The authors would like to acknowledge the contributions of
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, Minshall, Thomas Narten, Erik Nordmark, Yakov Rekhter, Bill Simpson
and Sue Thomson
IPv6 addresses are 128-bit identifiers for interfaces and sets
interfaces. There are three types of addresses
Unicast: An identifier for a single interface. A packet sent
a unicast address is delivered to the
identified by that address
Anycast: An identifier for a set of interfaces (
belonging to different nodes). A packet sent to
anycast address is delivered to one of the
identified by that address (the "nearest" one,
to the routing protocols' measure of distance).
Multicast: An identifier for a set of interfaces (
belonging to different nodes). A packet sent to multicast address is delivered to all
identified by that address
In this document, fields in addresses are given a specific name,
example "subscriber". When this name is used with the term "ID" identifier after the name (e.g., "subscriber ID"), it refers to 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
including this field
In IPv6, all zeros and all ones are legal values for any field
unless specifically excluded. Specifically, prefixes may
zero-valued fields or end in zeros
IPv6 addresses of all types are assigned to interfaces, not nodes
An IPv6 unicast address refers to a single interface. Since 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
address (see section 2.8 for additionalrequiredaddresses).
single interface may also be assignedmultiple IPv6 addresses of
type (unicast, anycast, and multicast) or scope. Unicast
with scope greater than link-scope are not needed for interfaces
are not used as the origin or destination of any IPv6 packets to
from non-neighbors. This is sometimes convenient for point-to-
interfaces. There is one exception to this addressing model
Note that it is not necessary to write the leading zeros in individual field, but there must be at least one numeral in
field (except for the case described in 2.).
2. Due to some methods of allocating certain styles of IPv addresses, it will be common for addresses to contain long
of zero bits. In order to make writing addressescontaining
bits easier a special syntax is available to compress the zeros
The use of "::" indicatesmultiple groups of 16-bits of zeros
The "::" can only appear once in an address. The "::" can also
used to compress the leading and/or trailing zeros in an address
1080:0:0:0:8:800:200C:417A a unicast
FF01:0:0:0:0:0:0:101 a multicast
0:0:0:0:0:0:0:1 the loopback
0:0:0:0:0:0:0:0 the unspecified
may be represented as
1080::8:800:200C:417A a unicast
FF01::101 a multicast
::1 the loopback
:: the unspecified
3. An alternative form that is sometimes more convenient when
with a mixed environment of IPv4 and IPv6 nodes
x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values
the six high-order 16-bit pieces of the address, and the 'd's
the decimal values of the four low-order 8-bit pieces of
address (standard IPv4 representation). Examples
The specific type of an IPv6 address is indicated by the leading
in the address. The variable-length field comprising these
bits is called the Format Prefix (FP). The initial allocation
these prefixes is as follows
(1) The "unspecified address" (see section 2.5.2), the
address (see section 2.5.3), and the IPv6 Addresses Embedded IPv4 Addresses (see section 2.5.4), are assigned
of the 0000 0000 format prefix space
(2) The format prefixes 001 through 111, except for Addresses (1111 1111), are all required to have to have 64- interface identifiers in EUI-64 format. See section 2.5.1 definitions
Unicast addresses are distinguished from multicastaddresses by
value of the high-order octet of the addresses: a value of
(11111111) identifies an address as a multicast address; any
value identifies an address as a unicast address. Anycast
are taken from the unicast address space, and are not
distinguishable from unicast addresses
2.5 Unicast
IPv6 unicast addresses are aggregatable with contiguous bit-
masks similar to IPv4 addresses under Class-less Interdomain
[CIDR].
There are several forms of unicast address assignment in IPv6,
including the global aggregatable global unicast address, the
address, the IPX hierarchical address, the site-local address,
link-local address, and the IPv4-capable host address.
