Network Working Group Dave Thaler Internet-Draft Microsoft Expires:
December 2002 29 June 2002July 2004 19 January 2004 Unicast-Prefix-based IPv4 Multicast Addresses <draft-ietf-mboned-ipv4-uni-based-mcast-00.txt><draft-ietf-mboned-ipv4-uni-based-mcast-01.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Copyright Notice Copyright (C) The Internet Society (2002).(2004). All Rights Reserved. Abstract Draft Uni-Prefix-based IPv4 Multicast June 2002January 2004 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. 1. Introduction RFC 2770 [GLOP] defined an experimental allocation mechanism 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 only 256 addresses are automatically available per AS, and obtaining any more requires administrative effort. o there is work in progress [AS4B] on expanding the size of an AS number to 4 bytes, and GLOP cannot work with such AS's. 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 [MADCAP]. o during debugging, identifying the AS does not immediately identify the owning organization, when an AS covers multiple organizations. More recently, a mechanism [V6UPBM] has been developed for IPv6 which provides a multicast range to every IPv6 subnet, which is at a much finer granularity than an AS. As a result, the latter three disadvantages above are avoided (and the first disadvantage does not apply to IPv6 due to the extended size of the address space). Two significant advantages of providing multicast space to every Draft Uni-Prefix-based IPv4 Multicast June 2002January 2004 subnet (rather than just to an entire AS) are that: o multicast address allocation within the range need only be coordinated within the subnet (e.g., via ZMAAP [ZMAAP]),subnet, and hence can be done with zero configuration. o bidirectional shared tree routing protocols may easily locate the direction to the root by doing a route lookup on a unicast address derived from the multicast group address. This draft specifies a mechanism similar to [V6UPBM], whereby a range of IPv4 multicast address space is provided to most IPv4 subnets. A resulting advantage over GLOP is that the mechanisms in IPv4 and IPv6 become more similar. 2. Address Space IANA should assign a /8 for(RFC-editor: replace TBD below with IANA-assigned value, and delete this note.) A multicast address with the prefix TBD/8 indicates that the address is a Unicast-Based Multicast (UBM) mechanism (e.g., the 225/8 which was previously leased to MASC).address. The remaining 24 bits willcan be used as follows: Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | +-----+-----------------------+----------------------------+ Value: | 225TBD | Unicast Prefix | Group ID | +-----+-----------------------+----------------------------+ For subnets with a /24 or shorter prefix, the unicast prefix of the subnet is appended to the common /8. Any remaining bits may be locally assigned by hosts within the link (e.g., using manual configuration, or ZMAAP).configuration). Individual subnets with a prefix length longer than 24 do not receive any multicast address space from this mechanism; in such cases, MADCAP may 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. Draft Uni-Prefix-based IPv4 Multicast June 2002January 2004 3. IANA Considerations IANA should assign a /8 in the IPv4 multicast address space for this purpose. 4. Security Considerations Since dynamic assignment does not cross domain boundaries, the same well known intra-domain security techniques can be applied as with GLOP. Furthermore, the approach described here may have the effect of reduced exposure to denial of space attacks based on dynamic allocation, since the area of dynamic allocation is reduced from an entire AS to only within individual subnets. 4.5. Author's Address Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 Phone: +1 425 703 8835 EMail: firstname.lastname@example.org 5.6. Informative References [AS4B] Vohra, Q.,Q. and E. Chen, "BGP support for four-octet AS number space", draft-ietf-idr-as4bytes-05.txt,draft-ietf-idr-as4bytes-07.txt, Work in progress, May 2002.August 2003. [GLOP] Meyer, D.,D. and P. Lothberg, "GLOP Addressing in 233/8", RFC 2770, February 2000. [MADCAP] Hanna, S, Patel, B.,B. and M. Shah, "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, December 1999. [V6UPBM] Haberman, B.,B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", draft-ietf-ipngwg-uni-based- mcast-03.txt, October 2001. [ZMAAP] Catrina, O., Thaler, D., Aboba, B., and E. Guttman, "Zeroconf Multicast Address Allocation Protocol (ZMAAP)", draft-ietf- zeroconf-zmaap-02.txt, October 2001.RFC 3306, August 2002. Draft Uni-Prefix-based IPv4 Multicast June 2002 6.January 2004 7. Full Copyright Statement Copyright (C) The Internet Society (2002).(2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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.