The internet: Just as car number plates and telephone dialling codes need to be updated every so often to allow for growth, so does the internet’s addressing system. But it should not need updating again any time soon

REMEMBER the panic over the “millennium bug”, when computers everywhere were expected to go haywire on January 1st 2000, thanks to the way a lot of old software used just two digits to represent the year instead of four? Doomsters predicted all sorts of errors in calculations involving dates when the clocks rolled over from 99 to 00. In the event, the millennium dawned without incident.

Something similar is about to happen again, and this time it cannot be ignored. The problem is the exhaustion of internet protocol (IP) addresses—the four numbers ranging from 0 to 255, separated by dots, that uniquely identify every device attached to the internet. According to Hurricane Electric, an internet backbone and services provider based in Fremont, California, the internet ran out of bulk IP addresses on February 3rd.

The Internet Assigned Numbers Authority, which oversees such things, had doled out all its so-called “slash-eight” blocks of addresses to the five regional internet registries around the world. The registries are expected to allocate all their remaining addresses to local network operators over the coming months. After that, any organisation applying for new addresses will be told: Sorry, none left.

The issue is real and has been a long time in the making. The Economist first wrote about it ten years ago. The problem is that the current version of the internet’s address system, called IP version 4 (IPv4), uses 32-bit numbers, and the total number of addresses possible with such an arrangement is therefore two raised to the power of 32—or roughly 4.3 billion in decimal terms. Back in the 1980s, when the internet connected just a couple of dozen research institutes in America, that seemed like a huge number.

But with the invention of the web in 1990 came an explosion in demand. It was soon clear that it was only a matter of time before the internet would exhaust its supply of addresses. Work on a replacement for IPv4 began in the early 1990s, with IPv6 finally being made available in 1998 (IPv5 was an experimental protocol for streaming audio and video that was abandoned). By giving the new internet version an address space of 128 bits, the designers pretty well guaranteed that it would not run out of unique identifiers for decades, or even centuries, to come.

Two raised to the 128th power is an enormous number: roughly 340 billion billion billion billion—or, as Martin Levy of Hurricane Electric likes to say, “more than four quadrillion addresses for every star in the observable universe”. That will come in handy when the “internet of things” becomes a reality. Already, some 2 billion people have access to the internet, many of whom own multiple devices. The use of Wi-Fi base-stations and routers that allow sharing of a single IP address has put off the day of reckoning for a while. But add all the televisions, phones, cars and household appliances that are currently being given internet access—plus, eventually, every book, pill case and item of inventory as well—and the need for IPv6 is clear.

Though a vast improvement, IPv6 is not without its problems. The biggest is that it is not directly backward compatible with IPv4. To reduce the amount of processing the routing computers have to do as they direct packets of data over the internet, IPv6 was given a far simpler packet format. That speeds things up no end. But although the two internet versions can coexist on a single device, they have to operate as two separate networks. When an IPv4 device needs to communicate with an IPv6 device, various relay services and tunnelling tricks have to be employed, with IPv6 packets getting wrapped inside IPv4 packets and vice versa.

It seems likely that the two separate internets will have to live side by side for the foreseeable future. That could mean putting up with interoperability hassles for decades—in the United States, at least. Being the inventor and earliest user of the internet, America received the lion’s share of addresses before today’s rules were put in place. As a result, many large companies, universities and government agencies still have plenty of spare IPv4 addresses lying around unused. The pressure to upgrade has therefore been minimal.

That is not the case elsewhere. The biggest single demonstration of IPv6 to date was during the 2008 Summer Olympics in Beijing, when everything from live television and data feeds to security and traffic information was streamed over a vast IPv6 network. Being a relatively latecomer to the internet, China has only one address for every four people. Hence Beijing’s desire to adopt IPv6 as rapidly as possible. The same goes for Russia, South Korea and Japan. NTT, Japan’s largest telecoms firm, has been offering IPv6 services to the public since 2000.

The next showcase for the new internet technology will be “World IPv6 Day” on June 8th. While doing all he can to help, Vint Cerf, one of the fathers of the internet (who now works at Google), warns that the day could be marred by painful configuration problems. But the main purpose of the event is to air precisely such difficulties and get their fixes circulated. Meanwhile the American Registry for Internet Numbers, which allocates blocks of IP addresses to internet service providers and other network operators throughout North America, has suggested that all public-facing websites in its region be ready to support IPv6 by January 1st 2012. Such initiatives should gradually move the internet from today’s world, with islands of IPv6 systems in a sea of IPv4, to a world with islands of IPv4 in a vast ocean of IPv6.

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