SIMPLE Working Group C. Holmberg
Internet-Draft Ericsson
Updates: RFC 4975 S. Blau
(if approved) Ericsson AB
Expires: June 20, 2010 December 17, 2009
Session Matching Update for the Message Session Relay Protocol (MSRP)
draft-ietf-simple-msrp-sessmatch-01.txt
Abstract
This document updates the session matching procedure defined in
section 7.3 of RFC 4975, so that an MSRP UA only uses the session-id
part of the MSRP URI in order to perform the consistency checks. The
update allows intermediaries (ALGs) to modify the address information
in the MSRP URI of the SDP a=path attribute, without the need for the
intermediaries to terminate and do the correlating modifications in
the associated MSRP messages.
Status of this Memo
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Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability statement . . . . . . . . . . . . . . . . . . . . 3
4. Normative update of RFC 4975 . . . . . . . . . . . . . . . . . 3
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. RFC4975: 7.3 Receiving Requests . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
MSRP [RFC4975] is designed to use MSRP relays [RFC4976] as a means
for NAT traversal and policy enforcement.
Many networks in which MSRP usage is emerging also contain generic
ALGs, which might control media relays and perform tasks such as
performance monitoring, lawful intercept, address domain bridging,
interconnect SLA policy enforcement, etc. An example here is the
Interconnect Border Control Function (IBCF) [3GPP TS23.228] defined
by 3GPP, which controls a media relay that handles all types of SIP
session media (voice, video, MSRP, etc).
Due to the fact that MSRP UAs check consistency between address
information in the MSRP messages and in the SDP a=path attribute,
this forces the IBCF/media relay to act as an SDP aware MSRP B2BUA,
whereas for basically all other UDP and TCP transported based media
sessions it can acts as an SDP aware Relay- NAPT - which is much
simpler than having to act as an MSRP B2BUA.
In order to use general NAT traversal methods and ALGs, this document
updates the session matching procedures defined in section 7.3 of
[RFC4975], so that MSRP endpoints only use the session-id part when
they compare the MSRP URI in the SDP a=path attribute with the
corresponding MSRP URI in MSRP messages.
2. Conventions
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 BCP 14, RFC 2119
[RFC2119].
3. Applicability statement
This document updates section 7.3 (Receiving Requests) of [RFC4975].
An MSRP UA MUST implement the procedures defined in this document in
order to interwork with remote MSRP UAs in a network where
intermediaries might modify the address information in the MSRP URI
of the SDP a=path attribute.
4. Normative update of RFC 4975
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4.1. General
This section defines the updated text for section 7.3 (Receiving
Requests) of [RFC4975].
4.2. RFC4975: 7.3 Receiving Requests
The receiving endpoint MUST first check the URI in the To-Path to
make sure the request belongs to an existing session. When the
request is received, the To-Path will have exactly one URI, of which
the session-id part MUST map to an existing session that is
associated with the connection on which the request arrived. The
session-id part is compared as case sensitive, as specified in
Section 6.1 (point 4) of [RFC4975]. If this is not true, then the
receiver MUST generate a 481 error and ignore the request. Note that
if the Failure-Report header field had a value of "no", then no error
report would be sent.
5. Security Considerations
Due to the change of the session matching procedure, MSRP endpoints
can only check that the session-id part of the MSRP URI carried in
the MSRP messages matches the session-id which was provided in the
associated SDP a=path attribute. Differing from [RFC4975], the host/
domain part of the MSRP URI is thus not checked. However, since a
man-in-the-middle would in any case be able to modify the domain
information in both the SDP and the MSRP messages, this does not
introduce any new security risk.
Even if MSRP entities do not use the MSRP URI domain part to perform
session matching, if the domain information is different in the SDP
a=path attribute and the associated MSRP messages the MSRP entities
might be able to determine whether one or more intermediaries have
been inserted in the message path. With the current session matching
procedures, intermediaries would have to modify both the domain part
of the MSRP URI both in the SDP a=path attribute and the associated
MSRP messages, which means that MSRP entities cannot compare the
domain information in order to determine whether intermediaries have
been inserted in the message path.
When intermediaries are used, MSRP endpoints which uses security
mechanisms might not be able to determine whether security is
provided end-to-end. However, that issue is generic to all types of
media.
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6. IANA Considerations
This document updates section 7.3 of [RFC4975]
7. Acknowledgements
Thanks to Ben Campbell, Remi Denis-Courmont, Nancy Greene, Hadriel
Kaplan, Adam Roach, Robert Sparks, Salvatore Loreto and Shida
Schubert for their guidance and input in order to produce this
document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, July 2006.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
8.2. Informative References
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Authors' Addresses
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Staffan Blau
Ericsson AB
P.O Box 407
Sweden
Email: staffan.blau@ericsson.com
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