Cisco Certified Support Technician (CCST) NetworkingNetwork AccessMedium
A network professional is troubleshooting a slow network connection for a user. The user's computer is connected to a switch port. Examination of the switch interface status shows 'Half-Duplex' for the user's port, while the computer's network interface card (NIC) is configured for 'Auto-negotiate' and is expecting 'Full-Duplex'. This mismatch is causing significant performance degradation. What is the most common term for this specific issue?
- ASpeed Mismatch
- BDuplex Mismatch
- CNative VLAN Mismatch
- DVLAN Mismatch
Show answer & explanationAnswer & explanation
Correct answer: B. Duplex Mismatch
A duplex mismatch occurs when one side of an Ethernet link operates in full-duplex mode and the other side operates in half-duplex mode. This leads to severe performance issues, including late collisions, frame discards, and very slow throughput, because one side attempts to send and receive simultaneously while the other operates in a 'listen-before-talk' manner.
Why the other options are wrong
- A. Speed mismatch would mean one side is 100 Mbps and the other is 1 Gbps, which would likely result in no link or a link at the lowest common speed, but the core issue described is about duplex.
- C. Native VLAN mismatch applies to trunk links and causes communication issues for untagged traffic, not directly a performance degradation on an access link due to duplex settings.
- D. VLAN mismatch pertains to incorrect VLAN assignments, leading to communication issues between devices in different VLANs, not necessarily performance degradation on a single link.
Duplex Mismatch
A common Ethernet connectivity issue where one end of a link operates in full-duplex mode and the other operates in half-duplex mode.
- Results in late collisions, frame errors, and retransmissions.
- Causes severe network performance degradation.
- Often happens when auto-negotiation fails or is misconfigured.
Memory trick: Duplex mismatch: half-talk, full-listen, total confusion.