220-1101 Question 450
Single answerPort flappingA technician is troubleshooting intermittent network connectivity for a desktop connected to a managed switch. Users report that the connection drops for a few seconds several times an hour. The switch log shows repeated messages that the access port is going up and down. The NIC drivers are current, and the problem affects only this workstation. Which action is the BEST next step to address port flapping?
- A
Replace or reseat the Ethernet patch cable between the desktop and the wall jack
- B
Configure the switch port for trunking to stabilize the link
- C
Increase the DHCP lease duration for the workstation
- D
Change the workstation from dynamic to static IP addressing
Show answer and explanation
Correct answer: A
Explanation
Port flapping on a switch generally indicates that the link state is repeatedly transitioning between up and down. In a desktop troubleshooting scenario, the most likely causes are physical-layer issues such as a bad patch cable, a loose connector, damaged wall jack termination, or a failing NIC. Because the problem is limited to one workstation and the switch specifically reports the port changing state, the technician should start with the simplest and most common fix: reseat or replace the Ethernet cable. This aligns with standard troubleshooting best practices: verify the physical connection first before making logical network changes. Vendor switch documentation from Cisco, HPE, and similar manufacturers commonly associates frequent interface up/down events with cabling faults, duplex/speed negotiation issues, or hardware failure rather than DHCP or IP addressing settings.
- A. Correct.
Correct. Port flapping means the physical link is repeatedly dropping and reconnecting. A damaged, loose, or poorly terminated cable is a common cause. Since the issue is isolated to one workstation and the switch reports the port itself going up and down, checking and replacing the patch cable is the best first corrective step.
- B. Incorrect.
Incorrect. Trunking is used to carry multiple VLANs between network devices such as switches, routers, or hypervisors. It does not fix an unstable physical link to a single desktop access port. Choosing this reflects confusion between link-state problems and VLAN configuration.
- C. Incorrect.
Incorrect. DHCP lease duration affects how long an IP address assignment remains valid, not whether the Ethernet link physically drops. A flapping port is a Layer 1 or Layer 2 connectivity issue, so changing lease time would not address the root cause.
- D. Incorrect.
Incorrect. Assigning a static IP might avoid some addressing issues, but it does not prevent the switch port from losing carrier and renegotiating. This option reflects the misconception that all intermittent connectivity is caused by IP configuration rather than a physical connection problem.