Network Working Group Dave Thaler Internet-Draft Microsoft Expires:
July 2004 19 JanuaryApril 2005 October 18, 2004 Unicast-Prefix-based IPv4 Multicast Addresses <draft-ietf-mboned-ipv4-uni-based-mcast-01.txt><draft-ietf-mboned-ipv4-uni-based-mcast-02.txt> Status of this Memo This document is an Internet-DraftBy submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and isany of which I become aware will be disclosed, in full conformanceaccordance with all provisions of Section 10 of RFC2026.RFC 3668. 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 (2004). All Rights Reserved. AbstractDraft Uni-Prefix-based IPv4 Multicast JanuaryOctober 2004 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. 1. Introduction RFC 27703180 [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. othere 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. o only 256 addresses are automatically available per AS, and obtaining any more requires administrative effort. 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 latterfirst three disadvantages above are avoided (and the firstlast disadvantage does not apply to IPv6 due to the extended size of the address space). Two significant advantagesDraft Uni-Prefix-based IPv4 Multicast October 2004 Another advantage of providing multicast space to every Draft Uni-Prefix-based IPv4 Multicast January 2004subnet (rather than just to an entire AS) are that: ois that multicast address allocation within the range need only be coordinated within the 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.subnet. 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. This document proposes an experimental method of statically allocating multicast addresses with global scope. As described in section 4, this experiment will last for a period of one year, but may be extended. 2. Address Space (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) address. The remaining 24 bits can be used as follows: Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | +-----+-----------------------+----------------------------+ Value: | TBD | 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). 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 JanuaryOctober 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, theThe 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 based on dynamic allocation,attacks, since the topological area of dynamic allocationwithin which nodes compete for addresses within the same prefix is reduced from an entire AS to only within an individual subnets.subnet. 4. IANA Considerations IANA should assign a /8 in the IPv4 multicast address space for this purpose. This assignment should timeout one year after the assignment is made. The assignment may be renewed at that time. 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 6. Informative References [AS4B] Vohra, Q. and E. Chen, "BGP support for four-octet AS number space", draft-ietf-idr-as4bytes-07.txt,draft-ietf-idr-as4bytes-08.txt, Work in progress, August 2003.March 2004. [GLOP] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC 2770, February 2000.3180, September 2001. [MADCAP] Hanna, S, Patel, B. and M. Shah, "Multicast Address Dynamic Client Allocation Protocol (MADCAP)", RFC 2730, December 1999. Draft Uni-Prefix-based IPv4 Multicast October 2004 [V6UPBM] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. Draft Uni-Prefix-based IPv4 Multicast January 20047. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved.This document and translations of it may be copied and furnishedis subject 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 thatthe above copyright noticerights, licenses and this paragraph are included on all such copies and derivative works. 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