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draft-ietf-ipngwg-addr-arch
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INTERNET-DRAFT R. Hinden, Ipsilon Networks
May 10, 1995 S. Deering, Xerox PARC
Editors
IP Version 6 Addressing Architecture
<draft-ietf-ipngwg-addr-arch-02.txt>
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as ``work in progress.''
To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet- Drafts
Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim).
This Internet Draft expires November 1, 1995.
draft-ietf-ipngwg-addr-arch-02.txt [Page 1]
INTERNET-DRAFT IPv6 Addressing Architecture May 1995
1.0 INTRODUCTION
This specification defines the addressing architecture of the IP Version
6 protocol. It includes a detailed description of the 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 Rekhtor,
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superseded by multicast addresses.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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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 containing zero bits
easier a special syntax is available to compress the zeros. The
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use of two "::" indicate multiple groups of 16-bits of zeros. For
example the multicast address:
FF01:0:0:0:0:0:0:43
may be represented as:
FF01::43
The "::" can only appear once in an address. The "::" can also be
used to compress the leading or trailing zeros in an address.
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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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 Neutral-Interconnect-
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 neutral-interconnect 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 allocated. The
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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 neutral-interconnect
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 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
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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 the site or
organization.
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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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| 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] and [ADDRF]. This assignment strategy is similar to assignment
of IPv4 addresses under the CIDR scheme [CIDR]. The IPv6 global
provider-based unicast address format is as follows:
| 125-m-n- |
| 3 | n bits | m bits | o bits | p bits | o-p bits |
+---+-----------+-----------+-------------+---------+----------+
|010|registry ID|provider ID|subscriber ID|subnet ID| intf. ID |
+---+-----------+-----------+-------------+---------+----------+
The high-order part of the address is assigned to registries, who then
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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 subnet ID identifies a specific physical link. There can be
multiple subnets on the same physical link. A specific subnet can not
span multiple physical links. The term "subnet prefix" refers to the
high-order part of the address up to and including the subnet ID. The
group of nodes identified by the subnet ID must be attached to the same
link.
The interface ID identifies a single interface among the group of
interfaces identified by the subnet prefix.
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 or when no routers
are present.
Site-Local addresses have the following format:
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| 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.
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
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.
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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.
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.
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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)
B (unassigned)
C (unassigned)
D (unassigned)
E global scope
F reserved
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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
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
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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).
All Hosts Addresses: FF01:0:0:0:0:0:0:3
FF02:0:0:0:0:0:0:3
The above multicast addresses identify the group of all IPv6 hosts,
within scope 1 (node-local) or 2 (link-local).
2.7 A Node's Required Addresses
A host is required to recognize the following addresses as identifying
itself:
o Assigned Unicast Addresses
o Loopback Address
o All Nodes Multicast Address
o All Hosts Multicast Address
o All other Multicast Addresses to which the host belongs.
A router is required to recognize the following addresses as identifying
itself:
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 All other Multicast Addresses to which the router belongs.
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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).
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REFERENCES
[ADDRF] Rekhter, Y., Lothberg, P., "An IPv6 Global Unicast Address
Format", Internet Draft.
[ALLOC] Rekhter, Y., Li, T., "An Architecture for IPv6 Unicast Address
Allocation", Internet Draft.
[ANYCST]C. Partridge, T. Mendez, and W. Milliken, "Host Anycasting
Service", RFC-1546, November 1993.
[CIDR] V. Fuller, T. Li, K. Varadhan, J. Yu, "Supernetting: an
Address Assignment and Aggregation Strategy", RFC 1338.
[IPV6] S. Deering, R. Hinden, Editors, "Internet Protocol, Version 6
(IPv6) Specification", Internet Draft.
[MULT] S. Deering, "Host Extensions for IP multicasting", RFC 1112.
[NSAP] B.Carpenter, Editor, "Mechanisms for OSI NSAPs, CLNP and TP
over IPv6", Internet Draft.
DOCUMENT EDITOR'S ADDRESS
Robert M. Hinden Stephen E. Deering
Ipsilon Networks, Inc. Xerox Palo Alto Research Center
2465 Latham Street, Suite 100 3333 Coyote Hill Road
Mt. View, CA 94040 Palo Alto, CA 94304
USA USA
phone: +1 415 528 4604 phone: +1 415 812 4839
fax: +1 415 528 4653 fax: +1 415 812 4471
email: hinden@ipsilon.com email: deering@parc.xerox.com
draft-ietf-ipngwg-addr-arch-02.txt [Page 17]
INTERNET-DRAFT IPv6 Addressing Architecture May 1995
APPENDIX
This version of the "IPv6 Addressing Architecture" includes several
changes from the previous version:
<draft-ietf-ipngwg-addr-arch-01.txt>
dated March 27, 1995. These changes are:
o Added definition of Subnet-Router anycast address for use by
neighbor discovery and auto-addressing.
o Removed Community scop from multicast scop definitions.
o Added Local Use Prefixes (Link-Local and Site-Local) to list
of predefined prefixes that an implementation is required to
know.
o Minor clarifications, corrections, and typos fixed.
o New typos likely added.
draft-ietf-ipngwg-addr-arch-02.txt [Page 18]
