The internet passes a major milestone today in a transition designed to stop it running out of addresses.

Hoever, one service provider warned that the industry needs to do more to avoid big problems in two to three years.

Most of the web uses version 4 of the Internet Protocol (IPv4), dating from 1981 when the system was much smaller. This uses 32-bit addressing, allowing for some four billion unique numbers, which with the proliferation of devices including IP-enabled phones is no longer enough.

A new version, IPv6, is being phased in that uses 128-bit addressing to give a barely imaginable number of addresses - 50 billion, billion, billion for every person on the planet today. So many that each of us could (indeed may) be given a personal address space larger than that of the current internet to provide a new fast way to access resources.

Islands of IPv6 are already in use, and Windows and many home routers support it; but infrastructure support has a long way to go and IPv6 traffic has to go through a cumbersome process of remapping onto the IPv4 address space.

But from today it should be possible to set up an all-IPv6 link because internet root servers have all been provided with the necessary address information. This is just the top level of the routing hierarchy, however, and there needs to be a lengthy and costly upgrade throughout the system.

Basically this involves service providers spending money that benefits users but brings in no extra revenue. Predictably few have done so.

One of those who have is Claranet, where group network engineering manager David Freedman warns of a looming crisis. “The internet is going to run out of addresses in 2010 or 2011. People are going to start hoarding addresses if nothing is done about it. There will be a black market in addresses.”

Organisations are staving off the problem by using network address translation (NAT): assigning addresses on an as-needed basis within a private address space.

Freedman said: “We encouraging people to put a proper strategy in place. They are not doing it at the moment because there is no user demand. We are trying to raise awareness of the issue to create that demand.”

He warns there could also be issues for users as some older or cheaper home routers may not support IPv6.