A little over a year ago, I wrote an article about the IPv4 address consumption with the subtitle IPv4 Address Space: 2.46 Billion Down, 1.25 Billion to Go. A week ago, we reached the magic number of 2.7 billion IPv4 addresses used. With 3.7 billion possible addresses,¹ this means we now have less than a billion unused IPv4 addresses left. There are 39 blocks of 16.78 million addresses in the IANA global pool and another 339 million addresses that have been given out by IANA to the five Regional Internet Registries, but not yet delegated to ISPs or end-users.

So, how long will a billion quench our thirst for addresses? Geoff Huston at the Asia Pacific Network Information Centre has written a script that downloads the relevant information and creates daily predictions. The current ones target 10 February 2011 as the moment that IANA will give out the last of its blocks to one of the regional registries, and 17 December 2011 as the day that the last RIR will hand out the last IPv4 address to an ISP (or end-user).

Personally, I've always thought that Geoff's model is a bit pessimistic; in order to run out of addresses in a little over three years, we'd have to increase the rate at which addresses are handed out by 30 percent each year. In 2007, the increase over 2006 was 19 percent. The year before that there was no increase to speak of.

However, we're now so close to running out that the exact figures don't really matter anymore. Regardless of whether we see our yearly IPv4 use stay flat or increase by 70 percent, the results all point in the same direction:

Yearly increase Run out date 0 percent December 2013 10 percent November 2012 20 percent April 2012 30 percent December 2011 50 percent June 2011 70 percent February 2011

In other words, unless something unexpected happens, we'll be out of IPv4 addresses at some point in the neighborhood of 2012. So when the next Olympics come around, it's very possible that some of us will have to watch them online over IPv6. (Actually the official website of the 2008 Olympics is already available over IPv6.)

If all of this inspires you to try out IPv6 on your own system, have a look at SixXS.net. The people at SixXS run a "tunnel broker" and have developed an Automatic IPv6 Connectivity Client Utility (AICCU) that make it possible to get an IPv6 address and tunneled connectivity that works through Network Address Translators and most firewalls. Unfortunately, the AICCU utility isn't particularly easy to install and configure, so only give this a try if you're comfortable debugging network connectivity issues and running programs from the command line.

¹ 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.