Check if you are blacklisted by Google over IPv6.

Google used to perform IP prefix whitelisting to enable clients to receive IPv6 services. This was an opt-in process, where a dual-stacked user explicitly signed up to receive Google services over IPv6. Since, the World IPv6 Launch Day, in order to favor the IPv6 upgrade path, Google has changed the policy. The whitelist has now been replaced by a blacklist. If you're allocated an endpoint from a blacklisted prefix, you'll not receive Google services over IPv6 even though you may be receiving IPv6 connectivity from your provider.