Smart DNS A smart traffic filtering option that allows a Domain Name System (DNS) client to resolve a domain name from a DNS server while providing protection against DNS attacks from the network. This option blocks all Domain Name System (DNS) traffic except outgoing DNS requests and the corresponding reply. If a client computer sends a DNS request and another computer responds within five seconds, the communication is allowed. All other DNS packets are dropped. Smart DNS does not block any packets; blocking is done by the normal security rule set.