Network Working Group David Meyer
INTERNET DRAFT Sprint
Rob Rockell
Sprint
Greg Shepherd
Procket
Category Best Current Practices
January, 2003
Source-Specific Protocol Independent Multicast in 232/8
<draft-ietf-mboned-ssm232-04.txt>
1. Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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2. Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
3. 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 applications and protocols [IANA]. This document defines
operational recommendations to ensure source-specific behavior within
the 232/8 range.
The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED,
SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined
in RFC 2119 [RFC2119].
4. Introduction
Current PIM Sparse Mode [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 [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 [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
o Prevent local sources from sending to shared tree
o Prevent remote sources from being learned/joined via MSDP [MSDP]
o Prevent receivers from joining the shared tree
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o Prevent RP's as candidates for 232/8
5. Operational practices in 232/8
5.1. 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
5.2. Preventing remote sources from being learned/joined via MSDP
PIM-SS does not require active source announcements via MSDP. All
source announcements are received out of band, the the last hop
router is 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.
5.3. 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
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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.
5.4. Preventing RP's as candidates for 232/8
Because PIM-SS does not require an RP, all RPs SHOULD NOT offer them¡
selves 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
6. Informative References
[IANA] http://www.iana.org
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March, 1997.
7. Normative References
[MSDP] D. Meyer and Bill Fenner (Editors), "The Multicast
Source Discovery Protocol (MSDP)",
draft-ietf-msdp-spec-14.txt, November 2002.
[SSM] Holbrook, H., Cain, B., "Source-Specific Multicast",
draft-ietf-ssm-arch-01.txt, November, 2002.
[RFC2362] D. Estrin, et. al., "Protocol Independent Multicast-Sparse
Mode (PIM-SM): Protocol Specification", RFC 2362, June,
1998.
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8. Author's Addresses
David Meyer
Sprint
Email: dmm@sprint.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 doc¡
ument 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 develop¡
ing 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 MER¡
CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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