Network Working Group B. Haberman

Network Working Group B. Haberman
Request for Comments: 5186 Johns Hopkins University
Category: Informational J. Martin
Woven Systems
May 2008

Internet Group Management Protocol Version 3 (IGMPv3) /
Multicast Listener Discovery Version 2 (MLDv2) and
Multicast Routing Protocol Interaction

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Abstract

The definitions of the Internet Group Management Protocol Version 3
(IGMPv3) and Multicast Listener Discovery Version 2 (MLDv2) require
new behavior within the multicast routing protocols. The additional
source information contained in IGMPv3 and MLDv2 messages
necessitates that multicast routing protocols manage and utilize the
information. This document describes how multicast routing protocols
will interact with these source-filtering group management protocols.

1. Introduction

The definitions of IGMPv3 [IGMP3] and MLDv2 [MLDv2] require new
behavior within the multicast routing protocols. The additional
source information contained in IGMPv3 and MLDv2 messages
necessitates that multicast routing protocols manage and utilize the
information. This document will describe how multicast routing
protocols will interpret information learned from these source-
filtering group management protocols.

2. Multicast Forwarding State

Existing multicast routing protocols utilize the group management
database in determining if local members exist for a particular
multicast group. With previous group management protocols, this
database had one type of record indicating the group for which there
was interest and the associated local interfaces.

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In the case of IGMPv3 and MLDv2, these routing protocols may now
build multicast forwarding state based on the source filter
information available for each multicast group that has local
membership. This requires that the group management database have
four record types. Only one record may exist for a given interface
and a given multicast group.

1. EXCLUDE <>
The EXCLUDE <> record indicates interest in all sources
destined to this group address for a set of local interfaces.
It is equivalent to the single record type existing in previous
versions of the group management protocols.

2. INCLUDE <>
The INCLUDE <> record indicates that there is no interest in
any sources destined to this group address for a set of local
interfaces.

3. EXCLUDE <list>
The EXCLUDE <list> record indicates that there is interest in
all sources other than the specifically listed sources for a
set of local interfaces.

4. INCLUDE <list>
The INCLUDE <list> record indicates that there is interest in
only the specifically listed sources for a set of local
interfaces.

The records in the group management database should be utilized when
generating forwarding state for a multicast group. If the source
address in the multicast packet exists in the database for the
specified multicast group and is in an INCLUDE list or is not listed
in an EXCLUDE list, the multicast routing protocol should add the
interface to the list of downstream interfaces; otherwise, it should
not be added based on local group membership.

3. DVMRP Interaction

The Distance Vector Multicast Routing Protocol (DVMRP) [DVMRP] does
not incorporate any knowledge of the multicast group's senders.
Therefore, DVMRP will act only on the multicast group address
contained in an IGMPv3 or MLDv2 report.

Future standardized versions of DVMRP may incorporate pruning and
grafting messages similar to PIM-DM (discussed in Section 5). The
rules defined in Section 5 can be applied in this situation.

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4. MOSPF Interaction

In Multicast Extensions to OSPF (MOSPF) [MOSPF], the consideration of
source filter information in the group management database is limited
to the building of forwarding state (discussed above). This is due
to the flooding of group-membership-LSAs within MOSPF.

5. PIM-DM Interaction

The PIM-DM protocol [PIMDM] interaction with a source-filtering group
management protocol is important in two areas: multicast distribution
tree pruning and multicast distribution tree grafting. The following
sections will describe the behavior needed in PIM-DM to interoperate
with IGMPv3 and MLDv2.

5.1. PIM-DM Prunes

PIM-DM prune messages are initiated when a PIM-DM router determines
that there are no entities interested in the data flowing on the
(S,G) forwarding state. If the multicast router is running IGMPv3 or
MLDv2, this is determined by the source S being in EXCLUDE state in
the source filter for the destination G, or all interest in G being
terminated for an existing (S,G) forwarding entry.

5.2. PIM-DM Grafts

PIM-DM graft messages are sent in order to override an existing PIM-
DM prune. In the case of IGMPv3 or MLDv2, this occurs when prune
state exists for (S,G) and a state change occurs in which the source
filter state for S changes to INCLUDE for the specified G.

6. PIM-SM Interaction

A PIM-SM interaction takes place when a PM-SM [PIMSM] router receives
an IGMP or MLD message regarding a group address that is in the Any
Source Multicast (ASM) range. This range is defined as the entire
multicast address space excluding the global SSM range [SSM] and any
locally defined Source Specific space.

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6.1. PIM-SM Joins (ASM Behavior)

PIM-SM join messages are initiated when a PIM-SM router determines
that there are entities interested in a specific group or a specific
source sending to the group. If this is due to an IGMPv3 or MLDv2
report with a zero-length EXCLUDE list, then the join is sent as a
(*,G) join towards the RP.

If the join is triggered by an IGMPv3 or MLDv2 state change that
affects source information, the PIM-SM join is sent as a (S,G) join
towards the specific source. This behavior optimizes the join
process, as well as facilitates the adoption of the SSM model. The
generation of this (S,G) join can cause failures in architectures
where leaf routers do not have global reachability, and thus, can be
overridden by local policy. If this is the case, then all triggered
joins are sent towards the RP as (*,G) joins. The router sending the
(*,G) join is responsible for filtering the data as per the IGMPv3
database before forwarding.

6.2. PIM-SM Prunes (ASM Behavior)

PIM-SM prune messages are initiated when a PIM-SM router determines
that there are no entities interested in a specific group, or a
specific source sending to the group. If this is triggered by either
receiving a report with an EXCLUDE or if a specific Source/Group
times out, then an (S,G) prune is sent towards the upstream router.
If all of the IGMPv3 or MLDv2 derived requests for a group time out,
then (S,G) and (*,G) prunes are sent upstream as needed to stop all
flow of traffic for that group.

7. PIM-SSM Interaction

A PIM-SSM interaction takes place when a PIM-SM router receives an
IGMPv3 or MLDv2 message regarding a group address that is in the
Source Specific Multicast range. This behavior is not defined in
this document, but rather in [PIMSM].

8. Security Considerations

This document does not introduce any additional security issues above
and beyond those already discussed in [PIMDM], [PIMSM], [IGMP3], and
[MLDv2].

9. Acknowledgements

The authors would like to thank Murali Brahmadesam, Leonard Giuliano,
and Hal Sandick for their feedback and suggestions.

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10. Normative References

[IGMP3] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.

[MLDv2] Vida, R., Ed., and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

[DVMRP] Waitzman, D., Partridge, C., and S. Deering, "Distance Vector
Multicast Routing Protocol", RFC 1075, November 1988.

[MOSPF] Moy, J., "Multicast Extensions to OSPF", RFC 1584, March
1994.

[PIMDM] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent
Multicast - Dense Mode (PIM-DM): Protocol Specification
(Revised)", RFC 3973, January 2005.

[PIMSM] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.

[SSM] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
RFC 4607, August 2006.

Authors' Addresses

Brian Haberman
The Johns Hopkins University Applied Physics Laboratory
11100 Johns Hopkins Road
Laurel, MD 20723-6099
US

Phone: +1 443 778 1319
EMail: [email protected]

Jim Martin
Woven Systems
2455 Augustine Drive, Suite 211
Santa Clara, CA 95054
US

Phone: +1 408 654-8143
EMail: [email protected]

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RFC 5186 IGMPv3/MLDv2 and Multicast Protocols May 2008

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