CompTIA Network+ (N10-009)Network TroubleshootingMedium
A network technician is troubleshooting a server that is intermittently losing network connectivity. The server's event logs show 'Link down' and 'Link up' messages occurring frequently. The server is connected via a Cat6 cable to a switch port. A cable tester shows the cable is good, and the switch port has been verified as operational. What is the MOST likely cause of this intermittent issue?
- AIP address conflict.
- BLoose cable connection.
- CDuplex mismatch.
- DFaulty SFP/transceiver.
Show answer & explanationAnswer & explanation
Correct answer: B. Loose cable connection.
Frequent 'Link down' and 'Link up' messages directly indicate a physical layer issue where the connection is being lost and re-established. Given that the cable tests good and the switch port is fine, a loose or intermittent connection at either end of the cable is the most probable cause.
Why the other options are wrong
- A. An IP address conflict would cause connectivity issues but would not typically manifest as 'Link down/up' messages in the event logs.
- C. A duplex mismatch causes severe performance degradation but usually maintains a consistent link state, not frequent link flaps.
- D. This scenario specifies a Cat6 cable, implying copper, not fiber with SFP/transceivers. If fiber, a faulty SFP would be a strong candidate.
Link Flapping
A condition where a network interface or port repeatedly changes state from up to down and back up again.
- Often indicates a physical layer problem (cable, connector, NIC, port).
- Can be caused by loose connections, faulty hardware, or power issues.
- Causes network instability and intermittent connectivity.
Memory trick: Link keeps leaping, likely loose.