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Internet Engineering Task Force                              G. Shepherd
INTERNET-DRAFT                                             Cisco Systems
draft-ietf-mboned-ssm232-00.txt                              E. Luczycki
                                                           Broadcast.com
                                                              R. Rockell
                                                              Sprintlink
                                                          November, 2000
                                                      Expires April 2001

     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.


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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.









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


Operational practices in 232/8 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
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.
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 tringer (*,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.

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

References Internet Assigned Numbers Authority,
http://www.isi.edu/in-notes/iana/assignments/multicast-addresses.
Holbrook, H., Cain, B., "Source-Specific Multicast for IP (SSM)",
draft-holbrook-ssm-00.txt, September, 2000.  D. Estrin, et. al.,
"Protocol Independent Multicast-Sparse Mode (PIM-SM):  Protocol
Specification", RFC 2362, June, 1998 Bhaskar, N.,
"Source Specific Protocol Independent Multicast (PIM-SS)", draft-
bhaskar-pim-ss-00.txt, March, 2000.  Diot, C., Giuliano, L.,
Rockell, R., "Deployment of PIM-SO at Sprint (PIM-SO)", draft-
bhattach-diot-PIMSO-00.txt, March, 2000.
Farinacci, D., et. al.
"Multicast Source Discovery Protocol (MSDP)", draft-ietf-msdp-
spec-05.txt, February, 2000.

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 Engineering Reston, Virginia
rrockell@sprintlink.net


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