ip addressing

1. Introduction.................................................2
2. IPv6 Addressing..............................................2
2.1 Addressing Model.........................................3
2.2 Text Representation of Addresses.........................3
2.3 Text Representation of Address Prefixes..................5
2.4 Address Type Representation..............................6
2.5 Unicast Addresses........................................7
2.5.1 Interface Identifiers................................8
2.5.2 The Unspecified Address..............................9
2.5.3 The Loopback Address.................................9
2.5.4 IPv6 Addresses with Embedded IPv4 Addresses.........10
2.5.5 NSAP Addresses......................................10
2.5.6 IPX Addresses.......................................10
2.5.7 Aggregatable Global Unicast Addresses...............11
2.5.8 Local-use IPv6 Unicast Addresses....................11
2.6 Anycast Addresses.......................................12
2.6.1 Required Anycast Address............................13
2.7 Multicast Addresses.....................................14



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RFC 2373 IPv6 Addressing Architecture July 1998


2.7.1 Pre-Defined Multicast Addresses.....................15
2.7.2 Assignment of New IPv6 Multicast Addresses..........17
2.8 A Node's Required Addresses.............................17
3. Security Considerations.....................................18
APPENDIX A: Creating EUI-64 based Interface Identifiers........19
APPENDIX B: ABNF Description of Text Representations...........22
APPENDIX C: CHANGES FROM RFC-1884..............................23
REFERENCES.....................................................24
AUTHORS' ADDRESSES.............................................25
FULL COPYRIGHT STATEMENT.......................................26


1.0 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 authors would like to acknowledge the contributions of Paul
Francis, Scott Bradner, Jim Bound, Brian Carpenter, Matt Crawford,
Deborah Estrin, Roger Fajman, Bob Fink, Peter Ford, Bob Gilligan,
Dimitry Haskin, Tom Harsch, Christian Huitema, Tony Li, Greg
Minshall, Thomas Narten, Erik Nordmark, Yakov Rekhter, Bill Simpson,
and Sue Thomson.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].

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.



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RFC 2373 IPv6 Addressing Architecture July 1998


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.

2.1 Addressing Model

IPv6 addresses of all types are assigned to interfaces, not nodes.
An IPv6 unicast address refers to a single interface. Since each
interface belongs to a single node, any of that node's interfaces'
unicast addresses may be used as an identifier for the node.

All interfaces are required to have at least one link-local unicast
address (see section 2.8 for additional required addresses). A
single interface may also be assigned multiple IPv6 addresses of any
type (unicast, anycast, and multicast) or scope. Unicast addresses
with scope greater than link-scope are not needed for interfaces that
are not used as the origin or destination of any IPv6 packets to or
from non-neighbors. This is sometimes convenient for point-to-point
interfaces. There is one exception to this addressing model:

An unicast address or a set of unicast addresses may be assigned to
multiple physical interfaces if the implementation treats the
multiple physical interfaces as one interface when presenting it to
the internet layer. This is useful for load-sharing over multiple
physical interfaces.

Currently IPv6 continues the IPv4 model that a subnet prefix is
associated with one link. Multiple subnet prefixes may be assigned
to the same link.

2.2 Text Representation of Addresses

There are three conventional forms for representing IPv6 addresses as
text strings:

1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the
hexadecimal values of the eight 16-bit pieces of the address.
Examples:



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RFC 2373 IPv6 Addressing Architecture July 1998


FEDC:BA98:7654:3210:FEDC:BA98:7654:3210

1080:0:0:0:8:800:200C:417A

Note that it is not necessary to write the leading zeros in an
individual field, but there must be at least one numeral in every
field (except for the case described in 2.).

2. Due to some methods of allocating certain styles of IPv6
addresses, it will be common for addresses to contain long strings
of zero bits. In order to make writing addresses containing zero
bits easier a special syntax is available to compress the zeros.
The use of "::" indicates multiple groups of 16-bits of zeros.
The "::" can only appear once in an address. The "::" can also be
used to compress the leading and/or trailing zeros in an address.

For example the following addresses:

1080:0:0:0:8:800:200C:417A a unicast address
FF01:0:0:0:0:0:0:101 a multicast address
0:0:0:0:0:0:0:1 the loopback address
0:0:0:0:0:0:0:0 the unspecified addresses

may be represented as:

1080::8:800:200C:417A a unicast address
FF01::101 a multicast address
::1 the loopback address
:: the unspecified addresses

3. An alternative form that is sometimes more convenient when dealing
with a mixed environment of IPv4 and IPv6 nodes is
x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values of
the six high-order 16-bit pieces of the address, and the 'd's are
the decimal values of the four low-order 8-bit pieces of the
address (standard IPv4 representation). Examples:

0:0:0:0:0:0:13.1.68.3

0:0:0:0:0:FFFF:129.144.52.38

or in compressed form:

::13.1.68.3

::FFFF:129.144.52.38





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RFC 2373 IPv6 Addressing Architecture July 1998


2.3 Text Representation of Address Prefixes

The text representation of IPv6 address prefixes is similar to the
way IPv4 addresses prefixes are written in CIDR notation. An IPv6
address prefix is represented by the notation:

ipv6-address/prefix-length

where

ipv6-address is an IPv6 address in any of the notations listed
in section 2.2.

prefix-length is a decimal value specifying how many of the
leftmost contiguous bits of the address comprise
the prefix.

For example, the following are legal representations of the 60-bit
prefix 12AB00000000CD3 (hexadecimal):

12AB:0000:0000:CD30:0000:0000:0000:0000/60
12AB::CD30:0:0:0:0/60
12AB:0:0:CD30::/60

The following are NOT legal representations of the above prefix: