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incremental, with few or no critical interdependencies. Most of today's internet uses IPv4,
which is now nearly twenty years old. IPv4 has been remarkably resilient in spite of its age,
but it is beginning to have problems. Most importantly, there is a growing shortage of
IPv4 addresses, which are needed by all new machines added to the Internet.
IPv6 fixes a number of problems in IPv4, such as the limited number of available IPv4
addresses. It also adds many improvements to IPv4 in areas such as routing and network
auto configuration. IPv6 is expected to gradually replace IPv4, with the two coexisting for
a number of years during a transition period.
What’s changed in IPV6?
The changes from IPv4 to IPv6 fall primarily into the following categories:
• Expanded Routing and Addressing Capabilities – IPv6 increases the IP address size
from 32 bits to 128 bits, to support more levels of addressing hierarchy and a much
greater number of addressable nodes, and simpler auto-configuration of addresses.
The scalability of multicast routing is improved by adding a "scope" field to multicast
addresses.
• A new type of address called a "anycast address" is defined, to identify sets of nodes
where a packet sent to an anycast address is delivered to one of the nodes. The use of
anycast addresses in the IPv6 source route allows nodes to control the path which
their traffic flows.
• Header Format Simplification - Some IPv4 header fields have been dropped or made
optional, to reduce the common-case processing cost of packet handling and to keep
the bandwidth cost of the IPv6 header as low as possible despite the increased size of
the addresses. Even though the IPv6 addresses are four time longer than the IPv4
addresses, the IPv6 header is only twice the size of the IPv4 header.
• Improved Support for Options - Changes in the way IP header options are encoded
allows for more efficient forwarding, less stringent limits on the length of options, and
greater flexibility for introducing new options in the future.
• Quality-of-Service Capabilities - A new capability is added to enable the labeling of
packets belonging to particular traffic "flows" for which the sender requests special
handling, such as non-default quality of service or "real- time" service.
• Authentication and Privacy Capabilities - IPv6 includes the definition of extensions
which provide support for authentication, data integrity, and confidentiality. This is
included as a basic element of IPv6 and will be included in all implementations.
IPv6 Addressing
IPv6 addresses are 128-bits long and are identifiers for individual interfaces and sets of
interfaces. 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
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