Network Working Group                                          D. Thaler
Internet-Draft                                                 Microsoft
Expires: January 27, 2008                                  July 26, 2007


             Unicast-Prefix-based IPv4 Multicast Addresses
             draft-ietf-mboned-ipv4-uni-based-mcast-04.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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.

   This Internet-Draft will expire on January 27, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This specification defines an extension to the multicast addressing
   architecture of the IP Version 4 protocol.  The extension presented
   in this document allows for unicast-prefix-based allocation of
   multicast addresses.  By delegating multicast addresses at the same
   time as unicast prefixes, network operators will be able to identify
   their multicast addresses without needing to run an inter-domain
   allocation protocol.





Thaler                  Expires January 27, 2008                [Page 1]

 
Internet-Draft       Uni-Prefix-based IPv4 Multicast           July 2007


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Address Space . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Informative References  . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Intellectual Property and Copyright Statements  . . . . . . . . . . 6










































Thaler                  Expires January 27, 2008                [Page 2]

 
Internet-Draft       Uni-Prefix-based IPv4 Multicast           July 2007


.  Introduction

   RFC 3180 [RFC3180] defined an experimental allocation mechanism
   (called "GLOP") in 233/8 whereby an Autonomous System (AS) number is
   embedded in the middle 16 bits of an IPv4 multicast address,
   resulting in 256 multicast addresses per AS.  Advantages of this
   mechanism include the ability to get multicast address space without
   an inter-domain multicast address allocation protocol, and the ease
   of determining the AS of the owner of an address for debugging and
   auditing purposes.

   Some disadvantages of GLOP include:
   o  RFC 4893 [RFC4893] expands the size of an AS number to 4 bytes,
      and GLOP cannot work with 4-byte AS numbers.
   o  When an AS covers multiple sites or organizations, administration
      of the multicast address space within an AS must be handled by
      other mechanisms, such as manual administrative effort or MADCAP
      [RFC2730].
   o  During debugging, identifying the AS does not immediately identify
      the owning organization when an AS covers multiple organizations.
   o  Only 256 addresses are automatically available per AS, and
      obtaining any more requires administrative effort.

   More recently, a mechanism [RFC3306] has been developed for IPv6 that
   provides a multicast range to every IPv6 subnet, which is at a much
   finer granularity than an AS.  As a result, the first three
   disadvantages above are avoided (and the last disadvantage does not
   apply to IPv6 due to the extended size of the address space).

   Another advantage of providing multicast space to a subnet, rather
   than just to an entire AS, is that multicast address allocation
   within the range need only be coordinated within the subnet.

   This draft specifies a mechanism similar to [RFC3306], whereby a
   range of IPv4 multicast address space is provided to each
   organization that has unicast address space.  A resulting advantage
   over GLOP is that the mechanisms in IPv4 and IPv6 become more
   similar.

   This document proposes an experimental method of statically
   allocating multicast address ranges with global scope.  As described
   in section Section 4, this experiment will last for a period of one
   year, but may be extended.


.  Address Space

   (RFC-editor: replace TBD below with IANA-assigned value, and delete



Thaler                  Expires January 27, 2008                [Page 3]

 
Internet-Draft       Uni-Prefix-based IPv4 Multicast           July 2007


   this note.)

   A multicast address with the prefix TBD/8 indicates that the address
   is a Unicast-Based Multicast (UBM) address.  The remaining 24 bits
   are used as follows:

   Bits:  |  8  | Unicast Prefix Length | 24 - Unicast Prefix Length |
          +-----+-----------------------+----------------------------+
   Value: | TBD | Unicast Prefix        | Group ID                   |
          +-----+-----------------------+----------------------------+

   For organizations with a /24 or shorter prefix, the unicast prefix of
   the organization is appended to the common /8.  Any remaining bits
   may be assigned by any mechanism the organization wishes.  For
   example, an organization that has a subnet with a /24 or shorter
   prefix assigned to a link may wish to embed the entire subnet prefix
   within the multicast address, with the remaining bits assigned by
   hosts within the link (e.g., using manual configuration).
   Organizations with a prefix length longer than 24 do not receive any
   multicast address space from this mechanism; in such cases, another
   mechanism must be used.

   Compared to GLOP, an AS will receive more address space via this
   mechanism if it has more than a /16 for unicast space.  An AS will
   receive less address space than it does from GLOP if it has less than
   a /16.

   The owner of a UBM address can be determined by taking the multicast
   address, shifting it left by 8 bits, and identifying the owner of the
   address space covering the resulting unicast address.


.  Security Considerations

   The same well known intra-domain security techniques can be applied
   as with GLOP.  Furthermore, when dynamic allocation is used within a
   prefix, the approach described here may have the effect of reduced
   exposure to denial of space attacks, since the topological area
   within which nodes compete for addresses within the same prefix is
   reduced from an entire AS to only within an individual organization
   or an even smaller area.


.  IANA Considerations

   IANA should assign a /8 in the IPv4 multicast address space for this
   purpose.




Thaler                  Expires January 27, 2008                [Page 4]

 
Internet-Draft       Uni-Prefix-based IPv4 Multicast           July 2007


   This assignment should time out one year after the assignment is
   made.  The assignment may be renewed at that time.


.  Informative References

   [RFC2730]  Hanna, S., Patel, B., and M. Shah, "Multicast Address
              Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
              December 1999.

   [RFC3180]  Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8",
              BCP 53, RFC 3180, September 2001.

   [RFC3306]  Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
              Multicast Addresses", RFC 3306, August 2002.

   [RFC4893]  Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
              Number Space", RFC 4893, May 2007.


Author's Address

   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   USA

   Phone: +1 425 703 8835
   Email: dthaler@microsoft.com





















Thaler                  Expires January 27, 2008                [Page 5]

 
Internet-Draft       Uni-Prefix-based IPv4 Multicast           July 2007


Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   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 rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   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 may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Thaler                  Expires January 27, 2008                [Page 6]