AVT A. Begen Internet-Draft Cisco Updates: 3550 (if approved) C. Perkins Intended status: Standards Track University of Glasgow Expires: October 16, 2010 April 14, 2010 Guidelines for Choosing an RTP Control Protocol (RTCP) Canonical Name (CNAME) for Hosts with Private IP Addresses draft-begen-avt-rtp-cnames-00 Abstract The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a persistent transport-level identifier for an RTP endpoint. While the Synchronisation Source (SSRC) identifier of an RTP endpoint may change if a collision is detected, or when the RTP application is restarted, the CNAME is meant to stay unchanged, so that RTP endpoints can be uniquely identified and associated with their RTP media streams. For proper functionality, CNAMEs should be unique within the participants of an RTP session. The recommendations for choice of the RTCP CNAME provided in RFC 3550 are insufficient to achieve uniqueness in some environments, particularly private IP networks. This memo updates the guidelines in RFC 3550 to allow endpoints to choose unique CNAMEs in these environments. 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 October 16, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. Begen & Perkins Expires October 16, 2010 [Page 1]
Internet-Draft Choice of RTCP CNAME April 2010 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3 3. Choice of RTCP CNAME in Private Networks . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 6. Normative References . . . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 4 Begen & Perkins Expires October 16, 2010 [Page 2]
Internet-Draft Choice of RTCP CNAME April 2010 1. Introduction In Section 6.5.1 of [RFC3550], there are a number of recommendations for choosing the RTCP CNAME for an RTP endpoint. These recommend that the CNAME is 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 of the host from which the real-time data originates, or the numeric representation of the IP address of the interface from which the RTP data originates for hosts that do not have a domain name. As noted in [RFC3550], the use of private network address space (e.g., 10.0.0.0/8) can result in hosts having network addresses that are not globally unique, and can lead to non-unique CNAMEs 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. [RFC3550] suggests that such applications provide a configuration option to allow the user to choose a unique CNAME, and puts the burden on the translator to translate CNAMEs from private addresses to public addresses if necessary to keep private addresses from being exposed. Experience has shown that this does not work in practice, therefore this memo proposes an alternate algorithm for CNAME choice in private networks. 2. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Choice of RTCP CNAME in Private Networks In private IP networks, using the numeric representation of the private IP address as the RTCP CNAME is NOT RECOMMENDED, since it results in RTCP CNAMEs that are not globally unique. A host that does not know its fully qualified domain name, and is configured with a private IP address on the interface it is using for RTP communication, SHOULD use the numeric representation of the layer-2 (MAC) address of the interface it is using for RTP communication as the "host" part of its CNAME. For IEEE 802 MAC addresses, such as Ethernet, the standard colon-separated hexadecimal format is to be used, e.g., "00:23:32:af:9b:aa". Begen & Perkins Expires October 16, 2010 [Page 3]
Internet-Draft Choice of RTCP CNAME April 2010 4. Security Considerations The security considerations of [RFC3550] apply to this document as well. 5. IANA Considerations There are no IANA considerations in this document. 6. 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. Authors' Addresses Ali Begen Cisco 170 West Tasman Drive San Jose, CA 95134 USA Email: abegen@cisco.com Colin Perkins University of Glasgow Department of Computing Science Glasgow, G12 8QQ UK Email: csp@csperkins.org Begen & Perkins Expires October 16, 2010 [Page 4]