Which of the following is used to confirm that a physical port is working?

A loopback plug is a diagnostic tool used to test the functionality of a physical port on a device like a network interface card (NIC) or a switch. It redirects outgoing data signals from the transmit pins directly back to the receive pins of the same port. This allows diagnostic software to run a test, sending data and verifying it is received correctly, which confirms that the port's circuitry is working properly. It is a direct and definitive method for testing port hardware.

A. A network tap is a passive monitoring device used to capture and analyze traffic; it does not test the functionality of a port.
B. A crimper is a tool used to attach connectors, such as RJ45, to the ends of a cable. It is used for cable creation, not port testing.
C. A patch panel is a passive wiring component used to organize and connect network cables; it is not a diagnostic tool.

- University of Chicago, IT Services. (n.d.). Troubleshooting Network Connections. In guides for network technicians, the use of a loopback adapter is described as a standard procedure to test whether a network interface card is dispatching and receiving data correctly, isolating the port as a point of failure.

- Intel Corporation. (2021). Intel® Ethernet Adapters — Identify Your Wired Intel® Ethernet Adapter and Drivers. Vendor documentation for network adapters often includes troubleshooting steps that specify using a loopback plug to perform diagnostics on the physical port.