An RIR is entitled to ask for more addresses based on how fast it is assigning addresses and how many it has left, Vegoda said. For the Asia-Pacific, North American and European registries, that means being able to ask for new blocks of addresses if they are on a path to running out within nine months. (The Latin American and African RIRs are handing out addresses less quickly because demand is lower for them.) At its current rate, APNIC could need two /8 blocks within nine months, Vegoda said.

IPv4, instituted in 1983, allows for only about 4.3 billion addresses, and from the beginning there have only been 256 of the /8 blocks. , and many are reserved for special uses such as multicasting of video streams.

IPv6 has a much larger address space, which allows for an almost limitless number of unique addresses. The IANA allocates IPv6 addresses in a similar way to IPv4, except in much larger "/12" blocks, Vegoda said.

The expanded address space is expected to be most critical to users in quickly developing countries such as China and India, as well as for the many new mobile devices being used for Internet access. The transition to IPv6 will be gradual, but even an enterprise that has enough IPv4 addresses should start supporting IPv6 in order to reach the new end points that won't be able to get IPv4 addresses, Vegoda said. Otherwise, they eventually will need to go through devices on ISP networks that translate between the two protocols. Those could introduce delays, and possibly communication problems if they were incompatible with certain protocols, he said.

Google, Facebook, Cisco Systems, Verizon Business and other major vendors and service providers . For 24 hours, the participating companies will run their public websites on both IPv4 and IPv6.