Third Generation Firewall-Stateful Firewall

The stateful analysis technology is an extension of the packet filtering technology (also called "dynamic packet filtering" informally). Packet filtering based on connection state not only checks each packet as an independent unit, but also considers its history association.

The basic principle is described as follows:

The stateful firewall uses various state tables to keep track of activated Transmission Control Protocol (TCP) sessions and User Datagram Protocol (UDP) pseudo sessions. Then ACL determines the sessions that can be set up. Finally, only the packets associated with the sessions that are permitted are forwarded.