A penetration tester finds an unused Ethernet port during an on-site penetration test. Upon plugging a device into the unused port, the penetration tester notices that the machine is assigned an IP address, allowing the tester to enumerate the local network. Which of the following should an administrator implement in order to prevent this situation from happening in the future?

Port security is the correct answer because it allows administrators to restrict which devices can connect to specific switch ports, often by MAC address. If an unauthorized device, like the penetration tester's, attempts to connect, the port can be configured to disable or alert. This directly prevents unauthorized network access via unused ports. Transport Layer Security (TLS) encrypts communication between applications over a network but does not control physical port access. A proxy server acts as an intermediary for requests from clients seeking resources from other servers, which is irrelevant to preventing unauthorized physical network access. Security zones segment networks for different trust levels but don't inherently prevent unauthorized physical connections to a specific port.