Oops! How Many IP Addresses?

In our June article "Beating the Crunch", author Nicolas Boillot wrote about the coming upgrade to the Internet Protocol, the specification that rules the 'Net. The proposed upgrade, known as IPv6, for Version 6, is scheduled to launch in June of 2008. IPv6 will provide a startling number of new IP addresses for devices to communicate with one another. To make the point, Boillot wrote: "This number is so large that we have no words to describe it, but by one estimate there would be more than 2000 addresses for every square meter on Earth." Well, as one insightful Spectrum reader has pointed out, we vastly underestimated things.

IEEE Member Kenneth C. Miller has written a letter to the editor (which will appear in the Forum section of IEEE Spectrum magazine in August) that calls our attention to just how profoundly the number of addresses will increase using IPv6. We'll let him explain:

The value of 2128 is 340,282,366,920,938,463,463,374,607,431,768,211,456 . . . . Of more significance is the gross underestimation of the number of addresses per square meter of Earth's surface that IPv6 would afford. The surface of Earth is approximately 0.51 by 1015 square meters. Dividing that into 2128 addresses yields approximately 667 by 1021 (667 sextillion) addresses per square meter. So the estimate to which the author referred is short by a factor of roughly 333 quintillion.

According to the IPv6 Working Group, part of the Internet Engineering Task Force (IETF): "IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces. There are three types of addresses: Unicast, Anycast, and Multicast."

Sites such as Answers.com and the Wikipedia point to the number of addresses afforded by IPv6 as being 3.4 times 1038 addresses, or 5 times 1028 (50 octillion) for each of the roughly 6.5 billion people alive today. The first number agrees with Miller's math, the subsequent ones vary on details. However, let's not quibble. These are staggering amounts.

In defense of the author, we should note that the "2000 addresses per square meter" number has been bruted about by industry experts at conferences for years. Ever since its adoption by the IETF in 1994, champions of the new protocol have been trying to get 'Net users to imagine just how forward looking it is. Some of them, in their haste, may have shortchanged the mathematics and spoken in error with every good intention. And like any exciting anecdote about futuristic technology, it may have simply progressed to the level of a meme in the general discourse. These things happen. We hope this column helps to clear up the matter a little.

For the record, according to Miller, there are words to describe 2128: "three hundred forty undecillion." So, now we know. We apologize to our readers for any confusion.

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