draft-begen-avt-rtp-cnames-00.txt   draft-begen-avt-rtp-cnames-01.txt 
AVT A. Begen AVT A. Begen
Internet-Draft Cisco Internet-Draft Cisco
Updates: 3550 (if approved) C. Perkins Updates: 3550 (if approved) C. Perkins
Intended status: Standards Track University of Glasgow Intended status: Standards Track University of Glasgow
Expires: October 16, 2010 April 14, 2010 Expires: November 6, 2010 May 5, 2010
Guidelines for Choosing an RTP Control Protocol (RTCP) Canonical Name Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAME) for Hosts with Private IP Addresses (CNAMEs)
draft-begen-avt-rtp-cnames-00 draft-begen-avt-rtp-cnames-01
Abstract Abstract
The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a The RTP Control Protocol (RTCP) Canonical Name (CNAME) is a
persistent transport-level identifier for an RTP endpoint. While the persistent transport-level identifier for an RTP endpoint. While the
Synchronisation Source (SSRC) identifier of an RTP endpoint may Synchronization Source (SSRC) identifier of an RTP endpoint may
change if a collision is detected, or when the RTP application is change if a collision is detected, or when the RTP application is
restarted, the CNAME is meant to stay unchanged, so that RTP restarted, the CNAME is meant to stay unchanged, so that RTP
endpoints can be uniquely identified and associated with their RTP endpoints can be uniquely identified and associated with their RTP
media streams. For proper functionality, CNAMEs should be unique media streams. For proper functionality, CNAMEs should be unique
within the participants of an RTP session. The recommendations for within the participants of an RTP session. However, the
choice of the RTCP CNAME provided in RFC 3550 are insufficient to recommendations for choice of the RTCP CNAME provided in RFC 3550 are
achieve uniqueness in some environments, particularly private IP insufficient to achieve this uniqueness. This memo updates the
networks. This memo updates the guidelines in RFC 3550 to allow guidelines in RFC 3550 to allow endpoints to choose unique CNAMEs.
endpoints to choose unique CNAMEs in these environments.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 16, 2010. This Internet-Draft will expire on November 6, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 22 skipping to change at page 2, line 20
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3
3. Choice of RTCP CNAME in Private Networks . . . . . . . . . . . 3 3. Choice of RTCP CNAME in Private Networks . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 4 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
In Section 6.5.1 of [RFC3550], there are a number of recommendations In Section 6.5.1 of [RFC3550], there are a number of recommendations
for choosing the RTCP CNAME for an RTP endpoint. These recommend for choosing the RTCP CNAME for an RTP endpoint. These recommend
that the CNAME is of the form "user@host" for multiuser systems, or that the CNAME is of the form "user@host" for multiuser systems, or
"host" if the username is not available. The "host" part is "host" if the username is not available. The "host" part is
specified to be the fully qualified domain name of the host from specified to be the fully qualified domain name of the host from
which the real-time data originates, or the numeric representation of which the real-time data originates, or the numeric representation of
the IP address of the interface from which the RTP data originates the IP address of the interface from which the RTP data originates
for hosts that do not have a domain name. for hosts that do not have a domain name.
As noted in [RFC3550], the use of private network address space 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 [RFC1918] can result in hosts having network addresses that are not
are not globally unique, and can lead to non-unique CNAMEs if hosts globally unique. However, this problem is not solely with private
with private addresses and no direct IP connectivity to the public network addresses, but may also occur with public IP addresses, where
Internet have their RTP packets forwarded to the public Internet multiple hosts are assigned the same public IP address and connected
through an RTP-level translator. [RFC3550] suggests that such to a Network Address Translation (NAT) device
applications provide a configuration option to allow the user to [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 choose a unique CNAME, and puts the burden on the translator to
translate CNAMEs from private addresses to public addresses if translate CNAMEs from private addresses to public addresses if
necessary to keep private addresses from being exposed. Experience necessary to keep private addresses from being exposed. Experience
has shown that this does not work in practice, therefore this memo has shown that this does not work well in practice.
proposes an alternate algorithm for CNAME choice in private networks.
For all these reasons, this memo proposes alternative algorithms for
choosing CNAMEs.
2. Requirements Notation 2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Choice of RTCP CNAME in Private Networks 3. Choice of RTCP CNAME in Private Networks
In private IP networks, using the numeric representation of the It is a difficult task for a host to determine whether it resides
private IP address as the RTCP CNAME is NOT RECOMMENDED, since it behind a NAT without the help of an external mechanism such as STUN
results in RTCP CNAMEs that are not globally unique. [RFC5389]. Furthermore, even some public IP addresses can be shared
by multiple hosts in the Internet. Thus, using the numeric
representation of the IP address as the RTCP CNAME is NOT
RECOMMENDED.
A host that does not know its fully qualified domain name, and is In order to meet the SHOULD requirement of Section 6.5.1 of
configured with a private IP address on the interface it is using for [RFC3550], RTP endpoints SHOULD practice one of the following
RTP communication, SHOULD use the numeric representation of the 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 layer-2 (MAC) address of the interface it is using for RTP
communication as the "host" part of its CNAME. For IEEE 802 MAC communication as the "host" part of its CNAME. For IEEE 802 MAC
addresses, such as Ethernet, the standard colon-separated hexadecimal addresses, such as Ethernet, the standard colon-separated
format is to be used, e.g., "00:23:32:af:9b:aa". 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 4. Security Considerations
The security considerations of [RFC3550] apply to this document as The security considerations of [RFC3550] apply to this document as
well. well.
5. IANA Considerations 5. IANA Considerations
There are no IANA considerations in this document. There are no IANA considerations in this document.
6. Normative References 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.
7. References
7.1. Normative References
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 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 Authors' Addresses
Ali Begen Ali Begen
Cisco Cisco
170 West Tasman Drive 181 Bay Street
San Jose, CA 95134 Toronto, ON M5J 2T3
USA CANADA
Email: abegen@cisco.com Email: abegen@cisco.com
Colin Perkins Colin Perkins
University of Glasgow University of Glasgow
Department of Computing Science Department of Computing Science
Glasgow, G12 8QQ Glasgow, G12 8QQ
UK UK
Email: csp@csperkins.org Email: csp@csperkins.org
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