- A
The switch port is set to half duplex, and the router is set to full duplex, causing CRC errors and late collisions.
This is correct because a duplex mismatch occurs when one device is manually set to half duplex and the other is set to full duplex. CDP on the switch will show the router's duplex as full, while the switch port is half. This mismatch leads to CRC errors and late collisions on the switch interface.
- B
The switch port is set to full duplex, and the router is set to half duplex, causing runts and FCS errors.
Why wrong: This is incorrect because while a duplex mismatch can cause errors, the scenario describes the switch port as manually set to half duplex, not full. Additionally, runts and FCS errors are more commonly associated with collisions or physical layer issues, but late collisions and CRC errors are the classic symptoms of a duplex mismatch.
- C
The switch port and router are both set to half duplex, but the cable is faulty, causing CRC errors.
Why wrong: This is incorrect because if both devices are set to half duplex, there is no duplex mismatch. CRC errors can be caused by faulty cables, but the scenario specifically suspects a duplex mismatch, and CDP would show both devices as half duplex, not a mismatch.
- D
The switch port is set to auto-negotiation, and the router is set to half duplex, causing late collisions.
Why wrong: This is incorrect because if the switch port is set to auto-negotiation and the router is set to half duplex, the switch would typically negotiate to half duplex as well (since auto-negotiation defaults to half duplex if the other side does not advertise). This would not create a mismatch. Late collisions are a symptom of a mismatch, but this scenario would not produce one.
Quick Answer
The answer is that a duplex mismatch exists, with the switch port set to half duplex and the router set to full duplex, causing CRC errors and late collisions. This occurs because when one side is manually configured to half duplex while the other negotiates to full duplex, the collision detection mechanisms become misaligned—the half-duplex side waits for a clear channel while the full-duplex side transmits freely, leading to frame corruption. On the CCNA 200-301 v2 exam, this duplex mismatch troubleshooting scenario tests your ability to interpret CDP output and interface statistics, often appearing as a simulation where you must identify the mismatch from show commands. A common trap is assuming both sides will auto-negotiate to the same setting, but a manual configuration on one side breaks the process. Remember the memory tip: “Half waits, full talks—CRC errors walk.”
CCNA AI and Network Operations Practice Question
This 200-301 practice question tests your understanding of ai and network operations. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are connected to SW1, a Cisco switch that is experiencing intermittent connectivity issues. The network administrator suspects a duplex mismatch between SW1 and the connected router R1. Use CDP to verify the status and check interface statistics.
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
The switch port is set to half duplex, and the router is set to full duplex, causing CRC errors and late collisions.
The switch port is manually set to half duplex while the router likely negotiates to full duplex, causing a mismatch. CDP output from the switch will show the router's duplex as full. Interface statistics will show increasing CRC errors and late collisions. The solution is to set the switch port to auto-negotiation or match the duplex setting with the router.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The switch port is set to half duplex, and the router is set to full duplex, causing CRC errors and late collisions.
Why this is correct
This is correct because a duplex mismatch occurs when one device is manually set to half duplex and the other is set to full duplex. CDP on the switch will show the router's duplex as full, while the switch port is half. This mismatch leads to CRC errors and late collisions on the switch interface.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The switch port is set to full duplex, and the router is set to half duplex, causing runts and FCS errors.
Why it's wrong here
This is incorrect because while a duplex mismatch can cause errors, the scenario describes the switch port as manually set to half duplex, not full. Additionally, runts and FCS errors are more commonly associated with collisions or physical layer issues, but late collisions and CRC errors are the classic symptoms of a duplex mismatch.
- ✗
The switch port and router are both set to half duplex, but the cable is faulty, causing CRC errors.
Why it's wrong here
This is incorrect because if both devices are set to half duplex, there is no duplex mismatch. CRC errors can be caused by faulty cables, but the scenario specifically suspects a duplex mismatch, and CDP would show both devices as half duplex, not a mismatch.
- ✗
The switch port is set to auto-negotiation, and the router is set to half duplex, causing late collisions.
Why it's wrong here
This is incorrect because if the switch port is set to auto-negotiation and the router is set to half duplex, the switch would typically negotiate to half duplex as well (since auto-negotiation defaults to half duplex if the other side does not advertise). This would not create a mismatch. Late collisions are a symptom of a mismatch, but this scenario would not produce one.
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.
✓The switch port is set to half duplex, and the router is set to full duplex, causing CRC errors and late collisions.Correct answer▾
Why this is correct
This is correct because a duplex mismatch occurs when one device is manually set to half duplex and the other is set to full duplex. CDP on the switch will show the router's duplex as full, while the switch port is half. This mismatch leads to CRC errors and late collisions on the switch interface.
✗The switch port is set to full duplex, and the router is set to half duplex, causing runts and FCS errors.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the switch port is manually set to half duplex, not full duplex. Also, runts and FCS errors are not the primary indicators of a duplex mismatch.
Why candidates choose this
Candidates might pick this because they know duplex mismatches cause errors, but they confuse the direction of the mismatch or the specific error types.
✗The switch port and router are both set to half duplex, but the cable is faulty, causing CRC errors.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that a duplex mismatch requires different duplex settings; both half duplex would not cause a mismatch. Faulty cables are a different issue.
Why candidates choose this
Candidates might pick this because CRC errors are common in both duplex mismatches and cable faults, and they may overlook the CDP verification step.
✗The switch port is set to auto-negotiation, and the router is set to half duplex, causing late collisions.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that auto-negotiation would likely result in half duplex on both sides, avoiding a mismatch. The scenario states the switch port is manually set to half duplex, not auto.
Why candidates choose this
Candidates might pick this because they know auto-negotiation can cause issues if one side is manually configured, but they forget that auto-negotiation will match the manually set speed/duplex if possible.
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?”
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
This is incorrect because if both devices are set to half duplex, there is no duplex mismatch. CRC errors can be caused by faulty cables, but the scenario specifically suspects a duplex mismatch, and CDP would show both devices as half duplex, not a mismatch.
Scenario analysis trap
This is incorrect because while a duplex mismatch can cause errors, the scenario describes the switch port as manually set to half duplex, not full. Additionally, runts and FCS errors are more commonly associated with collisions or physical layer issues, but late collisions and CRC errors are the classic symptoms of a duplex mismatch.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 200-301 question test?
AI and Network Operations — This question tests AI and Network Operations — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The switch port is set to half duplex, and the router is set to full duplex, causing CRC errors and late collisions. — The switch port is manually set to half duplex while the router likely negotiates to full duplex, causing a mismatch. CDP output from the switch will show the router's duplex as full. Interface statistics will show increasing CRC errors and late collisions. The solution is to set the switch port to auto-negotiation or match the duplex setting with the router.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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Last reviewed: Jun 7, 2026
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.
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