What is a primary characteristic of a stateful firewall?

A primary characteristic of a stateful firewall is that it maintains a table of active connections. This feature is crucial because the firewall tracks the state of active connections, allowing it to make more informed decisions about incoming and outgoing traffic. The stateful firewall remembers the context of previous packets exchanged during a connection, enabling it to differentiate between legitimate traffic that is part of an established session and potential threats. This dynamic approach allows for greater security and efficiency compared to stateless firewalls, which treat each packet in isolation without keeping track of its state.

The other options do not capture this essential function of stateful firewalls. While categorizing packets based on pre-set rules can occur in stateful firewalls, it is not the defining characteristic that differentiates them. Packet header inspection is a feature found in both stateful and stateless firewalls, and blocking all traffic indiscriminately does not reflect the selective nature of stateful firewalls, which are designed to allow or block packets based on connection states rather than blindly filtering all traffic.