Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names (CNAMEs)
draft-ietf-avtcore-6222bis-05
The information below is for an old version of the document.
Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7022.
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Authors | Ali C. Begen , Colin Perkins , Dan Wing , Eric Rescorla | ||
Last updated | 2013-07-08 | ||
Replaces | draft-rescorla-avtcore-6222bis | ||
RFC stream | Internet Engineering Task Force (IETF) | ||
Formats | |||
Reviews | |||
Additional resources | Mailing list discussion | ||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Magnus Westerlund | ||
Shepherd write-up | Show Last changed 2013-06-21 | ||
IESG | IESG state | Became RFC 7022 (Proposed Standard) | |
Consensus boilerplate | Unknown | ||
Telechat date |
(None)
Needs a YES. Needs 10 more YES or NO OBJECTION positions to pass. |
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Responsible AD | Richard Barnes | ||
Send notices to | avtcore-chairs@tools.ietf.org, draft-ietf-avtcore-6222bis@tools.ietf.org | ||
IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-avtcore-6222bis-05
Network Working Group A. Begen Internet-Draft Cisco Obsoletes: 6222 (if approved) C. Perkins Updates: 3550 (if approved) University of Glasgow Intended status: Standards Track D. Wing Expires: January 09, 2014 Cisco E. Rescorla RTFM, Inc. July 08, 2013 Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names (CNAMEs) draft-ietf-avtcore-6222bis-05 Abstract The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a persistent transport-level identifier for an RTP endpoint. While the Synchronization Source (SSRC) identifier of an RTP endpoint may change if a collision is detected or when the RTP application is restarted, its RTCP CNAME is meant to stay unchanged, so that RTP endpoints can be uniquely identified and associated with their RTP media streams. For proper functionality, RTCP CNAMEs should be unique within the participants of an RTP session. However, the existing guidelines for choosing the RTCP CNAME provided in the RTP standard are insufficient to achieve this uniqueness. RFC 6222 was published to update those guidelines to allow endpoints to choose unique RTCP CNAMEs. Unfortunately, later investigations showed that some parts of the new algorithms were unnecessarily complicated and/or ineffective. This document addresses these concerns and replaces RFC 6222. 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." Begen, et al. Expires January 09, 2014 [Page 1] Internet-Draft Choosing an RTCP CNAME July 2013 This Internet-Draft will expire on January 09, 2014. Copyright Notice Copyright (c) 2013 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 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 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3 3. Deficiencies with Earlier Guidelines for Choosing an RTCP CNAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Choosing an RTCP CNAME . . . . . . . . . . . . . . . . . . . 4 4.1. Persistent RTCP CNAMEs versus Per-Session RTCP CNAMEs . . 4 4.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 5 5. Procedure to Generate a Unique Identifier . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6.1. Considerations on Uniqueness of RTCP CNAMEs . . . . . . . 7 6.2. Session Correlation Based on RTCP CNAMEs . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 8 1. Introduction Begen, et al. Expires January 09, 2014 [Page 2] Internet-Draft Choosing an RTCP CNAME July 2013 In Section 6.5.1 of [RFC3550], there are a number of recommendations for choosing a unique RTCP CNAME for an RTP endpoint. However, in practice, some of these methods are not guaranteed to produce a unique RTCP CNAME. [RFC6222] updated the guidelines for choosing RTCP CNAMEs, superseding those presented in Section 6.5.1 of [RFC3550]. Unfortunately, some parts of the new algorithms are rather complicated and also produce RTCP CNAMEs which in some cases are potentially linkable over multiple RTCP sessions even if a new RTCP CNAME is generated for each session. This document specifies a replacement for the algorithm in Section 5 of [RFC6222], which does not have this limitation and is also simpler to implement. For a discussion on the linkability of RTCP CNAMES produced by [RFC6222], refer to [I-D.rescorla-avtcore-random-cname]. 2. