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Source-Specific Protocol Independent Multicast in 232/8

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 4608.
Authors Robert Rockell , David Meyer , Greg Shepherd
Last updated 2015-10-14 (Latest revision 2006-07-17)
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
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IESG IESG state RFC 4608 (Best Current Practice)
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Responsible AD David Kessens
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Network Working Group                                           Shepherd
Internet-Draft                                                     Cisco
Expires: December 16, 2006                                       Rockell
                                                           June 14, 2006

        Source-Specific Protocol Independent Multicast in 232/8

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 16, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).


   IP Multicast group addresses in the 232/8 ( to range are designated as source-specific multicast
   destination addresses and are reserved for use by source-specific
   multicast applications and protocols.  This document defines
   operational recommendations to ensure source-specific behavior within

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   the 232/8 range.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  BCP, Experimental Protocols and Normative References  . . . 3
   2.  Operational practices in 232/8  . . . . . . . . . . . . . . . . 4
     2.1.  Preventing local sources from sending to shared tree  . . . 4
     2.2.  Preventing remote sources from being learned/joined
           via MSDP  . . . . . . . . . . . . . . . . . . . . . . . . . 5
     2.3.  Preventing receivers from joining the shared tree . . . . . 5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   7. Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
   8. Intellectual Property and Copyright Statements  . . . . . . . . . . 9

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1.  Introduction

   Current PIM Sparse Mode (PIM-SM) [I-D.pim-sm-v2-new] relies on the
   shared Rendezvous Point (RP) tree to learn about active sources for a
   group and to support group-generic (Any Source Multicast or ASM) data
   distribution.  The IP Multicast group address range 232/8 has been
   designated for Source-Specific Multicast (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-SM Designated
   Routers (DR), with local membership, are capable of joining the
   shortest path tree for the source directly using SSM functionality of

   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 [RFC3569], 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 receivers from joining the shared
   tree o Prevent RP's as candidates for 232/8 o Prevent remote sources
   from being learned/joined via MSDP [RFC3618]

1.1.  BCP, Experimental Protocols and Normative References

   This document describes the best current practice for a widely
   deployed Experimental protocol, MSDP.  There is no plan to advance
   the MSDP's status (for example, to Proposed Standard).  The reasons
   for this include:

   o  MSDP was originally envisioned as a temporary protocol to be
      supplanted by whatever the IDMR working group produced as an
      inter-domain protocol.  However, the IDMR WG (or subsequently, the
      BGMP WG) never produced a protocol that could be deployed to
      replace MSDP.

   o  One of the primary reasons given for MSDP to be classified as
      Experimental was that the MSDP Working Group came up with
      modifications to the protocol that the WG thought made it better
      but that implementors didn't see any reasons to deploy.  Without
      these modifications (e.g., UDP or GRE encapsulation), MSDP can
      have negative consequences to initial packets in datagram streams.

   o  Scalability: Although we don't know what the hard limits might be,
      readvertising everything you know every 60 seconds clearly limits

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      the amount of state you can advertise.

   o  MSDP reached near ubiquitous deployment as the de-facto standard
      inter-domain multicast protocol in the IPv4 Internet.

   o  No consensus could be reached regarding the reworking of MSDP to
      address the many concerns of various constituencies within the
      IETF.  As a result, a decision was taken to document what is
      (ubiquitously) deployed and move that document to Experimental.
      While advancement of MSDP to Proposed Standard was considered, for
      the reasons mentioned above, it was immediately discarded.

   o  The advent of source specific multicast and protocols such as bi-
      directional PIM, as well as embedded RP techniques for IPv6, have
      further reduced consensus that a replacement protocol for MSDP for
      the IPv4 Internet is required.

   The RFC Editor's policy regarding references is that they be split
   into two categories known as "normative" and "informative".
   Normative references specify those documents which must be read to
   understand or implement the technology in an RFC (or whose technology
   must be present for the technology in the new RFC to work) [RFCED].
   In order to understand this document, one must also understand both
   the PIM-SM and MSDP documents.  As a result, references to these
   documents are normative.  The IETF has adopted the policy that BCPs
   must not have normative references to Experimental protocols.
   However, this document is a special case in that the underlying
   Experimental document (MSDP) is not planned to be advanced to
   Proposed Standard.  The MBONED Working Group requests approval under
   the Variance Procedure as documented in RFC 2026 [RFC2026].  Note to
   RFC-Editor: If IETF/IESG approves this, please change the above
   sentence into: The MBONED Working Group has requested approval under
   the Variance Procedure as documented in RFC 2026 [RFC2026].  The IESG
   followed the Variance Procedure, and after an additional 4 week IETF
   Last Call evaluated the comments and status and has approved this

