CCNA Network Infrastructure and Connectivity Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Use the show interfaces command to examine the input errors, CRC, and late collisions counters.

  Why this is correct

  The `show interfaces` command is the essential first step in troubleshooting a suspected speed/duplex mismatch because it provides the error counters that confirm the problem. Specifically, you are looking for a high rate of input errors, CRC errors, and late collisions, which are the classic symptoms of a full-duplex/half-duplex mismatch on an Ethernet link. This diagnostic evidence must be gathered before any configuration changes, as it establishes a baseline and proves the interface is actually experiencing faults.

• ✓

  Use the show interfaces status command to display the current speed and duplex settings for the interface.

  Why this is correct

  The `show interfaces status` command displays the current administrative and operational status, speed, and duplex mode of an interface, but it does not show error counters. While this is a useful command later in the troubleshooting process to see what the interface negotiated to, it cannot be the first step because it gives no indication of whether the link is actually generating errors. A speed/duplex mismatch may still be present even if the interface status appears up, and only the error statistics from `show interfaces` will reveal the problem.

• ✓

  View the connected device's speed and duplex configuration using the show cdp neighbors detail command.

  Why this is correct

  Using `show cdp neighbors detail` can help identify the connected device's platform, interface, and its configured speed and duplex capabilities, but this step is not appropriate as the first action. CDP is a Cisco proprietary protocol and may not be enabled on the connected device, so you cannot always rely on it. Moreover, even with CDP information, you still need to check the local interface counters first to confirm that a mismatch is actually causing errors before you start comparing configurations.

• ✓

  Configure the interface with the matching or auto-negotiated speed and duplex settings using the speed and duplex commands.

  Why this is correct

  Configuring the interface with the `speed` and `duplex` commands is a corrective action, not a diagnostic one, and should never be done as the first step. Changing settings without first examining the existing error counters can make troubleshooting more difficult and may even introduce a new mismatch if you do not account for the remote device's configuration or auto-negotiation state. The correct sequence is to use `show interfaces` to identify the problem, then compare settings, and only then apply the appropriate speed and duplex configuration.

• ✓

  Issue the show interfaces command again to confirm that the error counters have stopped increasing and the interface is operating normally.

  Why this is correct

  Re-issuing `show interfaces` to confirm that error counters have stopped increasing is a verification step, not an initial troubleshooting action. To use this effectively, you first need an initial baseline reading of the counters before any changes are made, and you must already have implemented a fix or adjusted the configuration. Jumping straight to verification without first identifying the problem or taking corrective action is meaningless, as there would be nothing to compare and no expectation for the counters to change.