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.

• ✓

  Enter the 'show interfaces' command to examine interface status and error counters.

  Why this is correct

  As the immediate first step, 'show interfaces' (without an interface argument) gives a summary table of all interfaces, showing status (up/down), protocol, and error counters like runts, CRC, and late collisions. This broad view alerts you to anomalies on the link before narrowing down, making it the logical starting point to detect a duplex mismatch.

• ✓

  Identify increasing CRC, runt, and late collision errors as indicators of a duplex mismatch.

  Why this is correct

  Increasing CRC errors, runts (frames shorter than 64 bytes), and late collisions are classic symptoms of a duplex mismatch because one end transmits while the other end is not ready, corrupting frames. Recognizing this pattern is crucial, as these counters increment continuously under mismatched settings and are absent on healthy links.

• ✓

  Use the 'show interfaces <interface>' command to display the current duplex and speed settings.

  Why this is correct

  The command 'show interfaces <interface>' (e.g., show interfaces gigabitethernet0/1) displays the operational duplex and speed (e.g., Full-duplex, 100Mbps), as well as the configured values. This focused view allows you to compare the actual settings against the expected configuration and identify which end is auto-negotiating incorrectly.

• ✓

  Determine the expected duplex/speed configuration on both ends of the link.

  Why this is correct

  To resolve a mismatch, you must know the expected duplex/speed for both devices—typically from documentation or design specifications—so you can determine whether the interface is set incorrectly. A mismatch often occurs when one side is hardcoded and the other is set to auto-negotiate, so you need to verify the intended settings on both ends.

• ✓

  Reconfigure the interface with the correct duplex and speed settings using appropriate commands.

  Why this is correct

  Once you've identified the mismatch, you apply the correct settings using commands like 'duplex full' and 'speed 100' under interface configuration mode, or 'speed auto' and 'duplex auto' to restore negotiation. This step directly resolves the problem by aligning both ends to the same parameters, eliminating the errors.

• ✓

  Verify that error counters stop incrementing after the configuration change.

  Why this is correct

  After reconfiguration, re-run 'show interfaces' to confirm that CRC, runt, and late collision counters are no longer increasing; you may need to clear counters with 'clear counters' first to observe a clean baseline. If the counters remain stable, the duplex mismatch is resolved, but if they continue to increment, you may need to check for other issues like cabling faults.