A firewall is a hardware or software system designed to protect one network from another network. The various types of firewalls are covered in Table 4.
|Packet filtering||Uses lists to check the source/destination network address, source/destination port, and protocol.|
|Circuit-level gateway||Monitors at the Session layer of the OSI and checks relationships between hosts to ensure it is allowed traffic.|
|Application-level gateway||Known as a proxy, this device functions at the Application layer of the OSI. It has the most complex set of rules and can control access by user ID and policies.|
|Stateful inspection||Combination of all three of the other firewall types.|
A router is an ...