One of my colleague made me aware of this one today. I've seen this page in the past
] from Google and their IPv6 and didn't really read allt he details until today.
"Normally, if a DNS resolver requests an IPv6 address for a Google web site,
it will not receive one…
…but a DNS resolver with Google over IPv6 will receive an IPv6 address,
and its users will be able to connect to Google web sites using IPv6.
It looks like Google won't answer with its AAAA records to a DNS server if it has not been added to a white list ("qualified to Google Ipv6").
My explication: Google do not want their users to reach their web applications via a lame IPv6 connection when there's a fast and reliable IPv4 connection available. Modern operating systems prefer IPv6 and a dual stack user with a good IPv4 network and a lame IPv6 network will use the Ipv6 one to reach Google by default. If this is right I can say that they certainly care a lot for the user experience.... and the ability to display ads :)
What do you think of this?
P.S I don't think this applies to ipv6.google.com