INTERNET-DRAFT R. Hinden, Nokia
March 2, 2001 S. Deering, Cisco Systems
IP Version 6 Addressing Architecture
<draft-ietf-ipngwg-addr-arch-v3-05.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of [RFC2026].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
To view the list Internet-Draft Shadow Directories, see
http://www.ietf.org/shadow.html.
This Internet Draft expires September 2, 2001.
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 node's required addresses.
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Table of Contents
1. Introduction.................................................3
2. IPv6 Addressing..............................................3
2.1 Addressing Model.........................................4
2.2 Text Representation of Addresses.........................4
2.3 Text Representation of Address Prefixes..................5
2.4 Address Type Representation..............................6
2.5 Unicast Addresses........................................8
2.5.1 Interface Identifiers................................9
2.5.2 The Unspecified Address.............................10
2.5.3 The Loopback Address................................11
2.5.4 IPv6 Addresses with Embedded IPv4 Addresses.........11
2.5.5 NSAP Addresses......................................12
2.5.6 Aggregatable Global Unicast Addresses...............12
2.5.7 Local-use IPv6 Unicast Addresses....................12
2.6 Anycast Addresses.......................................13
2.6.1 Required Anycast Address............................14
2.7 Multicast Addresses.....................................15
2.7.1 Pre-Defined Multicast Addresses.....................17
2.7.2 Assignment of New IPv6 Multicast Addresses..........18
2.8 A Node's Required Addresses.............................19
3. Security Considerations.....................................19
APPENDIX A: Creating EUI-64 based Interface Identifiers........20
APPENDIX B: CHANGES FROM RFC-2373..............................23
REFERENCES.....................................................24
AUTHOR'S ADDRESSES.............................................25
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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,
Sue Thomson, Roger Fajman, Markku Savela, and Larry Masinter.
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 "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 address from the left
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.
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:
A 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:
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
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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
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
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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:
12AB:0:0:CD3/60 may drop leading zeros, but not trailing zeros,
within any 16-bit chunk of the address
12AB::CD30/60 address to left of "/" expands to
12AB:0000:0000:0000:0000:000:0000:CD30
12AB::CD3/60 address to left of "/" expands to
12AB:0000:0000:0000:0000:000:0000:0CD3
When writing both a node address and a prefix of that node address
(e.g., the node's subnet prefix), the two can combined as follows:
the node address 12AB:0:0:CD30:123:4567:89AB:CDEF
and its subnet number 12AB:0:0:CD30::/60
can be abbreviated as 12AB:0:0:CD30:123:4567:89AB:CDEF/60
2.4 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
Unassigned 0000 010 1/128
Unassigned 0000 011 1/128
Unassigned 0000 1 1/32
Unassigned 0001 1/16
Aggregatable Global Unicast Addresses 001 1/8
Unassigned 010 1/8
Unassigned 011 1/8
Unassigned 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 Unicast Addresses 1111 1110 10 1/1024
Site-Local Unicast Addresses 1111 1110 11 1/1024
Multicast Addresses 1111 1111 1/256
Notes:
(1) The "unspecified address" (see section 2.5.2), the loopback
address (see section 2.5.3), and the IPv6 Addresses with
Embedded IPv4 Addresses (see section 2.5.4), are assigned out
of the 0000 0000 format prefix space.
(2) The format prefixes 001 through 111, except for Multicast
Addresses (1111 1111), are all required to have 64-bit
interface identifiers in EUI-64 format. See section 2.5.1 for
definitions.
(3) All format prefixes labelled "Unassigned" must be treated as
if they were global unicast addresses, unless and until a
future standards document defines an exception for a
particular prefix. Thus, an implementation must not have
"wired-in" knowledge that a particular format prefix
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identifies global unicast addresses, but rather must treat all
addresses as global unicast unless they fall under one of the
defined exceptions or are explicitly configured otherwise (as
in the case of anycast addresses). The currently defined
exceptions are as follows:
::/128 the unspecified address
::1/128 the loopback address
::/96 IPv4-compatible address prefix
::FFFF:0:0/96 IPv4-mapped address prefix
FE80::/10 link-local unicast address prefix
FEC0::/10 site-local unicast address prefix
FF00::/8 multicast address prefix
This allocation supports the direct allocation of aggregation
addresses, local use addresses, and multicast addresses. Space is
reserved for NSAP addresses. The remainder of the address space is
unassigned for future use. This can be used for expansion of
existing use (e.g., additional aggregatable addresses, etc.) or new
uses (e.g., separate locators and identifiers). Fifteen percent of
the address space is initially 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.
