Network Working Group D. Thaler Internet-Draft Microsoft Expires:
September 5, 2007 March 4,January 27, 2008 July 26, 2007 Unicast-Prefix-based IPv4 Multicast Addresses draft-ietf-mboned-ipv4-uni-based-mcast-03.txtdraft-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 September 5, 2007.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. 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 1. 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 there is work in progress [AS4B] on expandingRFC 4893 [RFC4893] expands the size of an AS number to 4 bytes, and GLOP cannot work with such AS's.4-byte AS numbers. o whenWhen 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 duringDuring debugging, identifying the AS does not immediately identify the owning organization,organization when an AS covers multiple organizations. o onlyOnly 256 addresses are automatically available per AS, and obtaining any more requires administrative effort. More recently, a mechanism [RFC3306] has been developed for IPv6 whichthat 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 every subnet (rathera subnet, rather than just to an entire AS)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 most IPv4 subnets.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 addressesaddress ranges with global scope. As described in section 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 beare used as follows: Bits: | 8 | Unicast Prefix Length | 24 - Unicast Prefix Length | +-----+-----------------------+----------------------------+ Value: | TBD | Unicast Prefix | Group ID | +-----+-----------------------+----------------------------+ For subnetsorganizations with a /24 or shorter prefix, the unicast prefix of the subnetorganization is appended to the common /8. Any remaining bits may be locallyassigned 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). Individual subnetsOrganizations 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. 3. 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 subnet.organization or an even smaller area. 4. IANA Considerations IANA should assign a /8 in the IPv4 multicast address space for this purpose. This assignment should timeouttime out one year after the assignment is made. The assignment may be renewed at that time. 5. Informative References [AS4B] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", February 2007, <http://www.ietf.org/ internet-drafts/draft-ietf-idr-as4bytes-13.txt>.[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: firstname.lastname@example.org 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. 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