Web companies including Google, Facebook and Akamai are joining forces to test the Internet's readiness for a future in which billions more people and devices will be connected.
The pool of Internet addresses used for most traffic today is near exhaustion, but adopting IPv6 - a new Internet protocol with 4 billion times as many addresses - has been slow despite the fact that it is more than a decade old.
Publishers and Internet service providers have been waiting for the other to make the first move, and workarounds including translation services and address-sharing have become common.
But the prospect of large numbers of modern IPv6 networks coming online - especially in the developing world where systems based on the previous protocol, IPv4, are not widespread - is beginning to push organisations into action.
"What's at stake is the future scalability and utility of the Internet," says Matthew Ford, technology program manager of the Internet Society, a non-profit group dedicated to the open development of the Internet, which is organizing World IPv6 Day.
"IPv6 is fundamentally about allowing the Internet to scale to meet the expectations and demands of a global population of 7 billion, coupled with increased expectations of how many devices are expected to be able to connect to the Internet," he says.
IPv4's specifications were drawn up in 1981, when the population of the world was 4.5 billion and the personal computer age was just dawning with the launch of the IBM PC. It allowed for 4.3 billion IP addresses.
Today, more than 2 billion people are online, many with multiple computers and smartphones. By 2020, 50 billion devices may be connected as smart meters, connected TVs and remote health management proliferate.
For 24 hours on Wednesday, websites with more than 1 billion combined visits a day will join distribution companies to enable IPv6 on their main services. Yahoo, Limelight Networks and Verisign are some of those taking part.
It will be the first global test of IPv6 "in the wild." Previous tests in Germany and Norway showed positive results.
It is estimated that only one in 2,000 users will experience problems, but the aim is to identify unexpected problems and to raise awareness of the issue.
The collaboration of many top global Internet players is likely to prevent any single one being blamed for problems that may include slow connections or attempts timing out.
Less than 1 per cent of Internet traffic uses IPv6, but Internet registries, which manage the registration of domain names, say more computers are trying to connect on the new protocol.
Danny McPherson, chief security officer of network infrastructure company Verisign, expects interest to grow quickly as new IPv4 addresses run out. Asia-Pacific Internet registry APNIC is expected to be the first to exhaust its supply.
McPherson expects momentum to pick up as network equipment providers such as Cisco and Juniper finally see a market opportunity.
"It's more broken than people realize," he said. "People need to realize and move on."
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