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LinuxDig.com Request For Comments

RFC Number : 1884

Title : IP Version 6 Addressing Architecture.






Network Working Group R. Hinden, Ipsilon Networks
Request for Comments: 1884 S. Deering, Xerox PARC
Category: Standards Track Editors
December 1995


IP Version 6 Addressing Architecture




Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the 'Internet
Official Protocol Standards' (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.


Abstract

This specification defines the addressing architecture of the IP
Version 6 protocol [IPV6]. The document includes the IPv6 addressing
model, text representations of IPv6 addresses, definition of IPv6
unicast addresses, anycast addresses, and multicast addresses, and an
IPv6 nodes required addresses.
























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RFC 1884 IPv6 Addressing Architecture December 1995


Table of Contents

1. Introduction................................................3

2. IPv6 Addressing.............................................3
2.1 Addressing Model........................................4
2.2 Text Representation of Addresses........................4
2.3 Address Type Representation.............................5
2.4 Unicast Addresses.......................................7
2.4.1 Unicast Address Example.............................8
2.4.2 The Unspecified Address.............................9
2.4.3 The Loopback Address................................9
2.4.4 IPv6 Addresses with Embedded IPv4 Addresses.........9
2.4.5 NSAP Addresses......................................10
2.4.6 IPX Addresses.......................................10
2.4.7 Provider-Based Global Unicast Addresses.............10
2.4.8 Local-use IPv6 Unicast Addresses....................11
2.5 Anycast Addresses.......................................12
2.5.1 Required Anycast Address............................13
2.6 Multicast Addresses.....................................14
2.6.1 Pre-Defined Multicast Addresses.....................15
2.7 A Node's Required Addresses.............................17

REFERENCES.....................................................18

SECURITY CONSIDERATIONS........................................18

DOCUMENT EDITOR'S ADDRESSES....................................18























Hinden & Deering Standards Track [Page 2]

RFC 1884 IPv6 Addressing Architecture December 1995


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 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.





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RFC 1884 IPv6 Addressing Architecture December 1995


2.1 Addressing Model

IPv6 Addresses of all types are assigned to interfaces, not nodes.
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.

An IPv6 unicast address refers to a single interface. A single
interface may be assigned multiple IPv6 addresses of any type
(unicast, anycast, and multicast). There are two exceptions to this
model. These are:

1) A single address 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.

2) Routers may have unnumbered interfaces (i.e., no IPv6 address
assigned to the interface) on point-to-point links to eliminate
the necessity to manually configure and advertise the addresses.
Addresses are not needed for point-to-point interfaces on
routers if those interfaces are not to be used as the origins or
destinations of any IPv6 datagrams.

IPv6 continues the IPv4 model that a subnet is associated with one
link. Multiple subnets 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:

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 the method 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



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RFC 1884 IPv6 Addressing Architecture December 1995


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
FF01:0:0:0:0:0:0:43 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::43 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


2.3 Address Type Representation

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). The initial allocation of
these prefixes is as follows:







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RFC 1884 IPv6 Addressing Architecture December 1995


Allocation Prefix Fraction of
(binary) Address Space
------------------------------- -------- -------------
Reserved 0000 0000 1/256
Unassigned 0000 0001 1/256

Reserved for NSAP Allocation 0000 001 1/128
Reserved for IPX Allocation 0000 010 1/128

Unassigned 0000 011 1/128
Unassigned 0000 1 1/32
Unassigned 0001 1/16
Unassigned 001 1/8

Provider-Based Unicast Address 010 1/8

Unassigned 011 1/8

Reserved for Geographic-
Based Unicast Addresses 100 1/8

Unassigned 101 1/8
Unassigned 110 1/8
Unassigned 1110 1/16
Unassigned 1111 0 1/32
Unassigned 1111 10 1/64
Unassigned 1111 110 1/128

Unassigned 1111 1110 0 1/512

Link Local Use Addresses 1111 1110 10 1/1024
Site Local Use Addresses 1111 1110 11 1/1024

Multicast Addresses 1111 1111 1/256

Note: The 'unspecified address' (see section 2.4.2), the
loopback address (see section 2.4.3), and the IPv6 Addresses
with Embedded IPv4 Addresses (see section 2.4.4), are assigned
out of the 0000 0000 format prefix space.


