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Question 259 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 switches connected via a trunk link. The engineer captures traffic on the trunk interface using embedded packet capture on an IOS-XE switch. The capture shows frames with the destination MAC address 01:80:c2:00:00:00 and the EtherType 0x0800. 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 switch is forwarding IP packets with an STP multicast address; check for a misconfigured trunk or native VLAN mismatch.
The destination MAC address 01:80:c2:00:00:00 is a reserved multicast address used by Spanning Tree Protocol (STP) Bridge Protocol Data Units (BPDUs). The EtherType 0x0800 indicates an IPv4 packet, which is unexpected for BPDUs (normally 0x4242). This mismatch suggests that the switch is forwarding IP traffic (likely from a misconfigured host or VLAN) onto the trunk, potentially causing STP instability or loops. The correct action is to verify the switchport configuration, ensuring the interface is set as a trunk and not accidentally configured as an access port or with a native VLAN mismatch.
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 capture indicates a broadcast storm; disable the interface immediately.
Why it's wrong here
A broadcast storm would show excessive broadcasts, not specifically frames with that MAC and EtherType combination.
- ✓
The switch is forwarding IP packets with an STP multicast address; check for a misconfigured trunk or native VLAN mismatch.
Why this is correct
The destination MAC is an STP multicast address, but the EtherType 0x0800 (IPv4) indicates normal IP traffic, not BPDUs. This suggests that IP frames are being tagged with the STP multicast address, likely due to misconfiguration such as a native VLAN mismatch or a host sending IP traffic with a spoofed MAC.
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.
- ✗
This is normal BPDU traffic; no action is required.
Why it's wrong here
Normal BPDUs use EtherType 0x4242, not 0x0800. The presence of IPv4 EtherType indicates this is not a standard BPDU.
- ✗
The switch has a hardware failure; replace the line card.
Why it's wrong here
There is no evidence of hardware failure; the issue is likely configuration-related.
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 is forwarding IP packets with an STP multicast address; check for a misconfigured trunk or native VLAN mismatch.Correct answer▾
Why this is correct
The destination MAC is an STP multicast address, but the EtherType 0x0800 (IPv4) indicates normal IP traffic, not BPDUs. This suggests that IP frames are being tagged with the STP multicast address, likely due to misconfiguration such as a native VLAN mismatch or a host sending IP traffic with a spoofed MAC.
✗The capture indicates a broadcast storm; disable the interface immediately.Wrong answer — click to see why▾
Why this is wrong here
This answer mistakes a specific STP BPDU for a broadcast storm; the capture does not show high traffic volume.
✗This is normal BPDU traffic; no action is required.Wrong answer — click to see why▾
Why this is wrong here
This answer incorrectly assumes that any frame with STP MAC is a BPDU; the EtherType must match for it to be valid STP traffic.
✗The switch has a hardware failure; replace the line card.Wrong answer — click to see why▾
Why this is wrong here
This answer jumps to a hardware solution without considering the more common configuration errors indicated by the capture.
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 broadcast storm would show excessive broadcasts, not specifically frames with that MAC and EtherType combination.
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 switch is forwarding IP packets with an STP multicast address; check for a misconfigured trunk or native VLAN mismatch. — The destination MAC address 01:80:c2:00:00:00 is a reserved multicast address used by Spanning Tree Protocol (STP) Bridge Protocol Data Units (BPDUs). The EtherType 0x0800 indicates an IPv4 packet, which is unexpected for BPDUs (normally 0x4242). This mismatch suggests that the switch is forwarding IP traffic (likely from a misconfigured host or VLAN) onto the trunk, potentially causing STP instability or loops. The correct action is to verify the switchport configuration, ensuring the interface is set as a trunk and not accidentally configured as an access port or with a native VLAN mismatch.
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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