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Versions: 00 01 02 03 04 rfc3307                                        
   MALLOC Working Group                                         B. Haberman
   Internet Draft                                           Nortel Networks
   draft-ietf-malloc-ipv6-guide-00.txt
   May 2000
   Expires November 2000


                     Dynamic Allocation Guidelines
                      for IPv6 Multicast Addresses


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [RFC 2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


Abstract

   With the current multicast address architecture and the proposed
   multicast address architecture, a set of guidelines is needed for
   multicast address allocation servers to use in assigning IPv6
   multicast addresses.  The purpose of these rules is to reduce the
   possibility of address collision not only at layer 3, but also on
   devices at layer 2.


1. Terminology

   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. Introduction




Haberman                                                             1



Internet Draft   IPv6 Multicast Address Architecture          May 2000

   With the current multicast address architecture [RFC 2373] and the
   multicast address architecture proposed in [NEW ARCH], a set of
   guidelines is needed for multicast address allocation servers
   [MALLOC] to use in assigning IPv6 multicast addresses.  The purpose
   of these rules is to reduce the possibility of address collision not
   only at layer 3, but also on devices at layer 2.

   These guidelines specify how the lowest 32 bits of the IPv6
   multicast address are chosen and assigned.  The guidelines specify
   several mechanisms that can be used to determine the lowest 32 bits
   of the multicast address.  By having several mechanisms of varying
   complexity, implementers and operators have the flexibility to
   choose a mechanism that is appropriate for their application.

3. Assignment of New IPv6 Multicast Addresses

   The current approach [RFC 2464] to map IPv6 multicast addresses into
   IEEE 802 MAC addresses takes the low order 32 bits of the IPv6
   multicast address and uses it to create a MAC address.  Group ID's
   less than or equal to 32 bits long will generate unique MAC
   addresses.

   The goal of this document is to present several mechanisms
   implementers and operators can use to select the group ID portion of
   the address so that the possibility of collisions at the IP layer
   and at the IEEE 802 layer is reduced.  The following section
   presents several different mechanism of varying complexity that can
   be used to select an appropriate group ID.


4. Group ID Selection Guidelines

   The following guidelines assume that the upper 96 bits of the IPv6
   multicast address have been set up.  For unicast network prefix-
   based multicast addresses, the set up of those bits is done in the
   following manner:

           o  An IPv6 multicast address prefix is initialized with the
              appropriate flags and scope fields
           o  The IPv6 Network Prefix is inserted into the address and
              the plen field is set.  The Network Prefix is obtained
              from the periodic Router Advertisements.
           o  The reserved field in the IPv6 multicast address is set
              to zero

   With the multicast address architecture in [RFC 2373], the set up of
   those bits is done in the following manner:

           o  An IPv6 multicast address prefix is initialized with the
              appropriate flags and scope fields



Haberman                                                             2



Internet Draft   IPv6 Multicast Address Architecture          May 2000

           o  The reserved field in the IPv6 multicast address is set
              to zero

   The group ID portion of the address is set using either a pseudo-
   random 32-bit number or a 32-bit number created using the guidelines
   in [RFC 1750].  Possible approaches to creating a pseudo-random
   number are to use an MD5 message-digest [RFC 1321] or portions of an
   NTP [RFC 1305] timestamp.

   The assignment of the group ID portion of the address SHOULD take
   care to ensure that the generated multicast address does not share a
   group ID with a permanently assigned IPv6 multicast address.  The
   permanently assigned multicast addresses are defined in [RFC 2375].

   Requests for more than one multicast address SHOULD be handled
   atomically.  One possible approach is to use the initial group ID,
   created using the guidelines above, as the base address in a
   contiguous block of multicast addresses.  Another approach is to
   create multiple group IDs and generate the appropriate multicast
   addresses.


5. Multicast Address Lifetime

   The lifetime of the assignment of unicast prefix-based multicast
   addresses MUST be less than or equal to the Valid Lifetime field in
   the Prefix Information option contained in the Neighbor Discovery
   Router Advertisement message [RFC 2461].


6. Security Considerations

   This document does not have any direct impact on Internet
   infrastructure security.


7. References

   [RFC 2026] Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [NEW ARCH] Haberman, B., Thaler, D., "IP Version 6 Multicast
              Addressing Architecture",
              draft-ietf-ipngwg-mcast-arch-00.txt, April 2000.

   [RFC 2373] Hinden, R., Deering, S., "IP Version 6 Addressing
              Architecture", RFC 2373, July 1998.

   [MALLOC]   Thaler, D., Handley, M., and Estrin, D., "The Internet
              Multicast Address Allocation Architecture",
              draft-ietf-malloc-arch-04.txt, January 2000.


Haberman                                                             3



Internet Draft   IPv6 Multicast Address Architecture          May 2000


   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP14, March 1999.

   [RFC 2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC 1305] Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation", RFC 1305, March 1992.

   [RFC 1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC 1750] Eastlake, D., Crocker, S., Schiller, J., "Randomness
              Recommendations for Security", RFC 1750, December 1994.

   [RFC 2375] Hinden, R., Deering, S., "IPv6 Multicast Address
              Assignments", RFC 2375, July 1998.

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































Haberman                                                             4




Author's Address

   Brian Haberman
   Nortel Networks
   4309 Emperor Blvd.
   Suite 200
   Durham, NC  27703
   1-919-992-4439
   Email : haberman@nortelnetworks.com












































Haberman                                                             5