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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4941 (Obsoleted by RFC 8981) ** Downref: Normative reference to an Informational RFC: RFC 2104 Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT A. Begen 3 Internet-Draft Cisco 4 Updates: 3550 (if approved) C. Perkins 5 Intended status: Standards Track University of Glasgow 6 Expires: November 25, 2010 D. Wing 7 Cisco 8 May 24, 2010 10 Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names 11 (CNAMEs) 12 draft-begen-avt-rtp-cnames-02 14 Abstract 16 The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a 17 persistent transport-level identifier for an RTP endpoint. While the 18 Synchronization Source (SSRC) identifier of an RTP endpoint may 19 change if a collision is detected, or when the RTP application is 20 restarted, the CNAME is meant to stay unchanged, so that RTP 21 endpoints can be uniquely identified and associated with their RTP 22 media streams. For proper functionality, CNAMEs should be unique 23 within the participants of an RTP session. However, the existing 24 guidelines for choosing the RTCP CNAME provided in the RTP standard 25 are insufficient to achieve this uniqueness. This memo updates these 26 guidelines to allow endpoints to choose unique CNAMEs. 28 Status of this Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on November 25, 2010. 45 Copyright Notice 47 Copyright (c) 2010 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3 64 3. Deficiencies with Earlier RTCP CNAME Guidelines . . . . . . . . 3 65 4. Choosing an RTCP CNAME . . . . . . . . . . . . . . . . . . . . 4 66 4.1. Persistent vs. Per-Session CNAMEs . . . . . . . . . . . . . 4 67 4.2. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . 4 68 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 69 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 70 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 71 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 73 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 76 1. Introduction 78 In Section 6.5.1 of [RFC3550], there are a number of recommendations 79 for choosing a unique RTCP CNAME for an RTP endpoint. However, in 80 practice, some of these methods are not guaranteed to produce a 81 unique CNAME. This memo proposes updated guidelines for choosing 82 CNAMEs, superceding those presented in Section 6.5.1 of [RFC3550]. 84 2. Requirements Notation 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 88 document are to be interpreted as described in [RFC2119]. 90 3. Deficiencies with Earlier RTCP CNAME Guidelines 92 The recommendation in [RFC3550] is to generate the CNAME of the form 93 "user@host" for multiuser systems, or "host" if the username is not 94 available. The "host" part is specified to be the fully qualified 95 domain name (FQDN) of the host from which the real-time data 96 originates. However, FQDNs are not necessarily unique, and can 97 sometimes be common across several endpoints in large service 98 provider networks. Thus, the use of FQDN as the CNAME is strongly 99 discouraged. 101 For hosts that do not have a unique domain name, the "host" part of 102 the RTCP CNAME could be the numeric representation of the IP address 103 of the interface from which the RTP data originates. However, as 104 noted in [RFC3550], the use of private network address space 105 [RFC1918] can result in hosts having network addresses that are not 106 globally unique. This can also occur with public IP addresses, if 107 multiple hosts are assigned the same public IP address and connected 108 to a Network Address Translation (NAT) device [RFC3022]. When 109 multiple hosts share the same IP address, whether private or public, 110 using the IP address as the CNAME leads to CNAMEs that are not 111 necessarily unique. 113 [RFC3550] also notes that if hosts with private addresses and no 114 direct IP connectivity to the public Internet have their RTP packets 115 forwarded to the public Internet through an RTP-level translator, 116 they may end up having non-unique CNAMEs. [RFC3550] suggests that 117 such applications provide a configuration option to allow the user to 118 choose a unique CNAME, and puts the burden on the translator to 119 translate CNAMEs from private addresses to public addresses if 120 necessary to keep private addresses from being exposed. Experience 121 has shown that this does not work well in practice. 123 4. Choosing an RTCP CNAME 125 It is difficult, and in some cases impossible, for a host to 126 determine if there is a NAT between itself and its RTP peer. 127 Furthermore, even some public IPv4 addresses can be shared by 128 multiple hosts in the Internet. Thus, using the numeric 129 representation of the IPv4 address as the "host" part of the RTCP 130 CNAME is NOT RECOMMENDED. 132 4.1. Persistent vs. Per-Session CNAMEs 134 The RTCP CNAME can either be persistent across different RTP sessions 135 for an RTP endpoint; or it can be unique per session, meaning that an 136 RTP endpoint chooses a different CNAME for each RTP session. 138 Persistent CNAMEs: To provide a binding across multiple media tools 139 used by one participant in a set of related RTP sessions, the CNAME 140 SHOULD be fixed for that participant. A persistent CNAME is also 141 useful to facilitate third-party monitoring, allowing network 142 management tools to correlate the ongoing quality of service across 143 multiple RTP sessions for fault diagnosis and to understand long-term 144 network performance statistics. 