Stateful Inspection Firewall
• The packet filtering that remembers what has happened in the recent past and changes its filtering rules dynamically as a result.
• A stateful inspection packet firewall tightens up the rules for TCP traffic by creating a directory of outbound TCP connections.
• There is an entry for each currently established connection. The packet filter will now allow incoming traffic to high-numbered ports only for those packets that fit the profile of one of the entries in this directory.
• A stateful packet inspection firewall reviews the same packet information as a packet filtering firewall, but also records information about TCP connections.
• Some stateful firewalls also keep track of TCP sequence numbers to prevent attacks that depend on the sequence number, such as session hijacking.