Hundreds of companies, organizations and institutions around the world are taking part in "World IPv6 Day," including Internet giants such as Facebook, Google, Microsoft and Yahoo!
Internet Protocol version 6 is the new system of unique identifying numbers for websites, computers and other Internet-connected gadgets and is replacing the original addressing system, IPv4, which is nearing exhaustion.
IPv6 provides more than four billion times more addresses than IPv4 -- more addresses, for example, than there are grains of sand on Earth.
The number of available IPv4 addresses will run out later this year and the transition to IPv6 is needed to keep pace with the explosive growth in Internet use.
US networking company Cisco forecast in a report released this month that the number of devices connected to the Internet will top more than 15 billion by the year 2015, more than double the world's population.
Web users, for the most part, will be oblivious to the switch to IPv6 since an IP address such as 18.104.22.168, for example, will still appear in the address bar as google.com.
Google, which is enabling IPv6 on Google Search, Gmail, YouTube and other services, said "the vast majority (99.95 percent) of people will be able to access services without interruption" during the IPv6 test, which began at 0000 GMT Wednesday and is to last for 24 hours.