address types can be defined in the future
IPv6 nodes may have considerable or little knowledge of the structure of the IPv6 address, depending on the role the node
(for instance, host versus router). At a minimum, a node consider that unicast addresses (including its own) have no structure
A slightly sophisticated host (but still rather simple)
additionally be aware of subnet prefix(es) for the link(s) it attached to, where differentaddresses may have different values
n
| n bits | 128-n bits |
+------------------------------------------------+----------------+
| subnet prefix | interface ID |
+------------------------------------------------+----------------+
Still more sophisticated hosts may be aware of other
boundaries in the unicast address. Though a very simple router
have no knowledge of the internalstructure of IPv6 addresses, routers will more generally have knowledge of one or
of the hierarchical boundaries for the operation of
protocols. The known boundaries will differ from router to router
depending on what positions the router holds in the
hierarchy
Interface identifiers in IPv6 unicast addresses are used to
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 interface's identifier will be the same as that interface's link
layer address. The same interfaceidentifier may be used on
interfaces on a single node
In a number of the format prefixes (see section 2.4) Interface
are required to be 64 bits long and to be constructed in IEEE EUI-64
format [EUI64]. EUI-64 based Interface identifiers may have
scope when a global token is available (e.g., IEEE 48bit MAC) or
have local scope where a global token is not available (e.g.,
links, tunnel end-points, etc.). It is required that the "u"
(universal/local bit in IEEE EUI-64 terminology) be inverted
forming the interfaceidentifier from the EUI-64. The "u" bit is
to one (1) to indicate global scope, and it is set to zero (0) indicate local scope. The first three octets in binary of an EUI-64 identifier are as follows
The motivation for inverting the "u" bit when forming the identifier is to make it easy for system administrators to configure local scope identifiers when hardware tokens are available. This is expected to be case for serial links, tunnel end
points, etc. The alternative would have been for these to be of
form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler ::1,
::2, etc
The address 0:0:0:0:0:0:0:0 is called the unspecified address.
must never be assigned to any node. It indicates the absence of
address. One example of its use is in the Source Address field
any IPv6 packets sent by an initializing host before it has
its own address
The unspecified address must not be used as the destination
of IPv6 packets or in IPv6 Routing Headers
2.5.3 The Loopback
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
never be assigned to any physicalinterface. It may be thought of
being associated with a virtual interface (e.g., the interface).
The loopback address must not be used as the source address in IPv
packets that are sent outside of a single node. An IPv6 packet
a destination address of loopback must never be sent outside of
single node and must never be forwarded by an IPv6 router
The IPv6 transition mechanisms [TRAN] include a technique for
and routers to dynamically tunnel IPv6 packets over IPv4 infrastructure. IPv6 nodes that utilize this technique are
special IPv6 unicast addresses that carry an IPv4 address in the low
order 32-bits. This type of address is termed an "IPv4-
IPv6 address" and has the format
A second type of IPv6 address which holds an embedded IPv4 address
also defined. This address is used to represent the addresses
IPv4-only nodes (those that *do not* support IPv6) as IPv6 addresses
This type of address is termed an "IPv4-mapped IPv6 address" and
the format
This mapping of NSAP address into IPv6 addresses is defined
[NSAP]. This document recommends that network implementors who
planned or deployed an OSI NSAP addressing plan, and who wish
deploy or transition to IPv6, should redesign a native IPv addressing plan to meet their needs. However, it also defines a
of mechanisms for the support of OSI NSAP addressing in an IPv
network. These mechanisms are the ones that must be used if
support is required. This document also defines a mapping of IPv addresses within the OSI address format, should this be required
2.5.6 IPX
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
The global aggregatable global unicast address is defined in [AGGR].
This address format is designed to support both the current
based aggregation and a new type of aggregation called exchanges
The combination will allow efficient routing aggregation for
sites which connect directly to providers and who connect
exchanges. Sites will have the choice to connect to either type aggregation point
The IPv6 aggregatable global unicast address format is as follows
| 3| 13 | 8 | 24 | 16 | 64 bits |
+--+-----+---+--------+--------+--------------------------------+
|FP| TLA |RES| NLA | SLA | Interface ID |
| | ID | | ID | ID | |
+--+-----+---+--------+--------+--------------------------------+
There are two types of local-use unicast addresses defined.
