Cisco CCNA Exam: Reasons for Difficult Diagnosing of Duplex Mismatches

Reasons for Diagnosing Duplex Mismatches

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What are two reasons that duplex mismatches can be difficult to diagnose? (Choose two.)



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A. B. C. D. E.


Duplex mismatch is a network issue that occurs when two devices are configured with different duplex settings, such as one device operating in half-duplex mode and the other in full-duplex mode. This can cause performance issues, packet loss, and connectivity problems.

Here are the two reasons why duplex mismatches can be difficult to diagnose:

  1. The interface displays a connected (up/up) state even when the duplex settings are mismatched: This means that the physical layer connection is established and the interface is considered "up" by both devices. However, this does not mean that the devices are communicating effectively. When there is a duplex mismatch, one device may be transmitting while the other is receiving, causing collisions and retransmissions. These collisions can cause performance degradation, which may not be immediately apparent. Therefore, the "up/up" state can be misleading, and the true cause of the problem may not be immediately apparent.

  2. The symptoms of a duplex mismatch may be intermittent: Duplex mismatches can be caused by a variety of factors, including manual configuration errors, autonegotiation failures, or faulty cabling. The symptoms of a duplex mismatch may be intermittent, depending on the cause of the problem. For example, a cable fault may cause the duplex setting to change periodically, leading to intermittent connectivity issues. Similarly, an autonegotiation failure may only occur when devices are rebooted or when new devices are added to the network, making it difficult to identify the root cause of the problem. These intermittent issues can be difficult to diagnose, as they may not occur consistently or predictably.

In conclusion, duplex mismatches can be difficult to diagnose due to the "up/up" state displayed on interfaces even when mismatches occur and the intermittent nature of symptoms that can be caused by a variety of factors. It is important to verify the duplex settings on both ends of a connection to prevent this issue from occurring and to identify and correct duplex mismatches quickly when they do occur.