Stateful inspection

Also referred to as dynamic packet filtering. Stateful inspection is a firewall architecture that works at the network layer. Unlike static packet filtering, which examines a packet based on the information in its header, stateful inspection examines not just the header information but also the contents of the packet up through the application layer in order to determine more about the packet than just information about its source and destination.

A firewall architecture that tracks each connection traversing all interfaces of the firewall and makes sure they are valid.

A firewall inspection technique that examines the claimed purpose of a communication for validity. For example, a communication claiming to respond to a request is compared to a table of outstanding requests.