It is probable that a single machine gets a /64 ipv6 range, but the first 64 bits are consistent. When ipv6 gets more common it will probably be more acceptab

It is probable that a single machine gets a /64 ipv6 range, but the first 64 bits are consistent. When ipv6 gets more common it will probably be more acceptable to block an entire /64 if you suspect a brute force attack.