This allocation supports the direct allocation of provider addresses,
local use addresses, and multicast addresses. Space is reserved for
NSAP addresses, IPX addresses, and geographic addresses. The
remainder of the address space is unassigned for future use. This
can be used for expansion of existing use (e.g., additional provider
addresses, etc.) or new uses (e.g., separate locators and
identifiers). Fifteen percent of the address space is initially



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RFC 1884 IPv6 Addressing Architecture December 1995


allocated. The remaining 85% is reserved for future use.

Unicast addresses are distinguished from multicast addresses by the
value of the high-order octet of the addresses: a value of FF
(11111111) identifies an address as a multicast address; any other
value identifies an address as a unicast address. Anycast addresses
are taken from the unicast address space, and are not syntactically
distinguishable from unicast addresses.


2.4 Unicast Addresses

The IPv6 unicast address is contiguous bit-wise maskable, similar to
IPv4 addresses under Class-less Interdomain Routing [CIDR].

There are several forms of unicast address assignment in IPv6,
including the global provider based unicast address, the geographic
based unicast address, the NSAP address, the IPX hierarchical
address, the site-local-use address, the link-local-use address, and
the IPv4-capable host address. Additional address types can be
defined in the future.

IPv6 nodes may have considerable or little knowledge of the internal
structure of the IPv6 address, depending on the role the node plays
(for instance, host versus router). At a minimum, a node may
consider that unicast addresses (including its own) have no internal
structure:

| 128 bits |
+-----------------------------------------------------------------+
| node address |
+-----------------------------------------------------------------+


A slightly sophisticated host (but still rather simple) may
additionally be aware of subnet prefix(es) for the link(s) it is
attached to, where different addresses may have different values for
n:

| n bits | 128-n bits |
+------------------------------------------------+----------------+
| subnet prefix | interface ID |
+------------------------------------------------+----------------+


Still more sophisticated hosts may be aware of other hierarchical
boundaries in the unicast address. Though a very simple router may
have no knowledge of the internal structure of IPv6 unicast



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RFC 1884 IPv6 Addressing Architecture December 1995


addresses, routers will more generally have knowledge of one or more
of the hierarchical boundaries for the operation of routing
protocols. The known boundaries will differ from router to router,
depending on what positions the router holds in the routing
hierarchy.


2.4.1 Unicast Address Examples

An example of a Unicast address format which will likely be common on
LANs and other environments where IEEE 802 MAC addresses are
available is:


| n bits | 80-n bits | 48 bits |
+--------------------------------+-----------+--------------------+
| subscriber prefix | subnet ID | interface ID |
+--------------------------------+-----------+--------------------+

Where the 48-bit Interface ID is an IEEE-802 MAC address. The use of
IEEE 802 MAC addresses as a interface ID is expected to be very
common in environments where nodes have an IEEE 802 MAC address. In
other environments, where IEEE 802 MAC addresses are not available,
other types of link layer addresses can be used, such as E.164
addresses, for the interface ID.

The inclusion of a unique global interface identifier, such as an
IEEE MAC address, makes possible a very simple form of auto-
configuration of addresses. A node may discover a subnet ID by
listening to Router Advertisement messages sent by a router on its
attached link(s), and then fabricating an IPv6 address for itself by
using its IEEE MAC address as the interface ID on that subnet.

Another unicast address format example is where a site or
organization requires additional layers of internal hierarchy. In
this example the subnet ID is divided into an area ID and a subnet
ID. Its format is:

| s bits | n bits | m bits | 128-s-n-m bits |
+----------------------+---------+--------------+-----------------+
| subscriber prefix | area ID | subnet ID | interface ID |
+----------------------+---------+--------------+-----------------+

This technique can be continued to allow a site or organization to
add additional layers of internal hierarchy. It may be desirable to
use an interface ID smaller than a 48-bit IEEE 802 MAC address to
allow more space for the additional layers of internal hierarchy.
These could be interface IDs which are administratively created by



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RFC 1884 IPv6 Addressing Architecture December 1995


the site or organization.


