In approximately 500 days, planet Earth is expected to run out of the unique numbers that identify the world's networked devices. The numbers are known as internet protocol addresses but if that sounds like geek, don't fret. They are probably more familiar than you realise.

An IP address uses four numbers from 0 to 255 to distinguish one computer from another. As an example, computers around the world can recognise the IP address 203.26.51.71 as a server for fairfax.com.au, which publishes this newspaper online.

There are more than 4 billion combinations. But the proliferation of networked devices means soon that will no longer be enough.

In a way, IP addresses are like phone numbers. Enter the digits of a phone correctly and your mum answers. Enter them incorrectly and a confused man named Sven hangs up. So the ability to uniquely identify everything in the computer world is essential.

IP addresses are like phone numbers in another way, too. Just as Australia had to move from seven-digit phone numbers to eight digits in the early 1990s, massive change will now be required globally to resolve the problem.

However, there's a complication.

''Unlike the telephone system, it's not easy to just add more digits,'' says the chief scientist at the Asia Pacific Network Information Centre, Geoff Huston.

Although every telephone number in Australia was successfully altered, the phones themselves didn't change. Humans simply dialled an extra number and mothers everywhere still answered.

But every web server, every iPhone, every router and everything else - possibly billions of devices - will need to be reconfigured or upgraded. ''The idea that every last one has to go back into the doctor for a new transplant does sound a bit frightening,'' Huston says. ''It's almost like having to teach every device a new language.''

Fortunately, a new language exists.

Computers now use IP version 4 and have since the 1980s. Its replacement is version 6, known as IPv6. For humans, little will change. The traditional way we visit a website, by typing google.com or facebook.com, won't be any different and personal computers will automatically use IPv4 or IPv6 as required.

The impending shortage has been apparent for more than a decade as the volume of networked devices has escalated but inertia has stymied efforts to prepare for IPv6, Huston says.

While personal computers have been capable of understanding IPv6 since Windows XP and Apple OS X, Huston says only about 5 per cent of devices are configured to do so. Among web servers, the figure is less than 1 per cent.

Internode is one of the few internet service providers that offers an IPv6 service. Telstra is among the many that do not. Tens of millions of mobile phones are on an IPv4 network only.

Technically, it's not all that difficult to enable IPv6. Logistically, it's a horrendous challenge.

The conversion can involve substantial costs, with little in return. ''It doesn't make your internet any shinier or any brighter, so customers won't pay more,'' he says.

Consequently, Huston predicts we will get to a point where large numbers of people will no longer be able to see everything on the internet.

So far, the dwindling storehouse of IP addresses has been managed with trickery that translates one IP address to another.

But by about late September next year, the key body that distributes IP addresses will run out of them. Three months after that, every drop in the pipeline will dry up and the only way to get an IPv4 address will be to buy one from someone else.

Lacking that, consumers whose computers are not configured to use IPv6 won't see new websites.

Likewise, iPhones, which don't understand IPv6, will be limited to the ''old'' internet. For businesses that are not prepared, this could spell trouble. Unless web servers and mobile phone services are configured to send information via IPv4 as well as IPv6, companies could be left with a fraction of their current customers.

The good news is that once IPv6 is in place, it should satisfy demand as far as a computer can calculate. ''If every single address was one grain of sand,'' Huston says, ''in IPv6 you could build 300 million planets the size of Earth.''