Four of the root servers on the Internet will support IPv6 natively as of February 4, 2008. It will be possible for some servers to contact each other without using the IPv4 infrastructure that has served as the foundation of the Internet for the last 26 years. We’ve been hearing for more than a decade that our tried and true four octet IP addresses have to go because we’ll run out of them. You’ve seen IP addresses before. A common ‘private’ addresses is and it’s likely that your home network is on this subnet. With four digits, each from 1 to 255, there are 4,294,967,296 possible addresses. Or to put it another way, 232 addresses.

We haven’t run out because of NAT and the extensive use of private network addresses. Still, the time is coming and current estimates forecast that we’ll run out of IPv4 addresses in 4 to 20 years if we continue as we are.

So here comes IPv6 to solve the problem with 2128 addresses for us to use. At first glance, if you’re not a math geek, the difference between 32 and 128 doesn’t seem so large. It’s only 96, right? Yes it is, but the difference between 232 and 2128 is another matter entirely. When expressed as a power of two, the number doubles in size every time the exponent increases by one. So 232 is 4.29 billion and 233 is 8.59 billion. Double the number another ninety-five times and you’ve got a big number! Written out, IPv6 provides just over 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. That’s about 52,351,133,372,452,071,302,057,631,912 addresses for every person on earth (assuming an even 6.5 billion people). The Wikipedia states that this is more than a trillion addresses for every square centimetre on the surface of the Earth or, put another way, a million more addresses for every star in the observable universe than IPv4 provides in total.

Is it any wonder that critics say the size of the address space is overkill?

The transition will be long and troublesome. Windows Vista supports IPv6, The Mac’s OS 10.3 had it, and the Linux kernel has supported it since 1996. I imagine bad implementations of the IPv6 stack will cause trouble for a time. Even worse is the requirement that routers and other hardware be replaced with new models that support IPv6. It’ll take time, but it will happen eventually. I suspect regular users will be shielded from IPv6 for years because of NAT and tunnelling so there’s nothing for us to worry about yet.

One thing we take for granted that will be lost forever is the ability to remember an address. I can easily remember the IP addresses of my machines at home as well as a few at work, but this becomes unlikely when instead of the IPv4 address, an IPv6 address might be 2001:0db8:85a3:08d3:1319:8a2e:0370:7344.