RFC 3424 (rfc3424) - Page 1 of 9


IAB Considerations for UNilateral Self-Address Fixing (UNSAF) Across Network Address Translation



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Network Working Group                                     L. Daigle, Ed.
Request for Comments: 3424                   Internet Architecture Board
Category: Informational                                              IAB
                                                           November 2002


     IAB Considerations for UNilateral Self-Address Fixing (UNSAF)
                   Across Network Address Translation

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   As a result of the nature of Network Address Translation (NAT)
   Middleboxes, communicating endpoints that are separated by one or
   more NATs do not know how to refer to themselves using addresses that
   are valid in the addressing realms of their (current and future)
   peers.  Various proposals have been made for "UNilateral Self-Address
   Fixing (UNSAF)" processes.  These are processes whereby some
   originating endpoint attempts to determine or fix the address (and
   port) by which it is known to another endpoint - e.g. to be able to
   use address data in the protocol exchange, or to advertise a public
   address from which it will receive connections.

   This document outlines the reasons for which these proposals can be
   considered at best as short term fixes to specific problems and the
   specific issues to be carefully evaluated before creating an UNSAF
   proposal.

1. Introduction

   As a result of the nature of Network Address (and port) Translation
   (NAT) Middleboxes, communicating endpoints that are separated by one
   or more NATs do not know how to refer to themselves using addresses
   that are valid in the addressing realms of their (current and future)
   peers - the address translation is locked within the NAT box.  For
   some purposes, endpoints need to know the addresses (and/or ports) by
   which they are known to their peers.  There are two cases: 1) when
   the client initiates communication, starting the communication has
   the side effect of creating an address binding in the NAT device and



Daigle & IAB                 Informational


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