Stateful packet inspection firewalls Second-generation stateful packet inspection (also known as dynamic packet filtering) firewalls have the following characteristics:

● They operate up to Layer 4 (Transport layer) of the OSI model and maintain state information about the communication sessions that have been established between hosts on the trusted and untrusted networks.

● They inspect individual packet headers to determine source and destination IP address, protocol (TCP, UDP, and ICMP), and port number (during session establishment only) to

determine whether the session should be allowed, blocked, or dropped based on configured

firewall rules.

● After a permitted connection is established between two hosts, the firewall creates and

deletes firewall rules for individual connections as needed, thus effectively creating a tunnel that allows traffic to flow between the two hosts without further inspection of individual packets during the session.

● This type of firewall is very fast, but it is port-based and it is highly dependent on the

trustworthiness of the two hosts because individual packets aren’t inspected after the

connection is established.