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Deficiencies with Earlier Guidelines for Choosing an RTCP CNAME The recommendation in [RFC3550] is to generate an RTCP CNAME of the form "user@host" for multiuser systems, or "host" if the username is not available. The "host" part is specified to be the fully qualified domain name (FQDN) of the host from which the real-time data originates. While this guidance was appropriate at the time [RFC3550] was written, FQDNs are no longer necessarily unique and can sometimes be common across several endpoints in large service provider networks. This document replaces the use of FQDN as an RTCP CNAME by alternative mechanisms. IPv4 addresses are also suggested for use in RTCP CNAMEs in [RFC3550], where the "host" part of the RTCP CNAME is the numeric representation of the IPv4 address of the interface from which the RTP data originates. As noted in [RFC3550], the use of private network address space [RFC1918] can result in hosts having network addresses that are not globally unique. Additionally, this shared use of the same IPv4 address can also occur with public IPv4 addresses if multiple hosts are assigned the same public IPv4 address and connected to a Network Address Translation (NAT) device [RFC3022]. When multiple hosts share the same IPv4 address, whether private or public, using the IPv4 address as the RTCP CNAME leads to RTCP CNAMEs that are not necessarily unique. Begen, et al. Expires January 09, 2014 [Page 3] Internet-Draft Choosing an RTCP CNAME July 2013 It is also noted in [RFC3550] that if hosts with private addresses and no direct IP connectivity to the public Internet have their RTP packets forwarded to the public Internet through an RTP-level translator, they could end up having non-unique RTCP CNAMEs. The suggestion in [RFC3550] is that such applications provide a configuration option to allow the user to choose a unique RTCP CNAME; this technique puts the burden on the translator to translate RTCP CNAMEs from private addresses to public addresses if necessary to keep private addresses from being exposed. Experience has shown that this does not work well in practice. 4. Choosing an RTCP CNAME It is difficult, and in some cases impossible, for a host to determine if there is a NAT between itself and its RTP peer. Furthermore, even some public IPv4 addresses can be shared by multiple hosts in the Internet. Using the numeric representation of the IPv4 address as the "host" part of the RTCP CNAME is NOT RECOMMENDED. 4.1. Persistent RTCP CNAMEs versus Per-Session RTCP CNAMEs The RTCP CNAME can be either persistent across different RTP sessions for an RTP endpoint or unique per session, meaning that an RTP endpoint chooses a different RTCP CNAME for each RTP session. An RTP endpoint that is emitting multiple related RTP streams that require synchronization at the other endpoint(s) MUST use the same RTCP CNAME for all streams that are to be synchronized. This requires a short-term persistent RTCP CNAME that is common across several RTP streams, and potentially across several related RTP sessions. A common example of such use occurs when lip-syncing audio and video streams in a multimedia session, where a single participant has to use the same RTCP CNAME for its audio RTP session and for its video RTP session. Another example might be to synchronize the layers of a layered audio codec, where the same RTCP CNAME has to be used for each layer. If the multiple RTP streams in an RTP session are not related, thus do not require synchronization, an RTP endpoint can use different RTCP CNAMEs for these streams. A longer-term persistent RTCP CNAME is sometimes useful to facilitate third-party monitoring, consistent with [RFC3550]. One such use might be to allow network management tools to correlate the ongoing quality of service for a participant across multiple RTP sessions for fault diagnosis, and to understand long-term network performance statistics. An application developer that wishes to discourage this Begen, et al. Expires January 09, 2014 [Page 4] Internet-Draft Choosing an RTCP CNAME July 2013 type of third-party monitoring can choose to generate a unique RTCP CNAME for each RTP session, or group of related RTP sessions, that the application will join. Such a per-session RTCP CNAME cannot be used for traffic analysis, and so provides some limited form of privacy. Note that there are non-RTP means that can be used by a third party to correlate RTP sessions, so the use of per-session RTCP CNAMEs will not prevent a determined traffic analyst from monitoring such sessions. This memo defines several different ways by which an implementation can choose an RTCP CNAME. It is possible, and legitimate, for independent implementations to make different choices of RTCP CNAME when running on the same host. This can hinder third-party monitoring, unless some external means is provided to configure a persistent choice of RTCP CNAME for those implementations. Note that there is no backwards compatibility issue (with [RFC3550]-compatible implementations) introduced in this memo, since the RTCP CNAMEs are opaque strings to remote peers. 