DNS Recursion Desire restriction and Blacklist

Hi Kai, Thanks for your input.. i need DNS response to customize the DNS answer and redirect the request to some other server. But anyway, my iRule for DNS services is required for as " DNS will work ANS & recursive for ISPs own subscirbers, for external users only respond authoritative and redirect/drop the blacklist domain. I've written on rule but CPU goes high. Can you share some idea on it? Thanks.