together; one of these networks (designated as inside) is addressed with either private or obsolete addresses that need to be converted into legal addresses before packets are forwarded onto the other network (designated as outside). The translation operates in conjunction with routing, so that NAT can simply be enabled on a customer-side Internet access router when translation is desired.
NAPT (Port NAT) NAPT maps a single public address to one, or many internal addresses and all network IP addresses on the connected computers are local and cannot be seen by the outside world.
NAT with Port Address Translation (PAT or NAPT) is an extension to NAT in that PAT uses TCP/UDP ports in addition to network addresses (IP addresses) to map many private network addresses to a single outside address.As far as the throughput and bandwith, I have no knowledge of any studies that would indicate that one is faster than the other. I would assume that NAT would be faster, as NAPT is a subset (layer) within NAT.
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This was first published in March 2001