NAT Port Mapping Protocol (NAT-PMP) is anetwork protocol for establishingnetwork address translation (NAT) settings andport forwarding configurations automatically without user effort.[1] The protocol automatically determines the externalIPv4 address of a NAT gateway, and provides means for an application to communicate the parameters for communication to peers.Apple introduced NAT-PMP in 2005 by as part of theBonjour specification, as an alternative to the more common ISO StandardInternet Gateway Device Protocol implemented in many NATrouters. The protocol was published as an informationalRequest for Comments (RFC) by theInternet Engineering Task Force (IETF) in RFC 6886.
NAT-PMP runs over theUser Datagram Protocol (UDP) and usesport number 5351 on the server, whilst port 5350 is used on the client, as per spec. It has no built-inauthentication mechanisms because forwarding a port typically does not allow any activity that could not also be achieved usingSTUN 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 of thePort Control Protocol (PCP).
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