Authentication identifies users and accounting tracks user services. Security fundamentals questions test the boundary between identity, authorization, accounting, encryption, inspection, and access-control functions. Cisco CCNA 200-301 v1.1 includes this topic under Security Fundamentals, so the answer must be validated against normal Cisco device behavior and the operational wording of the scenario. The key is not simply recognizing a familiar acronym; it is identifying what the feature does, where it is configured, and what result it produces. The other answers confuse identity checking with traffic filtering, or they assign the correct security idea to the wrong device or protocol. In a real network, selecting the wrong option would either leave the feature nonfunctional, create a forwarding or security gap, or send troubleshooting in the wrong direction. The selected answer is the only one that matches the stated requirement and the way Cisco switching, routing, services, security, wireless, or automation functions are expected to operate. This is why the verified answer remains the best technical choice for the question.