INTERNET-DRAFT                                              J. Hawkinson
draft-ietf-mboned-pruning-02.txt                              BBN Planet
Category: Best Current Practice                             30 July 1997

                     Multicast pruning a necessity

Status of this Memo

   This document specifies a Best Current Practice for the Internet
   Community, and requests discussion and suggestions for improvements.
   Distribution of this memo is unlimited.

Internet Drafts

   This document is an Internet-Draft.  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.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

Abstract

   This document calls for the MBone to be free of non-pruning multicast
   as soon as possible, due to the high cost to the Internet of the
   traffic resulting from them. Consensus is that [DATE 1 month from RFC
   publication] is the goal date for elimating non-pruning multicast
   routers.

   It cites several ways to eliminate non-pruning multicast from a
   network, allowing per-site flexibility.

   This is a product of the Multicast Deployment Working Group in the
   Operational Requirements area of the Internet Engineering Task Force.
   Submit comments to <mboned@ns.uoregon.edu> or the author.

Discussion

   The MBone (Multicast Backbone) of the Internet is composed of a DVMRP



Hawkinson                                                       [Page 1]

Expires 30 February 1998    INTERNET-DRAFT                  30 July 1997


   backbone connected to regions that may be running other multicast
   routing protocols.

   DVMRP versions prior to 3 do not support pruning. Every multicast
   packet transmitted is delivered to every non-pruning router (subject
   to scoping rules), regardless of the presence of members of that
   group. Network paths between each source and each non-pruning router
   are thus forced to carry all multicast traffic from those sources.
   This behavior is fundamentally incompatible with a scalable multicast
   backbone.

   Effective [DATE], the MBone community will no longer accept such
   non-pruning implementations as a part of the MBone. Such
   implementations should be upgraded or disconnected from the MBone
   prior to that date. Service providers should assist their customers
   in these processes.

   DVMRP implementations that do not support pruning include mrouted
   versions prior to 3, and Cisco Systems IOS prior to version 11.0(3).
   3Com's NETBuilder routers and LANplex switches have supported pruning
   as long as DVMRP has been available for them (releases 8.3 and 7.0,
   respectively).  Bay Networks' implementation supports pruning in
   version 9.00 and up.

   In the case where the existing infrastructure cannot be upgraded to
   support pruning, sites may wish to consider deploying lightweight
   multicast routers instead. For instance, popular free unixes (e.g.
   FreeBSD, NetBSD, and Linux) that run on cheap PC hardware all support
   pruning multicast using mrouted.

   Within non-DVMRP regions, software that does not support DVMRP
   pruning but does support a similar mechanism of a different protocol
   (such as CBT, MOSPF, or PIM) is acceptable, as long as the border
   routers of such a region can translate that mechansism into DVMRP
   pruning.

Security Considerations

   Security considerations are not addressed in this memo.

References

   [IPMULTI] S.E. Deering, "Host extensions for IP multicasting", RFC1112,
           1 August 1989.

   [MREQ] R. Braudes, S. Zabele, "Requirements for Multicast Protocols",
           RFC1458, 26 May 1993.




Hawkinson                                                       [Page 2]

Expires 30 February 1998    INTERNET-DRAFT                  30 July 1997


   [DVMRP] T. Pusateri, "Distance Vector Multicast Routing Protocol",
           Work in progress (internet-draft).

Author's Address

   John Hawkinson
   BBN Planet
   150 CambridgePark Drive
   Cambridge, MA 02140

   phone: +1 617 873 3180
   email: jhawk@bbnplanet.com







































Hawkinson                                                       [Page 3]