are Link-Local and Site-Local. The Link-Local is for use on a
link and the Site-Local is for use in a single site. Link- addresses have the following format
Anycast addresses are allocated from the unicast address space,
any of the defined unicast address formats. Thus, anycast
are syntactically indistinguishable from unicast addresses. When
unicast address is assigned to more than one interface, thus
it into an anycast address, the nodes to which the address assigned must be explicitly configured to know that it is an
address
For any assigned anycast address, there is a longest address prefix
that identifies the topological region in which all
belonging to that anycast address reside. Within the
identified by P, each member of the anycast set must be advertised
a separate entry in the routing system (commonly referred to as
"host route"); outside the region identified by P, the
address may be aggregated into the routing advertisement for
P
Note that in, the worst case, the prefix P of an anycast set may
the null prefix, i.e., the members of the set may have no locality. In that case, the anycast address must be advertised as separate routing entry throughout the entire internet, which
a severe scaling limit on how many such "global" anycast sets may supported. Therefore, it is expected that support for global
sets may be unavailable or very restricted
There is little experience with widespread, arbitrary use of
anycast addresses, and some known complications and hazards
using them in their full generality [ANYCST]. Until more
has been gained and solutions agreed upon for those problems, following restrictions are imposed on IPv6 anycast addresses
o An anycast address must not be used as the source address of
IPv6 packet
o An anycast address must not be assigned to an IPv6 host,
is, it may be assigned to an IPv6 router only
The "subnet prefix" in an anycast address is the prefix
identifies a specific link. This anycast address is
the same as a unicast address for an interface on the link with interfaceidentifier set to zero
Packets sent to the Subnet-Router anycast address will be
to one router on the subnet. All routers are required to support
Subnet-Router anycast addresses for the subnets which they
interfaces
The subnet-router anycast address is intended to be used applications where a node needs to communicate with one of a set
routers on a remote subnet. For example when a mobile host needs communicate with one of the mobile agents on its "home" subnet
FF01:0:0:0:0:0:0:101 means all NTP servers on the same node as
sender
FF02:0:0:0:0:0:0:101 means all NTP servers on the same link as
sender
FF05:0:0:0:0:0:0:101 means all NTP servers at the same site as
sender
FF0E:0:0:0:0:0:0:101 means all NTP servers in the internet
Non-permanently-assignedmulticastaddresses are meaningful
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
site bears no relationship to a group using the same address at different site, nor to a non-permanent group using the same group
with different scope, nor to a permanent group with the same
ID
The above multicast address is computed as a function of a node'
unicast and anycast addresses. The solicited-node multicast
is formed by taking the low-order 24 bits of the address (unicast
anycast) and appending those bits to the
FF02:0:0:0:0:1:FF00::/104 resulting in a multicast address in
The current approach [ETHER] to map IPv6 multicastaddresses
IEEE 802 MAC addresses takes the low order 32 bits of the IPv multicast address and uses it to create a MAC address. Note
Token Ring networks are handled differently. This is defined
[TOKEN]. Group ID's less than or equal to 32 bits will
unique MAC addresses. Due to this new IPv6 multicast
should be assigned so that the group identifier is always in the
order 32 bits as shown in the following
| 8 | 4 | 4 | 80 bits | 32 bits |
+------ -+----+----+---------------------------+-----------------+
|11111111|flgs|scop| reserved must be zero | group ID |
+--------+----+----+---------------------------+-----------------+
While this limits the number of permanent IPv6 multicast groups
2^32 this is unlikely to be a limitation in the future. If
becomes necessary to exceed this limit in the future multicast
still work but the processing will be sightly slower
o Its Link-Local Address for each
o Assigned Unicast
o Loopback
o All-Nodes Multicast
o Solicited-Node Multicast Address for each of its
unicast and anycast
o MulticastAddresses of all other groups to which the
belongs
APPENDIX A : Creating EUI-64 based Interface
--------------------------------------------------------
Depending on the characteristics of a specific link or node there
a number of approaches for creating EUI-64 based
identifiers. This appendix describes some of these approaches
The only change is inverting the value of the universal/local bit
Links or Nodes with IEEE 802 48 bit MAC'
[EUI64] defines a method to create a EUI-64 identifier from an
48bit MAC identifier. This is to insert two octets, with
values of 0xFF and 0xFE, in the middle of the 48 bit MAC (between
company_id and vendor supplied id). For example the 48 bit MAC
global scope
Note that this results in the universal/local bit set to "0" indicate local scope
Links without
There are a number of links that do not have any type of built- identifier. The most common of these are serial links and
tunnels. Interface identifiers must be chosen that are unique
the link
Manual Generated Random
Node Serial Number (or other node-specific token
The link-unique interfaceidentifier should be generated in a
that it does not change after a reboot of a node or if interfaces
added or deleted from the node
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
