Have you ever wondered how your email or web page manages to travel across the Internet and end up where it's meant to be? You'd be right in assuming that there is a scheme that controls this: before any message can be sent across the Internet it must be given a kind of digital envelope, and like a letter, it must have a destination address and a return address.
The Internet Protocol (IP) is the precise definition of the digital envelope and the format of its addresses. The current version of the Internet Protocol, from the early 1980s, is number 4 - hence IPv4 - and its modern replacement is IPv6. (IPv5 was assigned to a project but not implemented.)
For Internet computers to be able to send and receive messages, their addresses must be unique and of a fixed size. With IPv4 there are only a certain number of possible addresses - just as the number of digits in a telephone number determines the maximum number of subscribers. IPv4 has almost reached its use-by date. Nearly all possible IPv4 addresses have been allocated to networks and computers - and unlike telephone numbers, when you run out of IP addresses you can't just add another digit.
It is hard for us to remember numbers, so there is an overlay called the Domain Name System (DNS) that allows us to give names to commonly used addresses; this lets you go to www.yourcompany.com.au instead of having to remember and type in a dozen digits. But the numbers - the IP addresses - form the real foundation of the Internet.
IPv4 provides 4.2 billion (4.294 x 109) addresses. Though this sounds like a very large number, in today's mobile world it isn't. With widespread and increasing adoption worldwide, it was only a matter of time before IPv4 came under pressure. It took 38 years for radio to achieve an audience of 50 million; it took 13 years for TV, and just 4 years for the Internet, so the writing is on the wall.
Even though most computers and networks today are perfectly capable of handling IPv6, this was not true when the address shortage began to bite about ten years ago. Various stopgap solutions were invented to eke out IPv4 resources, and because they seemed to solve the problem, the world just went on using IPv4.
One way was with the use of 'private' IP addresses. Think of these like an office block with a street address where mail is delivered. People in the foyer have to distribute the mail and know about every business in the building. No-one can send anything directly to a particular office (they have to hand it over in the foyer), and it is hard to know what went wrong if a package gets lost. If there are a lot of businesses or a lot of mail, delivery takes longer.
Security on the Internet is another issue where private addresses pose a problem. For instance, it's difficult to trace where attacks comes from - the best you can do is identify an 'office block'. Trusted systems can't really be trusted if they traverse private networks. The compromises being made across the IPv4 network are costing a lot of time and money and are hampering innovation.
In fact, these stopgap solutions just delayed the inevitable. Today we face the same shortage again, but this time there are no more quick fixes to be had. Soon there will be no more new IPv4 allocations, and existing IPv4 addresses will become a limited, expensive, dead-end commodity. Imagine trying to set up a new business and being told you couldn't have a telephone because there were no more numbers!
Having lots of addresses doesn't just fix the scarcity problem: with IP addresses available in abundance, new ways of thinking and new ways of doing things can be dreamed up. Innovation can flourish. IPv6 is a cleaner and more elegant protocol, so software, routing and addressing equipment can be made simpler - thus cheaper, more robust, and easier to build new things with - another stimulus for innovation. There is a world of benefit in IPv6.