According to CompTIA A+ Core 1 220-1201 objectives under Networking:
A loopback plug is used to test a network interface card (NIC) port by sending a signal out of the port and back into the same port, verifying that the NIC can send and receive data properly .
This is a common diagnostic tool when troubleshooting network connectivity issues on individual devices.
Why the other options are incorrect:
B. Toner probe: Used for tracing and locating cables, not for testing NIC ports.
C. Cable tester: Checks the integrity of network cables but does not verify NIC send/receive functionality.
D. Network tap: Passively monitors network traffic but does not test the NIC port itself.
[References:, CompTIA A+ Core 1 (220-1201) Exam Objectives – Networking: “Given a scenario, use tools such as loopback plugs and cable testers to verify network connectivity.” , Mike Meyers’ CompTIA A+ Certification Guide, 13th Edition, Chapter on Network Troubleshooting Tools., , ]
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