INTERNET-DRAFT David Meyer
draft-ietf-mboned-ssm232-06.txt Rob Rockell
Greg Shepherd
Category Best Current Practice
Expires: March 2004 September 2003
Source-Specific Protocol Independent Multicast in 232/8
<draft-ietf-mboned-ssm232-06.txt>
Status of this Document
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 RFC 2119 [RFC 2119].
This document is a product of the MBONED WG. Comments should be
addressed to the authors, or the mailing list at
mboned@ns.uoregon.edu.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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Abstract
IP Multicast group addresses in the 232/8 (232.0.0.0 to
232.255.255.255) range are designated as source-specific multicast
[SSM] destination addresses and are reserved for use by source-
specific multicast applications and protocols. This document defines
operational recommendations to ensure source-specific behavior within
the 232/8 range.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Operational practices in 232/8 . . . . . . . . . . . . . . . . 4
2.1. Preventing local sources from sending to shared tree. . . . 4
2.2. Preventing remote sources from being learned/joined via MSDP. 4
2.3. Preventing receivers from joining the shared tree . . . . . 5
2.4. Preventing RP's as candidates for 232/8 . . . . . . . . . . 5
3. Intellectual Property. . . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations. . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References. . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References. . . . . . . . . . . . . . . . . . . 8
8. Author's Addresses . . . . . . . . . . . . . . . . . . . . . . 9
9. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Current PIM Sparse Mode (PIM-SM) [RFC2362] relies on the shared
Rendezvous Point (RP) tree to learn about active sources for a group
and to support group-generic (not source specific) data distribution.
The IP Multicast group address range 232/8 has been designated for
Source-Specific PIM [SSM] applications and protocols [IANA] and
SHOULD support source-only trees only, precluding the requirement of
an RP and a shared tree; active sources in the 232/8 range will be
discovered out of band. PIM Sparse Mode Designated Routers (DR), with
local membership, are capable of joining the shortest path tree for
the source directly using Source-Specific PIM (also know as PIM-SSM
or simply SSM).
Operational best common practices in the 232/8 group address range
are necessary to ensure shortest path source-only trees across
multiple domains in the Internet [SSM], and to prevent data from
sources sending to groups in the 232/8 range from arriving via shared
trees. This avoids unwanted data arrival, and allows several sources
to use the same group address without conflict at the receivers.
The operational practices SHOULD:
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o Prevent local sources from sending to shared tree
o Prevent receivers from joining the shared tree
o Prevent RP's as candidates for 232/8
o Prevent remote sources from being learned/joined via MSDP [MSDP]
2. Operational practices in 232/8
2.1. Preventing local sources from sending to shared tree
Eliminating the use of shared trees for groups in 232/8, while
maintaining coexistence with PIM-SM, behavior of the RP and/or the DR
needs to be modified. This can be accomplished by
- preventing data for 232/8 groups from being sent encapsulated to
the RP by the DR
- preventing the RP from accepting registers for 232/8 groups from
the DR
- preventing the RP from forwarding accepted data down (*,G)
tree for 232/8 groups
2.2. Preventing remote sources from being learned/joined via MSDP
PIM-SSM does not require active source announcements via MSDP. All
source announcements are received out of band, the the last hop
router being responsible for sending (S,G) joins directly to the
source. To prevent propagation of SAs in the 232/8 range, an RP
SHOULD
- never originate an SA for any 232/8 groups
- never accept or forward an SA for any 232/8 groups.
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2.3. Preventing receivers from joining the shared tree
Local PIM domain practices need to be enforced to prevent local
receivers from joining the shared tree for 232/8 groups. This can be
accomplished by
- preventing DR from sending (*,G) joins for 232/8 groups
- preventing RP from accepting (*,G) join for 232/8 groups
However, within a local PIM domain, any last-hop router NOT
preventing (*,G) joins may trigger unwanted (*,G) state toward
the RP which intersects an existing (S,G) tree, allowing the
receiver on the shared tree to receive the data, breaking the
source-specific [SSM] service model. It is therefore recommended
that ALL routers in the domain MUST reject AND never originate
(*,G) joins for 232/8 groups.
In those cases in which an ISP is offering its customers (or
others) the use of the ISP's RP, the ISP SHOULD NOT allow (*,G)
joins in the 232/8 range.
2.4. Preventing RP's as candidates for 232/8
Because PIM-SSM does not require an RP, all RPs SHOULD NOT offer
themselves as candidates in the 232/8 range. This can be accomplished
by
- preventing RP/BSR from announcing in the 232/8 range
- preventing ALL routers from accepting RP delegations in the
232/8 range
- precluding RP functionality on RP for the 232/8 range
Note that in typical practice, RP's announce themselves as candidates
for the 224/4 (which obviously includes 232/8). It is still
acceptable to allow the advertisement of 224/4 (or any other superset
of 232/8); however, this approach relies on the second point, above,
namely, that routers silently just ignore the RP delegation in the
232/8 range, and prevent sending or receiving using the shared tree,
as described previously. Finally, an RP SHOULD NOT be configured as
a candidate RP for 232/8 (or more specific range).
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3. Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11 [RFC2028].
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementors or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
4. Acknowledgments
This document is the work of many people in the multicast community,
including (but not limited to) Dino Farinacci, John Meylor, John
Zwiebel, Tom Pusateri, Dave Thaler, Toerless Eckert, Leonard
Giuliano, Mike McBride, and Pekka Savola.
5. Security Considerations
This document describes operational practices that introduce no new
security issues to either PIM-SM or PIM-SSM.
However, in the event that the operational practices described in
this document are not adhered to, some problems may surface. In
particular, section 2.3 describes the effects of non-compliance of
last-hop routers (or to some degree, rogue hosts sending PIM messages
themselves) on the source-specific service model; creating the (*,G)
state for source-specific (S,G) could enable a receiver to receive
data it should not get. This can be mitigated by host-side multicast
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source filtering.
6. IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC2434].
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7. References
7.1. Normative References
[MSDP] Meyer, D. and B. Fenner (Editors), "The Multicast
Source Discovery Protocol (MSDP)",
draft-ietf-msdp-spec-20.txt. Work in Progress.
[SSM] Holbrook, H., and B. Cain,, "Source-Specific
Multicast", draft-ietf-ssm-arch-03.txt. Work in
Progress.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", RFC 2119, March,
1997.
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026/BCP 9, October, 1996.
[RFC2028] Hovey, R. and S. Bradner, "The Organizations
Involved in the IETF Standards Process", RFC
2028/BCP 11, October, 1996.
[RFC2362] Estrin, D., et. al., "Protocol Independent
Multicast-Sparse Mode (PIM-SM): Protocol
Specification", RFC 2362, June, 1998.
[RFC2434] Narten, T., and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
RFC 2434/BCP 26, October 1998.
7.2. Informative References
[IANA] http://www.iana.org
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8. Author's Addresses
David Meyer
Email: dmm@1-4-5.net
Robert Rockell
Sprint
Email: rrockell@sprint.net
Greg Shepherd
Procket
Email: shep@procket.com
9. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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