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Mboned                                                          T. Chown
Internet-Draft                                 University of Southampton
Intended status: Informational                              July 4, 2011
Expires: January 5, 2012

                     Multicast Filtering Practices


   Operators of multicast networks may apply various filters to
   multicast traffic at boundary routers or on MSDP peerings.  The aim
   of this text is to document existing filtering practices, with a view
   to generating some discussion towards producing guidance on best
   filtering practice.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 5, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Internet-Draft        Multicast Filtering Practices            July 2011

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Border and MSDP Filtering . . . . . . . . . . . . . . . . . . . 3
   3.  Subnet filtering  . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Informative References  . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   Multicast filtering can be applied at a multicast boundary or on an
   MSDP peering as a means to prevent unintended leakage of multicast
   traffic beyond its desired scope.  An informal discussion of
   filtering practices suggested that those practices vary from
   organisation to organisation.  The aim of this text is to gather and
   document commonly used existing filtering practices.  Whether it is
   then possible to draw up a definitive best practice is to be
   determined; it is quite possible that due to the shifting nature of
   the target that a point-in-time recommendation would quickly be
   overtaken by events.  For example, the recent addition of unicast
   prefix-based IPv4 multicast addresses [RFC6034] meant that filtering
   of all of became undesirable.  However, general
   principles may remain valid over time.

   For sites on academic research networks, some examples of filtering
   recommendations already exists, e.g. in documentation [I2multicast]
   from the Internet2 Multicast WG, and in the JANET IPv4 Multicast
   Guide [JANETmulticast].

   An additional resource is the registry of IPv4 multicast address
   space held by IANA [IANAmulticast].  This registry should be a
   definitive guide to the formal use of ranges of addresses within the
   overall IPv4 multicast address space.  A similar registry is
   maintained for IPv6 multicast address space [IANA6multicast].

   This text is a very early draft, aimed at soliciting feedback, both
   on content and whether the goal of the draft is actually worthwhile.
   Different sites may have different requirements.  There may also be
   issues with handling scope boundaries that need to be considered.  So
   there may be general principles that could be captured in a document
   such as this, even if specific filtering rules are not included.

2.  Border and MSDP Filtering

   In this section we summarise IPv4 multicast addresses that are
   commonly filtered at site borders or on MSDP peerings.  Based on
   responses we received from a couple of multicast community lists, it
   wasn't clear which filters are applied on border routers and which on
   MSDP SA messages.  Some sites apply minimal traffic filters, but
   heavier MSDP filtering.

   Some sites choose to route multicast around their unicast firewalls,
   for performance or other operational reasons, but this shouldn't
   alter the requirement to filter groups appropriately where necessary.

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   In this section we draw on the small number contributions so far; we
   hope to get more inputs in time.  In general, many 224.0.0.*
   addresses that are used by infrastructure are typically blocked, as
   well as some addresses that are global scope but should not be, like
   Ghostcast.  Local scope multicast should also generally be
   constrained to the intended site scope.

   The following list currently includes multicast IP addresses that are
   being filtered based on the union of responses received so far (hence
   the apparent duplication of certain prefixes).  The list of filters
   applied by all respondents would be somewhat shorter.       SGI-Dogfight       Rwhod       SUN NIS+      any private experiment      SVRLOC      microsoft-ds      nbc-pro      SVRLOC-DA      cisco-rp-announce      cisco-rp-discovery      gatekeeper      hp-device-disc      iapp      IAPP       rwho       SUN RPC       EPSON-disc-set      Ricoh-device-ctrl      Ricoh-device-ctrl       ?   Norton Ghost ?       Altiris   ?  Norton Ghost  ? ImageCast       ImageCast       ImageCast       ImageCast       ImageCast      ImageCast      ImageCast      ImageCast ImageCast     Scoped groups

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Internet-Draft        Multicast Filtering Practices            July 2011  Scoped groups

   Different networks make different use of the scoped address space
   under, which may lead to different organisational filters
   in different scenarios.

   The SSM range should not be carried in MSDP peerings.

   As a general principle, multicast sourced from private address ranges
   [RFC1918] or from, or should
   be dropped, regardless of the multicast destination.

   In certain cases, rate limiting may be desirable, where complete
   filtering might not, e.g. in mitigating against SAP [RFC2974] storms,
   or against unintended MSDP SA bursts.

3.  Subnet filtering

   Two respondents are currently filtering uPNP between subnets, and one
   is filtering mDNS.  One reason for the uPNP filtering was due to
   issues with errant Ricoh printers which flood announcements with too-
   large TTLs.

4.  Conclusions

   This text is a very drafty first version of a document aimed to
   summarise the use of multicast filtering practices in the wild.  It
   includes filters at various boundaries as well as MSDP SA filters.
   Further feedback on the text, and the practices reported to date is

5.  Security Considerations

   There are no extra security consideration for this document.

6.  IANA Considerations

   There are no extra IANA consideration for this document.

7.  Acknowledgments

   The author would like to thank the following people for their
   contributions to this text: Scott Bertilson, Alan Buxey, Bruce

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   Curtis, Andy Gatward, Jeffry J. Handal, Lonnie Leger, and William F.
   Maton Sotomayor.

8.  Informative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
              Announcement Protocol", RFC 2974, October 2000.

   [RFC6034]  Thaler, D., "Unicast-Prefix-Based IPv4 Multicast
              Addresses", RFC 6034, October 2010.

              Price, D., "IPv4 Multicast on JANET", 2006, <http://

              "IPv6 Multicast Address Space Registry", <http://

              "IPv4 Multicast Address Space Registry", <http://

              "Enabling IP Multicast with Internet2", <http://

Author's Address

   Tim Chown
   University of Southampton
   Southampton, Hampshire  SO17 1BJ
   United Kingdom

   Email: tjc@ecs.soton.ac.uk

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