AVTCORE                                                M. Petit-Huguenin
Internet-Draft                                        Impedance Mismatch
Updates: 5764 (if approved)                                 G. Salgueiro
Intended status: Standards Track                           Cisco Systems
Expires: September 25, 2015                               March 24, 2015

  Multiplexing Scheme Updates for Secure Real-time Transport Protocol
     (SRTP) Extension for Datagram Transport Layer Security (DTLS)
                draft-ietf-avtcore-rfc5764-mux-fixes-01
                draft-ietf-avtcore-rfc5764-mux-fixes-02

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), and Stream Control
   Transmission Protocol (SCTP) over UDP (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
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   This Internet-Draft will expire on September 25, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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.  Multiplexing Byte Allocation for SCTP over UDP  . . . . .   4
     1.3.  Implicit Allocation of New Codepoints for TLS
           ContentTypes  . . . . . . . . . . . . . . . . . . . . . .   4
     1.4.
     1.3.  Multiplexing of TURN Channels . . . . . . . . . . . . . .   5
     1.5.
     1.4.  Demultiplexing Algorithm Test Order . . . . . . . . . . .   6
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  RFC 5764 Updates  . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  STUN Methods  . . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  TLS ContentType . . . . . . . . . . . . . . . . . . . . .   9
     6.3.  TURN Channel Numbers  . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11  10
   Appendix A.  Release notes  . . . . . . . . . . . . . . . . . . .  11
     A.1.  Modifications between draft-ietf-avtcore-rfc5764-mux-
           fixes-01 and draft-ietf-avtcore-rfc5764-mux-fixes-00  . .  11
     A.2.  Modifications between draft-ietf-avtcore-rfc5764-mux-
           fixes-01 and draft-ietf-avtcore-rfc5764-mux-fixes-00  . .  11
     A.3.  Modifications between draft-ietf-avtcore-rfc5764-mux-
           fixes-00 and draft-petithuguenin-avtcore-rfc5764-mux-
           fixes-02  . . . . . . . . . . . . . . . . . . . . . . . .  12
     A.3.
     A.4.  Modifications between draft-petithuguenin-avtcore-rfc5764
           -mux-fixes-00 and draft-petithuguenin-avtcore-rfc5764
           -mux-fixes-01 . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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] [I-D.ietf-tram-stunbis] 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 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.

   4.  The current ranges are not efficiently allocated making it harder
       to introduce new protocols that might require multiplexing.

   These flaws in the demultiplexing scheme were unavoidably inherited
   by other documents, such as [RFC7345] and
   [I-D.ietf-mmusic-sdp-bundle-negotiation].  These will need to be
   corrected with the updates this document provides.

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).

   To preserve the Designated Expert range, this document allocates the
   value 2 and 3 to also identify STUN methods.

   The IANA Registry for STUN methods is modified to mark the codepoints
   from 0x100 to 0xFFF as Reserved.  These codepoints can still be
   allocated, but require IETF Review with a document that will properly
   evaluate the risk of an assignment overlapping with other registries.

   In addition, this document also updates the IANA registry such that
   the STUN method codepoints assigned in the 0x080-0x0FF range are also
   assigned via Designated Expert.  The proposed changes to the STUN
   Method Registry are:

   OLD:

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

   NEW:

   0x000-0x07F     IETF Review
   0x080-0x0FF     Designated Expert
   0x100-0xFFF     Reserved

1.2.  Multiplexing Byte Allocation for SCTP over UDP

   [I-D.ietf-tram-stunbis] defines two new transports for STUN, SCTP
   over UDP and SCTP over DTLS over UDP.  This document allocates the
   value 5 as to multiplex SCTP over STUN.  This value restricts the
   source and destination port numbers that can be used by SCTP over
   UDP.

1.3.  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.  These codepoints can
   still be allocated, but require Standards Action with a document that
   will properly evaluate the risk of an assignment overlapping with
   other registries.  The proposed changes to the TLS ContentTypes
   Registry are:

   OLD:

   0-19    Unassigned
   20      change_cipher_spec
   21      alert
   22      handshake
   23      application_data
   24      heartbeat
   25-255  Unassigned

   NEW:

   0-19    Reserved (MUST be allocated with Standards Action)
   20      change_cipher_spec
   21      alert
   22      handshake
   23      application_data
   24      heartbeat
   25-63   Unassigned
   64-255  Reserved (MUST be allocated with Standards Action)

1.4.

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

   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 by
   allocating the values from 64 to 79 for this purpose.

   An implementation that uses the source IP address and port to
   identify TURN channel messages MAY not need to restrict the channel
   numbers to the above range.

1.5.

1.4.  Demultiplexing Algorithm Test Order

   This document also changes the demultiplexing algorithm by imposing
   the order in which the first byte is tested against the list of
   existing protocol ranges.  This is done in order to ensure that all
   implementations fail identically in the presence of a new range.

