The number Internet addresses grew from 4.3 billion unique addresses to 340 undecillion (trillion trillion trillion). That's growth of 79 octillion (billion billion billion). The Internet is running out of addresses.
The current IP standard, IPv4, was structured like this: xxx.xxx.xxx.xxx, with each "xxx" able to go from 0 to 255. IPv6 is structured like this: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx. expands that so each "x" can be a 0 through 9 or "a" through "f,". IPv4 will continue to exist alongside IPv6 for years, just as digital and analog TV were broadcast side-by-side for years.
Major Internet players will be IPv6 compliant going forward. many However routers, devices and operating systems won't be. For instance, Microsoft Windows XP, which is still the world's most-used desktop operating system, is not IPv6-compliant.
A year ago, on June 8, 2011, all those participating networks and sites turned on IPv6 for a day-long test run to look for potential cyber attack opportunities. It went off without any significant problems and they reverted to IPv4 the next day. This time, the change is permanent. It'll be a slow transition, but it needs to be done.