Internet DRAFT - draft-petithuguenin-avtcore-rfc5764-mux-fixes
draft-petithuguenin-avtcore-rfc5764-mux-fixes
AVTCORE M. Petit-Huguenin
Internet-Draft Impedance Mismatch
Updates: 5764 (if approved) G. Salgueiro
Intended status: Standards Track Cisco Systems
Expires: September 7, 2015 March 6, 2015
Multiplexing Scheme Updates for Secure Real-time Transport Protocol
(SRTP) Extension for Datagram Transport Layer Security (DTLS)
draft-petithuguenin-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) 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 September 7, 2015.
Copyright Notice
Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . 6
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. STUN Methods . . . . . . . . . . . . . . . . . . . . . . 8
6.2. TLS ContentType . . . . . . . . . . . . . . . . . . . . . 8
6.3. TURN Channel Numbers . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . 10
A.1. Modifications between draft-petithuguenin-avtcore-rfc5764
-mux-fixes-00 and draft-petithuguenin-avtcore-rfc5764
-mux-fixes-01 . . . . . . . . . . . . . . . . . . . . . . 10
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.
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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.
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 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. 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
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NEW:
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
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+------+
| 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.
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.
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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 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.
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+----------------+
| 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.]]
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.
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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
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
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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.
Thanks to Simon Perreault, Colton Shields and Cullen Jennings 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.
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[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-12 (work in progress), October 2014.
Appendix A. Release notes
This section must be removed before publication as an RFC.
A.1. Modifications between draft-petithuguenin-avtcore-rfc5764-mux-
fixes-00 and draft-petithuguenin-avtcore-rfc5764-mux-fixes-01
o Change affiliation.
Authors' Addresses
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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
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