2.  Operational practices in 232/8

2.1.  Preventing local sources from sending to shared tree

   Eliminating the use of shared trees for groups in 232/8, while
   maintaining coexistence with ASM in PIM-SM, behavior of the RP and/or
   the DR needs to be modified.  This can be accomplished by

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   o  preventing data for 232/8 groups from being sent encapsulated to
      the RP by the DR.

   o  preventing the RP from accepting registers for 232/8 groups from
      the DR.

   o  preventing the RP from forwarding accepted data down (*,G) tree
      for 232/8 groups.

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

   SSM does not require active source announcements via MSDP.  All
   source announcements are received out of band, the the last hop
   router being responsible for sending (S,G) joins directly to the
   source.  To prevent propagation of SAs in the 232/8 range, an RP

   o  never originate an SA for any 232/8 groups.

   o  never accept or forward an SA for any 232/8 groups.

2.3.  Preventing receivers from joining the shared tree

   Local PIM-SM domain practices need to be enforced to prevent local
   receivers from joining the shared tree for 232/8 groups.  This can be
   accomplished by 232/8 range.

   o  preventing DR from sending (*,G) joins for 232/8 groups.

   o  preventing RP from accepting (*,G) join for 232/8 groups.

   However, within a local PIM-SM domain, any last-hop router NOT
   preventing (*,G) joins may trigger unwanted (*,G) state toward the RP
   which intersects an existing (S,G) tree, allowing the receiver on the
   shared tree to receive the data, breaking the source-specific
   [RFC3569] service model.  It is therefore recommended that ALL
   routers in the domain MUST reject AND never originate (*,G) joins for
   232/8 groups.  In those cases in which an ISP is offering its
   customers (or others) the use of the ISP's RP, the ISP SHOULD NOT
   allow (*,G) joins in the 232/8 range.

   Because SSM does not require a PIM-SM RP, all RPs SHOULD NOT offer
   themselves as candidates in the 232/8 range.  This can be
   accomplished by

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

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   o  preventing ALL routers from accepting RP delegations in the 232/8

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

   Note that in typical practice, RP's announce themselves as candidates
   for the 224/4 (which obviously includes 232/8).  It is still
   acceptable to allow the advertisement of 224/4 (or any other superset
   of 232/8); however, this approach relies on the second point, above,
   namely, that routers silently just ignore the RP delegation in the
   232/8 range, and prevent sending or receiving using the shared tree,
   as described previously.  Finally, an RP SHOULD NOT be configured as
   a candidate RP for 232/8 (or more specific range).

3.  IANA Considerations

   This document creates no new requirements on IANA namespaces

4.  Security Considerations

   This document describes operational practices that introduce no new
   security issues to PIM-SM in either SSM or ASM operation.  However,
   in the event that the operational practices described in this
   document are not adhered to, some problems may surface.  In
   particular, section 2.3 describes the effects of non-compliance of
   last-hop routers (or to some degree, rogue hosts sending PIM-SM
   messages themselves) on the source-specific service model; creating
   the (*,G) state for source-specific (S,G) could enable a receiver to
   receive data it should not get.  This can be mitigated by host-side
   multicast source filtering.

5.  Acknowledgements

   This document is the work of many people in the multicast community,
   including (but not limited to) Dino Farinacci, John Meylor, John
   Zwiebel, Tom Pusateri, Dave Thaler, Toerless Eckert, Leonard
   Giuliano, Mike McBride, and Pekka Savola.

6.  References

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6.1.  Normative References

              Fenner, B., "Protocol Independent Multicast - Sparse Mode
              (PIM-SM): Protocol  Specification (Revised)",
              draft-ietf-pim-sm-v2-new-12 (work in progress),
              March 2006.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2028]  Hovey, R. and S. Bradner, "The Organizations Involved in
              the IETF Standards Process", BCP 11, RFC 2028,
              October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC3569]  Bhattacharyya, S., "An Overview of Source-Specific
              Multicast (SSM)", RFC 3569, July 2003.

   [RFC3618]  Fenner, B. and D. Meyer, "Multicast Source Discovery
              Protocol (MSDP)", RFC 3618, October 2003.

6.2.  Informative References

   [IANA]  "", 2005.

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7. Authors' Addresses

   Greg Shepherd


   Robert Rockell


   Dave Meyer


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8. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at

Disclaimer of Validity

   This document and the information contained herein are provided on an

Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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