Editing Network address translation (section)

==Related techniques==
[[IEEE]] Reverse Address and Port Translation (RAPT or RAT) allows a host whose real [[IP address]] changes from time to time to remain reachable as a server via a fixed home IP address.<ref>{{cite book |pages=32–40 |doi=10.1109/MCSA.1999.749275 |chapter=RAT: A quick (and dirty?) push for mobility support |year=1999 |last1=Singh |first1=R. |last2=Tay |first2=Y.C. |last3=Teo |first3=W.T. |last4=Yeow |first4=S.W. |title=Proceedings WMCSA'99. Second IEEE Workshop on Mobile Computing Systems and Applications |isbn=978-0-7695-0025-6 |citeseerx=10.1.1.40.461|s2cid=7657883 }}</ref> [[Cisco]]'s RAPT implementation is PAT or NAT overloading and maps multiple private IP addresses to a single public IP address. Multiple addresses can be mapped to a single address because each private address is tracked by a port number. PAT uses unique source port numbers on the inside global IP address to distinguish between translations.{{efn|The port numbers are 16-bit integers. The total number of internal addresses that can be translated to one external address could theoretically be as high as 65,536 per IP address. Realistically, the number of ports that can be assigned a single IP address is around 4000.}} PAT attempts to preserve the original source port. If this source port is already used, PAT assigns the first available port number starting from the beginning of the appropriate port group 0–511, 512–1023, or 1024–65535. When there are no more ports available and there is more than one external IP address configured, PAT moves to the next IP address to try to allocate the original source port again. This process continues until it runs out of available ports and external IP addresses.

[[Mapping of Address and Port]] is a Cisco proposal that combines [[Address plus Port]] translation with tunneling of the IPv4 packets over an ISP provider's internal [[IPv6]] network. In effect, it is an (almost) [[stateless protocol|stateless]] alternative to [[carrier-grade NAT]] and [[DS-Lite]] that pushes the [[IPv4 address]]/port translation function (and the maintenance of NAT state) entirely into the existing [[customer premises equipment]] NAT implementation. Thus avoiding the [[NAT444]] and statefulness problems of carrier-grade NAT, and also provides a transition mechanism for the deployment of native IPv6 at the same time with very little added complexity.