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

                  Link Scoped IPv6 Multicast Addresses

Status of this Memo

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     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 then, that, each node
     can generate their unique multicast addresses automatically without
     conflicts.  Basically, it 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 the link-local scope rather than unicast-prefix-based unicast-
     prefix-based IPv6 multicast
     addresses [RFC 3306]. 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. Considerations..............................................4 Consideration of Lifetime ..................................4
     6. Security Considerations.....................................4
     7. References..................................................4 Acknowledgments.............................................4
     8. Acknowledgments.............................................5 References..................................................5
     Author's Addresses.............................................5

1. Introduction

     This specification 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 then, 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) is 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", "MAY", "June", 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, nodes hosts which are
     supplied multicast services, easily consist of services from multicast servers then make
     multicast addresses of multicast servers using NDP 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

     [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 IID
     information in the multicast addresses.  The idea of delegating
     multicast addresses can be applicable to link-local scope.

     Figure 2 1 illustrates the new format for link scoped multicast

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

           Figure 2: 1: Link scoped multicast IPv6 address format

     flgs MUST be "0011".  (The first two bits have been yet undefined,
     sent as set to zero by the
     sending node and ignored on receipt) flgs 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 (Link Scoped Multicast) 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, scop, and LSM plen fields are used to identify whether
     an address is a multicast address as specified in this document.

     The IID 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 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 June 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

     Since 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, 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 joining the in merged network that uses the same IID. IID and a powered
     node.  The document does not consider this case at this phase.  It
     is another challenging issue and out of scope of this document.

6. Security Considerations

     The link scoped multicast address format supports source-specific uniqueness of multicast addresses using this method is
     guaranteed by the same method, as defined by DAD process.  So, it is needed to get a secure
     DAD process for stability of this method.  This document proposes
     the mechanism in [RFC 3306].

6. Security Considerations 3041] for this purpose.

     [RFC 3041] describes the privacy extension to IPv6 stateless
     address autoconfiguration for an IID. IID and how to configure the
     global-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 IID
     embedded in the link scoped multicast address MUST only come from
     the IID of the link-local unicast address on the interface after
     DAD has completed, the secure IID, generated by [RFC 3041], can not
     be used for consisting of a link scoped multicast
     address since the uniqueness address.  But, it
     is verified by possible to use secure IID for expanding the DAD procedure as
     part intensity of the secure auto-configuration process.
     security regardless of a difficulty of acquisition of 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

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