I have two domain controller (fault tolerance), both running DNS services, and the clients use these two dns addresses. I read in MS articles that I cannot add External ISP DNS to the Domain controller dns (fwd. servers) since it will make the AD services v. slow and not reliable. Is this true? If yes, where should I point to the external ISP DNS address? I have to define the External DNS so the clients can obtain the IP address for external websites.