IPV6

INTRODUCTION

This specification defines the addressing architecture of the IP
Version 6 protocol. It includes a detailed description of the
currently defined address formats for IPv6 [IPV6].

The editors would like to acknowledge the contributions of Paul
Francis, Jim Bound, Brian Carpenter, Deborah Estrin, Peter Ford, Bob
Gilligan, Christian Huitema, Tony Li, Greg Minshall, Erik Nordmark,
Yakov Rekhter, Bill Simpson, and Sue Thomson.

2.0 IPv6 ADDRESSING

IPv6 addresses are 128-bit identifiers for interfaces and sets of
interfaces. There are three types of addresses:

Unicast: An identifier for a single interface. A packet sent
to a unicast address is delivered to the interface
identified by that address.

Anycast: An identifier for a set of interfaces (typically
belonging to different nodes). A packet sent to an
anycast address is delivered to one of the interfaces
identified by that address (the "nearest" one,
according to the routing protocols' measure of
distance).

Multicast: An identifier for a set of interfaces (typically
belonging to different nodes). A packet sent to a
multicast address is delivered to all interfaces
identified by that address.

There are no broadcast addresses in IPv6, their function being
superseded by multicast addresses.

In this document, fields in addresses are given a specific name, for
example "subscriber". When this name is used with the term "ID" for
identifier after the name (e.g., "subscriber ID"), it refers to the
contents of the named field. When it is used with the term "prefix"
(e.g., "subscriber prefix") it refers to all of the address up to and
including this field.

In IPv6, all zeros and all ones are legal values for any field,
unless specifically excluded. Specifically, prefixes may contain
zero-valued fields or end in zeros.