Several of the internet's most popular websites - including Facebook, Google and Yahoo - have agreed to participate in the first global-scale trial of IPv6, the long-anticipated upgrade to the internet's main communications protocol known as IPv4.

The trial - dubbed 'World IPv6 Day' - requires participants to support native IPv6 traffic on their main websites on June 8 2011. Leading content delivery networks Akamai and Limelight Networks have also committed to the IPv6 trial, which is being sponsored by the Internet Society.

"It's an exciting opportunity to take IPv6 for a test flight and try it on for a full 24 hours," says Leslie Daigle, the Internet Society's chief internet technology officer. "Hopefully, we will see positive results from this trial so we will see more IPv6 sooner rather than later."

IPv6: running out of addresses

IPv6 is a necessary upgrade because the internet is running out of IP addresses using the 30-year-old IPv4 standard.

Less than 5 percent of IPv4 addresses are left unallocated to the regional internet registries, which in turn dole them out to network operators. Experts say the free pool of IPv4 addresses will be depleted in a matter of weeks. IPv4 uses 32bit addresses and can support 4.3 billion devices connected directly to the internet. IPv6, on the other hand, uses 128bit addresses and supports a virtually unlimited number of devices - 2 to the 128th power.

When World IPv6 Day occurs, there's likely to be a surge of IPv6 traffic across the internet. Today, IPv6 represents less than one-twentieth of 1 percent of overall Internet traffic, according to Arbor Networks.

One issue is whether IPv6 will be up to the task of providing production-grade performance on such heavily trafficked sites.

The Internet Society estimates that a minority of internet users - 0.05 percent - will experience slowdowns or have trouble connecting to participating websites during the trial because of misconfigured or misbehaving network equipment, primarily in their home networks.

"There may be some individual hiccups for some small access providers or users, but IPv6 is not an experimental technology," Daigle says. "I do believe it will work."

The day-long IPv6 trial is a critical development for content providers such as Google and Facebook, which until now have been supporting IPv6 at separate, dedicated web addresses rather than on their main traffic-heavy websites. Google, for example, says it will enable IPv6 on its main websites - including and - for World IPv6 Day.

The event is also a big deal for Yahoo, which has been reluctant to support IPv6 because of concerns about using a DNS whitelisting approach like Google's, which provides IPv6 content only to users with known end-to-end IPv6 connectivity.

"Participating in World IPv6 Day will allow us to obtain real-life data that we can use to ensure a seamless user experience as we transition to IPv6," said Adam Bechtel, vice president of Yahoo's Infrastructure Group. "We welcome this opportunity to collaborate with the technical community and provide leadership in addressing the scaling challenges facing the internet."

In order to participate in 'World IPv6 Day', these companies must adopt a dual-stack deployment, which allows native IPv6 traffic to run alongside IPv4 traffic without shortcuts like whitelisting.

"These organisations have committed to full-on IPv6 access, with no whitelists or other [workarounds]," Daigle says. "Everybody who has an IPv6 address will get in their sites on that day.''

The Internet Society initiative comes on the heels of a move by the US military to nudge its IT vendors to support IPv6 on their public facing websites.The Office of Management and Budget went a step further in September, when it mandated federal agencies to support IPv6 in dual-stack mode on their public facing websites by fall of 2012.

The Internet Society is hoping that its World IPv6 Day will have a similar ripple effect, prompting content providers, ISPs, hardware manufacturers and operating system suppliers to transition to IPv6 as soon as possible.

"With IPv4 addresses running out, IPv6 is going to be the priority for network-dependent companies over the course of the next couple years," Daigle says. "This trial is an important step in demonstrating that IPv6 is a viable and feasible technology."

See also: Web addresses 'will run out by 2012'