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Internet Engineering Task Force (IETF)                     S. NandakumarRequest for Comments: 7064                                  G. SalgueiroCategory: Standards Track                                       P. JonesISSN: 2070-1721                                            Cisco Systems                                                       M. Petit-Huguenin                                                      Impedance Mismatch                                                           November 2013URI Scheme for the Session Traversal Utilities for NAT (STUN) ProtocolAbstract   This document specifies the syntax and semantics of the Uniform   Resource Identifier (URI) scheme for the Session Traversal Utilities   for NAT (STUN) protocol.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7064.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Nandakumar, et al.           Standards Track                    [Page 1]

RFC 7064                        STUN URI                   November 2013Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .32.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .33.  Definition of the "stun" or "stuns" URI . . . . . . . . . . .33.1.  URI Scheme Syntax . . . . . . . . . . . . . . . . . . . .33.2.  URI Scheme Semantics  . . . . . . . . . . . . . . . . . .44.  Security Considerations . . . . . . . . . . . . . . . . . . .45.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .55.1.  "stun" URI Registration . . . . . . . . . . . . . . . . .55.2.  "stuns" URI Registration  . . . . . . . . . . . . . . . .66.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .67.  References  . . . . . . . . . . . . . . . . . . . . . . . . .77.1.  Normative References  . . . . . . . . . . . . . . . . . .77.2.  Informative References  . . . . . . . . . . . . . . . . .7Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .8Appendix B.  Design Notes . . . . . . . . . . . . . . . . . . . .8Nandakumar, et al.           Standards Track                    [Page 2]

RFC 7064                        STUN URI                   November 20131.  Introduction   This document specifies the syntax and semantics of the Uniform   Resource Identifier (URI) scheme for the Session Traversal Utilities   for NAT (STUN) protocol.   STUN is a protocol that serves as a tool for other protocols in   dealing with Network Address Translator (NAT) traversal.  It can be   used by an endpoint to determine the IP address and port allocated to   it by a NAT, to perform connectivity checks between two endpoints,   and as a keepalive protocol to maintain NAT bindings.RFC 5389   [RFC5389] defines the specifics of the STUN protocol.   The "stun" and "stuns" URI schemes are used to designate a stand-   alone STUN server or any Internet host performing the operations of a   STUN server in the context of STUN usages (Section 14 of RFC 5389   [RFC5389]).  With the advent of standards such as WebRTC [WEBRTC], we   anticipate a plethora of endpoints and web applications to be able to   identify and communicate with such a STUN server to carry out the   STUN protocol.  This implies that endpoints and/or applications must   be provisioned with the appropriate configuration to identify the   STUN server. Having an inconsistent syntax adds ambiguity and can   result in non-interoperable solutions and implementation limitations.   The "stun" and "stuns" URI schemes help alleviate most of these   issues by providing a consistent way to describe, configure, and   exchange the information identifying a STUN server.2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "MAY", and "OPTIONAL"   in this document are to be interpreted as described in [RFC2119] when   they appear in ALL CAPS.  When these words are not in ALL CAPS (such   as "should" or "Should"), they have their usual English meanings and   are not to be interpreted asRFC 2119 key words.3.  Definition of the "stun" or "stuns" URI3.1.  URI Scheme Syntax   "stun" and "stuns" URIs have the following formal ABNF syntax   [RFC5234]:   stunURI       = scheme ":" host [ ":" port ]   scheme        = "stun" / "stuns"   <host> and <port> are specified in [RFC3986].  While these two ABNF   productions are defined in [RFC3986] as components of the generic   hierarchical URI, this does not imply that the "stun" and "stuns" URINandakumar, et al.           Standards Track                    [Page 3]

RFC 7064                        STUN URI                   November 2013   schemes are hierarchical URIs.  Developers MUST NOT use a generic   hierarchical URI parser to parse a "stun" or "stuns" URI.3.2.  URI Scheme Semantics   The "stun" and "stuns" URI schemes are used to designate a stand-   alone STUN server or any Internet host performing the operations of a   STUN server in the context of STUN usages (Section 14 of RFC 5389   [RFC5389]).  The STUN protocol supports sending messages over UDP,   TCP, or TLS-over-TCP.  The "stuns" URI scheme MUST be used when STUN   is run over TLS-over-TCP (or in the future DTLS-over-UDP), and the   "stun" scheme MUST be used otherwise.   The required <host> part of the "stun" URI denotes the STUN server   host.   For the optional DNS discovery procedure mentioned inSection 9 of   RFC 5389, the "stun" URI scheme implies UDP as the transport protocol   for SRV lookup, and the "stuns" URI scheme indicates TCP as the   transport protocol.   As specified in [RFC5389], the <port> part, if present, denotes the   port on which the STUN server is awaiting connection requests.  If it   is absent, the default port is 3478 for both UDP and TCP.  The   default port for STUN over TLS is 5349 as perSection 9 of [RFC5389].4.  Security Considerations   The "stun" and "stuns" URI schemes do not introduce any specific   security issues beyond the security considerations discussed in   [RFC3986].  These URI schemes are intended for use in specific   environments that involve NAT traversal.  Users of the scheme need to   carefully consider the security properties of the context in which   they are using them.   Although a "stun" or "stuns" URI does not itself include the username   or password that will be used to authenticate the STUN client, in   certain environments, such as WebRTC, the username and password will   almost certainly be provisioned remotely by an external agent at the   same time as a "stuns" URI is sent to that client.  Thus, in such   situations, if the username and password were received in the clear,   there would be little or no benefit to using a "stuns" URI.  For this   reason, a STUN client MUST ensure that the username, password,   "stuns" URI, and any other security-relevant parameters are received   with equivalent security before using the "stuns" URI.  Receiving   those parameters over another TLS session can provide the appropriate   level of security if both TLS sessions are similarly parameterized,   e.g., with commensurate strength ciphersuites.Nandakumar, et al.           Standards Track                    [Page 4]

