Network Address Translation (NAT) Behavioral Requirements for the Datagram Congestion Control Protocol
RFC 5597

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Network Working Group                                  R. Denis-Courmont
Request for Comments: 5597                              VideoLAN project
BCP: 150                                                  September 2009
Category: Best Current Practice

   Network Address Translation (NAT) Behavioral Requirements for the
                  Datagram Congestion Control Protocol

Abstract

   This document defines a set of requirements for NATs handling the
   Datagram Congestion Control Protocol (DCCP).  These requirements
   allow DCCP applications, such as streaming applications, to operate
   consistently, and they are very similar to the TCP requirements for
   NATs, which have already been published by the IETF.  Ensuring that
   NATs meet this set of requirements will greatly increase the
   likelihood that applications using DCCP will function properly.

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  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
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   publication of this document.  Please review these documents
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   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
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may

Denis-Courmont           Best Current Practice                  [Page 1]
RFC 5597                 NAT DCCP Requirements            September 2009

   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  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 3
   4.  DCCP Connection Initiation  . . . . . . . . . . . . . . . . . . 4
   5.  NAT Session Refresh . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Application-Level Gateways  . . . . . . . . . . . . . . . . . . 5
   7.  Other Requirements Applicable to DCCP . . . . . . . . . . . . . 5
   8.  Requirements Specific to DCCP . . . . . . . . . . . . . . . . . 6
   9.  DCCP without NAT Support  . . . . . . . . . . . . . . . . . . . 7
   10. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.  Introduction

   For historical reasons, NAT devices are not typically capable of
   handling datagrams and flows for applications that use the Datagram
   Congestion Control Protocol (DCCP) [RFC4340].

   This memo discusses the technical issues involved and proposes a set
   of requirements for NAT devices to handle DCCP in a way that enables
   communications when either or both of the DCCP endpoints are located
   behind one or more NAT devices.  All definitions and requirements in
   [RFC4787] are inherited here.  The requirements are otherwise
   designed similarly to those in [RFC5382], from which this memo
   borrows its structure and much of its content.

   Note however that, if both endpoints are hindered by NAT devices, the
   normal model for DCCP of asymmetric connection will not work.  A
   simultaneous-open must be performed, as in [RFC5596].  Also, a
   separate, unspecified mechanism may be needed, such as Unilateral
   Self Address Fixing (UNSAF) [RFC3424] protocols, if an endpoint needs
   to learn its own external NAT mappings.

2.  Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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RFC 5597                 NAT DCCP Requirements            September 2009

   This document uses the term "DCCP connection" to refer to individual