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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

IPv6 Overview, Changes and Transition 1 2 3 Major Changes And Additions In IPv6

“If it ain't broke, don't fix it.” I consider this one of my favorite pieces of folk wisdom. I generally like to stick with what works, as do most people. And IP version 4 works pretty darned well. It's been around for decades now and has survived the growth of the Internet from a small research network into a globe-spanning powerhouse. So, like a trusty older car that we've operated successfully for years, why should we replace it if it still gets the job done?

Like that older car, we could continue to use IPv4 for the foreseeable future. The question is: at what cost? An older car can be kept in good working order if you are willing to devote the time and money it takes to maintain and service it. However, it will still be limited in some of its capabilities. Its reliability may be suspect. It won't have the latest features. With the exception of those who like to work on cars as a hobby, it eventually stops making sense to keep fixing up an older vehicle.

In some ways, this isn't even that great of an analogy. Our highways aren’t all that much different than they were in the 1970s, and most other issues related to driving a car haven't changed all that much in the last 25 years either. The choice of updating a vehicle or not is based on practical considerations more than necessity.

In contrast, look at what has happened to the computer and networking worlds in the last 25 years! Today's handheld PCs can do more than the most powerful servers could back then. Networking technologies are 100 or even 1000 times as fast. The number of people connecting to the global Internet has increased by an even larger factor. And the ways that computers communicate have, in many cases, changed dramatically.

IPv4 could be considered in some ways like an older car that has been meticulously maintained and repaired over time. It gets the job done, but its age is starting to show. The main problem with IPv4 is its relatively small address space, a legacy of the decision to use only 32 bits for the IP address. Under the original “classful” addressing allocation scheme, we would have probably already run out of IPv4 addresses by now. Moving to classless addressing has helped postpone this, as have technologies like IP Network Address Translation (NAT) that allow privately-addressed hosts to access the Internet.

In the end, however, these represent patch jobs and imperfect repairs applied to keep the aging automobile that is IPv4 on the road. The core problem, the 32-bit address space that is too small for the current and future size of the Internet, can only be addressed by moving to a larger address space. This was the primary motivating factor in creating the next version of the Internet Protocol, IPv6.

IPv6 Overview, Changes and Transition 1 2 3 Major Changes And Additions In IPv6