2.5 Unicast Addresses
IPv6 unicast addresses are aggregatable with contiguous bit-wise
masks similar to IPv4 addresses under Class-less Interdomain Routing
[CIDR].
There are several forms of unicast address assignment in IPv6,
including the aggregatable global unicast address, the NSAP address,
the site-local address, the link-local 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:
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| 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 positions the router holds in the routing
hierarchy.
2.5.1 Interface Identifiers
Interface identifiers in IPv6 unicast addresses are used to identify
interfaces on a link. They are required to be unique on that link.
They may also be unique over a broader scope. In many cases an
interface's identifier will be derived directly from that interface's
link-layer address. The same interface identifier may be used on
multiple interfaces on a single node.
Note that the use of the same interface identifier on multiple
interfaces of a single node does not affect the interface
identifier's global uniqueness or each IPv6 address's global
uniqueness created using that interface identifier.
In a number of the format prefixes (see section 2.4) Interface IDs
are required to be 64 bits long and to be constructed in IEEE EUI-64
format [EUI64]. EUI-64 based Interface identifiers may have global
scope when a global token is available (e.g., IEEE 48bit MAC) or may
have local scope where a global token is not available (e.g., serial
links, tunnel end-points, etc.). It is required that the "u" bit
(universal/local bit in IEEE EUI-64 terminology) be inverted when
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forming the interface identifier from the EUI-64. The "u" bit is set
to one (1) to indicate global scope, and it is set to zero (0) to
indicate local scope. The first three octets in binary of an EUI-64
identifier are as follows:
0 0 0 1 1 2
|0 7 8 5 6 3|
+----+----+----+----+----+----+
|cccc|ccug|cccc|cccc|cccc|cccc|
+----+----+----+----+----+----+
written in Internet standard bit-order , where "u" is the
universal/local bit, "g" is the individual/group bit, and "c" are the
bits of the company_id. Appendix A: "Creating EUI-64 based Interface
Identifiers" provides examples on the creation of different EUI-64
based interface identifiers.
The motivation for inverting the "u" bit when forming the interface
identifier is to make it easy for system administrators to hand
configure local scope identifiers when hardware tokens are not
available. This is expected to be case for serial links, tunnel end-
points, etc. The alternative would have been for these to be of the
form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler 1, 2,
etc.
The use of the universal/local bit in the IEEE EUI-64 identifier is
to allow development of future technology that can take advantage of
interface identifiers with global scope.
The details of forming interface identifiers are defined in the
appropriate "IPv6 over <link>" specification such as "IPv6 over
Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc.
2.5.2 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 packets 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 packets or in IPv6 Routing Headers. An IPv6 packet with a
source address of unspecified must never be forwarded by an IPv6
router.
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2.5.3 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 packet to itself. It may
never be assigned to any physical interface. It may be thought of as
being associated with a virtual interface (e.g., the loopback
interface).
The loopback address must not be used as the source address in IPv6
packets that are sent outside of a single node. An IPv6 packet with
a destination address of loopback must never be sent outside of a
single node and must never be forwarded by an IPv6 router. A packet
received on an interface with destination address of loopback must be
dropped.
2.5.4 IPv6 Addresses with Embedded IPv4 Addresses
The IPv6 transition mechanisms [TRAN] 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 type is used to represent the addresses
of IPv4 nodes as IPv6 addresses. This type of address is termed an
"IPv4-mapped IPv6 address" and has the format:
| 80 bits | 16 | 32 bits |
+--------------------------------------+--------------------------+
|0000..............................0000|FFFF| IPv4 address |
+--------------------------------------+----+---------------------+
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2.5.5 NSAP Addresses
This mapping of NSAP address into IPv6 addresses is defined in
[NSAP]. This document recommends that network implementors who have
planned or deployed an OSI NSAP addressing plan, and who wish to
deploy or transition to IPv6, should redesign a native IPv6
addressing plan to meet their needs. However, it also defines a set
of mechanisms for the support of OSI NSAP addressing in an IPv6
network. These mechanisms are the ones that must be used if such
support is required. This document also defines a mapping of IPv6
addresses within the OSI address format, should this be required.
