Internet Engineering Task Force                              G. Shepherd
INTERNET-DRAFT                                             Cisco Systems
draft-shepherd-ssm232-00.txt                                 E. Luczycki
                                                           Broadcast.com
                                                              R. Rockell
                                                              Sprintlink
                                                             March, 2000
                                                  Expires September 2000

        Source-Specific Protocol Independent Multicast in 232/8

Status of this Memo

This document is an Internet Draft and is in full conformance with all
provisions of Section 10 of RFC2026.Internet Drafts are working
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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 applications and protocols [IANA-ALLOCATION]. This
     document defines operational recommendations to ensure source-
     specific behavior within the 232/8 range.






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1.  Introduction

Current PIM Sparse Mode [PIM-SM] 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-ALLOCATION] 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. The
PIM Sparse Mode [PIM-SM] Designated Routers (DR), with local membership,
are capable of joining the shortest path tree for the source directly
using Source-Specific PIM [PIM-SS].

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 [PIM-SO], 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

 o Prevent receivers from joining the shared tree

 o Prevent RP's as candidates for 232/8



2.  Operational practices in 232/8

2.1.  Preventing local sources from sending to shared tree

Eliminatng the use of shared trees for groups in 232/8, while mainaining
coexistance 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


2.2.  Preventing remote sources from being learned/joined via MSDP

PIM-SS does not require active source announcements via MSDP. All source



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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.


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
 - preventing RP from accepting (*,G) join


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

Because PIM-SS 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 DRs from accepting deligations in this range
 - precluding RP functionality on RP for the 232/8 range


3.

References

IANA-ALLOCATION
     Internet Assigned Numbers Authority, http://www.isi.edu/in-
     notes/iana/assignments/multicast-addresses.

SSM  Holbrook, H., Cain, B., "Source-Specific Multicast for IP (SSM)",
     draft-holbrook-ssm-00.txt, September, 2000.

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

PIM-SSBhaskar, N., "Source-Specific Protocol Independent Multicast
     (PIM-SS)", draft-bhaskar-pim-ss-00.txt, March, 2000.

PIM-SODiot, C., Giuliano, L., Rockell, R., "Deployment of PIM-SO at
     Sprint (PIM-SO)", draft-bhattach-diot-PIMSO-00.txt, March, 2000.




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MSDP Farinacci, D., et. al. "Multicast Source Discovery Protocol
     (MSDP)", draft-ietf-msdp-spec-05.txt, February, 2000.

4.  Author's Addresses


   Greg Shepherd
   Cisco Systems
   170 Tasman Drive
   San Jose, CA, 95134
   Phone: +1 541 912 9758
   Email: shep@cisco.com

   Ed Luczycki
   Broadcast.com
   eds@yahoo-inc.com

   Robert Rockell
   Sprint Internet Service Center
   Reston, Virginia
   rrockell@sprintlink.net