Chapter 2. IPv6 Overview


This chapter covers the following subjects:

  • IPv6 Addresses

  • IPv6 Packet Header Format

  • Extension Headers

  • ICMPv6

  • Neighbor Discovery Protocol

When the networks that eventually evolved into what we now call the Internet were first launched, they were the exclusive realm of academics and researchers. And when Vint Cerf and Bob Kahn invented TCP/IP for these networks, no one envisioned the Internet as it now is. At the time a 32-bit address space, yielding almost 4.3 billion addresses, seemed inexhaustible.

But as the kids who worked with these networks in college went out into the "real world," they took with them an appreciation of the possibilities for what could be done with a peer-to-peer network built on open standards. Increasingly useful network applications began cropping up, and recognition of the value of corporate connections to a public network began the push for a commercial Internet. At the same time that all this was happening, desktop computers were becoming common not only in the office but, most significantly, in the home. Yet modems were not a common accessory on those early home computers because few home users saw the value of being connected to a public network.

That changed with the advent of the World Wide Web. Suddenly, easy acquisition and sharing of information exponentially increased the value of desktop computers as a tool for nontechnical users. As a result, in less than 20 years the Internet has changed the way we communicate, do business, and learn. It has made the world a much smaller place, and has had profound impact on world economics and politics.

But this explosion in the size and diversity of the "Internet population" has introduced, along with daily nuisances such as spam and viruses, a serious technical concern: The once inexhaustible supply of IPv4 addresses has become distinctly finite.

The problem of IPv4 address exhaustion was recognized in the early 1990s, when various experts made projections showing that if the increasing rate of the allotment of IPv4 addresses continued, the entire address space could be depleted in just a few short years. A new version of IPknown in the development stage as IP Next Generation or IPng, and which is now IPv6was the proposed solution. But it was recognized that developing the new standards would take time, and that a short-term solution to IPv4 address depletion also was needed.

That short-term solution was Network Address Translation (NAT), which allows multiple hosts to share one or a few public IP addresses. Behind the NAT device, private IP addresses as specified in RFC 1918, and which you see in most examples in this book, are used. NAT has been so successful in slowing IPv4 address depletion, and has become such a standard part of most networks, that to this day many still question the need for a new version of IP. But the widespread use of NAT has changed the open, transparent, peer-to-peer Internet into something much more like a huge collection of client-server networks. Users are seen as being connected around the "edge" of the Internet, and services flow out to them. Seldom do users contribute to the overall wealth of the Internet. Seen from a more economic perspective, Internet users have become consumers only, not producers.

Although most of the IPv6 standards were completed years ago, it is only recently that serious interest in migrating from IPv4 to IPv6 has been shown. There are two fundamental drivers behind the growing recognition of the need for IPv6. The first is widespread vision of new applications using core concepts such as mobile IP, service quality guarantees, end-to-end security, grid computing, and peer-to-peer networking. NAT stifles innovation in these areas, and the only way to get NAT out of the way is to make public IP addresses abundant and readily available.

The second fundamental driver for IPv6 is the rapid modernization of heavily populated countries such as India and China. A compelling statistic is that the number of remaining unallocated IPv4 addresses is almost the same as the population of China: about 1.3 billion. With its aggressive expansion of its Internet infrastructure, China alone in the near future will represent an unsupportable pressure on an already strained IPv4 address pool. In India, with a population size close to China's, 4- and 5-layer NAT hierarchies exist just to support the present demands for IP addresses.

IPv6 replaces the 32-bit IPv4 address with a 128-bit address, making 340 trillion trillion trillion IP addresses available. That number will meet the demands for public IP addresses, and answer the needs of the two fundamental drivers discussed here, well into the foreseeable future.[1]

[1] Given what was unforeseen when IPv4's 4.3 billion addresses were thought to be limitless for all practical purposes, the almost inconceivably vast IPv6 address space will never be considered inexhaustible.




CCIE Professional Development Routing TCP/IP (Vol. 12005)
Routing TCP/IP, Volume 1 (2nd Edition)
ISBN: 1587052024
EAN: 2147483647
Year: 2005
Pages: 233

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net