RFC 2374 (rfc2374) - Page 2 of 12
An IPv6 Aggregatable Global Unicast Address Format
Alternative Format: Original Text Document
RFC 2374 IPv6 Global Unicast Address Format July 1998
2.0 Overview of the IPv6 Address
IPv6 addresses are 128-bit identifiers for interfaces and sets of
interfaces. There are three types of addresses: Unicast, Anycast,
and Multicast. This document defines a specific type of Unicast
address.
In this document, fields in addresses are given specific names, for
example "subnet". When this name is used with the term "ID" (for
"identifier") after the name (e.g., "subnet ID"), it refers to the
contents of the named field. When it is used with the term "prefix"
(e.g. "subnet prefix") it refers to all of the addressing bits to
the left of and including this field.
IPv6 unicast addresses are designed assuming that the Internet
routing system makes forwarding decisions based on a "longest prefix
match" algorithm on arbitrary bit boundaries and does not have any
knowledge of the internal structure of IPv6 addresses. The structure
in IPv6 addresses is for assignment and allocation. The only
exception to this is the distinction made between unicast and
multicast addresses.
The specific type of an IPv6 address is indicated by the leading bits
in the address. The variable-length field comprising these leading
bits is called the Format Prefix (FP).
This document defines an address format for the 001 (binary) Format
Prefix for Aggregatable Global Unicast addresses. The same address
format could be used for other Format Prefixes, as long as these
Format Prefixes also identify IPv6 unicast addresses. Only the "001"
Format Prefix is defined here.
3.0 IPv6 Aggregatable Global Unicast Address Format
This document defines an address format for the IPv6 aggregatable
global unicast address assignment. The authors believe that this
address format will be widely used for IPv6 nodes connected to the
Internet. This address format is designed to support both the
current provider-based aggregation and a new type of exchange-based
aggregation. The combination will allow efficient routing
aggregation for sites that connect directly to providers and for
sites that connect to exchanges. Sites will have the choice to
connect to either type of aggregation entity.
Hinden, et. al. Standards Track