4.2. Requirements RTP endpoints will choose to generate RTCP CNAMEs that are persistent or per-session. An RTP endpoint that wishes to generate a persistent RTCP CNAME MUST use one of the following two methods: o To produce a long-term persistent RTCP CNAME, an RTP endpoint MUST generate and store a Universally Unique IDentifier (UUID) [RFC4122] for use as the "host" part of its RTCP CNAME. The UUID MUST be version 1, 2, or 4, as described in [RFC4122], with the "urn:uuid:" stripped, resulting in a 36-octet printable string representation. o To produce a short-term persistent RTCP CNAME, an RTP endpoint MUST generate and use an identifier by following the procedure described in Section 5. That procedure is performed at least once per initialization of the software. After obtaining an identifier, minimally the least significant 96 bits SHOULD be converted to ASCII using Base64 encoding [RFC4648] (to compromise between packet size and uniqueness - refer to Section 6.1). If 96 bits are used, the resulting string will be 16 octets. In the two cases above, the "user@" part of the RTCP CNAME MAY be omitted on single-user systems and MAY be replaced by an opaque token on multi-user systems, to preserve privacy. An RTP endpoint that wishes to generate a per-session RTCP CNAME MUST use the following method: Begen, et al. Expires January 09, 2014 [Page 5] quot; This Internet-Draft will expire on April 23, 2014. Copyright Notice Copyright (c) 2013 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 to this document. This document may not be modified, and derivative works of it may not be created, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Background and Introduction . . . . . . . . . . . . . . . . . 3 2. Overview of Saratoga File Transfer . . . . . . . . . . . . . 6 3. Optional Parts of Saratoga . . . . . . . . . . . . . . . . . 11 3.1. Optional but useful functions in Saratoga . . . . . . . . 11 3.2. Optional congestion control . . . . . . . . . . . . . . . 12 3.3. Optional functionality requiring other protocols . . . . 12 4. Packet Types . . . . . . . . . . . . . . . . . . . . . . . . 13 4.1. BEACON . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.2. REQUEST . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.3. METADATA . . . . . . . . . . . . . . . . . . . . . . . . 26 4.4. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4.5. STATUS . . . . . . . . . . . . . . . . . . . . . . . . . 35 5. The Directory Entry . . . . . . . . . . . . . . . . . . . . . 42 6. Behaviour of a Saratoga Peer . . . . . . . . . . . . . . . . 45 6.1. Saratoga Sessions . . . . . . . . . . . . . . . . . . . . 45 6.2. Beacons . . . . . . . . . . . . . . . . . . . . . . . . . 48 6.3. Upper-Layer Interface . . . . . . . . . . . . . . . . . . 49 6.4. Inactivity Timer . . . . . . . . . . . . . . . . . . . . 49 6.5. Streams and wrapping . . . . . . . . . . . . . . . . . . 50 6.6. Completing file delivery and ending the session . . . . . 50 7. Mailing list . . . . . . . . . . . . . . . . . . . . . . . . 51 8. Security Considerations . . . . . . . . . . . . . . . . . . . 51 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52 Wood, et al. Expires April 23, 2014 [Page 2] Internet-Draft Saratoga October 2013 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 52 11. A Note on Naming . . . . . . . . . . . . . . . . . . . . . . 52 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 53 12.1. Normative References . . . . . . . . . . . . . . . . . . 53 12.2. Informative References . . . . . . . . . . . . . . . . . 53 Appendix A. Timestamp/Nonce field considerations . . . . . . . . 