AVT A. Begen
Internet-Draft Cisco
Updates: 3550 (if approved) C. Perkins
Intended status: Standards Track University of Glasgow
Expires: November 6, 2010 May 5, 2010
Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAMEs)
draft-begen-avt-rtp-cnames-01
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, 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. However, the
recommendations for choice of the RTCP CNAME provided in RFC 3550 are
insufficient to achieve this uniqueness. This memo updates the
guidelines in RFC 3550 to allow endpoints to choose unique CNAMEs.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 6, 2010.
Copyright Notice
Copyright (c) 2010 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
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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. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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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
[RFC1918] can result in hosts having network addresses that are not
globally unique. However, this problem is not solely with private
network addresses, but may also occur with public IP addresses, where
multiple hosts are assigned the same public IP address and connected
to a Network Address Translation (NAT) device
[I-D.miles-behave-l2nat]. When multiple hosts share the same IP
address, using the IP address as the CNAME can lead to non-unique
CNAMEs.
[RFC3550] also notes 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 may end up having non-unique CNAMEs. [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 well in practice.
For all these reasons, this memo proposes alternative algorithms for
choosing CNAMEs.
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
It is a difficult task for a host to determine whether it resides
behind a NAT without the help of an external mechanism such as STUN
[RFC5389]. Furthermore, even some public IP addresses can be shared
by multiple hosts in the Internet. Thus, using the numeric
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representation of the IP address as the RTCP CNAME is NOT
RECOMMENDED.
In order to meet the SHOULD requirement of Section 6.5.1 of
[RFC3550], RTP endpoints SHOULD practice one of the following
guidelines:
o Given that IPv6 addresses are naturally unique, a host MAY use its
IPv6 address as the CNAME when using an IPv6 interface for RTP
communication. If the RTP endpoint is associated with a unique
local IPv6 unicast address [RFC4193], that address MAY be used as
the CNAME as well. Using IPv6 addresses as CNAMEs was originally
suggested in [RFC3550].
o 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, MAY 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".
o A host MAY use its Universally Unique IDentifier (UUID) [RFC4122]
as the CNAME.
This memo does not mandate a specific order in which these methods
should be practiced. A specific order would be only needed if an RTP
endpoint was expected to be comprised of multiple programs that
independently needed to choose the same CNAME. Since this is not a
common implementation technique, a specific order is not needed.
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. Acknowledgments
Thanks to Dan Wing who pointed out the concerns about cases where two
hosts could share the same public IP address. Also, thanks to Marc
Petit-Huguenin who suggested to use UUIDs as CNAMEs.
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7. References
7.1. 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.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
7.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[I-D.miles-behave-l2nat]
Miles, D. and M. Townsley, "Layer2-Aware NAT",
draft-miles-behave-l2nat-00 (work in progress),
March 2009.
Authors' Addresses
Ali Begen
Cisco
181 Bay Street
Toronto, ON M5J 2T3
CANADA
Email: abegen@cisco.com
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Colin Perkins
University of Glasgow
Department of Computing Science
Glasgow, G12 8QQ
UK
Email: csp@csperkins.org
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