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Question 668 of 1,052
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CCNA Practice Question: Is troubleshooting a connectivity issue between…
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.
A network engineer is troubleshooting a connectivity issue between two hosts on different VLANs. The engineer captures traffic on an IOS-XE router's GigabitEthernet0/1 interface using embedded packet capture (EPC). The output shows ARP requests from Host A (192.168.1.10) but no ARP replies from Host B (192.168.2.20). What is the most likely cause of this 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 router's interface does not have an IP address configured in the VLAN 2 subnet.
The correct answer is B. Inter-VLAN routing requires a Layer 3 interface (SVI or routed port) with an IP address in each VLAN's subnet. If the router's interface has no IP address in VLAN 2, it cannot respond to ARP requests for 192.168.2.20, and it will not forward packets between VLANs. Option A is incorrect because a trunk is needed only if the router connects to a switch; here the router may be directly connected. Option C is incorrect because ARP requests are broadcast and reach the router regardless of VLAN membership if the interface is in the correct VLAN. Option D is incorrect because the absence of ARP replies indicates a Layer 3 issue, not a duplex mismatch (which would cause CRC errors or collisions).
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 router's interface is configured as an access port instead of a trunk.
- ✓
The router's interface does not have an IP address configured in the VLAN 2 subnet.
Why this is correct
For inter-VLAN routing, the router must have an IP address in each VLAN's subnet to act as the default gateway and respond to ARP requests. Without an IP in VLAN 2, it cannot reply to ARP requests for 192.168.2.20.
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.
- ✗
Host A is in a different VLAN than the router's interface.
- ✗
The router's interface has a duplex mismatch with the switch.
Why it's wrong here
A duplex mismatch would cause frame errors and retransmissions, but it would not specifically prevent ARP replies. The capture shows ARP requests but no replies, pointing to a Layer 3 addressing issue rather than a physical layer problem.
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 router's interface does not have an IP address configured in the VLAN 2 subnet.Correct answer▾
Why this is correct
For inter-VLAN routing, the router must have an IP address in each VLAN's subnet to act as the default gateway and respond to ARP requests. Without an IP in VLAN 2, it cannot reply to ARP requests for 192.168.2.20.
✗The router's interface is configured as an access port instead of a trunk.Wrong answer — click to see why▾
Why this is wrong here
If the router has a separate interface for each VLAN, access ports are correct; the problem is the missing IP address, not the port mode.
✗Host A is in a different VLAN than the router's interface.Wrong answer — click to see why▾
Why this is wrong here
Even if the router's interface is in the same VLAN, it will receive the ARP broadcast; the problem is at Layer 3, not Layer 2.
✗The router's interface has a duplex mismatch with the switch.Wrong answer — click to see why▾
Why this is wrong here
Duplex mismatch typically causes collisions or CRC errors, not a complete absence of ARP replies for a specific IP address.
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
A duplex mismatch would cause frame errors and retransmissions, but it would not specifically prevent ARP replies. The capture shows ARP requests but no replies, pointing to a Layer 3 addressing issue rather than a physical layer problem.
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 router's interface does not have an IP address configured in the VLAN 2 subnet. — The correct answer is B. Inter-VLAN routing requires a Layer 3 interface (SVI or routed port) with an IP address in each VLAN's subnet. If the router's interface has no IP address in VLAN 2, it cannot respond to ARP requests for 192.168.2.20, and it will not forward packets between VLANs. Option A is incorrect because a trunk is needed only if the router connects to a switch; here the router may be directly connected. Option C is incorrect because ARP requests are broadcast and reach the router regardless of VLAN membership if the interface is in the correct VLAN. Option D is incorrect because the absence of ARP replies indicates a Layer 3 issue, not a duplex mismatch (which would cause CRC errors or collisions).
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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