NAT Port Mapping Protocol
The NAT Port Mapping Protocol is a network protocol for establishing network address translation settings and port forwarding configurations automatically without user effort. The protocol automatically determines the external IPv4 address of a NAT gateway, and provides means for an application to communicate the parameters for communication to peers. NAT-PMP was introduced in 2005 by Apple as an alternative to the more common ISO Standard[ ISO/IEC 29341, http://www.iso.org/iso/home/news_index/news_archive/news.htm?refid=Ref1185] Internet Gateway Device Protocol implemented in many NAT routers. The protocol was published as an informational Request for Comments by the Internet Engineering Task Force in RFC 6886.
NAT-PMP runs over the User Datagram Protocol and uses port number 5351. It has no built-in authentication mechanisms because forwarding a port typically does not allow any activity that could not also be achieved using STUN methods. The benefit of NAT-PMP over STUN is that it does not require a STUN server and a NAT-PMP mapping has a known expiration time, allowing the application to avoid sending inefficient keep-alive packets.
NAT-PMP is the predecessor to the Port Control Protocol.
