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Major Changes And Additions In IPv6
the preceding overview, I explained that
the primary motivator for creating a new version of IP was to fix the
problems with addressing under IPv4. But as we also saw there, numerous
other design goals existed for the new protocol as well. Once the decision
was made to take the significant step of creating a new version of a
protocol as important as IP, it made sense to use the opportunity to
make as many improvements as possible.
Of course, there is still the problem
of the pain of change to worry about, so each potential change or addition
in IPv6 had to have benefits that would outweigh its costs. The resulting
design does a good job of providing useful advantages while maintaining
most of the core of the original Internet Protocol. The following list
provides a summary of the most important changes between IPv4 and IPv6,
showing some of the ways that the IPv6 team met the design goals for
the new protocol:
- Larger Address Space: IPv6
addresses are 128 bits long instead of
32 bits. This expands the address space from around 4 billion addresses
to, well, an astronomic number (over 300 trillion trillion trillion
- Hierarchical Address Space: One reason
why the IPv6 address size was expanded so much was to allow it to be
divided to provide a large number of each
of many classes of addresses.
- Hierarchical Assignment of Unicast Addresses:
A special global
unicast address format was created to
allow addresses to be easily allocated across the entire Internet. It
allows for multiple levels of network and subnetwork hierarchies both
at the ISP and organizational level. It also permits generating
IP addresses based on underlying hardware interface device IDs
such as Ethernet MAC addresses.
- Better Support for Non-Unicast Addressing:
for multicasting is improved, and support
is added for a new type of addressing: anycast addressing. This
new kind of addressing basically says deliver this message to
the easiest-to-reach member of this group, and potentially enables
new types of messaging functionality.
- Autoconfiguration and Renumbering: A provision
is included to allow easier autoconfiguration
of hosts and renumbering of the IP addresses in networks and subnetworks
as needed. A technique also exists for renumbering router addresses.
- New Datagram Format: The
IP datagram format has been redefined
and given new capabilities. The main header of each IP datagram has
been streamlined, and support added for easily extending
the header for datagrams requiring more
- Support for Quality of Service: IPv6 datagrams
include QoS features, allowing better support for multimedia and other
applications requiring quality of service.
- Security Support: Security support is
designed into IPv6 using the authentication
and encryption extension headers and other
- Updated Fragmentation and Reassembly Procedures:
The way that fragmentation
and reassembly of datagrams works has
been changed in IPv6, to improve efficiency of routing and better reflect
the realities of today's networks.
- Modernized Routing Support: The
IPv6 protocol is designed to support modern routing systems,
and to allow expansion as the Internet grows.
- Transition Capabilities: Since it was
recognized from the start that going from IPv4 to IPv6 is a big move,
support for the IPv4/IPv6 transition has been provided in numerous areas.
This includes a
plan for interoperating IPv4 and IPv6 networks,
between IPv4 and IPv6 addresses and more.
The rest of the sections on IPv6
provide much more detail on these changes and additions to IP. You'll
notice that the majority of these are related to addressing, since that
is where the greatest number of important changes have been made in
IPv6. Of course, routing and addressing are closely related, and the
changes to addressing has had a big impact on routing as well.
Another change that I should mention
is that with the introduction of IPv6, several other TCP/IP protocols
that deal intimately with IP have also had to be updated. One of these
the most important support protocol for IPv4, which has been revised
through the creation of ICMPv6 for IPv6. An addition to TCP/IP is the
Discovery (ND) protocol, which performs
several functions for IPv6 that were done by ARP
and ICMP in version 4.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
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