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Versions: 00 01 02 draft-ietf-avtcore-rfc5764-mux-fixes

AVTCORE                                                M. Petit-Huguenin
Internet-Draft                                       Jive Communications
Updates: 5764 (if approved)                                 G. Salgueiro
Intended status: Standards Track                           Cisco Systems
Expires: January 3, 2015                                    July 2, 2014


  Multiplexing Scheme Updates for Secure Real-time Transport Protocol
     (SRTP) Extension for Datagram Transport Layer Security (DTLS)
            draft-petithuguenin-avtcore-rfc5764-mux-fixes-00

Abstract

   This document defines how Datagram Transport Layer Security (DTLS),
   Real-time Transport Protocol (RTP), Real-time Transport Control
   Protocol (RTCP), Session Traversal Utilities for NAT (STUN), and
   Traversal Using Relays around NAT (TURN) packets are multiplexed on a
   single receiving socket.  It overrides the guidance from SRTP
   Extension for DTLS [RFC5764], which suffered from three issues
   described and fixed in this document.

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-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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 January 3, 2015.

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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Implicit Allocation of Codepoints for New STUN Methods  .   3
     1.2.  Implicit Allocation of New Codepoints for TLS
           ContentTypes  . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Multiplexing of TURN Channels . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  RFC 5764 Updates  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  STUN Methods  . . . . . . . . . . . . . . . . . . . . . .   7
     6.2.  TLS ContentType . . . . . . . . . . . . . . . . . . . . .   8
     6.3.  TURN Channel Numbers  . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Section 5.1.2 of Secure Real-time Transport Protocol (SRTP) Extension
   for DTLS [RFC5764] defines a scheme for a Real-time Transport
   Protocol (RTP) [RFC3550] receiver to demultiplex Datagram Transport
   Layer Security (DTLS) [RFC6347], Session Traversal Utilities for NAT
   (STUN) [RFC5389] and Secure Real-time Transport Protocol
   (SRTP)/Secure Real-time Transport Control Protocol (SRTCP) [RFC3711]
   packets that are arriving on the RTP port.  Unfortunately, this
   demultiplexing scheme has created three problematic issues:

   1.  It implicitly allocated codepoints for new STUN methods without
       an IANA registry reflecting these new allocations.

   2.  It implicitly allocated codepoints for new Transport Layer
       Security (TLS) ContentTypes without an IANA registry reflecting
       these new allocations.

   3.  It did not take into account the fact that the Traversal Using
       Relays around NAT (TURN) usage of STUN can create TURN channels
       that also need to be demultiplexed with the other packet types
       explicitly mentioned in Section 5.1.2 of RFC 5764.



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   These flaws in the demultiplexing scheme were unavoidably inherited
   by other documents, such as [I-D.ietf-mmusic-udptl-dtls] and
   [I-D.ietf-mmusic-sdp-bundle-negotiation].  These will need to be
   corrected with the updates this document provides when it become
   normative.

1.1.  Implicit Allocation of Codepoints for New STUN Methods

   The demultiplexing scheme in [RFC5764] states that the receiver can
   identify the packet type by looking at the first byte.  If the value
   of this first byte is 0 or 1, the packet is identified to be STUN.
   The problem that arises as a result of this implicit allocation is
   that this restricts the codepoints for STUN methods (as described in
   Section 18.1 of [RFC5389]) to values between 0x000 and 0x07F, which
   in turn reduces the number of possible STUN method codepoints
   assigned by IETF Review (i.e., the range from (0x000 - 0x7FF) from
   2048 to only 128 and entirely obliterating those STUN method
   codepoints assigned by Designated Expert (i.e., the range 0x800 -
   0xFFF).  In fact, RFC 5764 implicitly (and needlessly) allocated a
   very large range of STUN methods, but at a minimum the IANA STUN
   Methods registry should properly reflect this.

   There are only a few STUN method codepoints currently allocated, but
   this is largely attributed to the fact that STUN did not see much
   deployment until the development of WebRTC.  For this reason, simply
   marking the implicit allocations made by RFC 5764 in the STUN Method
   registry may create a shortage of codepoints at a time when interest
   in STUN and STUN Usages (especially TURN) is growing rapidly.
   Consequently, this document also changes the RFC 5764 packet
   identification algorithm to expand the range assigned to the STUN
   protocol from 0 - 1 to 0 - 19, as the values 2-19 are unused.

