Which of the following is a common feature of stateful firewalls?

Stateful firewalls are characterized by their ability to track the state of active connections and make decisions based on this context. They analyze the traffic contextually by keeping a record of all ongoing connections, allowing them to understand whether incoming packets are part of an established connection or if they are unsolicited requests. This contextual awareness enables stateful firewalls to provide more robust security than stateless firewalls, which treat each packet in isolation without regard for its connection state.

In contrast, focusing solely on IP addresses, as suggested in the first option, is a function of stateless filtering that does not take connection status into consideration. The third option, inspecting payload contents, is more aligned with deep packet inspection techniques, which can be applied in various types of firewalls, not specifically stateful ones. Lastly, while manual rule updates can be a part of firewall management, stateful firewalls can automatically track and manage active connections, reducing the need for constant manual adjustments for every individual connection.