Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan
RFC 4632
Document | Type |
RFC - Best Current Practice
(August 2006; Errata)
Obsoletes RFC 1519
Also known as BCP 122
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Authors | Vince Fuller , Tony Li | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4632 (Best Current Practice) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | David Kessens | ||
Send notices to | gih@telstra.net, isoc-contact@aarnet.edu.au |
Network Working Group V. Fuller Request for Comments: 4632 Cisco Systems BCP: 122 T. Li Obsoletes: 1519 Tropos Networks Category: Best Current Practice August 2006 Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan Status of This Memo This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This memo discusses the strategy for address assignment of the existing 32-bit IPv4 address space with a view toward conserving the address space and limiting the growth rate of global routing state. This document obsoletes the original Classless Inter-domain Routing (CIDR) spec in RFC 1519, with changes made both to clarify the concepts it introduced and, after more than twelve years, to update the Internet community on the results of deploying the technology described. Fuller & Li Best Current Practice [Page 1] RFC 4632 CIDR Address Strategy August 2006 Table of Contents 1. Introduction ....................................................3 2. History and Problem Description .................................3 3. Classless Addressing as a Solution ..............................4 3.1. Basic Concept and Prefix Notation ..........................5 4. Address Assignment and Routing Aggregation ......................8 4.1. Aggregation Efficiency and Limitations .....................8 4.2. Distributed Assignment of Address Space ...................10 5. Routing Implementation Considerations ..........................11 5.1. Rules for Route Advertisement .............................11 5.2. How the Rules Work ........................................12 5.3. A Note on Prefix Filter Formats ...........................13 5.4. Responsibility for and Configuration of Aggregation .......13 5.5. Route Propagation and Routing Protocol Considerations .....15 6. Example of New Address Assignments and Routing .................15 6.1. Address Delegation ........................................15 6.2. Routing Advertisements ....................................17 7. Domain Name Service Considerations .............................18 8. Transition to a Long-Term Solution .............................18 9. Analysis of CIDR's Effect on Global Routing State ..............19 10. Conclusions and Recommendations ...............................20 11. Status Updates to CIDR Documents ..............................21 12. Security Considerations .......................................23 13. Acknowledgements ..............................................24 14. References ....................................................25 14.1. Normative References .....................................25 14.2. Informative References ...................................25 Fuller & Li Best Current Practice [Page 2] RFC 4632 CIDR Address Strategy August 2006 1. Introduction This memo discusses the strategy for address assignment of the existing 32-bit IPv4 address space with a view toward conserving the address space and limiting the growth rate of global routing state. This document obsoletes the original CIDR spec [RFC1519], with changes made both to clarify the concepts it introduced and, after more than twelve years, to update the Internet community on the results of deploying the technology described. 2. History and Problem Description What is now known as the Internet started as a research project in the 1970s to design and develop a set of protocols that could be used with many different network technologies to provide a seamless, end- to-end facility for interconnecting a diverse set of end systems. When it was determined how the 32-bit address space would be used, certain assumptions were made about the number of organizations to be connected, the number of end systems per organization, and total number of end systems on the network. The end result was the establishment (see [RFC791]) of three classes of networks: Class A (most significant address bits '00'), with 128 possible networks each and 16777216 end systems (minus special bit values reserved for network/broadcast addresses); Class B (MSB '10'), with 16384 possible networks each with 65536 end systems (less reserved values); and Class C (MSB '110'), and 2097152 possible networks each and 254 endShow full document text