200-301 Question 78
Single answerA network administrator is troubleshooting a connectivity issue between two directly connected switches. The administrator notices that the connection is up, but there are frequent CRC errors and collisions reported on the interface. What is the MOST likely cause of this issue?
- A
The interfaces on both switches are configured with a speed mismatch.
- B
The interfaces on both switches are configured with a duplex mismatch.
- C
The Ethernet cable used between the switches is damaged.
- D
The interfaces on both switches are configured with different IP addresses.
Show answer and explanation
Correct answer: B
Explanation
CRC errors and collisions are commonly caused by a duplex mismatch. In this scenario, the connection is up, but frequent errors are observed, indicating that the physical layer is functional yet there is a misconfiguration at the data link layer. A duplex mismatch occurs when one side of the connection is set to full-duplex and the other to half-duplex, leading to collisions and errors during data transmission.
- A. Incorrect.
A speed mismatch typically causes a link to fail completely rather than result in CRC errors or collisions. The link would not come up if the speeds do not match.
- B. Correct.
A duplex mismatch is a common cause of CRC errors and collisions because one side of the link operates in full-duplex mode while the other operates in half-duplex mode, leading to improper communication.
- C. Incorrect.
A damaged Ethernet cable could cause CRC errors but is less likely to result in collisions unless the damage is severe or intermittent. However, this scenario points more towards a configuration issue.
- D. Incorrect.
IP address configuration differences are irrelevant to layer 1 and layer 2 issues like CRC errors or collisions. IP addresses operate at layer 3 and do not directly affect the physical or data link layer.