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Versions: 00                                                            
RTCWEB                                                     S. Nandakumar
Internet-Draft                                              G. Salgueiro
Intended status: Standards Track                                P. Jones
Expires: April 27, 2012                                    Cisco Systems
                                                        October 25, 2011


    URI Scheme for Traversal Using Relays around NAT (TURN) Protocol
                  draft-nandakumar-rtcweb-turn-uri-00

Abstract

   This document is the specification of the syntax and semantics of the
   Uniform Resource Identifier (URI) scheme for the Traversal Using
   Relays around NAT (TURN) protocol.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 27, 2012.

Copyright Notice

   Copyright (c) 2011 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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  URI Scheme Definition . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . . 3
     3.2.  URI Scheme Semantics  . . . . . . . . . . . . . . . . . . . 4
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  The 'turn' URI Scheme Registration  . . . . . . . . . . . . 5
     5.2.  The 'turns' URI Scheme Registration . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9


































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1.  Introduction

   This document specifies the syntax and semantics of the Uniform
   Resource Identifier (URI) scheme for the Traversal Using Relays
   around NAT (TURN) protocol.

   The TURN protocol is a specification allowing hosts behind NAT to
   control the operation of a relay server.  The relay server allows
   hosts to exchange packets with its peers.  The peers themselves may
   also be behind NATs.  RFC 5766 [RFC5766] defines the specifics of the
   TURN protocol.

   The 'turn/turns' URI scheme is used to designate a TURN server (also
   known as a relay) on Internet hosts accessible using the TURN
   protocol.  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 TURN server to carry out the
   TURN protocol.  This also implies those endpoints and/or applications
   to be provisioned with appropriate configuration required to identify
   the TURN server.  Having an inconsistent syntax has its drawbacks and
   can result in non-interoperable solutions.  It can result in
   solutions that are ambiguous and have implementation limitations on
   the different aspects of the syntax and alike.  The 'turn/turns' URI
   scheme helps alleviate most of these issues by providing a consistent
   way to describe, configure and exchange the information identifying a
   TURN server.  This would also prevent the shortcomings inherent with
   encoding similar information in non-uniform syntaxes such as the ones
   proposed in the WEBRTC Standards [WEBRTC], for example.

   The 'turn/turns' URI scheme adheres to the generic syntax defined in
   RFC 3986 [RFC3986].


2.  Terminology

   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 RFC 2119 [RFC2119].


3.  URI Scheme Definition

3.1.  URI Scheme Syntax

   The 'turn' URI takes the following form (the syntax below is non-
   normative):





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      turn:<userinfo>@<host>:<port>

      turns:<userinfo>@<host>:<port>

   Where <userinfo> with the "@" (at) sign character, as well as the
   <port> part and the preceding ":" (colon) character, is OPTIONAL.

   The normative syntax of the 'turn' URI is defined as shown in the
   following Augmented Backus-Naur Form (ABNF) [RFC5234] rule:

   turn-uri      = turn-scheme ":" [ userinfo "@" ] host [ ":" port ]
   turn-scheme   = "turn"/"turns"
   userinfo      = user [ ":" password ]
   user          = 1*(%x21-24 / %x26-39 / %x3B-3F / %x41-7F
                   / escaped)
                       ; The symbols "%", ":", "@", and symbols
                       ; with a character value below 0x21 may
                       ; be represented as escaped sequences.
   password      = 1*(%x21-24 / %x26-3F / %x41-7F / escaped)
                       ; The symbols "%", "@", and symbols with
                       ; a character value below 0x21 may be
                       ; represented as escaped sequences.
   host          = hostname / IPv4address / IPv6reference
   hostname      = *( domainlabel "." ) toplabel [ "." ]
   domainlabel   = alphanum / alphanum *( alphanum / "-" ) alphanum
   toplabel      = ALPHA / ALPHA *( alphanum / "-" ) alphanum
   IPv4address   = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT
   IPv6reference = "[" IPv6address "]"
   IPv6address   = hexpart [ ":" IPv4address ]
   hexpart       = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ]
   hexseq        = hex4 *( ":" hex4 )
   hex4          = 1*4HEXDIG
   port          = 1*DIGIT
   alphanum      = ALPHA / DIGIT
   escaped       = "%" HEXDIG HEXDIG

   The current ABNF proposal doesn't specify a mechanism for handling
   different transports.  We have identified a possible solution and
   will be included in the future version of the draft.

   The <host>, <port> and <userinfo> rules are described in Appendix A
   of RFC 3986 [RFC3986].  The core rules <ALPHA>, <DIGIT> and
   <HEXDIGIT> are used as described in Appendix B of RFC 5234 [RFC5234].

3.2.  URI Scheme Semantics

   The TURN protocol supports sending messages over UDP, TCP or TLS-
   over-TCP.  The 'turns' URI scheme SHALL be used when TURN is run over



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   TLS-over-TCP (or in the future DTLS-over-UDP) and the 'turn' scheme
   SHALL be used otherwise.  The <host> part of the 'turn' URI, which is
   REQUIRED, denotes the TURN server host.  The <userinfo> part,
   identifies the credential required for the long-term credential
   mechanism as described in the section 10.2 of RFC 5389 [RFC5389].
   The <port> part, if present, denotes the port on which the TURN
   server is awaiting connection requests.  If it is absent, the default
   port SHALL be 3478 for both UDP and TCP.  The default port for TURN
   over TLS SHALL be 5349.


