Which device performs stateful inspection of traffic?

A firewall performs stateful inspection of traffic. This means it monitors the state of active connections and makes decisions about packet filtering based on the context of these connections. For example, it will allow return traffic for an outbound request but block unsolicited inbound traffic. A switch operates at Layer 2 (data link layer) and forwards frames based on MAC addresses; it does not inspect traffic state. An access point provides wireless connectivity and bridges wireless to wired networks, without stateful inspection capabilities. A wireless controller manages multiple access points but does not perform stateful inspection of client traffic itself.