Internet DRAFT - draft-ietf-avtcore-rfc5764-mux-fixes
draft-ietf-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: November 26, 2016 May 25, 2016
Multiplexing Scheme Updates for Secure Real-time Transport Protocol
(SRTP) Extension for Datagram Transport Layer Security (DTLS)
draft-ietf-avtcore-rfc5764-mux-fixes-08
Abstract
This document defines how Datagram Transport Layer Security (DTLS),
Real-time Transport Protocol (RTP), RTP 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 November 26, 2016.
Copyright Notice
Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Implicit Allocation of Codepoints for New STUN Methods . . . 4
4. Implicit Allocation of New Codepoints for TLS ContentTypes . 5
5. Multiplexing of TURN Channels . . . . . . . . . . . . . . . . 6
6. RFC 5764 Updates . . . . . . . . . . . . . . . . . . . . . . 7
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9.1. STUN Methods . . . . . . . . . . . . . . . . . . . . . . 9
9.2. TLS ContentType . . . . . . . . . . . . . . . . . . . . . 9
9.3. TURN Channel Numbers . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Release notes . . . . . . . . . . . . . . . . . . . 12
A.1. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-08 and draft-ietf-avtcore-rfc5764-mux-fixes-07 . . 12
A.2. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-07 and draft-ietf-avtcore-rfc5764-mux-fixes-06 . . 12
A.3. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-06 and draft-ietf-avtcore-rfc5764-mux-fixes-05 . . 12
A.4. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-05 and draft-ietf-avtcore-rfc5764-mux-fixes-04 . . 12
A.5. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-04 and draft-ietf-avtcore-rfc5764-mux-fixes-03 . . 12
A.6. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-03 and draft-ietf-avtcore-rfc5764-mux-fixes-02 . . 12
A.7. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-02 and draft-ietf-avtcore-rfc5764-mux-fixes-01 . . 13
A.8. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-01 and draft-ietf-avtcore-rfc5764-mux-fixes-00 . . 13
A.9. Modifications between draft-ietf-avtcore-rfc5764-mux-
fixes-00 and draft-petithuguenin-avtcore-rfc5764-mux-
fixes-02 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.10. Modifications between draft-petithuguenin-avtcore-rfc5764
-mux-fixes-00 and draft-petithuguenin-avtcore-rfc5764
-mux-fixes-01 . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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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 RTP 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.
Having overlapping ranges between different IANA registries becomes
an issue when a new codepoint is allocated in one of these registries
without carefully analyzing the impact it could have on the other
registries when that codepoint is demultiplexed. Among other
downsides of the bad design of the demultiplexing algorithm detailed
in [RFC5764], it creates a requirement for coordination between
codepoint assignments where none should exist, and that is
organizationally and socially undesirable. However, RFC 5764 has
been widely deployed so there must be an awareness of this issue and
how it must be dealt with. Thus, even if a codepoint is not
initially thought to be useful, the respective IANA registry expert
should at least raise a flag when the allocated codepoint irrevocably
prevents multiplexing.
The first goal of this document is to make sure that future
allocations in any of the affected protocols are done with the full
knowledge of their impact on multiplexing. This is achieved by
modifying the IANA registries with instructions for coordination
between the protocols at risk.
A second goal is to permit the addition of new protocols to the list
of existing multiplexed protocols in a manner that does not break
existing implementations.
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The flaws in the demultiplexing scheme were unavoidably inherited by
other documents, such as [RFC7345] and
[I-D.ietf-mmusic-sdp-bundle-negotiation]. So in addition, these and
any other affected documents will need to be corrected with the
updates this document provides.
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. 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 eliminating the possibility of having 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:
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0x000-0x07F IETF Review
0x080-0x0FF Designated Expert
0x100-0xFFF Reserved
4. 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. For DTLS 1.0 [RFC4347] and DTLS 1.2 [RFC6347]
that first byte corresponds to the TLS ContentType field.
Considerations must be taken into account when assigning additional
ContentTypes in the code point ranges 0 to 19 and 64 to 255 so this
does not prevent demultiplexing when this functionality is desirable.
Note that [RFC5764] describes a narrow use of DTLS that works as long
as the specific DTLS version used abides by the restrictions on the
demultiplexing byte (the ones that this document imposes on the TLS
ContentType Registry). Any extension or revision to DTLS that causes
it to no longer meet these constraints should consider what values
may occur in the first byte of the DTLS message and what impact it
would have on the multiplexing that [RFC5764] describes.
With respect to TLS packet identification, this document explicitly
adds a warning to the codepoints from 0 to 19 and from 64 to 255
indicating that allocations in these ranges require coordination, as
described in this document. The proposed changes to the TLS
ContentType 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 Unassigned (Requires coordination, see RFCXXXX)
20 change_cipher_spec
21 alert
22 handshake
23 application_data
24 heartbeat
25-63 Unassigned
64-255 Unassigned (Requires coordination, see RFCXXXX)
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5. 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.
