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.

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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
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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