The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 6 (IPv6) / IP Next Generation (IPng)                      9  IPv6 Overview, Changes and Transition

Major Changes And Additions In IPv6 1 2 3 IPv6 Addressing

IPv4-IPv6 Transition Methods

Due to the time that change takes, IETF has been working on specific provisions to allow a smooth transition from version 4 to version 6, and hardware and software interoperability solutions to let newer IPv6 devices access IPv4 hosts. A technique was included in IPv6 to allow administrators to embed IPv4 addresses within IPv6 addresses. Special methods are defined to handle interoperability, including:

• “Dual Stack” Devices: Routers and some other devices may be programmed with both IPv4 and IPv6 implementations to allow them to communicate with both types of hosts.
  
  
• IPv4/IPv6 Translation: “Dual stack” devices may be designed to accept requests from IPv6 hosts, convert them to IPv4 datagrams, send the datagrams to the IPv4 destination and then process the return datagrams similarly.
  
  
• IPv4 Tunneling of IPv6: IPv6 devices that don't have a path between them consisting entirely of IPv6-capable routers may be able to communicate by encapsulating IPv6 datagrams within IPv4. In essence, they would be using IPv6 on top of IPv4; two network layers. The encapsulated IPv4 datagrams would travel across conventional IPv4 routers.

Bear in mind that these solutions generally only address backward compatibility, to allow IPv6 devices to talk to IPv4 hardware. Forward compatibility between IPv4 and IPv6 is not possible because IPv4 hosts cannot communicate with IPv6 hosts—they lack the knowledge of how IPv6 works. It is possible that certain special adaptations might be created to allow IPv4 hosts to access IPv6 hosts. But eventually, all IPv4 devices of any importance will want to migrate to IPv6.

The IETF has done such a good job in the past with introducing new technologies, and so much effort has been put into the IPv6 transition, that I am quite confident that the transition to IPv6 will come off with few, if any, problems. One good thing about the transition is that IPv4 is, at the present time, still getting the job done, so there is no big hurry to make the move to version 6. While technologies such as CIDR and NAT are “band-aids” on IPv4, they have been very successful ones in extending the useful life of the aging protocol.

Major Changes And Additions In IPv6 1 2 3 IPv6 Addressing