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Question 501 of 1,052
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CCNA Practice Question: A network administrator notices that devices…
This 200-301 practice question tests your understanding of 200-301 exam topics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
Switch# show interface status Port Name Status Vlan Duplex Speed Type Gi0/1 PC1 err-disabled 10 auto auto 10/100/1000BaseTX Gi0/2 PC2 connected 10 a-full a-100 10/100/1000BaseTX Gi0/3 PC3 connected 10 a-full a-100 10/100/1000BaseTX Gi0/4 PC4 connected 10 a-full a-100 10/100/1000BaseTX Gi0/5 PC5 connected 10 a-full a-100 10/100/1000BaseTX Gi0/6 PC6 connected 10 a-full a-100 10/100/1000BaseTX Gi0/7 PC7 connected 10 a-full a-100 10/100/1000BaseTX Gi0/8 PC8 connected 10 a-full a-100 10/100/1000BaseTX
A network administrator notices that devices connected to interface GigabitEthernet0/1 on a Cisco Catalyst 9300 switch are experiencing intermittent connectivity. The interface is configured as an access port in VLAN 10. The show interface status command output is provided. What is the most likely cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 interface is in err-disabled state due to a port security violation.
The interface is in err-disabled state, which is a security-related error condition that disables the port when certain events occur. The most common cause is a port security violation, such as when the maximum MAC address limit is exceeded or an unauthorized MAC address is detected. In this scenario, the port likely learned a MAC address that violated the configured port security policy. The err-disabled state can be cleared by manually shutting and no-shutting the interface or by configuring errdisable recovery.
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 interface has a duplex mismatch with the connected device.
Why it's wrong here
A duplex mismatch would result in high error rates and poor performance, but would not cause the port to enter err-disabled state.
- ✓
The interface is in err-disabled state due to a port security violation.
Why this is correct
The err-disabled state is commonly caused by port security violations, such as when the maximum number of MAC addresses is exceeded or an unauthorized MAC address is detected.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The interface is down because the cable is faulty or disconnected.
Why it's wrong here
The status shows 'err-disabled' not 'notconnect' or 'down', indicating the interface is administratively functional but disabled by a security mechanism.
- ✗
The interface has a speed mismatch between the switch and the connected device.
Why it's wrong here
A speed mismatch would prevent the link from coming up, but the status would show 'notconnect' or 'down' rather than err-disabled.
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 interface is in err-disabled state due to a port security violation.Correct answer▾
Why this is correct
The err-disabled state is commonly caused by port security violations, such as when the maximum number of MAC addresses is exceeded or an unauthorized MAC address is detected.
✗The interface has a duplex mismatch with the connected device.Wrong answer — click to see why▾
Why this is wrong here
Duplex mismatch causes CRC and collision errors but does not trigger err-disable.
✗The interface is down because the cable is faulty or disconnected.Wrong answer — click to see why▾
Why this is wrong here
Cable faults result in 'notconnect' or 'down' status, not err-disabled.
✗The interface has a speed mismatch between the switch and the connected device.Wrong answer — click to see why▾
Why this is wrong here
Speed mismatch prevents link negotiation and results in 'notconnect' status, not err-disabled.
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
The status shows 'err-disabled' not 'notconnect' or 'down', indicating the interface is administratively functional but disabled by a security mechanism.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: The interface is in err-disabled state due to a port security violation. — The interface is in err-disabled state, which is a security-related error condition that disables the port when certain events occur. The most common cause is a port security violation, such as when the maximum MAC address limit is exceeded or an unauthorized MAC address is detected. In this scenario, the port likely learned a MAC address that violated the configured port security policy. The err-disabled state can be cleared by manually shutting and no-shutting the interface or by configuring errdisable recovery.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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