Stateful packet filtering, also known as stateful packet inspection, monitors all active network connections, checking to ensure they are valid. This form of filtering analyzes the application layer of network packets to determine if they should be allowed through the firewall. Network administrators can set specific parameters for what packets are authorized to pass through to the network.
By recording session information, such as port numbers or IP addresses, this form of dynamic, stateful filtering offers a more robust form of network security.