DNSクライアント関連テストなど
http://www.test-ipv6.com/
The test is entirely client-side javascript. To determine reachability, a series of ajax requests are made from the web server, using various DNS names that force the use of IPv6 only, or dual stack, or other such scenarios. The pass/fail of such fetches, as well as how long they take, are taken into account.
