There are a finite number of Internet protocol, or IP, addresses, the numeric codes that identify devices and destinations for the Internet. The current system, IPv4, has 4.3 billion (or 4.3 x 10^9) combinations to go around. This might all sound like boring Internet infrastructure stuff, but there's some serious drama going down, because the IPv4 addresses are almost all gone.
The Wall Street Journal reports that all remaining IP addresses in the United States will be claimed as of this summer. It's not a doomsday scenario—Asia ran out in 2011 and Europe in 2012—but it's a reality that companies and developers will need to face now, if they haven't started already.
Concerns about IPv4 are nothing new. A replacement for IPv4, known as IPv6, was approved in 1998 and has been available and implementable ever since. It offers 3.4 x 10^38 addresses (otherwise known as 340 trillion trillion trillion), so it's certainly a viable solution.
In a big systems transition, though, there are always groups that hold out as long as possible on a legacy system, either out of laziness or lack of economic incentive. You don't need to look any further than the transition away from Windows XP to find a good example.
Some companies have been diligently preparing. Facebook, for example, has switched 90 percent of its network to IPv6. In contrast, Microsoft spent $7.5 million in 2011 buying 666,624 IPv4 addresses.
James Cowie, the chief scientist at Internet consulting firm Dyn, told the Journal, “Enterprises that don’t have a plan for what to do with this will have this brought up by their board.”
A number of sites, including Test-IPv6.com, will tell you whether or not your Internet connection supports IPv6 and if you're currently able to browse the IPv6-only Web (almost everything is still compatible with both systems right now). As I wrote almost two years ago, "we’re not exactly being blindsided by this issue."