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IPv6 is designed to be an evolutionary step from IPv4, rather than a revolutionary
upheaval. The changes introduced in the new protocol fall primarily into the
following categories::
- Expanded routing and addressing capabilities.
IPv6 increases the IP address size from 32 bits to 128 bit in order to support more
levels of addressing hierarchy and a much greater number of addressable nodes.
- Header format simplification.
As can be seen by comparing the headers for IP version 4 and version 6, several
of the IPv4 header fields have been dropped or made optional in order to reduce
the datagram processing cost and to reduce the header's bandwidth occupation as
much as possible, despite the fact that addresses are larger. Thus, even though
IPv6 addresses are four times longer than their IPv4 counterparts, the IPv6 header
is only twice as large as the IPv4 header.
- Improved support for options.
Changes in the way the IP header options are encoded allow for more efficient
forwarding, less stringent limits on the length of options, and greater
flexibility for introducing new options in the future. Using options becomes
a real possibility.
- Flow labeling capability.
A new capability is added to make it possible to label packets belonging to
particular traffic flows for which the sender requests special handing.
- Provision for future protocol extensions.
Perhaps the most significant change made in IPv6 is the abandonment of a protocol
which specifies all details completely in favor of a protocol whereby extensions
can be inserted.
- Control function optimization.
The ICMP (Internet Control Message Protocol) protocol for IPv6 is capable of managing
Multicast Groups and includes the so-called Neighbor Discovery mechanisms: among the
latter, the terminal autoconfiguration mechanisms and address resolution mechanisms
are particularly important.
- A new type of address called anycast address..
This address identifies a set of nodes, though a datagram sent to this address will
be forwarded only to one of the nodes.
- Authentication and privacy capabilities.
- 64-bit rather than 32-bit alignment.
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Suggested books:
- C. Huitema, "IPv6 The new Internet Protocol", Second Edition, Prentice Hall 1998
- S. Gai, "Guida a IPv6", Mc Graw Hill 1997
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