2.4.2 The Unspecified Address

The address 0:0:0:0:0:0:0:0 is called the unspecified address. It
must never be assigned to any node. It indicates the absence of an
address. One example of its use is in the Source Address field of
any IPv6 datagrams sent by an initializing host before it has learned
its own address.

The unspecified address must not be used as the destination address
of IPv6 datagrams or in IPv6 Routing Headers.


2.4.3 The Loopback Address

The unicast address 0:0:0:0:0:0:0:1 is called the loopback address.
It may be used by a node to send an IPv6 datagram to itself. It may
never be assigned to any interface.

The loopback address must not be used as the source address in IPv6
datagrams that are sent outside of a single node. An IPv6 datagram
with a destination address of loopback must never be sent outside of
a single node.


2.4.4 IPv6 Addresses with Embedded IPv4 Addresses

The IPv6 transition mechanisms include a technique for hosts and
routers to dynamically tunnel IPv6 packets over IPv4 routing
infrastructure. IPv6 nodes that utilize this technique are assigned
special IPv6 unicast addresses that carry an IPv4 address in the
low-order 32-bits. This type of address is termed an 'IPv4-
compatible IPv6 address' and has the format:


| 80 bits | 16 | 32 bits |
+--------------------------------------+--------------------------+
|0000..............................0000|0000| IPv4 address |
+--------------------------------------+----+---------------------+


A second type of IPv6 address which holds an embedded IPv4 address is
also defined. This address is used to represent the addresses of
IPv4-only nodes (those that *do not* support IPv6) as IPv6 addresses.
This type of address is termed an 'IPv4-mapped IPv6 address' and has
the format:



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RFC 1884 IPv6 Addressing Architecture December 1995



| 80 bits | 16 | 32 bits |
+--------------------------------------+--------------------------+
|0000..............................0000|FFFF| IPv4 address |
+--------------------------------------+----+---------------------+



2.4.5 NSAP Addresses

This mapping of NSAP address into IPv6 addresses is as follows:


| 7 | 121 bits |
+-------+---------------------------------------------------------+
|0000001| to be defined |
+-------+---------------------------------------------------------+

The draft definition, motivation, and usage are under study [NSAP].


2.4.6 IPX Addresses

This mapping of IPX address into IPv6 addresses is as follows:


| 7 | 121 bits |
+-------+---------------------------------------------------------+
|0000010| to be defined |
+-------+---------------------------------------------------------+

The draft definition, motivation, and usage are under study.


2.4.7 Provider-Based Global Unicast Addresses

The global provider-based unicast address is assigned as described in
[ALLOC]. This initial assignment plan for these unicast addresses is
similar to assignment of IPv4 addresses under the CIDR scheme [CIDR].
The IPv6 global provider-based unicast address format is as follows:


| 3 | n bits | m bits | o bits | 125-n-m-o bits |
+---+-----------+-----------+-------------+--------------------+
|010|registry ID|provider ID|subscriber ID| intra-subscriber |
+---+-----------+-----------+-------------+--------------------+





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RFC 1884 IPv6 Addressing Architecture December 1995


The high-order part of the address is assigned to registries, who
then assign portions of the address space to providers, who then
assign portions of the address space to subscribers, etc.

The registry ID identifies the registry which assigns the provider
portion of the address. The term 'registry prefix' refers to the
high-order part of the address up to and including the registry ID.

The provider ID identifies a specific provider which assigns the
subscriber portion of the address. The term 'provider prefix' refers
to the high-order part of the address up to and including the
provider ID.

The subscriber ID distinguishes among multiple subscribers attached
to the provider identified by the provider ID. The term 'subscriber
prefix' refers to the high-order part of the address up to and
including the subscriber ID.

The intra-subscriber portion of the address is defined by an
individual subscriber and is organized according to the subscribers
local internet topology. It is likely that many subscribers will
choose to divide the intra-subscriber portion of the address into a
subnet ID and an interface ID. In this case the subnet ID identifies
a specific physical link and the interface ID identifies a single
interface on that subnet.


