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IPv6 Working Group                                             J-S. Park
INTERNET DRAFT                                                      ETRI
Expires: February 2005                                         M-K. Shin
                                                               ETRI/NIST
                                                                H-J. Kim
                                                                    ETRI
                                                             August 2004

                  Link Scoped IPv6 Multicast Addresses
               <draft-ietf-ipv6-link-scoped-mcast-05.txt>


Status of this Memo

     By submitting this Internet-Draft, I certify that any applicable
     patent or other IPR claims of which I am aware have been disclosed,
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     with RFC 3668.

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     This Internet-Draft will expire on February 2005.


Abstract

     This document specifies an extension to the multicast addressing
     architecture of the IPv6 protocol. The extension allows for the use
     of interface-IDs to allocate multicast addresses.  When a link-
     local unicast address is configured at each interface of a node, an
     interface ID is uniquely determined.  By delegating multicast
     addresses at the same time as the interface ID, each node can
     generate their unique multicast addresses automatically without
     conflicts.  Basically, it is preferred to use this method for the
     link-local scope rather than unicast-prefix-based IPv6 multicast
     addresses [RFC 3306].





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Table of Contents:

     1. Introduction................................................2
     2. Applicability...............................................2
     3. Link scoped multicast address format........................2
     4. Example ....................................................4
     5. Considerations..............................................4
     6. Security Considerations.....................................4
     7. References..................................................4
     8. Acknowledgments.............................................4
     Authors' Addresses.............................................5



1. Introduction

     This specification defines an extension to the multicast portion of
     the IPv6 addressing architecture [RFC 3513].  The current
     architecture does not contain any built-in support for dynamic
     address allocation.  The extension allows for use of interface-IDs
     to allocate multicast addresses.  When a link-local unicast address
     is configured at each interface of a node, an interface ID is
     uniquely determined.  By delegating multicast addresses at the same
     time as the interface ID, each node can generate their unique
     multicast addresses automatically without conflicts.

     Basically, it is preferred to use this method for the link-local
     scope rather than unicast-prefix-based IPv6 multicast addresses
     [RFC 3306].  This document restricts the usage of defined fields
     such as scope, plen and network prefix fields of [RFC 3306].
     Therefore, this document specifies encoded information for link-
     local scope in the multicast addresses.

     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].


2. Applicability

     The allocation technique in this document is designed to be used in
     any environment in which link-local scope IPv6 multicast addresses
     are assigned or selected.  Especially, this method goes well with
     nodes supplying multicast services in a zeroconf/serverless
     environment.  For example, multicast addresses less than or equal
     to link-local scope are themselves generated by nodes supplying
     multicast services without conflicts.

     Consequently, this technique MUST be used for link scoped multicast
     addresses.  If you want to use multicast addresses greater than
     link-local scope, you need other methods such as [RFC 3306].





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3. Link scoped multicast address format

     [RFC 3306] defines the following format of unicast-prefix-based
     IPv6 multicast addresses:

      |   8    |  4 |  4 |   8    |    8   |       64       |    32    |
      +--------+----+----+--------+--------+----------------+----------+
      |11111111|flgs|scop|reserved|  plen  | network prefix | group ID |
      +--------+----+----+--------+--------+----------------+----------+

        Figure 1: Unicast-Prefix-based IPv6 multicast address format

     This document specifies a new format that incorporates interface ID
     information in the multicast addresses.  The idea of delegating
     multicast addresses at the same time as the interface ID can be
     applicable to link-local scope.

     Figure 2 illustrates the new format for link scoped multicast
     addresses.

      |   8    |  4 |  4 |   8    |    8   |       64       |    32    |
      +--------+----+----+--------+--------+----------------+----------+
      |11111111|flgs|scop|reserved|  LSM   |  Interface ID  | group ID |
      +--------+----+----+--------+--------+----------------+----------+

           Figure 2: Link scoped multicast IPv6 address format

     flgs MUST be "0011".  (The first two bits have been yet undefined,
     sent as zero and ignored on receipt.)  flgs MUST use the same flag
     defined in section 4 of [RFC 3306].

     scop MUST be <= 2. It is preferred to use this method for the link-
     local scope rather than unicast-prefix-based IPv6 multicast
     addresses [RFC 3306].