2.5.6 Aggregatable Global Unicast Addresses
The aggregatable global unicast address is defined in [AGGR]. It is
a specific example of the following general format for global unicast
addresses:
| n |
|bits| m bits | p bits | 128-n-m-p bits |
+----+-------------------+-----------+----------------------------+
| FP | routing prefix | subnet ID | interface ID |
+----+-------------------+-----------+----------------------------+
where FP is a format prefix (see section 2.4), and the format of the
routing prefix, subnet ID, and interface ID are specific to a given
FP. Note that, as specified in section 2.4, for all FPs whose high-
order three bits have binary value 001 or greater, excluding the
multicast FP 11111111, the interface ID is a 64-bit field in EUI-64
format.
2.5.7 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 | 54 bits | 64 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
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discovery, or when no routers are present.
Routers must not forward any packets with link-local source or
destination addresses to other links.
Site-Local addresses have the following format:
| 10 |
| bits | 38 bits | 16 bits | 64 bits |
+----------+-------------+-----------+----------------------------+
|1111111011| 0 | subnet ID | interface ID |
+----------+-------------+-----------+----------------------------+
Site-Local addresses are designed to be used for addressing inside of
a site without the need for a global prefix.
Routers must not forward any packets with site-local source or
destination addresses outside of the site.
2.6 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
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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.
One expected use of anycast addresses is to identify the set of
routers belonging to an organization providing internet service.
Such addresses could be used as intermediate addresses in an IPv6
Routing header, to cause a packet to be delivered via a particular
aggregation or sequence of aggregations. 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.
2.6.1 Required Anycast Address
The Subnet-Router anycast address is predefined. Its 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
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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.
2.7 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 Internet Assigned Number
Authority (IANA).
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:
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0 reserved
1 interface-local scope
2 link-local scope
3 reserved for subnet-local scope
4 admin-local scope
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
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
101 (hex), then:
FF01:0:0:0:0:0:0:101 means all NTP servers on the same node as
the sender.
FF02:0:0:0:0:0:0:101 means all NTP servers on the same link as
the sender.
FF05:0:0:0:0:0:0:101 means all NTP servers at the same site as
the sender.
FF0E:0:0:0:0:0:0:101 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 FF15:0:0:0:0:0:0:101 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
packets or appear in any routing header.
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Routers must not forward any multicast packets outside of the scope
indicated by the scop field in the multicast address.
2.7.1 Pre-Defined Multicast Addresses
The following well-known multicast addresses are pre-defined. The
group ID's defined in this section are defined for explicit scope
values. Use of these group ID's for any other scope values is not
allowed.
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
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 (interface-local) or 2 (link-local).
All Routers Addresses: FF01:0:0:0:0:0:0:2
FF02:0:0:0:0:0:0:2
FF05:0:0:0:0:0:0:2
The above multicast addresses identify the group of all IPv6 routers,
within scope 1 (interface-local), 2 (link-local), or 5 (site-local).
Solicited-Node Address: FF02:0:0:0:0:1:FFXX:XXXX
The above multicast address is computed as a function of a node's
unicast and anycast addresses. The solicited-node multicast address
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INTERNET-DRAFT IPv6 Addressing Architecture March 2001
is formed by taking the low-order 24 bits of the address (unicast or
anycast) and appending those bits to the prefix
FF02:0:0:0:0:1:FF00::/104 resulting in a multicast address in the
range
FF02:0:0:0:0:1:FF00:0000
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:FF0E:8C6C. IPv6
addresses that differ only in the high-order bits, e.g. due to
multiple high-order prefixes associated with different aggregations,
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 join the associated Solicited-Node
multicast addresses for every unicast and anycast address it is
assigned.
2.7.2 Assignment of New IPv6 Multicast Addresses
The current approach [ETHER] to map IPv6 multicast addresses into
IEEE 802 MAC addresses takes the low order 32 bits of the IPv6
multicast address and uses it to create a MAC address. Note that
Token Ring networks are handled differently. This is defined in
[TOKEN]. IPv6 multicast addresses, in which the 32-bit group ID
portion of the address are unique will generate unique MAC addresses.
