Internet Protocol Version 4, or IPv4, is the original addressing system for the Internet. IPv4 addresses are made of 32-bits of recombined digits, for a total of 4.3 billion unique addresses.
As of 2012, the number of usable IPv4 addresses was running out. Some prominent Internet companies, such as Google and Facebook, are currently deploying IPv6, the successor to IPv4. IPv6, which utilizes 128-bit addresses, has support for about 340 undecillion addresses.
On June 6, 2012, "World IPv6 Launch Day" was held. The purpose of the launch day was to push companies to transition their websites to support IPv6 connections.