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Versions: 00 01 02 03                                                   
Internet Engineering Task Force                                 MAGMA WG
INTERNET-DRAFT                                     Isidor Kouvelas/Cisco
draft-ietf-magma-mrdssm-00.txt                          21 February 2002
                                                    Expires: August 2002

              Multicast Router Discovery SSM Range Option

Status of this Document

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

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

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This document is a product of the IETF IDMR WG.  Comments should be
addressed to the authors, or the WG's mailing list at


     This document defines the Multicast Router Discovery option
     for advertising the configured Source Specific Multicast
     destination address range.

Kouvelas                                                        [Page 1]

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1.  Introduction

     With current multicast deployment in the Internet, different
multicast routing protocols coexist and operate under separate parts of
the multicast address space [1]. Multicast routers are consistently
configured with information that maps specific multicast destination
address ranges to multicast routing protocols. Part of this
configuration describes the subset of the address space that is used by
source-specific multicast (SSM) [2].

     There are currently two requirements for a router to advertise its
configured SSM range on its attached links:

o On links with multiple multicast routers, advertisement of the
  configured SSM range by each router can be used to discover miss-

o IP systems with multicast sources or receivers can use the
  advertisements to learn the SSM group range with which the network is

     This document defines an optional extension for the Multicast
Router Discovery protocol [3] which can be used to advertise the SSM

2.  SSM Range Option

     The SSM Range option SHOULD be included in all Multicast Router
Advertisement messages for IPv4 [3] and all Neighbour Discovery Protocol
Router Advertisement messages for IPv6 [4]. It contains the list of
multicast destination address ranges that are configured to operate
under Source Specific Multicast on this router.  The format of the
option is as follows:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|    Type=Y     |   Length=var  |  Mask-Len-1   |    Prefix-1 ...
|  Mask-Len-2   |   Prefix-2 ...
|                            ...                                |

Kouvelas                                            Section 2.  [Page 2]

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Type The type value of the SSM Range option is TBD-X when present in
     IPv4 Multicast Router Advertisement messages and TBD-Z when present
     in IPv6 Neighbour Discovery Protocol Advertisement messages.

     The length of the SSM Range Discovery option is variable and
     depends on the number of destination ranges present in the option
     as well as the sizes of the ranges.

     The mask length for the nth address range.

     The multicast destination address prefix of the nth range present
     in this option. The size of the prefix field is variable and
     depends on the number of significant bits in the prefix (specified
     in the corresponding Mask-Len field). The field is padded by enough
     trailing bits to make the end of the field fall on an octet
     boundary. Note that the value of the trailing bits is irrelevant.

     A router receiving a Multicast Router Advertisement message or a
Neighbour Discovery Protocol Router Advertisement message with an SSM
Range Discovery Option must compare the contents of the option with the
multicast address ranges in the local SSM configuration and signal any
differences to the administrator in a rate-limited manner.

3.  Acknowledgements

The author would like to thank Bill Fenner and Dave Thaler for their
contribution to this document.

4.  Authors' Addresses

     Isidor Kouvelas
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134

Kouvelas                                            Section 4.  [Page 3]

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5.  References

[1] Z. Albanna, K. Almeroth, D. Meyer, "IANA Guidelines for IPv4
     Multicast Address Allocation", Best Current Practices, <draft-ietf-
     iana-IPv4-mcast-guidelines-00.txt>, 2001.

[2] H. Holbrook, B. Cain, "Source-Specific Multicast for IP", work in
     progress, <draft-ietf-ssm-arch-00.txt>, 21 November 2001.

[3] S. Biswas, B. Haberman, "IGMP Multicast Router Discovery", Work In
     Progress, <draft-ietf-idmr-igmp-mrdisc-??.txt>, 2002.

[4] T. Narten, E. Nordmark, W. Simpson, "Neighbour Discovery for IP
     Version 6 (IPv6)", Standards Track RFC2461, December 1998.

Kouvelas                                            Section 5.  [Page 4]

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Kouvelas                                            Section 5.  [Page 5]