IPv4 Address Behaviour Today
RFC 2101
| Document | Type |
RFC - Informational
(February 1997; No errata)
Was draft-iab-ip-ad-today (individual)
|
|
|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | Legacy | ||
| Formats | plain text pdf html 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
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