Last month's World IPv6 Day created some excitement about IPv6. Once it was over, however, everyone went back to work—which for most people doesn't include anything IPv6-related.

The idea behind World IPv6 Day on the 8th of June was to flush out broken IPv6 setups by simultaneously turning on IPv6 across a large number of Web properties—including the four largest in the world. Few, if any, problems were reported, so in that sense WIPv6D was a resounding success. Apparently, it's possible to add IPv6 addresses to large Web destinations without significant adverse effects.

In the video above from the Velocity 2011 conference, Yahoo's Ian Flint explained that none of this was as easy as it looks to outsiders. The video starts getting interesting at around the six-minute mark. For instance, Yahoo had decided that it would pull out of the experiment if traffic dropped by 5 percent or more. The Web giant did two 15-minute trials before IPv6 Day, and when it began the second one, traffic dropped by 5 percent. But strangely, the drop started shortly before IPv6 was enabled at 2am. It turned out that traffic drops by 5 percent every day at 2am, so when they enabled IPv6 for World IPv6 Day, they did so 17 minutes before the hour, a nice round prime number, just in case.

The big question is whether WIPv6D has moved closer the day that we'll all be running IPv6, leaving IPv4 to connoisseurs of obsolete technologies. Well, yes, a little. Looking at the graphs at the bottom of Lars Eggert's IPv6 deployment trends page, there is a big spike in the number of Alexa top 500 Web destinations that have an IPv6 address in the DNS on June 8. But in the way of WIPv6D, IPv6 capability remains at a higher level than before. For some measured countries, this level is still visibly increasing, while for others it looks stable. The United States is an exception to this trend, with the number of websites with IPv6 having declined somewhat in the previous 40 days.

Looking at the yearly trends picture of the IPv6 traffic of the DE-CIX Internet exchange in Frankfurt, IPv6 traffic did go up with WIPv6D and not back down afterwards. However, IPv6 traffic was much higher until a year ago. In this case, I suspect that the big decrease around July 2010 was the result of the increasing IPv6 traffic being rerouted around the exchange point and not because of an actual reduction in IPv6 traffic. But it's hard to know these things for sure.

But as I wrote in February, it's unfortunate that the Internet Society and the Web companies that initiated World IPv6 Day made it a one-off event. APNIC, the organization that distributes IP addresses in the Asia-Pacific region, is only distributing one last block of 1024 addresses per ISP because it's down to its last 17 million addresses. The RIPE NCC, which performs the same function in Europe, the former Soviet Union, and the Middle East, will be facing the same situation within twelve months, possibly even before the end of the year. The other regions have a little more time, but not by much.

The IETF realized almost two decades ago that the Internet couldn't continue to work with 32-bit addresses. A few years later, it published the first IPv6 specification, upgrading the address length to 128 bits. Many more IPv6-related protocol specifications followed. And even though most of these specifications have been implemented in hard- and software and the world has been running on IPv4 address fumes since February.

There are people who think it's possible to have a usable Internet once we reach the stage where the different pools of unused IPv4 addresses have been exhausted without using IPv6. It looks like we're going to find out the hard way whether this is the case.