As of one week ago the total number of IPv4 addresses in use reached 2.7billion, with a total of 3.7billion possible. This means that there are less than 1billion IPv4 addresses that are currently available for use.
IPv4 addresses are 32 bits long, which allows for 4,294.97 million unique combinations. However, the addresses starting with 0 and 127 (33.55 million in total) can’t be used because those address ranges are shortcuts for the default route and localhost address. Addresses starting with 224 – 239 are multicast addresses (268.44 million) and those starting with 240 – 255 are “class E” addresses (another 268.44 million), which are reserved for future use. Unfortunately, almost all operating systems and routers block these addresses in some way, so in practice they’re unusable. The three ranges of private addresses (10.x.x.x, 172.16.x.x – 172.31.x.x, and 192.168.x.x) add up to 17.89 million addresses, making for a total of 588.32 million unusable addresses.
Current estimates claim that the last IPv4 addresses will be assigned in 2012, just in time for the next Summer Olympics.
IPv6 will fix a number of issues in IPv4, such as the total number of available addresses. IPv6 also adds many improvements to IPv4, such as routing and network auto-configuration. IPv6 will eventually replace IPv4, however the two will coexist for a number of years during the transition.
Some websites are currently available in IPv6, such as the 2008 Olympics Website, however setting up your system to work with IPv6 takes a little bit of work, and it only suggested for those who are comfortable with debugging their network.
While IPv6 is the future, users will have at least four years before they really need to worry about changing over to the new IPv6 standards; and hopefully new computers will come with the IPv6 standards installed.