146 Per-Session CNAMEs: The advantage of this approach is that the CNAME 147 is unique for each RTP session. This prevents the CNAME from being 148 used for traffic analysis. In other words, the RTP endpoints cannot 149 be identified based on their CNAMEs. This provides privacy, but 150 inhibits the use of RTCP as a tool for long-term network management 151 and monitoring. 153 4.2. Guidelines 155 RTP endpoints SHOULD practice one of the following guidelines in 156 choosing RTCP CNAME: 158 o Given that IPv6 addresses are naturally unique, an endpoint MAY 159 use its IPv6 address as the "host" part of its CNAME regardless of 160 whether that IPv6 interface is being used for RTP communication or 161 not. If the RTP endpoint is associated with an IPv6 privacy 162 address [RFC4941] or a unique local IPv6 unicast address 163 [RFC4193], that address MAY be used as well. Using IPv6 addresses 164 as the "host" part of a CNAME was originally suggested in 165 [RFC3550]. 167 o An endpoint that does not know its fully qualified domain name, 168 and is configured with a private IP address on the interface it is 169 using for RTP communication, MAY use the numeric representation of 170 the layer-2 (MAC) address of that interface as the "host" part of 171 its CNAME. For IEEE 802 MAC addresses, such as Ethernet, the 172 standard colon-separated hexadecimal format is to be used, e.g., 173 "00:23:32:af:9b:aa". 175 o An endpoint MAY use its Universally Unique IDentifier (UUID) 176 [RFC4122] to generate the "host" part of its CNAME. The string 177 representation described in Section 3 of [RFC4122] should be used, 178 which results in a 288-bit string representation. 180 o To generate a unique CNAME for each RTP session, an endpoint MAY 181 perform SHA1-HMAC [RFC2104] on the concatenated values of the RTP 182 endpoint's initial SSRC, the source and destination IP addresses 183 and ports, and a randomly-generated value [RFC4086], and then 184 truncate the 160-bit output to 96 bits and finally convert the 96 185 bits to ASCII using Base64 encoding [RFC4648]. This results in a 186 128-bit printable CNAME. Note that the CNAME MUST NOT change if 187 an SSRC collision occurs, hence only the initial SSRC value chosen 188 by the endpoint is used. 190 Each of the techniques is equally effective in generating unique 191 CNAMEs, and an RTP application MAY choose any of these techniques to 192 use. 194 5. Security Considerations 196 The security considerations of [RFC3550] apply to this document as 197 well. 199 In some environments, notably telephony, a fixed CNAME value allows 200 separate RTP sessions to be correlated and eliminates the obfuscation 201 provided by IPv6 privacy addresses [RFC4941] or IPv4 NAPT [RFC3022]. 202 Secure RTP (SRTP) [RFC3711] can help prevent such correlation by 203 encrypting Secure RTCP (SRTCP) but it should be noted that SRTP only 204 mandates SRTCP integrity protection (not encryption). Thus, RTP 205 applications used in such environments should consider encrypting 206 their SRTCP or generate a new CNAME value for each RTP session as 207 described in Section 4. 209 6. IANA Considerations 211 There are no IANA considerations in this document. 213 7. Acknowledgments 215 Thanks to Marc Petit-Huguenin who suggested to use UUIDs in 216 generating CNAMEs. 218 8. References 220 8.1. Normative References 222 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 223 Jacobson, "RTP: A Transport Protocol for Real-Time 224 Applications", STD 64, RFC 3550, July 2003. 226 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 227 Requirement Levels", BCP 14, RFC 2119, March 1997. 229 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 230 Addresses", RFC 4193, October 2005. 232 [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy 233 Extensions for Stateless Address Autoconfiguration in 234 IPv6", RFC 4941, September 2007. 236 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 237 Unique IDentifier (UUID) URN Namespace", RFC 4122, 238 July 2005. 240 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 241 Hashing for Message Authentication", RFC 2104, 242 February 1997. 244 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 245 Requirements for Security", BCP 106, RFC 4086, June 2005. 247 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 248 Encodings", RFC 4648, October 2006. 250 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 251 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 252 RFC 3711, March 2004. 254 8.2. Informative References 256 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 257 E. Lear, "Address Allocation for Private Internets", 258 BCP 5, RFC 1918, February 1996. 260 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network 261 Address Translator (Traditional NAT)", RFC 3022, 262 January 2001. 264 Authors' Addresses 266 Ali Begen 267 Cisco 268 181 Bay Street 269 Toronto, ON M5J 2T3 270 CANADA 272 Email: abegen@cisco.com 274 Colin Perkins 275 University of Glasgow 276 Department of Computing Science 277 Glasgow, G12 8QQ 278 UK 280 Email: csp@csperkins.org 282 Dan Wing 283 Cisco 284 170 West Tasman Dr. 285 San Jose, CA 95134 286 USA 288 Email: dwing@cisco.com