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v6ops WG                                                   S. Gundavelli
Internet-Draft                                               M. Townsley
Intended status: Standards Track                                O. Troan
Expires: February 11, 2011                                        W. Dec
                                                                   Cisco
                                                         August 10, 2010


     Unicast Transmission of IPv6 Multicast Messages on Link-layer
                draft-gundavelli-v6ops-l2-unicast-02.txt

Abstract

   When transmitting an IPv6 packet to a multicast group, the
   destination address in the link-layer header is typically set to the
   corresponding mapped address of the destination address from the IP
   header.  However, it is not mandatory that the destination address in
   the link-layer header is always a mapped multicast equivalent of its
   IP destination address.  There are various deployment scenarios where
   there is an opportunity for the sender to transmit the message as an
   unicast message on the link-layer.  Unfortunately, the IPv6
   specifications do not clearly state this.  This document explicitly
   clarifies this point and makes such packet construct and transmission
   legal and valid.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on February 11, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal



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   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4

   3.  Sending and Receiving IPv6 Multicast Packets . . . . . . . . .  5

   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6

   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7

   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8

   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  9

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10






















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1.  Introduction

   This document is about a clarification to the construction and
   processing rules of IPv6 multicast messages [RFC2464].  When there
   are multiple link-layer receivers for an IP multicast message on a
   broadcast LAN, the link layer multicast address corresponding to the
   IP address is the one to be used.  However, if there is only one
   receiver and its link-layer address is known, as in some cases of
   sparse mode multicast or certain special cases, it is legal and
   correct to send the IP multicast to the unicast link-layer address of
   that system.  Senders therefore have that option, and receivers
   should not refuse the message on that basis.

   The function of the link-layer is purely for transmitting the frame
   to a peer or to a set of peers on a given media.  A received
   multicast message may have been transmitted as a unicast message on
   the link-layer.  The destination address in the link-layer header of
   that packet will be a unicast address, while the destination address
   in the IP header can be a multicast address.  It is inconsequential
   for the network layer protocols or the IP stack to go across the
   layers and check the semantics of message delivery.  Any such check
   is a violation of the principles of protocol layering and does not
   serve any purpose.  Unfortunately, [RFC4861] or [RFC2464] does not
   explicitly state this.  However, we have verified this on many open
   source and commercial IPv6 implementations on the behavior of the
   existing IPv6 stacks, firewalls and we could not find any
   implementation that drops IPv6 packets sent to a multicast
   destination address in the IP header, but with a unicast destination
   address in the link-layer header.

   As a result of this analysis, it appears to be quite safe to
   explicitly state that such message construct is valid, so future
   implementations do not drop packets based on these checks.  Section
   3.0 of this document defines the additional normative considerations
   for IPv6 sender and receiver nodes for allowing this mode of packet
   transmission.















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2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].














































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3.  Sending and Receiving IPv6 Multicast Packets

   The following additional considerations MUST be applied by all IPv6
   nodes when sending and receiving IPv6 multicast messages.

   o  An IPv6 receiver node SHOULD NOT drop a received IPv6 multicast
      message containing a multicast destination address in the IPv6
      header, but with a unicast destination address in the link-layer
      header, withstanding all other validity considerations as
      specified in the relevant IPv6 standards specifications.

   o  An IPv6 sender node in some special cases and specifically when
      the link-layer address of the target node is known, MAY choose to
      transmit an IPv6 multicast message as a link-layer unicast message
      to that node.  In this case, the destination address in the IPv6
      header will be a multicast group address, but the destination
      address in the link-layer header will be an unicast address.


































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4.  IANA Considerations

   This specification does not require any IANA actions.
















































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5.  Security Considerations

   This document is about a clarification to the construction and
   processing rules of IPv6 multicast messages.  This clarification
   makes it legal for an IPv6 sender node to transmit a layer-3
   multicast message to the unicast link-layer address of the target
   node.  This change does not introduce any security vulnerabilities.

   Network firewalls and Deep Packet inspection tools that perform any
   such improper checks matching the destination address types in IP
   header and link-layers have to modified to allow such packet
   transmission.  However, the authors of this document could not find a
   single such implementation that drops IP packets based on this check.






































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6.  Acknowledgements

   The authors would like to acknowledge Stig Venaas, Fred Baker, Dave
   Thaler, Phil Roberts, Mark Smith, Hemant Singh, Wes Beebee, Olaf
   Bonness, Suresh Krishnan, Behcet Sarikaya, Eric Levy, Pascal Thubert
   and Eric Voit for all the discussions on this topic.













































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7.  References

7.1.  Normative References

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

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

7.2.  Informative References

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.




































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Authors' Addresses

   Sri Gundavelli
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sgundave@cisco.com


   Mark Townsley
   Cisco
   L'Atlantis, 11, Rue Camille Desmoulins
   ISSY LES MOULINEAUX, ILE DE FRANCE  92782
   France

   Email: townsley@cisco.com


   Ole Troan
   Cisco
   Skoyen Atrium, Drammensveien 145A
   Oslo,   N-0277
   Norway

   Email: otroan@cisco.com


   Wojciech Dec
   Cisco
   Haarlerbergweg 13-19
   Amsterdam, Noord-Holland  1101 CH
   Netherlands

   Email: wdec@cisco.com















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