2.4.8 Local-use IPv6 Unicast Addresses

There are two types of local-use unicast addresses defined. These
are Link-Local and Site-Local. The Link-Local is for use on a single
link and the Site-Local is for use in a single site. Link-Local
addresses have the following format:

| 10 |
| bits | n bits | 118-n bits |
+----------+-------------------------+----------------------------+
|1111111010| 0 | interface ID |
+----------+-------------------------+----------------------------+

Link-Local addresses are designed to be used for addressing on a
single link for purposes such as auto-address configuration, neighbor
discovery, or when no routers are present.

Routers MUST not forward any packets with link-local source
addresses.





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RFC 1884 IPv6 Addressing Architecture December 1995


Site-Local addresses have the following format:

| 10 |
| bits | n bits | m bits | 118-n-m bits |
+----------+---------+---------------+----------------------------+
|1111111011| 0 | subnet ID | interface ID |
+----------+---------+---------------+----------------------------+


Site-Local addresses may be used for sites or organizations that are
not (yet) connected to the global Internet. They do not need to
request or 'steal' an address prefix from the global Internet address
space. IPv6 site-local addresses can be used instead. When the
organization connects to the global Internet, it can then form global
addresses by replacing the site-local prefix with a subscriber
prefix.

Routers MUST not forward any packets with site-local source addresses
outside of the site.

2.5 Anycast Addresses

An IPv6 anycast address is an address that is assigned to more than
one interface (typically belonging to different nodes), with the
property that a packet sent to an anycast address is routed to the
'nearest' interface having that address, according to the routing
protocols' measure of distance.

Anycast addresses are allocated from the unicast address space, using
any of the defined unicast address formats. Thus, anycast addresses
are syntactically indistinguishable from unicast addresses. When a
unicast address is assigned to more than one interface, thus turning
it into an anycast address, the nodes to which the address is
assigned must be explicitly configured to know that it is an anycast
address.

For any assigned anycast address, there is a longest address prefix P
that identifies the topological region in which all interfaces
belonging to that anycast address reside. Within the region
identified by P, each member of the anycast set must be advertised as
a separate entry in the routing system (commonly referred to as a
'host route'); outside the region identified by P, the anycast
address may be aggregated into the routing advertisement for prefix
P.

Note that in, the worst case, the prefix P of an anycast set may be
the null prefix, i.e., the members of the set may have no topological
locality. In that case, the anycast address must be advertised as a



Hinden & Deering Standards Track [Page 12]

RFC 1884 IPv6 Addressing Architecture December 1995


separate routing entry throughout the entire internet, which presents
a severe scaling limit on how many such 'global' anycast sets may be
supported. Therefore, it is expected that support for global anycast
sets may be unavailable or very restricted.

One expected use of anycast addresses is to identify the set of
routers belonging to an internet service provider. Such addresses
could be used as intermediate addresses in an IPv6 Routing header, to
cause a packet to be delivered via a particular provider or sequence
of providers. Some other possible uses are to identify the set of
routers attached to a particular subnet, or the set of routers
providing entry into a particular routing domain.

There is little experience with widespread, arbitrary use of internet
anycast addresses, and some known complications and hazards when
using them in their full generality [ANYCST]. Until more experience
has been gained and solutions agreed upon for those problems, the
following restrictions are imposed on IPv6 anycast addresses:

o An anycast address MUST NOT be used as the source address of an
IPv6 packet.

o An anycast address MUST NOT be assigned to an IPv6 host, that
is, it may be assigned to an IPv6 router only.


2.5.1 Required Anycast Address

The Subnet-Router anycast address is predefined. It's format is as
follows:


| n bits | 128-n bits |
+------------------------------------------------+----------------+
| subnet prefix | 00000000000000 |
+------------------------------------------------+----------------+


The 'subnet prefix' in an anycast address is the prefix which
identifies a specific link. This anycast address is syntactically
the same as a unicast address for an interface on the link with the
interface identifier set to zero.

Packets sent to the Subnet-Router anycast address will be delivered
to one router on the subnet. All routers are required to support the
Subnet-Router anycast addresses for the subnets which they have
interfaces.




