IPv4 Address Behaviour Today
RFC 2101
Document | Type |
RFC - Informational
(February 1997; No errata)
Was draft-iab-ip-ad-today (individual)
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Authors | Yakov Rekhter , Jon Crowcroft , Brian Carpenter | ||
Last updated | 2013-03-02 | ||
Stream | Legacy | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | Legacy state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) | ||
IESG | IESG state | RFC 2101 (Informational) | |
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group B. Carpenter Request for Comments: 2101 J. Crowcroft Category: Informational Y. Rekhter IAB February 1997 IPv4 Address Behaviour Today Status of this Memo This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Abstract The main purpose of this note is to clarify the current interpretation of the 32-bit IP version 4 address space, whose significance has changed substantially since it was originally defined. A short section on IPv6 addresses mentions the main points of similarity with, and difference from, IPv4. Table of Contents 1. Introduction.................................................1 2. Terminology..................................................2 3. Ideal properties.............................................3 4. Overview of the current situation of IPv4 addresses..........4 4.1. Addresses are no longer globally unique locators.........4 4.2. Addresses are no longer all temporally unique............6 4.3. Multicast and Anycast....................................7 4.4. Summary..................................................8 5. IPv6 Considerations..........................................8 ANNEX: Current Practices for IPv4 Address Allocation & Routing..9 Security Considerations........................................10 Acknowledgements...............................................11 References.....................................................11 Authors' Addresses.............................................13 1. Introduction The main purpose of this note is to clarify the current interpretation of the 32-bit IP version 4 address space, whose significance has changed substantially since it was originally defined in 1981 [RFC 791]. Carpenter, et. al. Informational [Page 1] RFC 2101 IPv4 Address Behavior Today February 1997 This clarification is intended to assist protocol designers, product implementors, Internet service providers, and user sites. It aims to avoid misunderstandings about IP addresses that can result from the substantial changes that have taken place in the last few years, as a result of the Internet's exponential growth. A short section on IPv6 addresses mentions the main points of similarity with, and difference from, IPv4. 2. Terminology It is well understood that in computer networks, the concepts of directories, names, network addresses, and routes are separate and must be analysed separately [RFC 1498]. However, it is also necessary to sub-divide the concept of "network address" (abbreviated to "address" from here on) into at least two notions, namely "identifier" and "locator". This was perhaps less well understood when RFC 791 was written. In this document, the term "host" refers to any system originating and/or terminating IPv4 packets, and "router" refers to any system forwarding IPv4 packets from one host or router to another. For the purposes of this document, an "identifier" is a bit string which is used throughout the lifetime of a communication session between two hosts, to identify one of the hosts as far as the other is concerned. Such an identifier is used to verify the source of incoming packets as being truly the other end of the communication concerned, e.g. in the TCP pseudo-header [RFC 793] or in an IP Security association [RFC 1825]. Traditionally, the source IPv4 address in every packet is used for this. Note that other definitions of "identifier" are sometimes used; this document does not claim to discuss the general issue of the semantics of end-point identifiers. For the purposes of this document, a "locator" is a bit string which is used to identify where a particular packet must be delivered, i.e. it serves to locate the place in the Internet topology where the destination host is attached. Traditionally, the destination IPv4 address in every packet is used for this. IP routing protocols interpret IPv4 addresses as locators and construct routing tables based on which routers (which have their own locators) claim to know a route towards the locators of particular hosts. Both identifiers and locators have requirements of uniqueness, but these requirements are different. Identifiers must be unique with respect to each set of inter-communicating hosts. Locators must be Carpenter, et. al. Informational [Page 2] RFC 2101 IPv4 Address Behavior Today February 1997Show full document text