Remember Y2K The Internet today is facing a similarly big problem all over again, but nobody knew exactly when it would hit--until now.

The problem is the day the conventional Internet runs out of room for new computers because the world has used up the supply of Internet addresses that computers need to communicate over the Net.

It's likely that this week or next, the central supplier of Internet Protocol version 4 (IPv4) addresses will dole out the last ones at the wholesale level. That will set the clock ticking for the moment in coming months when those addresses will all be snapped by corporate Web sites, Internet service providers, or other eventual owners.

And that means it's now a necessity, not a luxury, to rebuild the Net on a more modern foundation called IPv6.

It's taken a long time because there was little immediate payback for companies spending money and time to build IPv6 support. But even though the carrot to motivate people has been pretty small, the stick now is getting bigger with each passing week.

"Many are waiting for a 'killer application' for IPv6. This is a misconception," said Lorenzo Colitti, the Google engineer overseeing the search giant's years-long transition to IPv6, in a 2010 talk. "The killer application of IPv6 is the survival of the open Internet as we know it."

Only a tiny fraction of Google users--about 0.2 percent--are equipped to use the next-generation IPv6 technology that will relieve growth pressures on the Internet.

Minimizing disruptions Many expect some disruptions as the IPv6 shift takes place. Web sites could be slow or inaccessible, companies could have a harder time setting up new services, Internet service providers could have a hard time keeping up with subscriber growth, and security will have to adapt to the new technology.

The Net won't collapse, though.

Leslie Daigle, chief technology officer of the Internet Society, a standards and advocacy group, likens the situation to a changing separation of railroad tracks. Trains for one can't travel on tracks for the other, and moving data between the networks is, in effect, as onerous as unloading and reloading train cars' cargo.

"If you have a Web site, you are basically going to have some customers coming on wide gauge and on narrow gauge," Daigle said. "Narrow gauge is going away."

To give the world a chance to wrestle the IPv6 bull directly by the horns, the Internet Society is helping to organize the World IPv6 Day. On June 8, content providers such as Google and Yahoo and content distributors such as Akamai and Limelight Networks will offer their services over IPv6 for 24 hours for a collective evaluation and troubleshooting session.

That means, for example, that Google will enable IPv6 service on its primary domains, not just in a dedicated corner such as today's ipv6.google.com (that link won't work for most folks today). Those with IPv6 connectivity will help to stress test a tender new Internet.

People who want to get an earlier start can point their browser to an IPv6 readiness test page to see how far along they are. All modern personal computer operating systems can handle IPv6 with no trouble, but the connection to the Internet is another question entirely.

The end in sight--for years Experts have known for ages that the limit of 4.3 billion IP addresses would be a problem with the prevailing Internet Protocol version 4. The problem stemmed from a 1977 decision by Vint Cerf, who now is an Internet evangelist at Google.

At the time, just a few years into the Internet's history, he decided to use 32-bit Internet addresses. But 2 to the 32nd power, about 4.3 billion, looks a lot smaller in 2011 than in 1977.

"Who the hell knew how much address space we needed" Cerf told journalists in Sydney, Australia, recently.

It didn't take until today to figure out an answer to that question, though. That's why in the 1990s, Internet engineers developed IPv6, which has a practically inexhaustible supply. To be precise, 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses.

The big problem, though: IPv6 isn't compatible with IPv4, so making the transition is painful for a wide spectrum of the computing industry.

The Internet Assigned Numbers Authority, which doles out IPv4 addresses in blocks of 16.8 million called slash-eights or /8s to five organizations called regional Internet registries (RIRs), only has seven of the 256 "slash-8" blocksoriginal 256 /8s left. And after the next two are handed out, the remaining five will automatically be distributed to each of the RIRs, which in turn will offer them to Internet service providers, hosting companies, and others with an appetite.

Yahoo Japan&39's broadband service has been evaluating the best ways to offer IPv6 connections. It&39's not simple.

The imminent exhaustion of IANA's IPv4 addresses helps put a timetable on the IPv6 transition. That's a big change from the last decade, when IPv4 exhaustion was clearly going to happen but not on some specific schedule.

Setting a deadline The timing is helpful for getting planning in gear. In fact, it makes makes the IPv6 transition look more like Y2K, the expensive problem that peaked on January 1, 2000, when computers storing dates with only two digits could confuse 2000 with 1900. Like Y2K, the IPv6 transition requires companies to spend money on mundane infrastructure upgrades rather than exciting new revenue-generating services.