Hinden & Deering Standards Track [Page 13]

RFC 1884 IPv6 Addressing Architecture December 1995


The subnet-router anycast address is intended to be used for
applications where a node needs to communicate with one of a set of
routers on a remote subnet. For example when a mobile host needs to
communicate with one of the mobile agents on it's 'home' subnet.


2.6 Multicast Addresses

An IPv6 multicast address is an identifier for a group of nodes. A
node may belong to any number of multicast groups. Multicast
addresses have the following format:

| 8 | 4 | 4 | 112 bits |
+------ -+----+----+---------------------------------------------+
|11111111|flgs|scop| group ID |
+--------+----+----+---------------------------------------------+

11111111 at the start of the address identifies the address as
being a multicast address.

+-+-+-+-+
flgs is a set of 4 flags: |0|0|0|T|
+-+-+-+-+

The high-order 3 flags are reserved, and must be
initialized to 0.

T = 0 indicates a permanently-assigned ('well-known')
multicast address, assigned by the global internet
numbering authority.

T = 1 indicates a non-permanently-assigned ('transient')
multicast address.

scop is a 4-bit multicast scope value used to limit the scope of
the multicast group. The values are:

0 reserved
1 node-local scope
2 link-local scope
3 (unassigned)
4 (unassigned)
5 site-local scope
6 (unassigned)
7 (unassigned)
8 organization-local scope
9 (unassigned)
A (unassigned)



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RFC 1884 IPv6 Addressing Architecture December 1995


B (unassigned)
C (unassigned)
D (unassigned)
E global scope
F reserved

group ID identifies the multicast group, either permanent or
transient, within the given scope.

The 'meaning' of a permanently-assigned multicast address is
independent of the scope value. For example, if the 'NTP servers
group' is assigned a permanent multicast address with a group ID of
43 (hex), then:

FF01:0:0:0:0:0:0:43 means all NTP servers on the same node as
the sender.

FF02:0:0:0:0:0:0:43 means all NTP servers on the same link as
the sender.

FF05:0:0:0:0:0:0:43 means all NTP servers at the same site as
the sender.

FF0E:0:0:0:0:0:0:43 means all NTP servers in the internet.

Non-permanently-assigned multicast addresses are meaningful only
within a given scope. For example, a group identified by the non-
permanent, site-local multicast address FF15:0:0:0:0:0:0:43 at one
site bears no relationship to a group using the same address at a
different site, nor to a non-permanent group using the same group ID
with different scope, nor to a permanent group with the same group
ID.

Multicast addresses must not be used as source addresses in IPv6
datagrams or appear in any routing header.


2.6.1 Pre-Defined Multicast Addresses

The following well-known multicast addresses are pre-defined:

Reserved Multicast Addresses: FF00:0:0:0:0:0:0:0
FF01:0:0:0:0:0:0:0
FF02:0:0:0:0:0:0:0
FF03:0:0:0:0:0:0:0
FF04:0:0:0:0:0:0:0
FF05:0:0:0:0:0:0:0
FF06:0:0:0:0:0:0:0



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RFC 1884 IPv6 Addressing Architecture December 1995


FF07:0:0:0:0:0:0:0
FF08:0:0:0:0:0:0:0
FF09:0:0:0:0:0:0:0
FF0A:0:0:0:0:0:0:0
FF0B:0:0:0:0:0:0:0
FF0C:0:0:0:0:0:0:0
FF0D:0:0:0:0:0:0:0
FF0E:0:0:0:0:0:0:0
FF0F:0:0:0:0:0:0:0

The above multicast addresses are reserved and shall never be
assigned to any multicast group.

All Nodes Addresses: FF01:0:0:0:0:0:0:1
FF02:0:0:0:0:0:0:1

The above multicast addresses identify the group of all IPv6 nodes,
within scope 1 (node-local) or 2 (link-local).

All Routers Addresses: FF01:0:0:0:0:0:0:2
FF02:0:0:0:0:0:0:2

The above multicast addresses identify the group of all IPv6 routers,
within scope 1 (node-local) or 2 (link-local).

DHCP Server/Relay-Agent: FF02:0:0:0:0:0:0:C

The above multicast addresses identify the group of all IPv6 DHCP
Servers and Relay Agents within scope 2 (link-local).

