What does the term "stateful inspection" refer to?

Stateful inspection refers to a firewall mechanism that monitors and records the state of active connections, allowing it to determine whether incoming packets are part of an established session or not. This capability enables the firewall to make more informed decisions about which packets to allow through based on the context of the connection, taking into account the state of the traffic and certain protocols involved.

Through stateful inspection, the firewall can maintain a state table that keeps track of ongoing sessions and their states, effectively allowing it to differentiate between legitimate return traffic from that which could be unsolicited or harmful. This is a key aspect of modern firewalls, enhancing security by providing more nuanced control compared to simpler packet-filtering techniques, which may only check header information without regard to connection states.

By focusing on the active state of connections, stateful inspection offers a more comprehensive approach to security, as it allows for rules to be applied dynamically based on the state of the connection rather than relying solely on static rules applied to incoming and outgoing traffic.