The Internet runs on a transport protocol called “Internet Protocol” or IP for short. As of 2007 the bulk of the Internet uses version 4 (aka IPv4). This transport protocol is used to move data between users, and is used by applications such as web browsers to talk to web servers.

As with any resource, their are a finite number of IPv4 addresses available and at some point in time the world is going to run out of IPv4 addresses. The exact timing is a hotly debated but the common consensus is that this will occur between 2010 and 2015. Once this point is reached no new computers can be added to the Internet.

To resolve this problem a new version of IP was created, version 6, or more commonly known as IPv6. IPv6 greatly increased the number of addresses available. The catch is that IPv6 is not compatible with IPv4. An IPv6 connected computer can not talk to an IPv4 computer. So several migration strategies exist, such as running both IPv4 and IPv6 on computers at the same time. Eventually the bulk of the world will convert to IPv6 and the IPv4 stack will be used less frequently and eventually die off (in the very *very* distant future).