Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 154
IPv6 Addresses with Embedded IPv4 Addresses

A transitioning strategy that allows movement from IPv4 to IPv6 will be key to the successful implementation of IPv6—IPv6 will never be accepted if a one-time complete cutover needs to be applied. IPv4 is working, stumbling with addressing and routing table explosion, but working. It is embedded. Therefore, installations must be allowed to “try before they buy” into it. This is why other protocols that have tried to overtake TCP/IP have failed (OSI). You must have a compatible procedure in place. A great example, is Microsoft when it introduced Windows 95. It allowed for most Windows 3.x programs to run. Another great example is OS/2. It did not run the very popular Windows 3.1 programs very well and basically required a major cutover to make it work. We now see where Windows 95 is and OS/2 is not, so I think you know how important it is for IPv6 to be backwards compatible with IPv4. A transition scheme is provided courtesy of RFC 1933 and is not that difficult to read.

IPv6 hosts can use the IPv4 network as a virtual interface that enables these hosts to reach other hosts through tunnels. The address that is used to allow for this is a special type of link local address called the IPv4-compatible address, shown in Slide 169. Also needed for the transition is for hosts to become dual stack (supporting both IPv4 and IPv6 IP stacks) and tunneling. To allow for this, a mechanism is provided in the IPv6 addressing structure.

IPv6 Addressing with Embedded IPv6 Addresses

IPv4-compatible IPv6 address-0::0:IPv4 address.

There was another address method known as the IPv4 mapped address that would allow for translation, but this is out of favor and the method today is the preceding stated address scheme.