Akamai is running an online dashboard to measure World IPv6 Day traffic.
NEW YORK (CNNMoney) -- Today hundreds of Internet giants, including Google and Facebook, are participating in the first worldwide "test flight" of a major engineering upgrade to the Internet's infrastructure.
You didn't notice a thing? Good.
Wednesday is World IPv6 Day, a clunky name for an experiment that should be invisible to Web surfers but plays a critical role in keeping the Internet running smoothly.
One of the Net's foundational layers is the Internet Protocol, a global communications standard used for linking connected devices together. Every networked device you own -- your PC, smartphone, laptop, tablet and other gizmos -- has a unique IP address. The problem is that we're running out of them. The current system, called IPv4, has the technical capacity to handle 4.3 billion addresses. They're almost all used up: The last remaining batch was assigned out in February.
The solution is a next-generation protocol called IPv6. Just as the U.S. telephone system handled soaring growth by increasing the digits in each telephone number, the new IP system -- under development for more than 12 years -- uses longer addresses to fit more devices into the network.
The old system could handle several billion addresses. IPv6 has room 340 undecillion of them. That's 34 followed by 37 zeros -- enough for every human on Earth to have trillions of personal gadgets.
But the two systems aren't easy to integrate; they're essentially parallel, independent networks. Internet service providers, operating system manufacturers, browser developers and website operators have been working for several years on the extensive technical changes needed for the switch. Wednesday's experiment is the first global road test of their work.
For 24 hours, starting at midnight UTC (8 p.m. ET) more than 400 major websites around the world are switching their sites over to IPv6 delivery. Google (GOOG, Fortune 500), Facebook and Yahoo (YHOO, Fortune 500) are leading the charge.
When all works well, users won't even notice the change.
"The vast majority (99.95%) of people will be able to access services without interruption: either they'll connect over IPv6, or their systems will successfully fall back to IPv4," Google wrote earlier this week in a blog post about the test. "However, as with any next-generation technology, there may be teething pains. We estimate that .05% of systems may fail to fall back to IPv4, so some people may find Google, Facebook, Yahoo, Bing and other participating websites slow or unresponsive on World IPv6 Day."
Google has a tool posted at http://ipv6test.google.com/ that you can use to test your own connection.
'Ready for prime time': Planning for World IPv6 Day began last year through the Internet Society, a global standards-setting organization with headquarters in Geneva, Switzerland, and Reston, Va. Internet service providers said they were ready to support IPv6 -- but it would be an empty gesture without IPv6 content for them to steer their customers to.
Getting Google, Yahoo and Facebook all on board for the test deployment was key, according to Leslie Daigle, the Internet Society's chief Internet technology officer. It's an "everyone leap at once" moment. Even if the forecasts prove true and just a fraction of 1% of the Internet's users encounter glitches, that adds up.
"From a commercial business point of view for major content providers, it can represent a sizeable chunk of your customer base," Daigle says. "You don't want to anger thousands of your customers if you don't really see the need."
The Internet's most-trafficked sites are now seeing it. Facebook says the IPv6 transition is "vital" to the Web's continuing growth. It set up a page to help any users who can't access the site troubleshoot their connections.
Key behind-the-scenes players are also ramping up their IPv6 evangelism. Delivery networks Akamai (AKAM) and Limelight Networks (LLNW), which handle online content for major customers like ESPN, Netflix (NFLX) and Amazon (AMZN, Fortune 500), are participating in Wednesday's experiment.
Akamai made the test an opt-in offering for its thousands of Web customers. Around 30 took the bait. The company is running an online dashboard to measure the day's IPv6 traffic.
"General awareness is still relatively low," says Andy Champagne, Akamai's vice president of engineering. "IPv6 up until now has been more of an academic test case rather than a production use case. We believe that within the next couple years, the transition will almost be required."
He predicts that most sites will make the switch within the next five years, and maybe much sooner.
The Internet Society hopes Wednesday's test will be a tipping point.
"The key thing here was really to do the test flight so we could see if IPv6 is ready for prime time," Daigle says. "In a lot of ways I hope we don't need another one, because I hope we answer that question." 