   In addition to explicitly allocating STUN methods codepoints from
   0x500 to 0xFFF as Reserved values, this document also updates the
   IANA registry such that the STUN method codepoints assigned via IETF
   Review are in the 0x000-0x27F range and those assigned via Designated
   Expert are in the 0x280-0x4FF range.  The proposed changes to the
   STUN Method Registry is:

   OLD:

   0x000-0x7FF     IETF Review
   0x800-0xFFF     Designated Expert

   NEW:






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   0x000-0x27F     IETF Review
   0x280-0x4FF     Designated Expert
   0x500-0xFFF     Reserved

1.2.  Implicit Allocation of New Codepoints for TLS ContentTypes

   The demultiplexing scheme in [RFC5764] dictates that if the value of
   the first byte is between 20 and 63 (inclusive), then the packet is
   identified to be DTLS.  The problem that arises is that this
   restricts the TLS ContentType codepoints (as defined in Section 12 of
   [RFC5246]) to this range, and by extension implicitly allocates
   ContentType codepoints 0 to 19 and 64 to 255.  Unlike STUN, TLS is a
   mature protocol that is already well established and widely
   implemented and thus we expect only relatively few new codepoints to
   be assigned in the future.  With respect to TLS packet
   identification, this document simply explicitly reserves the
   codepoints from 0 to 19 and from 64 to 255 so they are not
   inadvertently assigned in the future.

1.3.  Multiplexing of TURN Channels

   When used with ICE [RFC5245], an RFC 5764 implementation can receive
   packets on the same socket from three different paths, as shown in
   Figure 1:

   1.  Directly from the source

   2.  Through a NAT

   3.  Relayed by a TURN server

                     +------+
                     | TURN |<------------------------+
                     +------+                         |
                        |                             |
                        | +-------------------------+ |
                        | |                         | |
                        v v                         | |
                 NAT -----------                    | |
                        | | +---------------------+ | |
                        | | |                     | | |
                        v v v                     | | |
                    +----------+              +----------+
                    | RFC 5764 |              | RFC 5764 |
                    +----------+              +----------+

         Figure 1: Packet Reception by an RFC 5764 Implementation




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   Even if the ICE algorithm succeeded in selecting a non-relayed path,
   it is still possible to receive data from the TURN server.  For
   instance, when ICE is used with aggressive nomination the media path
   can quickly change until it stabilizes.  Also, freeing ICE candidates
   is optional, so the TURN server can restart forwarding STUN
   connectivity checks during an ICE restart.

   TURN channels are an optimization where data packets are exchanged
   with a 4-byte prefix, instead of the standard 36-byte STUN overhead
   (see Section 2.5 of [RFC5766]).  The problem is that the RFC 5764
   demultiplexing scheme does not define what to do with packets
   received over a TURN channel since these packets will start with a
   first byte whose value will be between 64 and 127 (inclusive).  If
   the TURN server was instructed to send data over a TURN channel, then
   the current RFC 5764 demultiplexing scheme will reject these packets.
   Current implementations violate RFC 5764 for values 64 to 127
   (inclusive) and they instead parse packets with such values as TURN.
   In order to prevent future documents from assigning values from the
   unused range to a new protocol, this document modifies the RFC 5764
   demultiplexing algorithm to properly account for TURN channels.

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 "must" or "Must"), they have their usual English meanings, and are
   not to be interpreted as RFC 2119 key words.

3.  RFC 5764 Updates

   This document updates the text in Section 5.1.2 of [RFC5764] as
   follows:

   OLD TEXT

   The process for demultiplexing a packet is as follows.  The receiver
   looks at the first byte of the packet.  If the value of this byte is
   0 or 1, then the packet is STUN.  If the value is in between 128 and
   191 (inclusive), then the packet is RTP (or RTCP, if both RTCP and
   RTP are being multiplexed over the same destination port).  If the
   value is between 20 and 63 (inclusive), the packet is DTLS.  This
   process is summarized in Figure 3.








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                    +----------------+
                    | 127 < B < 192 -+--> forward to RTP
                    |                |
        packet -->  |  19 < B < 64  -+--> forward to DTLS
                    |                |
                    |       B < 2   -+--> forward to STUN
                    +----------------+

     Figure 3: The DTLS-SRTP receiver's packet demultiplexing algorithm.
          Here the field B denotes the leading byte of the packet.