Solicited-Node Address: FF02:0:0:0:0:1:XXXX:XXXX

The above multicast address is computed as a function of a node's
unicast and anycast addresses. The solicited-node multicast address
is formed by taking the low-order 32 bits of the address (unicast or
anycast) and appending those bits to the 96-bit prefix FF02:0:0:0:0:1
resulting in a multicast address in the range

FF02:0:0:0:0:1:0000:0000

to

FF02:0:0:0:0:1:FFFF:FFFF

For example, the solicited node multicast address corresponding to
the IPv6 address 4037::01:800:200E:8C6C is FF02::1:200E:8C6C. IPv6
addresses that differ only in the high-order bits, e.g., due to
multiple high-order prefixes associated with different providers,



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RFC 1884 IPv6 Addressing Architecture December 1995


will map to the same solicited-node address thereby reducing the
number of multicast addresses a node must join.

A node is required to compute and support a Solicited-Node multicast
addresses for every unicast and anycast address it is assigned.

2.7 A Node's Required Addresses

A host is required to recognize the following addresses as
identifying itself:

o Its Link-Local Address for each interface
o Assigned Unicast Addresses
o Loopback Address
o All-Nodes Multicast Address
o Solicited-Node Multicast Address for each of its assigned
unicast and anycast addresses
o Multicast Addresses of all other groups which the host belongs.

A router is required to recognize the following addresses as
identifying itself:

o Its Link-Local Address for each interface
o Assigned Unicast Addresses
o Loopback Address
o The Subnet-Router anycast addresses for the links it has
interfaces.
o All other Anycast addresses with which the router has been
configured.
o All-Nodes Multicast Address
o All-Router Multicast Address
o Solicited-Node Multicast Address for each of its assigned
unicast and anycast addresses
o Multicast Addresses of all other groups which the router
belongs.

The only address prefixes which should be predefined in an
implementation are the:

o Unspecified Address
o Loopback Address
o Multicast Prefix (FF)
o Local-Use Prefixes (Link-Local and Site-Local)
o Pre-Defined Multicast Addresses
o IPv4-Compatible Prefixes

Implementations should assume all other addresses are unicast unless
specifically configured (e.g., anycast addresses).



Hinden & Deering Standards Track [Page 17]

RFC 1884 IPv6 Addressing Architecture December 1995


REFERENCES

[ALLOC] Rekhter, Y., and T. Li, 'An Architecture for IPv6 Unicast
Address Allocation', RFC 1887, cisco Systems, December
1995.

[ANYCST] Partridge, C., Mendez, T., and W. Milliken, 'Host
Anycasting Service', RFC 1546, BBN, November 1993.

[CIDR] Fuller, V., Li, T., Varadhan, K., and J. Yu, 'Supernetting:
an Address Assignment and Aggregation Strategy', RFC 1338,
BARRNet, cisco, Merit, OARnet, June 1992.

[IPV6] Deering, S., and R. Hinden, Editors, 'Internet Protocol,
Version 6 (IPv6) Specification', RFC 1883, Xerox PARC,
Ipsilon Networks, December 1995.

[MULT] Deering, S., 'Host Extensions for IP multicasting', STD 5,
RFC 1112, Stanford University, August 1989.

[NSAP] Carpenter, B., Editor, 'Mechanisms for OSIN SAPs, CLNP and
TP over IPv6', Work in Progress.



SECURITY CONSIDERATIONS

Security issues are not discussed in this document.


DOCUMENT EDITOR'S ADDRESSES

Robert M. Hinden Stephen E. Deering
Ipsilon Networks, Inc. Xerox Palo Alto Research Center
2191 E. Bayshore Road, Suite 100 3333 Coyote Hill Road
Palo Alto, CA 94303 Palo Alto, CA 94304
USA USA

Phone: +1 415 846 4604 Phone: +1 415 812 4839
Fax: +1 415 855 1414 Fax: +1 415 812 4471
EMail: hinden@ipsilon.com EMail: deering@parc.xerox.com










Hinden & Deering Standards Track [Page 18]




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