Facebook, Google and Yahoo are among the internet companies that will be trialling the IPv6 versions of their websites today, as part of World IPv6 Day.

This is the first global-scale trial of the long-anticipated upgrade to the internet's main communications protocol known as IPv4. IPv4 was first developed in 1977 and then it was believed the bundle of 4.3 billion IP addresses, which allow devices to access the web, would be more than enough. However, the last five blocks of IPv4 address space were allocated to each of the Regional Internet Registries (RIRs) in February. It is thought that by the end of August, all of these addresses will have been used up. As a result, the alternative IPv6 standard must be used, otherwise thousands of consumers will find themselves unable to connect to the web.

"This is not a year 2000 thing. Planes are not going to start falling out of the sky," Philip Sheldrake, from non-profit group 6UK, which is helping to promote the standard, told the BBC.

"The web will continue to work, but future growth would be stymied. It is just like when we used up the phone numbers in London."

However, net firms need to upgrade their technology and website to handle the new protocol and many have been slow to implement this. It's hoped that World IPv6 day will raise awareness of the issue as well as looking at how well the technology works.

Consumers will also need a router that is capable of handling the technology, although it's thought a simple firmware update can recitfy this in the future. But for today, it's unlikely they'll run into problems if their equipment does not support the standard.

"The vast majority (99.95 percent) 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 said in a blog.

"However, as with any next-generation technology, there may be teething pains. We estimate that .05 percent 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 said was probably due to "misconfigured or misbehaving home networking equipment, such as home routers, that can make a computer think it has IPv6 connectivity when in fact it's not working".

Meanwhile, RIPE NCC, the not-for-profit organisation that supports the infrastructure of the internet, will be monitoring the websites of organisations to see how well their IPv6 technology works. The firm is also testing connectivity and performance of the sites and displaying the results on its IPv6 Eye Chart, allowing web users to see if there are any problems.

According to Chris Davies, general Manager for D-Link UK and Ireland, while the transition to IPv6 will be hardly noticeable to most users, businesses have a cause for concern, especially if their daily operations depend on the internet.

"Networks using equipment lacking IPv6 support may experience complications when communicating with users operating IPv6 devices. Therefore, network administrators must make sure their current networks are IPv6-capable as soon as possible. In addition, as the transition from IPv4 to IPv6 will not happen overnight, businesses will need networks to support both protocols simultaneously."