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NAT Traversal Practices for Client-Server SIP
RFC 6314

Internet Engineering Task Force (IETF)                        C. Boulton
Request for Comments: 6314                               NS-Technologies
Category: Informational                                     J. Rosenberg
ISSN: 2070-1721                                                    Skype
                                                            G. Camarillo
                                                                Ericsson
                                                                F. Audet
                                                                   Skype
                                                               July 2011

             NAT Traversal Practices for Client-Server SIP

Abstract

   Traversal of the Session Initiation Protocol (SIP) and the sessions
   it establishes through Network Address Translators (NATs) is a
   complex problem.  Currently, there are many deployment scenarios and
   traversal mechanisms for media traffic.  This document provides
   concrete recommendations and a unified method for NAT traversal as
   well as documents corresponding flows.

Status of This Memo

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

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are 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/rfc6314.

Copyright Notice

   Copyright (c) 2011 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

Boulton, et al.               Informational                     [Page 1]
RFC 6314                      NAT Scenarios                    July 2011

   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Solution Technology Outline Description  . . . . . . . . . . .  8
     4.1.  SIP Signaling  . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.1.  Symmetric Response . . . . . . . . . . . . . . . . . .  8
       4.1.2.  Client-Initiated Connections . . . . . . . . . . . . .  9
     4.2.  Media Traversal  . . . . . . . . . . . . . . . . . . . . . 10
       4.2.1.  Symmetric RTP/RTCP . . . . . . . . . . . . . . . . . . 10
       4.2.2.  RTCP . . . . . . . . . . . . . . . . . . . . . . . . . 10
       4.2.3.  STUN/TURN/ICE  . . . . . . . . . . . . . . . . . . . . 11
   5.  NAT Traversal Scenarios  . . . . . . . . . . . . . . . . . . . 12
     5.1.  Basic NAT SIP Signaling Traversal  . . . . . . . . . . . . 12
       5.1.1.  Registration (Registrar/Edge Proxy Co-Located) . . . . 12
       5.1.2.  Registration(Registrar/Edge Proxy Not Co-Located)  . . 16
       5.1.3.  Initiating a Session . . . . . . . . . . . . . . . . . 19
       5.1.4.  Receiving an Invitation to a Session . . . . . . . . . 22
     5.2.  Basic NAT Media Traversal  . . . . . . . . . . . . . . . . 27
       5.2.1.  Endpoint-Independent NAT . . . . . . . . . . . . . . . 28
       5.2.2.  Address/Port-Dependent NAT . . . . . . . . . . . . . . 48
   6.  IPv4-IPv6 Transition . . . . . . . . . . . . . . . . . . . . . 57
     6.1.  IPv4-IPv6 Transition for SIP Signaling . . . . . . . . . . 57
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 57
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 57
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 58
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 58
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 59

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1.  Introduction

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