Which of the following is typically a characteristic of a stateful firewall?

A stateful firewall is designed to track the state of active connections and uses this information to determine which packets to allow through the firewall. By maintaining context about network connections, it can make more informed decisions based on the state of the traffic. This characteristic allows a stateful firewall to understand the context of traffic beyond just individual packets, enabling it to recognize whether packets are part of an established connection and to allow or block them accordingly.

This functionality is crucial for managing dynamic connections, such as those used in protocols like TCP, where the state of the communication is continuously evolving. A stateful firewall also keeps track of the connection state for both incoming and outgoing traffic, significantly enhancing security compared to packet-filtering firewalls that only inspect individual packets.

The other options do not accurately describe characteristics of stateful firewalls. For instance, checking packet headers only pertains to stateless firewalls. Blocking all incoming traffic is an overly simplistic and not inherently characteristic of stateful firewalls, as they can allow incoming traffic based on context. Finally, the notion of operating at the application layer is more aligned with application-layer firewalls rather than stateful firewalls, which generally function at the transport layer.