     The reserved field MUST be zero.

     LSM (Link Scoped Multicast) field MUST be "1111 1111" which maps to
     plen field in [RFC 3306], whereas the plen of [RFC 3306] MUST NOT
     be greater than 64.

     That is, flgs, scop, and LSM fields are used to identify whether an
     address is a multicast address as specified in this document and to
     be processed any further.

     Interface ID field is used to distinguish each node from others.
     And this value is obtained from the IEEE EUI-64 based interface
     identifier of the link-local unicast IPv6 address.  Given the use
     of this method for link-local scope, the interface ID embedded in
     the multicast address SHOULD come from the interface ID of the
     link-local unicast address on the interface after DAD has
     completed.  That is, the creation of the multicast address MUST




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     occur after DAD has completed as part of the auto-config process.

     Group ID is generated to indicate multicast application and is used
     to guarantee its uniqueness only in the host.  It may also be set
     on the basis of the guidelines outlined in [RFC 3307].

     The lifetime of link scoped multicast addresses has no dependency
     on the Valid Lifetime field in the Prefix Information option,
     corresponding to the unicast address being used, contained in the
     Router Advertisement message [RFC 2461].


4. Example

     This is an example of link scoped IPv6 multicast addresses.  For
     example in an ethernet environment, if the link-local unicast
     address is FE80::A12:34FF:FE56:7890, the link scoped multicast
     prefix of the node is FF32:00FF:A12:34FF:FE56:7890::/96.


5. Considerations

     The link scoped multicast address format supports source-specific
     multicast addresses by the same method, as defined by [RFC 3306].


6. Security Considerations

     [RFC 3041] describes the privacy extension to IPv6 stateless
     address autoconfiguration for an interface ID.  The interface ID,
     generated by [RFC 3041], is also used in this method since the
     uniqueness is verified by DAD procedure as part of the secure auto-
     config process.


7. Acknowledgements

     We would like to thank Dave Thaler and Brian Haberman for their
     comments related to the consistency between the unicast prefix-
     based multicast addresses [RFC 3306] and this one.  Special thanks
     are due to Erik Nordmark and Pekka Savola for valuable comments.


8. References

      Normative

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

       [RFC 3041] T. Narten and R. Draves, "Privacy Extensions for
                  Stateless Address Autoconfiguration in IPv6," RFC




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                  3041, April 2001.

       [RFC 3306] B. Haberman and D. Thaler, "Unicast-Prefix-based
                  IPv6 Multicast Addresses," RFC 3306, August 2002.

       [RFC 3307] B. Haberman, "Allocation Guidelines for IPv6
                  Multicast Addresses," RFC 3307, August 2002.

       [RFC 3513] R. Hinden and S. Deering, "IP Version 6 Addressing
                  Architecture," RFC 3513, April 2003.

      Informative

       [RFC 2461] T. Narten, E. Nordmark and W. Simpson, "Neighbor
                  Discovery for  IP Version 6 (IPv6)," RFC 2461,
                  December 1998.

       [SSM ARCH] H. Holbrook and B. Cain, "Source-Specific Multicast
                  for IP," Work In Progress, July 2004.



Authors' Addresses

       Jung-Soo Park
       ETRI PEC
       161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
       Phone: +82 42 860 6514
       Email: jspark@pec.etri.re.kr

       Myung-Ki Shin
       ETRI/NIST
       820 West Diamond Avenue
       Gaithersburg, MD 20899, USA
       Tel : +1 301 975-3613
       Fax : +1 301 590-0932
       E-mail : mshin@nist.gov

       Hyoung-Jun Kim
       ETRI PEC
       161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
       Phone: +82 42 860 6576
       Email: khj@etri.re.kr



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