NAT Port Mapping Protocol (NAT-PMP)
RFC 6886

Document Type RFC - Informational (April 2013; Errata)
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Last updated 2013-05-14
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Independent Submission                                       S. Cheshire
Request for Comments: 6886                                   M. Krochmal
Category: Informational                                       Apple Inc.
ISSN: 2070-1721                                               April 2013

                  NAT Port Mapping Protocol (NAT-PMP)

Abstract

   This document describes a protocol for automating the process of
   creating Network Address Translation (NAT) port mappings.  Included
   in the protocol is a method for retrieving the external IPv4 address
   of a NAT gateway, thus allowing a client to make its external IPv4
   address and port known to peers that may wish to communicate with it.
   From 2005 onwards, this protocol was implemented in Apple products
   including Mac OS X, Bonjour for Windows, and AirPort wireless base
   stations.  In 2013, NAT Port Mapping Protocol (NAT-PMP) was
   superseded by the IETF Standards Track RFC "Port Control Protocol
   (PCP)", which builds on NAT-PMP and uses a compatible packet format,
   but adds a number of significant enhancements.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6886.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Cheshire & Krochmal           Informational                     [Page 1]
RFC 6886                         NAT-PMP                      April 2013

Table of Contents

   1. Introduction ....................................................3
      1.1. Transition to Port Control Protocol ........................4
   2. Conventions and Terminology Used in This Document ...............5
   3. Protocol and Packet Format ......................................5
      3.1. Requests and Responses .....................................6
      3.2. Determining the External Address ...........................7
      3.3. Requesting a Mapping ......................................10
      3.4. Destroying a Mapping ......................................13
      3.5. Result Codes ..............................................14
      3.6. Seconds Since Start of Epoch ..............................16
      3.7. Recreating Mappings on NAT Gateway Reboot .................16
      3.8. NAT Gateways with NAT Function Disabled ...................18
      3.9. All Mappings Are Bidirectional ............................19
   4. UNSAF Considerations ...........................................20
      4.1. Scope .....................................................20
      4.2. Transition Plan ...........................................20
      4.3. Failure Cases .............................................21
      4.4. Long-Term Solution ........................................23
      4.5. Existing Deployed NATs ....................................23
   5. Security Considerations ........................................23
   6. IANA Considerations ............................................24
   7. Acknowledgments ................................................24
   8. Deployment History .............................................25
   9. Noteworthy Features of NAT Port Mapping Protocol and PCP .......26
      9.1. Simplicity ................................................27
      9.2. Focused Scope .............................................27
      9.3. Efficiency ................................................27
      9.4. Atomic Allocation Operations ..............................29
      9.5. Garbage Collection ........................................29
      9.6. State Change Announcements ................................30
      9.7. Soft State Recovery .......................................31
      9.8. On-Path NAT Discovery .....................................31
   10. References ....................................................32
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