But there's a big difference between the Y2K and IPv6 challenges. Y2K was mostly limited to isolated computing systems. With the exhaustion of IPv4 Internet addresses, the entire Internet needs to be upgraded to IPv6--everything from Web sites to smartphones, from networked gaming consoles to routers that pass information across the Internet.

That means regular folks are going to be dragged into the IPv6 transition, said Martin Levy, director of IPv6 strategy at Hurricane Electric, a back-end Internet service provider that has had a concentrated IPv6 program for years.

"When you walk into [electronics stores such as] Fry's, Dickson's, or Comet, you look at the shelves and pick the wireless gateway you want for your home. You may want 802.11n or a printer port or storage," Levy said. "But at what point do you say, 'I want v6 enabled' You don't have a realization as a consumer that this is important."

And as with Y2K, when companies bought a glut of new servers to replace aging systems, there's money to be made from the IPv6 transition. Hurricane Electric isn't the only one with a sales pitch.

NTT America has had a specialized service for helping companies through the change. And AT&T, which "has invested millions of dollars to ensure that its own network and services are ready to make the transition to the new Internet Protocol," yesterday announced a consulting service for businesses facing the change.

Early adopters Not everyone is scrambling, though. Google is perhaps the best example of a company that's been working to adjust to IPv6 before crunch time. It's used IPv6 both for internal operations and, increasingly, external sites.

In 2008 came Google search over IPv6, with a public launch in January 2009. In March 2009 came Google Maps, then in August the first IPv6-enabled Android phones. In Feburary 2010, YouTube showed up, leading to an overnight surge in Google's outgoing IPv6 traffic.

"The key lesson that we learned was starting early and taking the transition slowly. It was cheap and relatively easy," Colitti told CNET. "We also found that an incremental approach was key: by bringing IPv6 to one service at a time and using shim layers when communicating with back-ends, it's possible to achieve slow but steady progress rather than have to tackle the whole code base at once. Unfortunately, it's getting late for that approach now."

Facebook, too, has been working on the problem, and like Google, has been avoiding the idea of separate internal infrastructure for IPv4 and IPv6.

"Since last summer, we've offered Facebook over IPv6 at www.v6.facebook.com," said Donn Lee, a Facebook network engineer. We leverage as much of the existing systems in our data centers to minimize separate paths and functions for v6. We are not unique in this practice. Others are following similar strategies. Having a parallel Facebook for v6 won't scale."

Where's the appetite for IPv6 data A huge amount, at least for Google in 2010, was France. That's because, Free.fr, a French Internet service provider that offers phone and TV service as well, made the jump to IPv6 in 2008.

They're still a rarity. Google statistics show that a little over 0.2 percent of Google visitors today would get Google services over IPv6 if they were offered on the company's primary domains rather than IPv6-specific addresses.

Unfortunately for early adopters, there can be an IPv6 penalty. IPv6 routes across the Internet can meander through distant, sometimes overloaded gateways rather than connect computers more directly, Yahoo IPv6 expert Jason Fesler said in a presentation last year. "A small percentage of the users will, when given the chance to connect to an IPv6 address, time out instead of quickly and transparently failing over to IPv4," he said.

In other words, at times, IPv6 servers will appear to be offline--something that makes Yahoo "a bit timid" about serving content over IPv6. It lags Google and Facebook, in part because of higher priority engineering projects, and plans to begin offering its services over IPv6 in late 2011, Fesler said.

That's changing, though. Gradually, nodes on the Internet will start getting wired into the IPv6 Internet, relieving congestion. Right now, by Hurricane Electric's measurements, 8 percent of those nodes are on IPv6.

"More and more networks are going v6' but that's a measurement in the core of the networks, not the end user connections," Levy said. "We see that improving day over day."

Worth it in the end Perhaps the best news about the IPv6 transition is that, once it's mostly over, the Internet will be a qualitatively different place. With vast tracts of IP addresses available, individual ones can be assigned to phones, computers, cars, stereo components, living-room thermostats, heads-up display glasses, wristwatches, home solar panels--you name it. Where a case can be made for networking, these devices will be able to communicate directly without the network topology shenanigans such as network address translation necessary today.

One consequence of that more direct connection is the elevation of peer-to-peer communications in the network. Central servers will remain important, but no longer necessarily a gateway.

Less revolutionary but probably more persuasive for those in the computing trenches, IPv6 makes the more mundane business of networking easier, too. There, perhaps, people can relish a little taste of the carrot even as they smart from the stick .

"Direct connections between users and sites...allows for faster, more reliable, more secure, and less costly Internet service," Facebook's Lee said. "Almost everyone in the Internet ecosystem is motivated along these lines."