Due to this, new IPv6 multicast addresses should be assigned with an
attempt at keeping the group ID portions of the addresses unique with
respect to all other IPv6 multicast addresses. Note that address
assignments that result in MAC address collisions will still work
correctly, but possibly with reduced performance in some cases.
Thus, when assigning IPv6 multicast addresses, the performance costs
of such collisions should be weighed against the cost of assigning
addresses in a way that ensures the group ID maps into a unique MAC
address.
| 8 | 4 | 4 | 80 bits | 32 bits |
+------ -+----+----+---------------------------+-----------------+
|11111111|flgs|scop| reserved | group ID |
+--------+----+----+---------------------------+-----------------+
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While this limits the number of permanent IPv6 multicast groups to
2^32 this is unlikely to be a limitation in the future. If it
becomes necessary to exceed this limit in the future multicast will
still work but the processing will be sightly slower.
Additional IPv6 multicast addresses are defined and registered by the
IANA [MASGN].
2.8 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 The All-Nodes Multicast Addresses defined in section 2.7.1
o Solicited-Node Multicast Address for each of its assigned
unicast and anycast addresses
o Multicast Addresses of all other groups to which the host
belongs.
A router is required to recognize all addresses that a host is
required to recognize, plus the following addresses as identifying
itself:
o The Subnet-Router anycast addresses for the interfaces it is
configured to act as a router on.
o All other Anycast addresses with which the router has been
configured.
o The All-Routers Multicast Addresses defined in section 2.7.1
o Multicast Addresses of all other groups to which the router
belongs.
3. Security Considerations
IPv6 addressing documents do not have any direct impact on Internet
infrastructure security. Authentication of IPv6 packets is defined
in [AUTH].
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APPENDIX A : Creating EUI-64 based Interface Identifiers
--------------------------------------------------------
Depending on the characteristics of a specific link or node there are
a number of approaches for creating EUI-64 based interface
identifiers. This appendix describes some of these approaches.
Links or Nodes with EUI-64 Identifiers
The only change needed to transform an EUI-64 identifier to an
interface identifier is to invert the "u" (universal/local) bit. For
example, a globally unique EUI-64 identifier of the form:
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+
where "c" are the bits of the assigned company_id, "0" is the value
of the universal/local bit to indicate global scope, "g" is
individual/group bit, and "m" are the bits of the manufacturer-
selected extension identifier. The IPv6 interface identifier would
be of the form:
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc1gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+
The only change is inverting the value of the universal/local bit.
Links or Nodes with IEEE 802 48 bit MAC's
[EUI64] defines a method to create a EUI-64 identifier from an IEEE
48bit MAC identifier. This is to insert two octets, with hexadecimal
values of 0xFF and 0xFE, in the middle of the 48 bit MAC (between the
company_id and vendor supplied id). For example the 48 bit MAC with
global scope:
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INTERNET-DRAFT IPv6 Addressing Architecture March 2001
|0 1|1 3|3 4|
|0 5|6 1|2 7|
+----------------+----------------+----------------+
|cccccc0gcccccccc|ccccccccmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+
where "c" are the bits of the assigned company_id, "0" is the value
of the universal/local bit to indicate global scope, "g" is
individual/group bit, and "m" are the bits of the manufacturer-
selected extension identifier. The interface identifier would be of
the form:
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc1gcccccccc|cccccccc11111111|11111110mmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+
When IEEE 802 48bit MAC addresses are available (on an interface or a
node), an implementation should use them to create interface
identifiers due to their availability and uniqueness properties.
Links with Non-Global Identifiers
There are a number of types of links that, while multi-access, do not
have globally unique link identifiers. Examples include LocalTalk
and Arcnet. The method to create an EUI-64 formatted identifier is
to take the link identifier (e.g., the LocalTalk 8 bit node
identifier) and zero fill it to the left. For example a LocalTalk 8
bit node identifier of hexadecimal value 0x4F results in the
following interface identifier:
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|0000000000000000|0000000000000000|0000000000000000|0000000001001111|
+----------------+----------------+----------------+----------------+
Note that this results in the universal/local bit set to "0" to
indicate local scope.
Links without Identifiers
There are a number of links that do not have any type of built-in
identifier. The most common of these are serial links and configured
tunnels. Interface identifiers must be chosen that are unique for
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INTERNET-DRAFT IPv6 Addressing Architecture March 2001
the link.
