Thanks for answer. I don’t really care about 6to4, the sole fact that it didn’t work in the first place shows the exact reason why this technology has been deprecated.
But I guess you should apply similar ban to the Teredo well-known prefix 2001::/32, as there are also untrusted third-party gateways. Anyway, due to ephemeral nature of Teredo addresses, there would be virtually zero of then the public DNS, I guess.
But I still insist your servers should be polite and reply to ICMPv6 echo requests, like they do in the IPv4 world. I hope you also don’t block ICMPv6 “Packet Too Big” messages as such would break the Path-MTU discovery – see RFC 4890.