| IP version 6 (IPv6), also known as IP
next generation (IPng), is a move to improve the existing IPv4
implementation.
The IPng proposal was released in
July 1992 at the Boston IETF
meeting, and a number of working groups were formed in response.
IPv6 tackles issues such as the IP address depletion problem,
quality of service capabilities, address auto configuration,
authentication, and security capabilities.
IPv6 is still in its experimentation
stage. It is not easy for companies and administrators deeply
invested in the IPv4 architecture to migrate to a totally new
architecture. As long as the IPv4 implementation keeps providing
hooks and techniques as discussed in 2.3.3 (as cumbersome as they
might be) to tackle all the major issues that IPv6 will
solve, adopting IPv6 might not seem very compelling to many
companies. How soon or how late people will migrate to IPv6 is yet
to be seen.
This section touches on part of the
IPv6 addressing scheme and how it compares to what you already have
seen in IPv4.
The IPv6 addresses are 128 bits long
(compared to 32 bits in IPv4). This should provide ample address
space to handle scalability issues in the Internet (128 bits of
addressing will translate into 2128 -- which is a lot of addresses).
The types of IPv6 addresses are
indicated by the leftmost bits of the address in a variable length
field called the Format Prefix (FP). This is illustrated in
Figure .
Figure outlines the initial allocation of these prefixes. IPv6 has defined
multiple types of addresses; we are interested in the provider-based
unicast addresses and the local use addresses for comparison with
IPv4 techniques.
Provider-Based Unicast Addresses
Provider-based unicast addresses are
similar to the IPv4 global addresses. The format of these addresses
is illustrated in Figure .
Descriptions of the address fields are as follows:
--
First
three bits are 010, indicating a provider-based unicast address.
REGISTRY ID
-- Identifies
the Internet address registry that assigns the PROVIDER ID.
PROVIDER ID
-- Identifies
the service provider responsible for this address.
SUBSCRIBER ID --
Identifies
which subscriber is connected to the service provider.
SUBNET ID
-- Identifies
the physical link to which the address belongs.
INTERFACE ID --
Identifies
a single interface among interfaces that belong to the SUBNET ID.
For example, this could be the traditional 48-bit IEEE-802 MAC address.
The IPv6 global address incorporates
the CIDR functions of the IPv4 scheme. Addresses are defined in such
a way as to allow hierarchy, where each entity takes its portion of
the address from an entity above it, as illustrated in Figures
and .
Local-Use Addresses
Local-use addresses are similar to
the IPv4 private addresses defined in RFC 1918. Local-use addresses
are divided into two types: Link-Local Use (prefix 1111111010),
which are private to a particular physical segment, and Site-Local
Use (prefix 1111111011), which are private to a particular site.
Figure illustrates the format of these local use addresses.
The local-use addresses have local
meaning. The link addresses have local meaning to a particular
segment, and the site addresses have local meaning to a particular
site.
Companies that are not connected to
the Internet can easily assign their own addresses without a need
for requesting prefixes from the global address space. If the
company later decides to interconnect globally over the Internet, a
REGISTRY ID, PROVIDER ID, and SUBSCRIBER ID will be assigned to be
used with the already assigned local addresses. This is a major
improvement over having to replace all private addresses with global
addresses or using Network Address Translation tables to get things
working in the IPv4 addressing scheme.
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