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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.
6. 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. If the
value is between 20 and 63 (inclusive), then the packet is DTLS. If
the value is between 64 and 79 (inclusive), then the packet is TURN
Channel. 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 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.
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+----------------+
| [0..3] -+--> forward to STUN
| |
packet --> | [20..63] -+--> forward to DTLS
| |
| [64..79] -+--> forward to TURN Channel
| |
| [128..191] -+--> forward to RTP/RTCP
+----------------+
Figure 3: The DTLS-SRTP receiver's packet demultiplexing algorithm.
END NEW TEXT
7. 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.
8. Security Considerations
This document updates existing IANA registries and adds a new range
for TURN channels in the demuxing algorithm.
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These modifications do not introduce any specific security
considerations beyond those detailed in [RFC5764].
9. IANA Considerations
9.1. STUN Methods
This specification contains the registration information for reserved
STUN Methods codepoints, as explained in Section 3 and in accordance
with the procedures defined in Section 18.1 of [RFC5389].
Value: 0x100-0xFFF
Name: Reserved (MUST be allocated with IETF Review. For DTLS-SRTP
multiplexing collision avoidance see RFC XXXX)
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
9.2. TLS ContentType
This specification contains the registration information for reserved
TLS ContentType codepoints, as explained in Section 4 and in
accordance with the procedures defined in Section 12 of [RFC5246].
Value: 0-19
Description: Unassigned (Requires coordination, see RFCXXXX)
DTLS-OK: N/A
Reference: RFC5764, RFCXXXX
Value: 64-255
Description: Unassigned (Requires coordination, see RFCXXXX))
DTLS-OK: N/A
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Reference: RFC5764, RFCXXXX
9.3. TURN Channel Numbers
This specification contains the registration information for reserved
TURN Channel Numbers codepoints, as explained in Section 5 and in
accordance with the procedures defined in Section 18 of [RFC5766].
Value: 0x5000-0xFFFF
Name: Reserved (For DTLS-SRTP multiplexing collision avoidance see
RFC XXXX)
Reference: RFCXXXX
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
10. 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,
Justin Uberti, Joseph Salowey, Martin Thomson, Ben Campbell, Stephen
Farrell and Paul Kyzivat for the comments, suggestions, and questions
that helped improve this document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <http://www.rfc-editor.org/info/rfc3550>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<http://www.rfc-editor.org/info/rfc3711>.
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[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, DOI 10.17487/RFC4347, April 2006,
<http://www.rfc-editor.org/info/rfc4347>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.
[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,
DOI 10.17487/RFC5764, May 2010,
<http://www.rfc-editor.org/info/rfc5764>.
[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,
DOI 10.17487/RFC5766, April 2010,
<http://www.rfc-editor.org/info/rfc5766>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
11.2. Informative References
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
DOI 10.17487/RFC6982, July 2013,
<http://www.rfc-editor.org/info/rfc6982>.
[RFC7345] Holmberg, C., Sedlacek, I., and G. Salgueiro, "UDP
Transport Layer (UDPTL) over Datagram Transport Layer
Security (DTLS)", RFC 7345, DOI 10.17487/RFC7345, August
2014, <http://www.rfc-editor.org/info/rfc7345>.
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[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-23 (work in progress), July 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-08 and
draft-ietf-avtcore-rfc5764-mux-fixes-07
o Minor update to Security Considerations section.
A.2. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-07 and
draft-ietf-avtcore-rfc5764-mux-fixes-06
o Addresses Martin Thomson, Ben Campbell and Stephen Farrell's
review comments about TLS ContentType registrations.
A.3. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-06 and
draft-ietf-avtcore-rfc5764-mux-fixes-05
o Addresses Colin's WGLC review comments
A.4. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-05 and
draft-ietf-avtcore-rfc5764-mux-fixes-04
o Removed some remnants of the ordering from Section 6
o Moved Terminology from Section 5 to Section 2
A.5. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-04 and
draft-ietf-avtcore-rfc5764-mux-fixes-03
o Removed Section on "Demultiplexing Algorithm Test Order"
o Split the Introduction into separate sections
A.6. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-03 and
draft-ietf-avtcore-rfc5764-mux-fixes-02
o Revert to the RFC 5389, as the stunbis reference was needed only
for STUN over SCTP.
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A.7. Modifications between draft-ietf-avtcore-rfc5764-mux-fixes-02 and
draft-ietf-avtcore-rfc5764-mux-fixes-01
o Remove any discussion about SCTP until a consensus emerges in
TRAM.
A.8. 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.9. 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.10. 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
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Gonzalo Salgueiro
Cisco Systems
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
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