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

                  Link Scoped IPv6 Multicast Addresses
               <draft-ietf-ipv6-link-scoped-mcast-04.txt>
               <draft-ietf-ipv6-link-scoped-mcast-05.txt>

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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 the a link-
     local unicast address is configured at each interface of a host, node, an
     interface ID is uniquely determined.  By delegating multicast
     addresses at the same time as the interface ID, each host node can
     identify
     generate their unique multicast addresses automatically at Layer 1 without
     running an intra- or inter-domain allocation protocol in serverless
     environments.
     conflicts.  Basically, it is preferred to use this method for the
     link-local scope rather than Unicast-Prefix-based unicast-prefix-based IPv6 Multicast
     Addresses multicast
     addresses [RFC 3306].

Table of Contents:

     1. Introduction................................................2
     2. Applicability...............................................3 Applicability...............................................2
     3. Link scoped multicast address format........................3 format........................2
     4. Examples....................................................4 Example ....................................................4
     5. Considerations..............................................4
     6. Security Considerations.....................................5 Considerations.....................................4
     7. Acknowledgments.............................................5 References..................................................4
     8. References..................................................5 Acknowledgments.............................................4
     Authors' Addresses.............................................6 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 the a link-local unicast address
     is configured at each interface of a host, node, an interface ID is
     uniquely determined.  By delegating multicast addresses at the same
     time as the interface ID, each host node can identify its generate their unique
     multicast addresses automatically without running an intra- or inter-domain
     allocation protocol in serverless environments.

     The current multicast address allocation architecture [RFC 2908] is
     based on a multi-layered, multi-protocol system.  The goal of this
     proposal is to reduce the number of protocols and servers to get
     dynamic multicast address allocation.

     The use of interface ID-based multicast address allocation will, at
     a minimum, remove the need to run the Multicast Address-Set Claim
     (MASC) Protocol [RFC 2909] and the Multicast Address Allocation
     servers [RFC 2908]. conflicts.

     Basically, it is preferred to use this method for the link-local
     scope rather than Unicast-Prefix-based unicast-prefix-based IPv6 Multicast Addresses multicast addresses
     [RFC 3306].  This document restricts the usage of defined fields
     such as scope, plen and network prefix field in 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 zeroconf/serverless
     environment.  For example, multicast addresses less than or equal
     to link-local scope are themselves generated by nodes supplying
     multicast services. 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,
     link-local scope, you need other methods such as [RFC 3306].

3. Link scoped multicast address format

     Section 2.7 of [EFC 3513]

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

      |   8    |  4 |  4 |                     112   8    |    8   |       64       |    32    |
      +--------+----+----+--------+--------+----------------+----------+
      |11111111|flgs|scop|reserved|  plen  | network prefix |
      +--------+----+----+---------------------------------------------+
      |11111111|flgs|scop| group ID |
      +--------+----+----+---------------------------------------------+
      +--------+----+----+--------+--------+----------------+----------+

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

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

     Figure 2 illustrates the new format for link scoped multicast
     addresses.  That is, if the scope of the multicast address is link-
     local scope, it is this format.

      |   8    |  4 |  4 |     16   8    |    8   |       64       |    32    |
      +--------+----+----+------------+----------------+---------------+
      |11111111|flgs|scop|  reserved
      +--------+----+----+--------+--------+----------------+----------+
      |11111111|flgs|scop|reserved|  LSM   |  Interface ID  | group ID |
      +--------+----+----+------------+----------------+---------------+
      +--------+----+----+--------+--------+----------------+----------+

           Figure 2: link Link scoped multicast IPv6 address format

                                      +-+-+-+-+

     flgs is a set of 4 flags:       |0|0|P|T|
                                      +-+-+-+-+

          o P = 0 indicates a multicast address that is not assigned
                  on the basis of the interface ID.
          o P = 1 indicates a multicast address that is assigned
                  on the basis of the interface ID.
          o If P = 1, T MUST be set to 1, otherwise the setting of
                  the T bit is defined in Section 2.7 of [RFC 2373]. "0011".  (The first two bits have been yet undefined,
     sent as zero and ignored on receipt.)  flgs should MUST use the same flag
     defined in section 4 of [RFC 3306].
     That is, this document proposes the third bit of 'flgs' field to
     indicate an Interface ID-based multicast addresses.

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

     The reserved field MUST be zero zero.

     LSM (Link Scoped Multicast) field MUST be "1111 1111" which maps to a
     plen field in [RFC 3306], whereas the plen of zero [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 RFC
     3306. this document and to
     be processed any further.

     Interface ID field is used to distinguish each host 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
     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 an Interface ID-based link scoped multicast address 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. Examples Example

     This is an example of an interface ID-based link scoped IPv6 multicast address with
     link-local scope. addresses.  For
     example in an Ethernet ethernet environment, if the link-local unicast
     address is FE80::a12:34ff:fe56:7890, FE80::A12:34FF:FE56:7890, the link scoped multicast
     prefix of the host node is FF32:0:a12:34ff:fe56:7890::/96. FF32:00FF:A12:34FF:FE56:7890::/96.

5. Considerations

     It is preferred to use this method for scop <= 2 rather than
     Unicast-Prefix-based IPv6 Multicast Addresses [RFC 3306].  This
     document considers only link scoped multicast addresses.  For this
     purpose, scop field is used shown in figure 2.

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

     Note that if an SSM implementation checks for FF3x::/32, not
     FF3x::/96, the other nodes not implementing this specification will
     interpret the link-local multicast addresses generated using this
     specification as SSM addresses, since the document uses the
     reserved field in such a fashion that plen=0 [RFC 3306].  In order
     to avoid this conflict, we recommend SSM implementations must check
     for FF3x::/96, as described in Allocation Guidelines for IPv6
     Multicast Addresses [RFC 3307] section 3.

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.

     Using source-specific multicast addresses can sometimes aid in the
     prevention of denial-of-service attacks by arbitrary sources,
     although no guarantee is provided.  A more in-depth discussion of
     the security considerations for SSM can be found in [SSM ARCH].

7. Acknowledgements

     We would like to thank Dave Thaler and Brian Haberman for his their
     comments related to the consistency between the unicast prefix-
     based multicast draft 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
                  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",
                  Architecture," RFC 3513, April 2003.

      Informative

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

 [RFC 2908] D. Thaler, M. Handley and D. Estrin, "The Internet
            Multicast  Address Allocation Architecture," RFC 2908,
             September 2000.

 [RFC 2909] P. Radoslavov, D. Estrin, R. Govindan, M. Handley,
            S. Kumar, and D. Thaler, "The Multicast Address-Set Claim
            (MASC) Protocol", RFC 2909, September 2000.

       [SSM ARCH] H. Holbrook and B. Cain, "Source-Specific Multicast
                  for
            IP", IP," Work In Progress, October 2003. July 2004.

Authors' Addresses

       Jung-Soo Park
       ETRI PEC
       161 Gajeong-Dong, Yuseong-Gu, Daejon 305-600, 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, Daejon 305-600, Daejeon 305-350, Korea
       Phone: +82 42 860 6576
       Email: khj@etri.re.kr

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