IPv6 Working Group                                             J-S. Park
INTERNET DRAFT                                                      ETRI
Expires: June 2005                                             M-K. Shin
                                                                H-J. Kim
                                                           December 2004

                  Link Scoped IPv6 Multicast Addresses

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,
     and any of which I become aware will be disclosed, in accordance
     with RFC 3668.

     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups.  Note that
     other groups June may also distribute working documents as Internet-

     Internet-Drafts are draft documents valid for a maximum of six
     months and June may be updated, replaced, or obsoleted by other docu-
     ments at any time.  It is inappropriate to use Internet-Drafts as
     reference material or to cite them other than as "work in pro-

     The list of current Internet-Drafts can be accessed at

     The list of Internet-Draft Shadow Directories can be accessed at

     This Internet-Draft will expire on June 2005.


     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
     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 ....................................................3
     5. Consideration of Lifetime ..................................4 ..................................3
     6. Security Considerations.....................................4
     7. Acknowledgments.............................................4
     8. References..................................................5 References..................................................4
     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].  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", "June", "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.  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
     information in the
     link-local scope multicast addresses.  The idea of delegating
     multicast addresses can be applicable to link-local scope.

     Figure 1 illustrates the new format for link scoped multicast

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

           Figure 1: Link scoped multicast IPv6 address format

     flgs MUST be "0011".  (The first two bits set to zero by the
     sending node 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].  But, the users can choose whichever they
     wish and deem appropriate.

     The reserved field MUST be zero.

     LSM field MUST be "1111 1111" which maps to the plen field in [RFC
     3306], whereas the plen field in [RFC 3306] MUST NOT be greater
     than 64.

     That is, flgs,

     Flgs, scop, and plen fields are used to identify whether an address
     is a multicast address as specified in this document. 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.  And
     this  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 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 June may also be
     set on the basis of the guidelines outlined in [RFC 3307].

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 and as a powered
     node.  The

     This is a scenario where DAD also fails to guarantee the uniqueness
     of the unicast address, so this document does not consider this case at this phase.  It
     is another challenging issue and out of scope of try to address
     this document. 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 for an IID and to how to configure the
     global-scope IID of non-link-
     local scope unicast addresses.  The privacy extension method in
     [RFC 3041] is triggered when a host receives a router advertisement
     with a prefix information option carrying a global-scope prefix for
     the purpose of address auto-configuration.  That is,  [RFC 3041] can not be used for
     making a link-local unicast address.  Since the address, and hence it cannot be used to
     create an IID
     embedded in the link scoped for link-scoped multicast address MUST only come from address. However, as [RFC
     3041] does not protect the IID privacy of the link-local unicast address on the interface after
     DAD has completed, the secure IID, generated by [RFC 3041], can addresses,
     it does not
     be used for consisting protect the privacy of a link scoped multicast address.  But, link-local unicast addresses, it
     is possible
     does not seem to use secure IID for expanding be required to protect the intensity of
     security regardless of a difficulty of acquisition privacy of IID-based
     link-local multicast
     server 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.

8. References


       [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.


       [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
       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

Intellectual Property Statement

     The IETF takes no position regarding the validity or scope of any
     Intellectual Property Rights or other rights that might be claimed
     to pertain to the implementation or use of the technology described
     in this document or the extent to which any license under such
     rights might or might not be available; nor does it represent that
     it has made any independent effort to identify any such rights.
     Information on the procedures with respect to rights in RFC
     documents can be found in BCP 78 and BCP 79.

     Copies of IPR disclosures made to the IETF Secretariat and any
     assurances of licenses to be made available, or the result of an
     attempt made to obtain a general license or permission for the use
     of such proprietary rights by implementers or users of this
     specification can be obtained from the IETF on-line IPR repository
     at http://www.ietf.org/ipr.

     The IETF invites any interested party to bring to its attention any
     copyrights, patents or patent applications, or other proprietary
     rights that June may cover technology that June may be required to implement
     this standard.  Please address the information to the IETF at

Disclaimer of Validity

     This document and the information contained herein are provided on

Copyright Statement

     Copyright (C) The Internet Society (2004).  This document is
     subject to the rights, licenses and restrictions contained in BCP
     78, and except as set forth therein, the authors retain all their


     Funding for the RFC Editor function is currently provided by the
     Internet Society.