SEARCH Articles Figures Tables 1A and D Internet and other digital network data travel in packets of limited sizes. Consists of the Data, Ack, Request or Command, Protocol Information, Source and Destination IP Address, Port Error Checking Code, etc. Filtering consists of examining incoming and outgoing packets compared with a set of rules for allowing and disallowing transmission or acceptance. Rather fast because it really does not check any data in the packet except IP header. Works in the network layer model. Fast but not foolproof. IP address can be spoofed. [Publishers Imprint]