Which of the following firewall types keeps track of each ongoing dialog between internal and external systems?

A.
Packet filtering

B.
Circuit-level proxy

C.
Stateful

D.
Application-level proxy

Explanation:
Stateful firewalls use state tables to keep track of each step of
communication between systems. This provides a higher level of protection than
packet filtering, because it makes access decisions based on the steps that have
already been completed in the dialog.