Network Working Group D. Meyer
Request for Comments: 2770 Cisco Systems
Category: Experimental P. Lothberg
Sprint
February 2000
GLOP Addressing in 233/8
1. Problem Statement
Multicast addresses have traditionally been allocated by a dynamic mechanism such as SDR [SAP]. However, many current multicast deployment models are not amenable to dynamic allocation. For example, many content aggregators require group addresses which are fixed on a time scale which is not amenable to allocation by a mechanism such as described in [SAP]. Perhaps more seriously, since there isn't general consensus by providers, content aggregators, or application writers as to the allocation mechanism, the Internet is left without a coherent multicast address allocation scheme. The MALLOC working group is looking at a specific strategy for global multicast address allocation [MADCAP, MASC]. This experiment will proceed in parallel. MADCAP may be employed within AS's, if so desired.
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RFC 2770 GLOP Addressing in 233/8 February 2000
This document proposes an experimental method of statically allocating multicast addresses with global scope. This experiment will last for a period of one year, but may be extended as described in section 6.
2. Address Space
For purposes of the experiment described here, the IANA has allocated 233/8. The remaining 24 bits will be administered in a manner similar to that described in RFC 1797:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 233 | 16 bits AS | local bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1. Example
Consider, for example, AS 5662. Written in binary, left padded with 0s, we get 0001011000011110. Mapping the high order octet to the second octet of the address, and the low order octet to the third octet, we get 233.22.30/24.
3. Allocation
As mentioned above, the allocation proposed here follows the RFC 1797 (case 1) allocation scheme, modified as follows: the high order octet has the value 233, and the next 16 bits are a previously assigned Autonomous System number (AS), as registered by a network registry and listed in the RWhois database system. This allows a single /24 per AS.
3.1. Private AS Space
The address space mapped to the private AS space [RFC1930] is reserved for future allocation.
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RFC 2770 GLOP Addressing in 233/8 February 2000 4. Transition from GLOP to Other Address Allocation SchemesIt may not be necessary to transition from the address allocation scheme described here to a more dynamic approach (see, e.g., [MASC]). The reasoning here is that the statically assigned addresses taken from 233/8 may be sufficient for those applications which must have static addressing, and any other addressing can come from either a dynamic mechanism such as [MASC], the administratively scoped address space [RFC2365], or the Single-source address space [SS].
5. Security Considerations
The approach described here may have the effect of reduced exposure to denial of space attacks based on dynamic allocation. Further, since dynamic assignment does not cross domain boundaries, well known intra-domain security techniques can be applied.
6. IANA Considerations
IANA has allocated 233/8 for experimental assignments. This assignment should timeout one year after the assignment is made. The assignment may be renewed at that time. It should be noted that the experiment described here is in the same spirit the experiment described in [RFC1797].
7. Acknowledgments
This idea originated with Peter Lothberg's idea that we use the same allocation (AS based) as described in RFC 1797 in the class D address space. Randy Bush and Mark Handley contributed many insightful comments.
8. References
[RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address
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RFC 2770 GLOP Addressing in 233/8 February 2000
[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", RFC 1930, March 1996.
9. Authors' Addresses
David Meyer Cisco Systems, Inc. 170 W. Tasman Drive San Jose, CA 95134-1706 United States
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RFC 2770 GLOP Addressing in 233/8 February 2000 10. Full Copyright StatementCopyright (C) The Internet Society (2000). All Rights Reserved.
