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CCNA Network Infrastructure and Connectivity Practice Question
Drag and drop the following steps into the correct order to troubleshoot a suspected duplex mismatch and CRC errors on a Cisco switch interface using CLI commands.
⚠ Common exam trap
The trap is that candidates often clear counters before fixing the issue, thinking they need a clean baseline. However, you must first see the errors to confirm the problem. Also, some may try to fix before inspecting, which is not systematic troubleshooting.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
1. Use 'show interfaces' to check for CRC errors and duplex mismatch. 2. Manually set speed and duplex on both ends to match. 3. Use 'clear counters' to reset interface statistics. 4. Use 'show interfaces' again to verify no new errors.
Start by examining current interface stats, then fix the mismatch, and finally clear and recheck counters.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
1. Use 'show interfaces' to check for CRC errors and duplex mismatch. 2. Manually set speed and duplex on both ends to match. 3. Use 'clear counters' to reset interface statistics. 4. Use 'show interfaces' again to verify no new errors.
Why this is correct
Begin with 'show interfaces' to capture a baseline; this output reveals CRC errors, runts, or late collisions that point to a duplex mismatch. Manually configuring the same speed and duplex on both devices eliminates the negotiation failure at the root. Then 'clear counters' resets the interface statistics so the baseline does not pollute your verification. Finally, re-running 'show interfaces' and seeing no fresh errors proves the fix holds.
- ✗
1. Use 'clear counters' to reset interface statistics. 2. Use 'show interfaces' to check for CRC errors. 3. Manually set speed and duplex on both ends to match. 4. Use 'show interfaces' again to verify no new errors.
Why it's wrong here
Resetting counters first discards the very data you need to diagnose the issue: CRC error counters from before the fix are gone, so you cannot confirm the interface's historical state. The correct methodology requires 'show interfaces' first to establish a baseline and identify the duplex mismatch. Jumping to 'clear counters' also means that if the mismatch persists, the new counts will just start from zero, making the post-fix verification ambiguous. Essentially, you are erasing evidence before examining it.
- ✗
1. Use 'show interfaces' to check for CRC errors. 2. Use 'clear counters' to reset interface statistics. 3. Manually set speed and duplex on both ends to match. 4. Use 'show interfaces' again to verify no new errors.
Why it's wrong here
This sequence makes the common mistake of clearing counters after the initial diagnosis but before implementing the fix. Because the duplex mismatch is still active when counters are cleared, any errors that accumulate between the clear and the configuration change will be mixed into the post-fix verification. Even worse, if you configure speed/duplex after clearing, you have no pre-fix error count to compare against, so you cannot prove that the fix actually stopped the errors. The counters should be reset only after the corrective action is applied.
- ✗
1. Manually set speed and duplex on both ends to match. 2. Use 'show interfaces' to check for CRC errors. 3. Use 'clear counters' to reset interface statistics. 4. Use 'show interfaces' again to verify no new errors.
Why it's wrong here
Configuration without observation violates the fundamental troubleshooting principle: you cannot know whether the manual speed/duplex set is needed or whether it will harm an already-correct configuration. Skipping 'show interfaces' means you have no baseline, so any CRC errors that persist after the change cannot be attributed to the original mismatch. Additionally, forcing speed/duplex might break autonegotiation on one side if the interface was previously healthy, introducing a new network problem. Always gather operational data first, then intervene.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓1. Use 'show interfaces' to check for CRC errors and duplex mismatch. 2. Manually set speed and duplex on both ends to match. 3. Use 'clear counters' to reset interface statistics. 4. Use 'show interfaces' again to verify no new errors.Correct answer▾
Why this is correct
Begin with 'show interfaces' to capture a baseline; this output reveals CRC errors, runts, or late collisions that point to a duplex mismatch. Manually configuring the same speed and duplex on both devices eliminates the negotiation failure at the root. Then 'clear counters' resets the interface statistics so the baseline does not pollute your verification. Finally, re-running 'show interfaces' and seeing no fresh errors proves the fix holds.
✗1. Use 'clear counters' to reset interface statistics. 2. Use 'show interfaces' to check for CRC errors. 3. Manually set speed and duplex on both ends to match. 4. Use 'show interfaces' again to verify no new errors.Wrong answer — click to see why▾
Why this is wrong here
Clearing counters before inspection destroys the diagnostic data (CRC errors) that indicate the problem.
Why candidates choose this
Candidates might think clearing counters is a necessary first step to get a clean baseline, but you need to see the current errors first.
✗1. Use 'show interfaces' to check for CRC errors. 2. Use 'clear counters' to reset interface statistics. 3. Manually set speed and duplex on both ends to match. 4. Use 'show interfaces' again to verify no new errors.Wrong answer — click to see why▾
Why this is wrong here
Clearing counters before applying the fix means the counters will start from zero even though the mismatch still exists, leading to a false sense of resolution.
Why candidates choose this
Candidates may think clearing counters after inspection but before the fix is acceptable, but the correct sequence is to fix first, then clear, then verify.
✗1. Manually set speed and duplex on both ends to match. 2. Use 'show interfaces' to check for CRC errors. 3. Use 'clear counters' to reset interface statistics. 4. Use 'show interfaces' again to verify no new errors.Wrong answer — click to see why▾
Why this is wrong here
Skipping the initial inspection step means you are making changes without confirming the issue, which could be unnecessary or even harmful.
Why candidates choose this
Candidates might think that since duplex mismatch is suspected, they can go straight to fixing it, but proper troubleshooting requires verification first.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Half-Duplex vs Full-Duplex
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.