Diagnosing Duplex Mismatch: Interface Counters

B

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To diagnose a duplex mismatch problem, the interface counter you can use is the "late collisions" counter.

Duplex mismatch occurs when two devices connected to each other have different duplex settings, such as one device being set to full duplex while the other is set to half duplex. This can lead to various network issues, including performance degradation, packet loss, and connectivity problems.

Late collisions occur when a collision is detected on a network segment after the transmission has already begun. In Ethernet networks, a collision occurs when two or more devices transmit data simultaneously, resulting in the data becoming corrupted and needing to be retransmitted. Normally, collisions can occur during the initial transmission when two devices start transmitting simultaneously, but late collisions are an indication of a duplex mismatch problem.

When a duplex mismatch occurs, the device operating in full duplex mode can detect collisions from the device operating in half duplex mode. However, the device in half duplex mode cannot detect collisions from the device in full duplex mode because it is expecting to operate in a shared media environment where collisions are normal. As a result, late collisions are observed only on the side with the mismatched duplex setting.

By monitoring the "late collisions" counter on the affected interface, you can identify if a duplex mismatch is present. If you see a significant number of late collisions, it indicates a duplex mismatch issue between the devices connected to the interface.

Therefore, the correct answer to the question is:

B. late collisions