Page last updated at 08:25 GMT, Monday, 4 February 2008

Q&A: IP Version 6

On 4 February a milestone was reached in the net's move to a new addressing system based on a technology known as IP Version 6 (IPv6). Here we attempt to explain what it is and why it is important.

What is IPv6?

Hourglass, Eyewire
Time is running out for IPv4 addresses
The IP in IPv6 stands for Internet Protocol and this is one of the foundational technologies that helps keep the global network running.

Every computer connected to the net has a unique IP address which ensures that it can be found if it is requesting data or sending it out.

Servers that host websites may have many IP addresses for the different sites they hold.

For instance, the IP address for is Typing the numbers into a browser address bar will get you to the same place as typing the words.

Similarly, when you switch your home computer on and connect to the net it gets allocated an IP address so data you request, such as a video stream, reaches the right machine.

IPv6 is the sixth version of the internet protocol. The current version, IPv4, was dreamed up long before the modern boom in web use which has meant that the pool of unique addresses that it provides for is running out.

How does IPv6 help?

It helps simply because it has a vastly larger pool of unique addresses available.

The upper limit of addresses possible with IPv4 is 4,294,967,296. This seems a lot but, for a variety of reasons, only about 14% of this total is currently unallocated.

Estimates vary about when the pool will run out but most experts believe we only have three or four years left before the pool runs dry.

Just as phone numbers regularly need to expand to cope with growing numbers of users so the net has to expand to cope with its growth. IPv6 is the way that addresses get expanded.

How many addresses can IPv6 support?

The short answer is: lots. The long answer is: an unimaginably huge amount.

It has been calculated that the IPv6 address space can handle about 340 trillion, trillion, trillion addresses. That's enough for every person on the planet to have trillions of IP addresses without any fear of that pool being exhausted.

What happens when IPv4 addresses run out?

The average user will not notice much difference. However, it could put a brake on expansion of the web but already many technical work-arounds are being used to overcome the shortage.

It could be possible to develop even more ad hoc fixes but IPv6 is preferable because it removes the need for these short-term fixes and makes administration of large networks more straightforward.

Can I get an IPv6 address?

If you run your own website you can ask your hosting company about them to see if you can get one for your site. Many net hosting and domain firms are starting to offer them alongside IPv4 addresses.

If you own a PC running Vista or a Mac with OS X installed then you could already be using IPv6. Both operating systems can handle IPv6 addresses and will use them if they are presented to them.

However, at the moment few sites have got an IPv6 address so that ability of those operating systems may never have been called upon.

What happened to IPv5?

Work was started on the protocol but it was going to be put to very different uses to its forerunner. It was developed as a better way to handle video, voice and distributed simulation over the net and was known as the Internet Stream protocol.

Sadly, by the time it had proved its usefulness and won a formal designation of IPv5 work was long advanced on what would become IPv6 and a decision was taken to pursue that.

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