CompTIA A+ Core 1 (220-1201)Hardware and Network TroubleshootingMedium
A technician troubleshoots a workstation on a switch that intermittently drops packets and shows excessive collisions in the network adapter's statistics, even though the cable and NIC test as healthy. Which condition is the MOST likely cause?
- AAn IP address conflict with another device on the subnet
- BA misconfigured default gateway address
- CA duplex mismatch between the NIC and the switch port
- DAn expired DHCP lease on the workstation
Show answer & explanationAnswer & explanation
Correct answer: C. A duplex mismatch between the NIC and the switch port
A duplex mismatch, where one side is set to full-duplex and the other to half-duplex, commonly causes excessive collisions, late collisions, and intermittent packet loss even when the physical cable and NIC hardware are fine. This is a classic Layer 1/2 configuration issue distinct from IP-layer problems.
Why the other options are wrong
- A. An IP conflict typically causes connectivity errors or duplicate address warnings, not collision statistics.
- B. A bad gateway address affects routing to other networks, not local collisions.
- D. An expired DHCP lease would cause loss of an IP address, not collision counters.
Duplex Mismatch
Occurs when one network device is set to full-duplex and the connected device is set to half-duplex, causing collisions and degraded performance.
- Half-duplex expects collisions; full-duplex does not handle them
- Symptom: excessive collisions/late collisions with intermittent loss
- Fix: match duplex/speed settings, or use auto-negotiation on both ends
Memory trick: Two speakers talking at once (full) vs. taking turns (half) — mismatched, they collide.