Yahoo, Google, and Facebook have each been working on IPv6 for some time, but have been hesitant to simply flip the IPv6 switch and add an IPv6 address to their DNS records so everyone can reach them over IPv6. They fear becoming unreachable to users with broken IPv6 connectivity. Google did measurements in this area in 2008, which showed that at that time, 0.09 percent of their users would have to suffer delays as their computers try to connect over IPv6, and eventually fail and retry over IPv4.
So Google created the Google over IPv6 program, where network operators have to promise the search giant that they have good IPv6. In turn, Google will respond to DNS requests from those networks with IPv6 addresses for various Google properties such as google.com and youtube.com. The hoi polloi have to make do with just IPv4 or type ipv6.google.com. (Only works if you have IPv6.) Facebook has www.v6.facebook.com—with address 2620:0:1cfe:face:b00c::3. Ah, hexadecimal humor.
Yahoo, on the other hand, has suggested only giving IPv6 addresses to DNS servers that send requests over IPv6. (There is nothing wrong with sending a request for IPv6 addresses over IPv4 or the other way around, though.)
6to4 creates some problems
Broken IPv6 connectivity is often caused by 6to4 tunnels that don't work. 6to4 is a system whereby a computer or a home gateway can create IPv6 addresses from an IPv4 address and connect to the IPv6 Internet by encapsulating IPv6 packets inside IPv4 packets. A remote gateway then decapsulates the packets and encapsulates the packets in the other direction. The problem with 6to4 is that it depends on gateways operated by volunteers. Those gateways may work very well, be slow, or not work at all. And some ISPs don't bother delivering their user's packets to a gateway.
6to4 is only enabled if the system has a public IPv4 address. Places that give their users public IPv4 addresses, such as many universities, tend to use firewalls, which often filter out the IPv6-in-IPv4 packets. So broken 6to4 is not uncommon. However, after a recent Mac OS X 10.6 update, pretty much all operating systems prefer to use IPv4 over 6to4 IPv6 so broken 6to4 shouldn't cause any problems if there is still working IPv4.
The Internet Society expects that on IPv6 day, 0.05 percent of all users will see problems. With a billion unique visitors, that's still half a million people. If your job is phone support for one of these companies or an ISP, you may want to get your vacation request in as soon as possible. The advantage of many large Web destinations enabling IPv6 on the same day is that everyone will be on the lookout for IPv6-related problems, so those can be fixed quickly. If you don't want to wait that long, visit test-ipv6.com to evaluate your readiness.
At this point, it's hard to predict what this experiment could mean for the amount of IPv6 traffic that flows through the Intertubes. If a lot of users are IPv6-enabled, a good amount of traffic can move from IPv4 to IPv6 overnight. This depends on how many additional sites and networks join the effort, though.
In the meantime, on Monday, APNIC, the registry that gives out IP addresses in the Asia-Pacific region, got two more blocks of 16.78 million IPv4 addresses from IANA. APNIC burned through no less than 23.7 million in January—twice as much as their monthly rate in 2010. There's only five blocks left now. These final five are expected to find a home on Thursday morning during a webcast ceremony in Miami.
Oh, and what happens when World IPv6 Day is over?
They turn IPv6 off again. Considering the fact that we're scraping the bottom of the IPv4 barrel right now, and APNIC may even be clean out of addresses by June, maybe the Internet Society should reconsider that part of the plan.
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