4.  Examples

   URI to identify a long-term credential for the TLS-over-TCP
   connection to TURN server, example.com, on default port 5349:

      turns:username:password@example.com

   URI to identify a long-term credential for the connection to TURN
   server, example.com, on default port 3478:

      turn:username:password@example.com


5.  IANA Considerations

   This document instructs IANA to register the 'turn' and 'turns' URI
   schemes in the "Permanent URI Schemes" sub-registry in the "Uniform
   Resource Identifier (URI) Schemes" IANA registry [URIREG].  These
   registrations follows the URI Scheme Registration Template detailed
   in Section 5.4 of RFC 4395 [RFC4395].

5.1.  The 'turn' URI Scheme Registration

   IANA registration of the the 'turn' URI scheme:

      URI scheme name: turn

      Status: Permanent

      URI scheme syntax: see Section 3.1 of RFC XXXX [This document]

      URI scheme semantics: see Section 3.2 of RFC XXXX [This document]

      URI scheme encoding considerations: there are no other encoding
      considerations for 'turn' URIs that are not described in RFC 5766
      [RFC5766].




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      Protocols that use the scheme: Traversal Using Relays around NAT
      (TURN)

      Security Considerations: see Section 6 of RFC XXXX [This document]

      Contact: IESG <iesg@ietf.org>

      Author/Change controller: IETF <ietf@ietf.org>

      References: See Section 8 of RFC XXXX [This document]

5.2.  The 'turns' URI Scheme Registration

   IANA registration of the the 'turns' URI scheme:

      URI scheme name: turns

      Status: Permanent

      URI scheme syntax: see Section 3.1 of RFC XXXX [This document]

      URI scheme semantics: see Section 3.2 of RFC XXXX [This document]

      URI scheme encoding considerations: there are no other encoding
      considerations for 'turns' URIs that are not described in RFC 5766
      [RFC5766].

      Protocols that use the scheme: Traversal Using Relays around NAT
      (TURN) when run over TLS-over-TCP.

      Security Considerations: see Section 6 of RFC XXXX [This document]

      Contact: IESG <iesg@ietf.org>

      Author/Change controller: IETF <ietf@ietf.org>

      References: See Section 8 of RFC XXXX [This document]


6.  Security Considerations

   The URI Scheme defined by this document for the Traversal Using
   Relays around NAT (TURN) protocol needs to consider the security
   considerations detailed in Section 17 of RFC 5766 [RFC5766].

   As described in Section 3.2.1 of STD 66 [RFC3986], having
   authentication information (specifically passwords) in a URI means
   that the URI must be handled carefully:



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      The passing of authentication information in clear text has proven
      to be a security risk in almost every case where it has been used.

   Section 3.2.1 contains advice on handling URI that contain passwords
   in the userinfo portion.  Implementations of this specification MUST
   implement that advice.

   Specifically if a URI that contains credentials leaks, then it would
   allow an attacker to use the TURN server which is referenced by the
   URI.  Such an attack has two major impacts.  First, it uses up the
   operator's bandwidth.  Second, if the operator bills the user for
   TURN server usage, then it may expose the user to costs incurred by
   the attacker.  However, the attacker never obtains the user's private
   information, nor does this attack allow for traffic amplification.

   The expected use environment mitigates to some degree concerns about
   TURN URIs compared to other URIs, such as HTTPS.  First, users do not
   dereference TURN URIs directly.  Instead, they are passed to the TURN
   stack.  Thus, concerns about confusion or leakage due to the URI
   being displayed to the user are significantly reduced; indeed the URI
   need never be available to the user at all.

   One of the primary use cases for a TURN URI with credentials is
   WebRTC.  In this case, a web server will be offering a calling
   service and may have an associated TURN server it can use.  In this
   case, the browser will need to use the TURN server and the browser
   has no long term or preexisting relationship with the TURN server.
   The web server needs to provide some credential to the client which
   it can use to access the TURN server.  Since TURN authentication is
   via username and password, this implies that the credential is a
   username/password pair.  While this must be transmitted securely
   (i.e., over HTTPS), the security properties are the same whether the
   password is carried separately or is part of the URL.  Moreover,
   because the web server and TURN servers can cooperate, a new password
   can be issued for every call, making short-term credentials feasible
   and thus significantly mitigating the risk.

   If a TURN URI is transferred between hosts, it MUST be done over a
   protocol that provides confidentiality such as HTTPS [RFC2818].  It
   is RECOMMENDED that the credential only be valid for a single call
   and preferably for no more than one day. that "preferably" is bad.


7.  Acknowledgements

   Many thanks to Cullen Jennings for his detailed review and thoughtful
   comments on this document.




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   We acknowledge the existence of
   draft-petithuguenin-behave-turn-uri-bis-04 document as a parallel
   effort in defining the URI scheme for TURN.  Awareness of this draft
   came late in the process and we have not had to time to reach out to
   the author of that memo and discuss opportunities to collaborate on a
   single document.  It is our intentions to do so.


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.

8.2.  Informative References

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 35,
              RFC 4395, February 2006.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.

   [URIREG]   Internet Assigned Numbers Authority (IANA) Registry,
              "Uniform Resource Identifier (URI) Schemes",
              <http://www.iana.org/assignments/uri-schemes.html> .

   [WEBRTC]   W3C, "WebRTC 1.0: Real-time Communication Between
              Browsers",
              <http://dev.w3.org/2011/webrtc/editor/webrtc.html> .






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Authors' Addresses

   Suhas Nandakumar
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Email: snandaku@cisco.com


   Gonzalo Salgueiro
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: gsalguei@cisco.com


   Paul E. Jones
   Cisco Systems
   7025 Kit Creek Road
   Research Triangle Park, NC  27709
   US

   Email: paulej@packetizer.com
























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