54 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56 1. Background and Introduction Saratoga is a file transfer and content dissemination protocol capable of efficiently sending both small (kilobyte) and very large (exabyte) files, as well as streaming continuous content. Saratoga was originally designed for the purpose of large file transfer from small low-Earth-orbiting satellites. It has been used in daily operations since 2004 to move mission imaging data files of the order of several hundred megabytes each from the Disaster Monitoring Constellation (DMC) remote-sensing satellites to ground stations. The DMC satellites, built at the University of Surrey by Surrey Satellite Technology Ltd (SSTL), all use IP for payload communications and delivery of Earth imagery. At the time of this writing, in March 2013, nine DMC satellites have been launched into orbit since 2002, five of those are currently operational in orbit, and three more are planned. The DMC satellites use Saratoga to provide Earth imagery under the aegis of the International Charter on Space and Major Disasters. A pass of connectivity between a satellite and ground station offers an 8-12 minute time window in which to transfer imagery files using a minimum of an 8.1 Mbps downlink and a 9.6 kbps uplink. The latest operational DMC satellites have faster downlinks, capable of 20, 40, 80, 105 or 201 Mbps. Newer satellites are expected to use downlinks to 400 Mbps, without significant increases in uplink rates. This high degree of link asymmetry, with the need to fully utilize the available downlink capacity to move the volume of data required within the limited time available, motivates much of Saratoga's design. Further details on how these DMC satellites use IP to communicate with the ground and the terrestrial Internet are discussed elsewhere [Hogie05][Wood07a]. Saratoga has also been evaluated for use in high-speed private ground networks supporting radio astronomy sensors [Wood11]. Store-and-forward delivery relies on reliable hop-by-hop transfers of files, removing the need for the final receiver to talk to the original sender across long delays and allowing for the possibility that an end-to-end path may never exist between sender and receiver at any given time. Breaking an end-to-end path into multiple hops Wood, et al. Expires April 23, 2014 [Page 3] Internet-Draft Saratoga October 2013 allows data to be transferred as quickly as possible across each link; congestion on a longer Internet path is then not detrimental to the transfer rate on a space downlink. Use of store-and-forward hop- by-hop delivery is typical of scenarios in space exploration for both near-Earth and deep-space missions, and useful for other scenarios, such as underwater networking, ad-hoc sensor networks, and some message-ferrying relay scenarios. Saratoga is intended to be useful for relaying data in these scenarios. Saratoga can optionally also be used to carry the Bundle Protocol "bundles" intended for Delay and Disruption-Tolerant Networking (DTN) by the IRTF DTN Research Group [RFC5050]. This has been tested from orbit using the UK-DMC satellite [Ivancic10]. How Saratoga can optionally function as a "bundle convergence layer" alongside a DTN bundle agent is specified in a companion document [I-D.wood-dtnrg-saratoga]. Saratoga contains a Selective Negative Acknowledgement (SNACK) 'holestofill' mechanism to provide reliable retransmission of data. This is intended to correct losses of corrupted link-layer frames due to channel noise over a space link. Packet losses in the DMC are due to corruption introducing non-recoverable errors in the frame. The DMC design uses point-to-point links and scheduling of applications in order, so that the link is dedicated to one application transfer at a time, meaning that packet loss cannot be due to congestion when applications compete for link capacity simultaneously. In other wireless environments that may be shared by many nodes and applications, allocation of channel resources to nodes becomes a MAC- layer function. Forward Error Coding (FEC) to get the most reliable transmission through a channel is best left near the physical layer so that it can be tailored for the channel. Use of FEC complements Saratoga's transport-level negative-acknowledgement approach that provides a reliable ARQ mechanism. Saratoga is scalable in that it is capable of efficiently transferring small or large files, by choosing a width of file offset descriptor appropriate for the filesize, and advertising accepted offset descriptor sizes. 