Network Working Group                                   Greg Shepherd                                   David Meyer
INTERNET DRAFT                                          Juniper Networks                                          Sprint
                                                        Rob Rockell
                                                        David Meyer
                                                        Sprint
                                                        Greg Shepherd
                                                        Procket
Category                                                Best Current Practices
                                                        Feburary, 2002
                                                        January, 2003

        Source-Specific Protocol Independent Multicast in 232/8

                   <draft-ietf-mboned-ssm232-02.txt>

                   <draft-ietf-mboned-ssm232-03.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.

2. Copyright Notice

   Copyright (C) The Internet Society (2002). (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
    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

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

    - preventing RP from accepting (*,G) join

   Within a local PIM domain, any last-hop router NOT preventing (*,G)
   joins MAY trigger (*,G) state toward the RP which intersects an
   existing (S,G) tree, allowing the receiver on the shared tree to
   receive the data. So if the last-hop routers are not preventing (*,G)
   joins, then all routers in the domain must also prevent (*,G) joins.

5.4. Preventing RP's as candidates for 232/8

   Because PIM-SS does not require an RP, all RPs SHOULD NOT offer themí
   selves as candidates in the 232/8 range. This can be accomplished by

    - preventing RP/BSR from announcing in the 232/8 range

    - preventing DRs from accepting delegations in this range

    - precluding RP functionality on RP for the 232/8 range

6. References

   [IANA]      http://www.iana.org

   [SSM]       Holbrook, H., Cain, B., "Source-Specific Multicast",
               draft-ietf-ssm-arch-00.txt,
               draft-ietf-ssm-arch-01.txt, November, 2001. 2002.

   [RFC2119]   S. Bradner, "Key words for use in RFCs to Indicate
               Requirement Levels", RFC 2119, March, 1997.

   [RFC2362]   D. Estrin, et. al., "Protocol Independent Multicast-Sparse
               Mode (PIM-SM): Protocol Specification", RFC 2362, June,
               1998.

   [MSDP]       D. Meyer and Bill Fenner (Editors), "The Multicast
                Source Discovery Protocol (MSDP)", draft-ietf-msdp-spec-13.txt, draft-ietf-msdp-spec-14.txt,
                November 2001. 2002.

7. Author's Addresses

   Greg Shepherd
   Juniper Networks
   Procket
   Email: shep@juniper.net shep@procket.net

   Robert Rockell
   Sprint
   Email: rrockell@sprint.net

   David Meyer
   Sprint
   Email: dmm@sprint.net

8. Full Copyright Statement

   Copyright (C) The Internet Society (2002). (2003).  All Rights Reserved.

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