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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 4489

IPv6 Working Group                                             J-S. Park
INTERNET DRAFT                                                      ETRI
Expires: January 18, 2006                                      M-K. Shin
Updates: 3306                                                       ETRI
                                                                H-J. Kim
                                                                    ETRI
                                                           July 17, 2005

      A Method for Generating Link Scoped IPv6 Multicast Addresses
               <draft-ietf-ipv6-link-scoped-mcast-09.txt>


Status of this Memo

     By submitting this Internet-Draft, each author represents that any
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     This Internet-Draft will expire on January 18, 2006.


Copyright Notice

     Copyright (C) The Internet Society (2005).


Abstract

     This document specifies an extension to the multicast addressing
     architecture of the IPv6 protocol. The extension allows for the use
     of Interface Identifiers (IIDs) to allocate multicast addresses.
     When a link-local unicast address is configured at each interface
     of a node, an IID is uniquely determined.  After that, each node
     can generate their unique multicast addresses automatically without




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     conflicts.  Basically, this document proposes an alternative method
     for creating link-local multicast addresses over a known method
     like unicast-prefix-based IPv6 multicast addresses. It is preferred
     to use this method for link-local scope rather than unicast-
     prefix-based IPv6 multicast addresses.  This memo update RFC3306.


Table of Contents:

     1. Introduction................................................2
     2. Applicability...............................................2
     3. Link Scoped Multicast Address Format........................3
     4. Example ....................................................4
     5. Consideration of Lifetime ..................................4
     6. Security Considerations.....................................4
     7. Acknowledgments.............................................4
     8. References..................................................5
     Author's Addresses.............................................5


1. Introduction

     This document 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 IIDs to allocate
     multicast addresses.  When a link-local unicast address is
     configured at each interface of a node, an IID is uniquely
     determined.  After that, each node can generate their unique
     multicast addresses automatically without conflicts.  That is,
     these addresses could safely be configured at any time after DAD
     (Duplicate Address Detection) has completed.

     Basically, it is preferred to use this method for the link-local
     scope rather than unicast-prefix-based IPv6 multicast addresses
     [RFC 3306], since by delegating multicast addresses using the IID,
     each node can generate its multicast addresses automatically
     without allocation servers.  This method goes well with
     applications in serverless environment such as ad-hoc and network
     mobility rather thant unicast-prefix-based method.  This document
     restricts the usage of defined fields such as scop, plen and
     network prefix fields of [RFC 3306].  Therefore, this document
     specifies encoded information for link-local scope in 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





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     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.  Also, hosts which are
     supplied multicast services from multicast servers then make
     multicast addresses of multicast servers using ND (address
     resolution) and well-known group IDs.

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


3. Link Scoped Multicast Address Format

     This document specifies a new format that incorporates IID in the
     link-local scope multicast addresses.

     Figure 1 illustrates the new format for link scoped multicast
     addresses.

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

           Figure 1: Link scoped multicast IPv6 address format

     Flgs, scop, and plen fields are used to identify whether an address
     is a multicast address as specified in this document as follows:
      1. flgs MUST be "0011".
      2. scop MUST be <= 2.
      3. The reserved field MUST be zero.
      4. "plen" field is a special value "1111 1111" (decimal 255).

     The IID field (replacing the 64-bit prefix field from [RFC 3306])
     is used to distinguish each node from others.  Given the use of
     this method for link-local scope, the IID embedded in the multicast
     address MUST only come from the IID of the link-local unicast
     address on the interface after DAD has completed.  That is, the
     creation of the multicast address MUST only occur after DAD has
     completed as part of the auto-configuration process.

     Group ID is generated to indicate a 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].






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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. Consideration of Lifetime

     Generally, Link scoped multicast addresses have no lifetime because
     link-local unicast addresses also have no lifetime.  But, it is not
     true in environment of mobile.  Even though multicast addresses are
     created from the unique IID of unicast address, their useful
     lifetime is linked to the period during which the IID is known to
     be unique.  Thus, it is possible to conflict between IIDs, due to a
     new node in merged network that uses the same IID as a powered
     node.

     This is a scenario where DAD also fails to guarantee the uniqueness
     of the unicast address, so this document does not try to address
     this issue.


6. Security Considerations

     The uniqueness of multicast addresses using this method is
     guaranteed by the DAD process.  So, it is needed to get a secure
     DAD process for stability of this method.  This document proposes
     the mechanism in [RFC 3041] for this purpose.

     [RFC 3041] describes the privacy extension to IPv6 stateless
     address autoconfiguration to how to configure the IID of non-link-
     local scope unicast addresses.  [RFC 3041] can not be used for
     making a link-local unicast address, and hence it cannot be used to
     create an IID for link-scoped multicast address. However, as [RFC
     3041] does not protect the privacy of link-local unicast addresses,
     it does not protect the privacy of link-local unicast addresses, it
     does not seem to be required to protect the privacy of IID-based
     link-local multicast addresses.


7. Acknowledgements

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








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8. References

      Normative

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

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

       [RFC 3041] T. Narten and R. Draves, "Privacy Extensions for
                  Stateless Address Autoconfiguration in IPv6,"
                  RFC 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 3956] P. Savola and B. Haberman, "Embedding the Rendezvous
                  Point (RP) Address in an IPv6 Multicast Address

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




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       Phone: +82 42 860 6576
       Email: khj@etri.re.kr






















































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