All IP packets have a source IP address and a destination IP address. Typically, packets passing from the private network to the public network will have their source address modified, while packets passing from the public network back to the private network will have their destination address modified. To avoid ambiguity in how replies are translated, further modifications to the packets are required. The vast bulk of Internet traffic uses Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). For these protocols, the port numbers are changed so that the combination of IP address (within the IP header) and port number (within the Transport Layer header) on the returned packet can be unambiguously mapped to the corresponding private network destination. RFC 2663 uses the term network address and port translation (NAPT) for this type of NAT. Other names include port address translation (PAT), IP masquerading, NAT overload, and many-to-one NAT. This is the most common type of NAT and has become synonymous with the term NAT in common usage.
all ip packets have a source ip address and a destination ip address typically packets passing from the private network to the public network will have their source address modified while packets passing from the public network back to the private network will have their destination address modified to avoid ambiguity in how replies are translated further modifications to the packets are required the vast bulk of internet traffic uses transmission control protocol (tcp) or user datagram protocol (udp) for these protocols the port numbers are changed so that the combination of ip address (within the ip header) and port number (within the transport layer header) on the returned packet can be unambiguously mapped to the corresponding private network destination rfc 2663 uses the term network address and port translation (napt) for this type of nat other names include port address translation (pat) ip masquerading nat overload and many-to-one nat this is the most common type of nat and has become synonymous with the term nat in common usage