   END OLD TEXT

   NEW TEXT

   The process for demultiplexing a packet is as follows.  The receiver
   looks at the first byte of the packet.  If the value of this byte is
   in between 0 and 19 (inclusive), then the packet is STUN.  If the
   value is in between 128 and 191 (inclusive), then the packet is RTP
   (or RTCP, if both RTCP and RTP are being multiplexed over the same
   destination port).  If the value is between 20 and 63 (inclusive),
   the packet is DTLS.  If the value is between 64 and 127 (inclusive),
   the packet is TURN Channel.  This process is summarized in Figure 3.

                    +----------------+
                    | 127 < B < 192 -+--> forward to RTP
                    |                |
                    |  63 < B < 128 -+--> forward to TURN Channel
        packet -->  |                |
                    |  19 < B < 64  -+--> forward to DTLS
                    |                |
                    |       B < 20  -+--> forward to STUN
                    +----------------+

     Figure 3: The DTLS-SRTP receiver's packet demultiplexing algorithm.
          Here the field B denotes the leading byte of the packet.

   END NEW TEXT

   [[Note: we may want to use "<=" instead of "<" to make it easier on
   implementers.]]

4.  Implementation Status

   [[Note to RFC Editor: Please remove this section and the reference to
   [RFC6982] before publication.]]





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   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC6982].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC6982], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

   Note that there is currently no implementation declared in this
   section, but the intent is to add RFC 6982 templates here from
   implementers that support the modifications in this document.

5.  Security Considerations

   This document simply updates existing IANA registries and does not
   introduce any specific security considerations beyond those detailed
   in [RFC5764].

6.  IANA Considerations

6.1.  STUN Methods

   This specification contains the registration information for 2816
   STUN Methods codepoints, as explained in Section 1.1 and in
   accordance with the procedures defined in Section 18.1 of [RFC5389].

   Value:   0x500-0xFFF

   Name:   Reserved

   Reference:   RFC5764, RFCXXXX

   This specification also reassigns the ranges in the STUN Methods
   Registry as follow:

   Range:   0x000-0x27F



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   Registration Procedures:   IETF Review

   Range:   0x280-0x4FF

   Registration Procedures:   Designated Expert

6.2.  TLS ContentType

   This specification contains the registration information for 212 TLS
   ContentType codepoints, as explained in Section 1.2 and in accordance
   with the procedures defined in Section 12 of [RFC5246].

   Value:   0-19

   Description:   Reserved

   DTLS-OK:   N/A

   Reference:   RFC5764, RFCXXXX

   Value:   64-255

   Description:   Reserved

   DTLS-OK:   N/A

   Reference:   RFC5764, RFCXXXX

6.3.  TURN Channel Numbers

   This specification contains the registration information for 32768
   TURN Channel Numbers codepoints, as explained in Section 1.3 and in
   accordance with the procedures defined in Section 18 of [RFC5766].

   Value:   0x8000-0xFFFF

   Name:   Reserved

   Reference:   RFCXXXX

   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
   document.]

7.  Acknowledgements

   The implicit STUN Method codepoint allocations problem was first
   reported by Martin Thomson in the RTCWEB mailing-list and discussed
   further with Magnus Westerlund.



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   Thanks to Simon Perreault and Colton Shields for the comments,
   suggestions, and questions that helped improve this document.

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.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245, April
              2010.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

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

   [RFC5764]  McGrew, D. and E. Rescorla, "Datagram Transport Layer
              Security (DTLS) Extension to Establish Keys for the Secure
              Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.

   [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.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

8.2.  Informative References

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, July
              2013.





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   [I-D.ietf-mmusic-udptl-dtls]
              Holmberg, C., Sedlacek, I., and G. Salgueiro, "UDP
              Transport Layer (UDPTL) over Datagram Transport Layer
              Security (DTLS)", draft-ietf-mmusic-udptl-dtls-10 (work in
              progress), June 2014.

   [I-D.ietf-mmusic-sdp-bundle-negotiation]
              Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
              negotiation-07 (work in progress), April 2014.

Authors' Addresses

   Marc Petit-Huguenin
   Jive Communications
   1275 West 1600 North, Suite 100
   Orem, UT  84057
   USA

   Email: marcph@getjive.com


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

   Email: gsalguei@cisco.com





















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