Datagram Transport Layer Security (DTLS) as Transport for Session Traversal Utilities for NAT (STUN)
RFC 7350

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Internet Engineering Task Force (IETF)                 M. Petit-Huguenin
Request for Comments: 7350                           Jive Communications
Updates: 5389, 5928                                         G. Salgueiro
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                              August 2014

         Datagram Transport Layer Security (DTLS) as Transport
             for Session Traversal Utilities for NAT (STUN)

Abstract

   This document specifies the usage of Datagram Transport Layer
   Security (DTLS) as a transport protocol for Session Traversal
   Utilities for NAT (STUN).  It provides guidance on when and how to
   use DTLS with the currently standardized STUN usages.  It also
   specifies modifications to the STUN and Traversal Using Relay NAT
   (TURN) URIs and to the TURN resolution mechanism to facilitate the
   resolution of STUN and TURN URIs into the IP address and port of STUN
   and TURN servers supporting DTLS as a transport protocol.  This
   document updates RFCs 5389 and 5928.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc7350.

Petit-Huguenin & Salgueiro   Standards Track                    [Page 1]
RFC 7350                     STUN over DTLS                  August 2014

Copyright Notice

   Copyright (c) 2014 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 Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  DTLS as Transport for STUN  . . . . . . . . . . . . . . . . .   3
   4.  STUN Usages . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  NAT Discovery Usage . . . . . . . . . . . . . . . . . . .   4
       4.1.1.  DTLS Support in STUN URIs . . . . . . . . . . . . . .   5
     4.2.  Connectivity Check Usage  . . . . . . . . . . . . . . . .   5
     4.3.  Media Keep-Alive Usage  . . . . . . . . . . . . . . . . .   5
     4.4.  SIP Keep-Alive Usage  . . . . . . . . . . . . . . . . . .   6
     4.5.  NAT Behavior Discovery Usage  . . . . . . . . . . . . . .   6
     4.6.  TURN Usage  . . . . . . . . . . . . . . . . . . . . . . .   6
       4.6.1.  DTLS Support in TURN URIs . . . . . . . . . . . . . .   7
       4.6.2.  Resolution Mechanism for TURN over DTLS . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  S-NAPTR Application Protocol Tag  . . . . . . . . . . . .   9
     6.2.  Service Name and Transport Protocol Port Number . . . . .   9
       6.2.1.  The "stuns" Service Name  . . . . . . . . . . . . . .  10
       6.2.2.  The "turns" Service Name  . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  14

Petit-Huguenin & Salgueiro   Standards Track                    [Page 2]
RFC 7350                     STUN over DTLS                  August 2014

1.  Introduction

   STUN [RFC5389] defines Transport Layer Security (TLS) over TCP
   (simply referred to as TLS [RFC5246]) as the transport for STUN due
   to additional security advantages it offers over plain UDP or TCP
   transport.  But, TCP (and thus TLS-over-TCP) is not an optimal
   transport when STUN is used for its originally intended purpose,
   which is to support multimedia sessions.  This is a well documented
   and understood transport limitation for real-time communications.

   DTLS-over-UDP (referred to in this document as simply DTLS [RFC6347])