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.

             +----------------+
             | 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 3 (inclusive), then the packet is STUN.  Then if the
   value is 5, then the packet is SCTP.  Then if the value is between 20 and 63 (inclusive), the packet is DTLS.  Then if
   the value is between 64 and 79 (inclusive), the packet is TURN
   Channel.  Then 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).  Else if the value does
   not match any known range then the packet MUST be dropped and an
   alert MAY be logged.  This process is summarized in Figure 3.  When
   new values or ranges are added, they MUST be tested in ascending
   order.

                    +----------------+
                    |        [0..3] -+--> forward to STUN
                    |                |
                    |             5 -+--> forward to SCTP
                    |                |
        packet -->  |      [20..63] -+--> forward to DTLS
                    |                |
                    |      [64..79] -+--> forward to TURN Channel
                    |                |
                    |    [128..191] -+--> forward to RTP
                    +----------------+

     Figure 3: The DTLS-SRTP receiver's packet demultiplexing algorithm.

   END NEW TEXT

4.  Implementation Status

   [[Note to RFC Editor: Please remove this section and the reference to
   [RFC6982] before publication.]]
   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 reserved
   STUN Methods codepoints, as explained in Section 1.1 and in
   accordance with the procedures defined in Section 18.1 of [RFC5389].

   Value:   0x100-0xFFF

   Name:   Reserved (MUST be allocated with IETF Review)

   Reference:   RFC5764, RFCXXXX

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

   Range:   0x000-0x07F
   Registration Procedures:   IETF Review

   Range:   0x080-0x0FF

   Registration Procedures:   Designated Expert

6.2.  TLS ContentType

   This specification contains the registration information for reserved
   TLS ContentType codepoints, as explained in Section 1.3 1.2 and in
   accordance with the procedures defined in Section 12 of [RFC5246].

   Value:   0-19

   Description:   Reserved (MUST be allocated with Standards Action)

   DTLS-OK:   N/A

   Reference:   RFC5764, RFCXXXX

   Value:   64-255

   Description:   Reserved (MUST be allocated with Standards Action)

   DTLS-OK:   N/A

   Reference:   RFC5764, RFCXXXX

6.3.  TURN Channel Numbers

   This specification contains the registration information for reserved
   TURN Channel Numbers codepoints, as explained in Section 1.4 1.3 and in
   accordance with the procedures defined in Section 18 of [RFC5766].

   Value:   0x5000-0xFFFF

   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.

   Thanks to Simon Perreault, Colton Shields, Cullen Jennings, Colin
   Perkins, Magnus Westerlund, Paul Jones, Jonathan Lennox, Varun Singh
   and Justin Uberti 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.

   [RFC7345]  Holmberg, C., Sedlacek, I., and G. Salgueiro, "UDP
              Transport Layer (UDPTL) over Datagram Transport Layer
              Security (DTLS)", RFC 7345, August 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-18 (work in progress), March 2015.

   [I-D.ietf-tram-stunbis]
              Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
              D., Mahy, R., and P. Matthews, "Session Traversal
              Utilities for NAT (STUN)", draft-ietf-tram-stunbis-02
              (work in progress), March 2015.

Appendix A.  Release notes

   This section must be removed before publication as an RFC.

A.1.  Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-01 and
      draft-ietf-avtcore-rfc5764-mux-fixes-00

   o  Remove any discussion about SCTP until a consensus emerges in
      TRAM.

A.2.  Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-01 and
      draft-ietf-avtcore-rfc5764-mux-fixes-00

   o  Instead of allocating the values that are common on each registry,
      the specification now only reserves them, giving the possibility
      to allocate them in case muxing is irrelevant.

   o  STUN range is now 0-3m with 2-3 being Designated Expert.

   o  TLS ContentType 0-19 and 64-255 are now reserved.

   o  Add SCTP over UDP value.

   o  If an implementation uses the source IP address/port to separate
      TURN channels packets then the whole channel numbers are
      available.

   o  If not the prefix is between 64 and 79.

   o  First byte test order is now by incremental values, so failure is
      deterministic.

   o  Redraw the demuxing diagram.

A.2.

A.3.  Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-00 and
      draft-petithuguenin-avtcore-rfc5764-mux-fixes-02

   o  Adoption by WG.

   o  Add reference to STUNbis.

A.3.

A.4.  Modifications between draft-petithuguenin-avtcore-rfc5764-mux-
      fixes-00 and draft-petithuguenin-avtcore-rfc5764-mux-fixes-01

   o  Change affiliation.

Authors' Addresses

   Marc Petit-Huguenin
   Impedance Mismatch

   Email: marc@petit-huguenin.org

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

   Email: gsalguei@cisco.com