AVTCORE M. Petit-Huguenin Internet-Draft Impedance Mismatch Updates: 5764 (if approved) G. Salgueiro Intended status: Standards Track Cisco Systems Expires: April 21, 2016 October 19, 2015 Multiplexing Scheme Updates for Secure Real-time Transport Protocol (SRTP) Extension for Datagram Transport Layer Security (DTLS) draft-ietf-avtcore-rfc5764-mux-fixes-03 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 April 21, 2016. 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 Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 1] Internet-Draft RFC 5764 Mux Fixes October 2015 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 . . . . . . . . . . . . . . 5 1.4. Demultiplexing Algorithm Test Order . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. RFC 5764 Updates . . . . . . . . . . . . . . . . . . . . . . 7 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6.1. STUN Methods . . . . . . . . . . . . . . . . . . . . . . 9 6.2. TLS ContentType . . . . . . . . . . . . . . . . . . . . . 9 6.3. TURN Channel Numbers . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 8.2. Informative References . . . . . . . . . . . . . . . . . 11 Appendix A. Release notes . . . . . . . . . . . . . . . . . . . 12 A.1. Modifications between draft-ietf-avtcore-rfc5764-mux- fixes-03 and draft-ietf-avtcore-rfc5764-mux-fixes-02 . . 12 A.2. Modifications between draft-ietf-avtcore-rfc5764-mux- fixes-02 and draft-ietf-avtcore-rfc5764-mux-fixes-01 . . 12 A.3. Modifications between draft-ietf-avtcore-rfc5764-mux- fixes-01 and draft-ietf-avtcore-rfc5764-mux-fixes-00 . . 12 A.4. Modifications between draft-ietf-avtcore-rfc5764-mux- fixes-00 and draft-petithuguenin-avtcore-rfc5764-mux- fixes-02 . . . . . . . . . . . . . . . . . . . . . . . . 13 A.5. Modifications between draft-petithuguenin-avtcore-rfc5764 -mux-fixes-00 and draft-petithuguenin-avtcore-rfc5764 -mux-fixes-01 . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction [[TODO: Still need to come to resolution on Paul Kyzivat's comment on testing in a particular order in the face of overlapping/non- overlapping ranges.]] Section 5.1.2 of Secure Real-time Transport Protocol (SRTP) Extension for DTLS [RFC5764] defines a scheme for a Real-time Transport Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 2] Internet-Draft RFC 5764 Mux Fixes October 2015 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 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 anyalyzing the impact it could have on the other registries when that codepoint is demultiplexed. Even if a codepoint is not initially thought to be useful in an RFC 5764 implementation, 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. 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. 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. Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 3] Internet-Draft RFC 5764 Mux Fixes October 2015 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: 0x000-0x07F IETF Review 0x080-0x0FF Designated Expert 0x100-0xFFF 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. 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: Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 4] Internet-Draft RFC 5764 Mux Fixes October 2015 OLD: 0-19 Unassigned 20 change_cipher_spec 21 alert 22 handshake 23 application_data 24 heartbeat 25-255 Unassigned NEW: 0-19 Reserved (Requires coordination, see RFCXXXX) 20 change_cipher_spec 21 alert 22 handshake 23 application_data 24 heartbeat 25-63 Unassigned 64-255 Reserved (Requires coordination, see RFCXXXX) 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 Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 5] Internet-Draft RFC 5764 Mux Fixes October 2015 +------+ | 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. 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. Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 6] Internet-Draft RFC 5764 Mux Fixes October 2015 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 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. The Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 7] Internet-Draft RFC 5764 Mux Fixes October 2015 various range values for the first byte MUST be tested in ascending order. +----------------+ | [0..3] -+--> forward to STUN | | 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. Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 8] Internet-Draft RFC 5764 Mux Fixes October 2015 5. Security Considerations This document updates existing IANA registries, adds a new range for TURN channels in the demuxing algorithm, and madates an ascending order for testing the ranges in the demuxing algorithm. These modifications do 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. 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 6.2. TLS ContentType This specification contains the registration information for reserved 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 (MUST be allocated with Standards Action. For DTLS-SRTP multiplexing collision avoidance see RFC XXXX) DTLS-OK: N/A Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 9] Internet-Draft RFC 5764 Mux Fixes October 2015 Reference: RFC5764, RFCXXXX Value: 64-255 Description: Reserved (MUST be allocated with Standards Action. For DTLS-SRTP multiplexing collision avoidance see RFC XXXX) 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 1.3 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.] 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, DOI 10.17487/RFC2119, March 1997, . Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 10] Internet-Draft RFC 5764 Mux Fixes October 2015 [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, . [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, . [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, . [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, DOI 10.17487/RFC5389, 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, DOI 10.17487/RFC5764, 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, DOI 10.17487/RFC5766, April 2010, . [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, . 8.2. 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, . Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 11] Internet-Draft RFC 5764 Mux Fixes October 2015 [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, . [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-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. A.2. 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.3. 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. Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 12] Internet-Draft RFC 5764 Mux Fixes October 2015 o Redraw the demuxing diagram. A.4. 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.5. 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 Petit-Huguenin & SalgueirExpires April 21, 2016 [Page 13]