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IPv6 Addressing
IPv6 addresses are 128-bits long and
are identifiers for individual interfaces and sets of interfaces.
Since each interface belongs to a single node, any of that node's
interfaces' unicast addresses can be used as an identifier for the node.
A single interface may be assigned multiple IPv6 addresses of any type.
There are 3 types of addresses: unicast, anycast and multicast.
Approximately 15% of the address space is initially allocated to the
reserved addresses such as NSAP (Network Access Service Point)
addresses, IPX addresses, etc. The remaining 85% is reserved for
future use. |
| Unicast Addresses There are several forms of unicast address assignment
in IPv6. There are global provider based unicast addresses,
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.
Provider Based Unicast
Addresses: they are used for global communication.
| 3 | n bits
| m bits
| o bits
| p bits | o-p
bits |
+-----------+-----------+-------------+---------+----------+---------+----------+-------|010|REGISTRY
ID|PROVIDER ID|SUBSCRIBER ID|SUBNET ID| INTF. ID|
+-----------+-----------+-------------+---------+----------+---------+----------+------- |
1st 3 Bits: identifies the address as a provider - oriented unicast address.
REG: identifies the
internet address registry which assigns provider identifiers
(PROVIDER ID) to internet service providers, which then assign
portions of the address space to subscribers.
SUB: distinguishes
among multiple subscribers.
SUBID: identifies a specific physical link.
INTF.ID: identifies a single interface among the others identified by the subnet prefixes.
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Local-Use Addresses: has only local routability
scope (within the subnet r within a subscriber network), and may have
local or global uniqueness scope.
There are 2 types of local-use unicast addresses.
Link-local to use on a single link and the Site-Local to use in a single
site.
| 10
|
| bits
| n bits
| 118-n bits
|
+----------+-------------------------+----------------------------+
|1111111010|
0
| INTERFACE ID
|
+----------+-------------------------+----------------------------+
Link-Local-Use |
|
10 |
| bits
| n bits | m bits
| 118-n-m bits
|
+----------+---------+---------------+----------------------------+
|1111111011| 0 |
SUBNET ID |
INTERFACE ID |
+----------+---------+---------------+----------------------------+
Site-Local-Use |
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Interface ID: an identifier that has to
be unique in the domain in which it is being used, usually use a node's
IEEE-802 48 bits address.
Subnet ID: identifies a specific subnet in a site.
Both
together forms a local use address allowing a large private internet to be constructed without any other address allocation.
However, if the organization later wants to connect to the global
internet, it can use its SUBNET ID and INTERFACE ID in combination with
a global prefix (REGISTRY ID+ PROVIDER ID + SUBSCRIBER ID) to create a
global address. |
| Anycast Addresses
It is an address that is assigned to more than one
interfaces (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, when used as
part of an route sequence, permits a node to select which of several
internet service providers it wants to carry its traffic. This
capability is sometimes called "source selected policies". This would be
implemented by configuring anycast addresses to identify the set of
routers belonging to internet service providers (e.g., one anycast
address per internet service provider). These anycast addresses can 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. Other possible uses of anycast addresses are to identify the
set of routers attached to a particular subnet, or the set of routers
providing entry into a particular routing domain.
Anycast addresses are allocated
from the unicast address space, using any of the defined unicast address
formats. Thus, when a unicast address is assigned to more than one
interface, 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. |
| Multicast Addresses
It is an identifier for a group of interfaces.
| 8
| 4 | 4
|
112 bits
|
+------ -+----+----+---------------------------------------------+
|11111111|FLGS|SCOP|
GROUP ID
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+--------+----+----+---------------------------------------------+
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1s:
identifies the address as being a multicast address.
FLGS: reserved, and must be initialized to 0.
T=0 indicates a permanently assigned multicast address.
("well known")
assigned by the global internet numbering authority.
T=1 indicates a non-permanently assigned multicast address. ("transient")
SCOP: 4-bit multicast scope value used to limit the scope of the
multicast group.
GROUP ID: identifies the multicast group, either
permanent or transient. |
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