Port security is a feature used on switches that allows the administrator to limit access to an interface by defining allowed hardware identifiers, commonly known as physical hardware addresses. This restriction helps in preventing unauthorized devices from connecting to the network. Enabling an access control list (ACL) is incorrect because ACLs filter traffic based on IP protocol suite and do not restrict interface access by the physical address of a device. Automatic Private IP Addressing (APIPA) is a method for assigning IP addresses within a private range, not controlling port access. Lastly, Quality of Service (QoS) refers to the management of data traffic to reduce latency and improve user experience, which is unrelated to restricting access on a port by identifying devices.