When no built-in identifier is available on a link the preferred
approach is to use a global interface identifier from another
interface or one which is assigned to the node itself. To use this
approach no other interface connecting the same node to the same link
may use the same identifier.
If there is no global interface identifier available for use on the
link the implementation needs to create a local scope interface
identifier. The only requirement is that it be unique on the link.
There are many possible approaches to select a link-unique interface
identifier. They include:
Manual Configuration
Generated Random Number
Node Serial Number (or other node-specific token)
The link-unique interface identifier should be generated in a manner
that it does not change after a reboot of a node or if interfaces are
added or deleted from the node.
The selection of the appropriate algorithm is link and implementation
dependent. The details on forming interface identifiers are defined
in the appropriate "IPv6 over <link>" specification. It is strongly
recommended that a collision detection algorithm be implemented as
part of any automatic algorithm.
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APPENDIX B: CHANGES FROM RFC-2373
---------------------------------
The following changes were made from RFC-2373 "IP Version 6
Addressing Architecture":
- Added clarification that all unassigned FP's must be treated as
global unicast addresses unless unless another standards document
defines an exception.
- Added clarification that implementations must not have "wired-in"
knowledge that a particular format prefix identifies global
unicast addresses and that implementations must treat all
addresses as global unicast addresses unless they fall under a
defined exception.
- Moved the list of defined prefix exceptions from section 2.5.6 to
section 2.4.
- Revised section 2.5.6 "Aggregatable Global Unicast Addresses" to
generalize the description in this section and clarify that the
specifics are defined in the reference.
- Added clarification that routers must not forward multicast
packets outside of the scope indicated in the multicast address.
- Added clarification that routers must not forward packets with
source address of the unspecified address.
- Added clarification that routers must drop packets received on an
interface with destination address of loopback.
- Clarified the definition of IPv4-mapped addresses.
- Removed the ABNF Description of Text Representations Appendix.
- Changed the address block reserved for IPX addresses to
unassigned.
- Multicast scope name changes:
o Changed name of scope value 1 from "node-local" to
"interface-local"
o Reserved scope value 3 for "subnet-local" for multi-link
subnets
o Defined scope value 4 as "admin-local"
- Clarified text describing Exchanges.
- Corrected reference to RFC1933 and updated references.
- Several minor textual clarifications.
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REFERENCES
[AGGR] Hinden, R., S. Deering, M. O'Dell, "An Aggregatable Global
Unicast Address Format", RFC2374, July 1998.
[AUTH] Kent, S., R. Atkinson, "IP Authentication Header", RFC2402,
November 1998.
[ANYCST] Partridge, C., T. Mendez, and W. Milliken, "Host Anycasting
Service", RFC1546, November 1993.
[CIDR] Fuller, V., Li, T., Yu, J., Varadhan, K., "Classless Inter-
Domain Routing (CIDR): An Address Assignment and
Aggregation Strategy", RFC1519, September 1993.
[ETHER] Crawford, M., "Transmission of IPv6 Pacekts over Ethernet
Networks", RFC2464, December 1998.
[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/regauth/oui/tutorials/EUI64.html,
March 1997.
[FDDI] Crawford, M., "Transmission of IPv6 Packets over FDDI
Networks", RFC2467, December 1998.
[IPV6] Deering, S., R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC2460, December 1998.
[MASGN] Hinden, R., "IPv6 Multicast Address Assignments", RFC2375,
July 1998.
[NSAP] Bound, J., B. Carpenter, D. Harrington, J. Houldsworth, A.
Lloyd, "OSI NSAPs and IPv6", RFC1888, August 1996.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC2026, BCP00009, October 1996.
[TOKEN] Crawford, M., T. Narten, S. Thomas, "Transmission of IPv6
Packets over Token Ring Networks", RFC2470, December 1998.
[TRAN] Gilligan, R., E. Nordmark, "Transition Mechanisms for IPv6
Hosts and Routers", RFC1933, April 1996.
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AUTHOR'S ADDRESSES
Robert M. Hinden
Nokia
313 Fairchild Drive
Mountain View, CA 94043
USA
phone: +1 650 625-2004
email: hinden@iprg.nokia.com
Stephen E. Deering
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
phone: +1 408 527-8213
email: deering@cisco.com
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