The computing industry has begun a major 24-hour test today to work the kinks out of IPv6, a disruptive but necessary overhaul of the Internet's inner workings.

Starting at midnight, Universal Coordinated Time on June 8--or 5 p.m. PT today--dozens of companies lit up servers, Web sites, and network infrastructure that communicate using Internet Protocol version 6. The test, called World IPv6 Day, provides a bit of deadline, albeit one that's more artificial and less pressing than the Y2K bug's January 1, 2000, zero hour.

Unfortunately, the IPv6 test could disrupt the Net for some people who have badly configured hardware or software, with a Web site taking more than two minutes to load instead of a few seconds. Fortunately, though, the problem probably won't affect very many people, and the test will help identify any trouble spots.

Yahoo estimates 0.05 percent of visitors to its Web site will see very slow response when their computers request IPv6 information that can't actually be received. That's a tiny percentage, but multiplied by Yahoo's huge traffic, it's still something like 30,000 to 50,000 people a day, said Adam Bechtel, the vice president for Yahoo's Infrastructure Group, who's overseeing the company's IPv6 transition.

"It is significant. We have been notifying users," for example, by adding a notice on the Yahoo home page to notify users if their network connection may be broken, Bechtel said. "We've had over a million hits to our IPv6 help page."

What will the network look like for those who are affected

"These users will experience a range of symptoms which could include slow page load times--really slow, like several minutes, not just a little slow," said Owen DeLong, who runs the professional services division at Hurricane Electric, a back-end Internet service provider that has had a concentrated IPv6 program for years. "In fact, the most common characteristic symptom is that a page element will stall for 90 seconds, then load at normal speed at the end of that pause. In some cases, the pause could be as much as three minutes. Other symptoms could include simply being unable to reach certain Web sites and other intermittent connection issues.

"These users should contact their ISP for help in troubleshooting these issues as soon as they notice them," DeLong said. "This will allow the ISPs to identify the problems their customers are having and work on identifying resolutions to those problems before we try this again."

World IPv6 Day began at Google, Facebook, and Yahoo, and since then has spread to many other companies. It's overseen by the Internet Society, a standards and advocacy group.

Though some number of ordinary folk will find out they have a problem with their Net connections, there's a bigger agenda at work here, too: to get sysadmins the world over to make the necessary steps to support IPv6.

World IPv6 Day has been a hard-to-miss warning flag, an occasion where chief information officers might pester the IT staff to get cracking on IPv6 if they haven't already. And for those who have begun, it's an opportunity to find out if operations really are up to snuff.

The amount of Internet traffic going through Hurricane Electric&39's IPv6 global backbone soared as World IPv6 Day began.

Why bother IPv6 has one very compelling advantage over today's standard, IPv4: it accommodates vastly more Internet Protocol addresses--the numbers that are used to label every packet of data that traverses the Internet.

And guess what The Internet has run out of IPv4 addresses, at the wholesale level at least, meaning that it's getting harder to secure a new address for your new start-up or Web service unless you happen to be one of the lucky few early Internet arrivals that have large tracts of the Internet address space.

As a result of a 1977 decision by Vint Cerf, an Internet guru who now works for Google, IPv4 has 2^32 addresses, or about 4.3 billion. The computing industry has stretched that number through techniques such as network address translation (NAT) that let multiple devices share a single IP address, but that poses network complications, and even with it, Internet service providers and mobile phone operators who have to hand out lots of IP addresses are running out.

IPv6, though, offers 2^128 addresses. If you do the math, that works out to 340,282,366,920,938,463,463,374,607,431,768,211,456, or 340 undecillion for short.

The big problem, though, is that IPv4 and IPv6 networks are incompatible. That means the transition is more complicated than, say, moving from USB 2 to USB 3, where your USB 2 camera plugs into a USB 3 port with no troubles or your USB 3 hard drive still works over a USB 2 connection.

On World IPv6 Day, companies will indicate to the Internet's Domain Name System (DNS) when they have IPv6 servers available. That means IPv6-capable equipment will find and use the servers rather than just sticking with the IPv4 versions.

Exercising this system with real-world traffic should be instructive, said John Curran, chief executive of the American Registry for Internet Numbers (ARIN), a group that doles out IP addresses

"Internet service providers will have the first opportunity to gain insight into potential customer issues via World IPv6 day," Curran said. "World IPv6 Day...provides an important test of IPv6 functionality in the global Internet while also reminding people that we are indeed running out of IPv4 address space."

IPv6 has been around for more than a decade, but without the exhaustion of IPv4 addresses, there wasn't much incentive to add support. Now that's changing.

"In the first quarter alone of 2011, ARIN had already received requests from more than 500 service providers for IPv6 address space," Curran said. "That's greater than 400 or so requests in the entirely of 2009 and suggests that requests for the 2011 year may be three times greater than approximately 700 requests received in the entirely of 2010."

Smooth transition The IPv6 transition is complicated, expensive, and drawn-out.

CompTIA, a trade group for information technology professionals, surveyed 400 U.S. IT and business decision-makers about the IPv6 transition. The result: "Just 31 percent of respondents believe the transition to IPv6 will be mostly smooth," the organization said.

Yahoo's been working on its transition for three years already. It concluded that it's impractical to rewrite all its own software to be IPv6-compatible, Bechtel said. For example, software to target ads to particular regions or to prevent site abuse sometimes rely on IPv4 addresses. Instead of rewriting all the code, Yahoo has put a layer of proxy servers in front of its Web site that intercepts traffic and routes it accordingly.

New software from the company includes IPv6 support, but the legacy code base will probably take four years to gradually replace, Bechtel said.

But if you're not in charge of servers and networks, it shouldn't be so rough.

One reason: browser makers have begun to address the matter. For example, Google's Chrome will check both IPv4 and IPv6 connections, then deliver Web pages from whichever produces results fastest. That should help sidestep the super-slow Web page loading time that will afflict misconfigured equipment.

And as the transition spreads from the Internet's core systems to the broadband network gear people have in their homes, the transition should be less disruptive.

"Most users will be unaware that their ISP has switched them over to using IPv6," said Timothy Winters, senior manager for the University of New Hampshire's InterOperability Laboratory, which tests home network equipment for IPv6 support. That equipment, though, is only just beginning to support IPv6 fully, so there's still work to be done.

The tech industry is responding to the challenge the way it knows best: with another logo on the product box. The UNH-IOH is working with another group, the IPv6 Forum, to create an "IPv6 Ready" logo.

A logo won't patch over the difficulties of the transition. But it is a real signal that the industry is coming to terms with the IPv6 shift.