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Datagram Congestion Control Protocol (DCCP) Simultaneous-Open Technique to Facilitate NAT/Middlebox Traversal
RFC 5596

Network Working Group                                       G. Fairhurst
Request for Comments: 5596                        University of Aberdeen
Updates: 4340                                             September 2009
Category: Standards Track

              Datagram Congestion Control Protocol (DCCP)
   Simultaneous-Open Technique to Facilitate NAT/Middlebox Traversal

Abstract

   This document specifies an update to the Datagram Congestion Control
   Protocol (DCCP), a connection-oriented and datagram-based transport
   protocol.  The update adds support for the DCCP-Listen packet.  This
   assists DCCP applications to communicate through middleboxes (e.g., a
   Network Address Port Translator or a DCCP server behind a firewall),
   where peering endpoints need to initiate communication in a near-
   simultaneous manner to establish necessary middlebox state.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright and License Notice

   Copyright (c) 2009 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.  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 BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling

Fairhurst                   Standards Track                     [Page 1]
RFC 5596            DCCP Simultaneous-Open Technique      September 2009

   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Scope of This Document . . . . . . . . . . . . . . . . . .  3
     1.2.  DCCP NAT Traversal . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Structure of This Document . . . . . . . . . . . . . . . .  4
   2.  Procedure for Near-Simultaneous-Open . . . . . . . . . . . . .  5
     2.1.  Conventions and Terminology  . . . . . . . . . . . . . . .  5
     2.2.  Protocol Method  . . . . . . . . . . . . . . . . . . . . .  5
       2.2.1.  DCCP-Listen Packet Format  . . . . . . . . . . . . . .  6
       2.2.2.  Protocol Method for DCCP Server Endpoints  . . . . . .  7
       2.2.3.  Protocol Method for DCCP Client Endpoints  . . . . . . 11
       2.2.4.  Processing by Routers and Middleboxes  . . . . . . . . 11
     2.3.  Examples of Use  . . . . . . . . . . . . . . . . . . . . . 12
       2.3.1.  Repetition of DCCP-Listen  . . . . . . . . . . . . . . 13
       2.3.2.  Optional Triggered Retransmission of DCCP-Request  . . 14
     2.4.  Backwards Compatibility with RFC 4340  . . . . . . . . . . 16
   3.  Discussion of Design Decisions . . . . . . . . . . . . . . . . 16
     3.1.  Rationale for a New Packet Type  . . . . . . . . . . . . . 17
       3.1.1.  Use of Sequence Numbers  . . . . . . . . . . . . . . . 18
     3.2.  Generation of Listen Packets . . . . . . . . . . . . . . . 18
     3.3.  Repetition of DCCP-Listen Packets  . . . . . . . . . . . . 18
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 21
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 21
   Appendix A.  Discussion of Existing NAT Traversal Techniques . . . 23
     A.1.  NAT Traversal Based on a Simultaneous-Request  . . . . . . 24

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