16-bit, 32-bit, 64-bit and 128-bit descriptors can be selected, for maximum file sizes of 64KiB-1 (<64 Kilobytes of disk space), 4GiB-1 (<4 Gigabytes), 16EiB-1 (<16 Exabytes) and 256 EiEiB-1 (<256 Exa-exabytes) respectively. Earth imaging files currently transferred by Saratoga are mostly up to a few gigabytes in size. Some implementations do transfer more than 4 GiB in size, and so require offset descriptors larger than 32 bits. We believe that supporting a 128-bit descriptor can satisfy all future needs, but we expect current implementations to only support up to 32-bit or 64-bit descriptors, depending on their Wood, et al. Expires April 23, 2014 [Page 4] Internet-Draft Saratoga October 2013 application needs. The 16-bit descriptor is useful for small messages, including messages from 8-bit devices, and is always supported. The 128-bit descriptor can be used for moving very large files stored on a 128-bit filesystem, such as on OpenSolaris ZFS. As a UDP-based protocol, Saratoga can be used with either IPv4 or IPv6. Compatibility between Saratoga and the wide variety of links that can already carry IP traffic is assured. High link utilization is important during periods of limited connectivity. Given that Saratoga was originally developed for scheduled peer-to-peer communications over dedicated links in private networks, where each application has the entire link for the duration of its transfer, many Saratoga implementations deliberately lack any form of congestion control and send at line rate to maximise throughput and link utilisation in their limited, carefully controlled, environments. In accordance with UDP Guidelines [RFC5405] for protocols able to traverse the public Internet, newer implementations may perform TCP-Friendly Rate Control (TFRC) [RFC5348] or other congestion control mechanisms. This is described further in [I-D.wood-tsvwg-saratoga-congestion-control]. Saratoga was originally implemented as outlined in [Jackson04], but the specification given here differs substantially, as we have added a number of capabilities while cleaning up the initial Saratoga specification. The original Saratoga code uses a version number of 0, while code that implements this version of the protocol advertises a version number of 1. Further discussion of the history and development of Saratoga is given in [Wood07b]. This document contains an overview of the transfer process and sessions using Saratoga in Section 2, followed by a formal definition of the packet types used by Saratoga in Section 4, and the details of the various protocol mechanisms in Section 6. Here, Saratoga session types are labelled with underscores around lowercase names (such as a "_get_" session), while Saratoga packet types are labelled in all capitals (such as a "REQUEST" packet) in order to distinguish between the two. The remainder of this specification uses 'file' as a shorthand for 'binary object', which may be a file, or other type of data, such as a DTN bundle. This specification uses 'file' when also discussing streaming of data of indeterminate length. Saratoga uses unsigned integers in its fields, and does not use signed types. Wood, et al. Expires April 23, 2014 [Page 5] Internet-Draft Saratoga October 2013 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY&Internet-Draft Choosing an RTCP CNAME July 2013 o For every new RTP session, a new RTCP CNAME is generated following the procedure described in Section 5. After performing that procedure, minimally the least significant 96 bits SHOULD be converted to ASCII using Base64 encoding [RFC4648]. The RTCP CNAME cannot change over the life of an RTP session [RFC3550]. The "user@" part of the RTCP CNAME is omitted when generating per-session RTCP CNAMEs. It is believed that obtaining uniqueness (with a high probability) is an important property that requires careful evaluation of the method. This document provides a number of methods, at least one of which would be suitable for all deployment scenarios. This document therefore does not provide for the implementor to define and select an alternative method. A future specification might define an alternative method for generating RTCP CNAMEs, as long as the proposed method has appropriate uniqueness and there is consistency between the methods used for multiple RTP sessions that are to be correlated. However, such a specification needs to be reviewed and approved before deployment. The mechanisms described in this document are to be used to generate RTCP CNAMEs, and they are not to be used for generating general- purpose unique identifiers. 