RFC 7064                        STUN URI                   November 20135.  IANA Considerations   This section contains the registration information for the "stun" and   "stuns" URI schemes (in accordance with [RFC4395]).  Note that these   URI schemes are intended for use in very specific NAT traversal   environments and should not be used otherwise on the open Web or   Internet.5.1.  "stun" URI Registration   URI scheme name: stun   Status: permanent   URI scheme syntax: SeeSection 3.1   URI scheme semantics: SeeSection 3.2   Encoding considerations: There are no encoding considerations beyond   those in [RFC3986].   Applications/protocols that use this URI scheme name:      The "stun" URI scheme is intended to be used by applications with      a need to identify a STUN server to be used for NAT traversal.   Interoperability considerations: N/A   Security considerations: SeeSection 4   Contact: Suhas Nandakumar <snandaku@cisco.com>   Author/Change controller: The IESG   References:RFC 7064Nandakumar, et al.           Standards Track                    [Page 5]

RFC 7064                        STUN URI                   November 20135.2.  "stuns" URI Registration   URI scheme name: stuns   Status: permanent   URI scheme syntax: SeeSection 3.1   URI scheme semantics: SeeSection 3.2   Encoding considerations: There are no encoding considerations beyond   those in [RFC3986].   Applications/protocols that use this URI scheme name:      The "stuns" URI scheme is intended to be used by applications with      a need to identify a STUN server to be used for NAT traversal over      a secure connection.   Interoperability considerations: N/A   Security considerations: SeeSection 4   Contact: Suhas Nandakumar <snandaku@cisco.com>   Author/Change controller: The IESG   References:RFC 70646.  Acknowledgements   The authors would like to extend a very special thanks to Cullen   Jennings for bringing to our attention to WebRTC's need for this   document, as well as his detailed review and thoughtful comments on   this document.   This document has benefited from extensive discussion and review of   many of the members of the RTCWEB and BEHAVE working groups.  The   authors would also like to acknowledge Ted Hardie, Bjoern Hoehrmann,   Russ Housley, Subramanian Moonesamy, Hadriel Kaplan, Graham Klyne,   Peter Saint-Andre, Ted Lemon, Barry Leiba, Pete Resnick, Spencer   Dawkins, Stephen Farrell, and Harald Alvestrand for their invaluable   input, reviews, feedback comments, and suggestions that helped to   improve this document.   The authors would also like to express their gratitude to Dan Wing   for his assistance in shepherding this document.  We also want to   thank Gonzalo Camarillo, the Real-time Applications andNandakumar, et al.           Standards Track                    [Page 6]

RFC 7064                        STUN URI                   November 2013   Infrastructure Area Director, for sponsoring this document as well as   his careful reviews.7.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC3986, January 2005.   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234, January 2008.7.2.  Informative References   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML",RFC 2629,              June 1999.   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and              Registration Procedures for New URI Schemes",BCP 35,RFC4395, February 2006.   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,              "Session Traversal Utilities for NAT (STUN)",RFC 5389,              October 2008.   [WEBRTC]   Bergkvist, A., Burnett, D., Jennings, C., and A.              Narayanan, "WebRTC 1.0: Real-time Communication Between              Browsers", World Wide Web Consortium WD WD-              webrtc-20120821, August 2012,              <http://www.w3.org/TR/2012/WD-webrtc-20120821>.Nandakumar, et al.           Standards Track                    [Page 7]

RFC 7064                        STUN URI                   November 2013Appendix A.  Examples   Table 1 shows examples for the "stun" and "stuns" URI schemes.  For   all these examples, the <host> component is populated with   "example.org".                          +-----------------------+                          | URI                   |                          +-----------------------+                          | stun:example.org      |                          | stuns:example.org     |                          | stun:example.org:8000 |                          +-----------------------+                                  Table 1Appendix B.  Design Notes   o  One recurring comment was to stop using the suffix "s" on the URI      scheme and to move the secure option to a parameter (e.g.,      ";proto=tls").  We decided against this idea because the need for      ";proto=" for the STUN URI cannot be sufficiently explained, and      supporting it would render an incomplete specification.  This      would also result in lost symmetry between the TURN and STUN URIs.   o  Following the advice ofSection 2.2 of [RFC4395], and because the      STUN URI does not describe a hierarchical structure, the STUN URIs      are opaque.Nandakumar, et al.           Standards Track                    [Page 8]

RFC 7064                        STUN URI                   November 2013Authors' Addresses   Suhas Nandakumar   Cisco Systems   170 West Tasman Drive   San Jose, CA  95134   USA   EMail: snandaku@cisco.com   Gonzalo Salgueiro   Cisco Systems   7200-12 Kit Creek Road   Research Triangle Park, NC  27709   USA   EMail: gsalguei@cisco.com   Paul E. Jones   Cisco Systems   7025 Kit Creek Road   Research Triangle Park, NC  27709   USA   EMail: paulej@packetizer.com   Marc Petit-Huguenin   Impedance Mismatch   EMail: petithug@acm.orgNandakumar, et al.           Standards Track                    [Page 9]