5. Procedure to Generate a Unique Identifier To locally produce a unique identifier, one simply generates a cryptographically pseudorandom value as described in [RFC4086]. This value MUST be at least 96 bits and MAY be up to 512 bits. The biggest bottleneck to implementation of this algorithm is the availability of an appropriate cryptographically secure pseudorandom number generator (CSPRNG). In any setting which already has a secure PRNG, this algorithm described is far simpler than the algorithm described in Section 5 of [RFC6222]. SIP stacks [RFC3261] are required to use cryptographically random numbers to generate To and From tags (Section 19.3). RTCWEB implementations [I-D.ietf-rtcweb-security-arch] will need to have secure PRNGs to implement ICE [RFC5245] and DTLS-SRTP [RFC5764]. And, of course, essentially every Web browser already supports TLS, which requires a secure PRNG. 6. Security Considerations The security considerations of [RFC3550] apply to this memo. Begen, et al. Expires January 09, 2014 [Page 6] Internet-Draft Choosing an RTCP CNAME July 2013 6.1. Considerations on Uniqueness of RTCP CNAMEs The considerations in this section apply to random RTCP CNAMEs. The recommendations given in this document for RTCP CNAME generation ensure that a set of cooperating participants in an RTP session will, with very high probability, have unique RTCP CNAMEs. However, neither [RFC3550] nor this document provides any way to ensure that participants will choose RTCP CNAMEs appropriately, and thus implementations MUST NOT rely on the uniqueness of RTCP CNAMEs for any essential security services. This is consistent with [RFC3550], which does not require that RTCP CNAMEs are unique within a session but instead says that condition SHOULD hold. As described in the Security Considerations section of [RFC3550], because each participant in a session is free to choose its own RTCP CNAME, they can do so in such a way as to impersonate another participant. That is, participants are trusted to not impersonate each other. No recommendation for generating RTCP CNAMEs can prevent this impersonation, because an attacker can neglect the stipulation. Secure RTP (SRTP) [RFC3711] keeps unauthorized entities out of an RTP session, but it does not aim to prevent impersonation attacks from authorized entities. Because of the properties of the PRNG, there is no significant privacy/linkability difference between long and short RTCP CNAMEs. However, the requirement to generate unique RTCP CNAMEs implies a certain minimum length. A length of 96 bits allows on the order of 2^{40} RTCP CNAMEs globally before there is a large chance of collision (there is about a 50% chance of one collision after 2^{48} RTCP CNAMEs). 6.2. Session Correlation Based on RTCP CNAMEs Earlier recommendations for RTCP CNAME generation allowed a fixed RTCP CNAME value, which allows an attacker to easily link separate RTP sessions, eliminating the obfuscation provided by IPv6 privacy addresses [RFC4941] or IPv4 Network Address Port Translation (NAPT) [RFC3022]. This specification no longer describes a procedure to generate fixed RTCP CNAME values, so RTCP CNAME values no longer provide such linkage between RTP sessions. This was necessary to eliminate such linking by an attacker, but of course complicates linking by traffic analysis devices (e.g., devices that are looking for dropped or delayed packets). 7. IANA Considerations Begen, et al. Expires January 09, 2014 [Page 7] Internet-Draft Choosing an RTCP CNAME July 2013 No IANA actions are required. 8. Acknowledgments Thanks to Marc Petit-Huguenin, who suggested using UUIDs in generating RTCP CNAMEs. Also, thanks to David McGrew for providing text for the Security Considerations section in RFC 6222. 9. References 9.1. Normative References [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage for IEEE 802 Parameters", BCP 141, RFC 5342, September 2008. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. 9.2. Informative References [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names (CNAMEs)", RFC 6222, April 2011. [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001. Begen, et al. Expires January 09, 2014 [Page 8] Internet-Draft Choosing an RTCP CNAME July 2013 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [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. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [I-D.ietf-rtcweb-security-arch] Rescorla, E., "RTCWEB Security Architecture", draft-ietf- rtcweb-security-arch-06 (work in progress), January 2013. [I-D.rescorla-avtcore-random-cname] Rescorla, E., "Random algorithm for RTP CNAME generation", draft-rescorla-avtcore-random-cname-00 (work in progress), July 2012. Authors' Addresses Ali Begen Cisco 181 Bay Street Toronto, ON M5J 2T3 CANADA EMail: abegen@cisco.com Begen, et al. Expires January 09, 2014 [Page 9] Internet-Draft Choosing an RTCP CNAME July 2013 Colin Perkins University of Glasgow School of Computing Science Glasgow G12 8QQ UK EMail: csp@csperkins.org Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, California 95134 USA EMail: dwing@cisco.com Eric Rescorla RTFM, Inc. 2064 Edgewood Drive Palo Alto, CA 94303 USA Phone: +1 650 678 2350 EMail: ekr@rtfm.com Begen, et al. Expires January 09, 2014 [Page 10]