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Question 191 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Notices that a newly connected access switch…
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
SW1# show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24586
Address 0011.2233.4455
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address 0011.2233.4455
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.1 P2p
Gi0/2 Desg FWD 4 128.2 P2p
Gi0/3 Desg BKN*4 128.3 P2p *PVID_Inc
Gi0/4 Desg FWD 4 128.4 P2p EdgeA network engineer notices that a newly connected access switch (SW3) is not forwarding traffic for VLAN 10. Hosts on SW3 cannot ping the default gateway (SW1). The engineer checks SW1 and sees the following output. 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
✓
Configure the same native VLAN on both ends of the trunk link between SW1 and SW3.
The output shows that interface Gi0/3 is in a BKN (broken) state due to a PVID inconsistency (PVID_Inc). This occurs when the native VLAN on one end of a trunk does not match the native VLAN on the other end. In this case, the native VLAN configured on SW1's Gi0/3 is not the same as the native VLAN configured on the corresponding interface of SW3. This causes STP to block the port to prevent a bridging loop, effectively isolating SW3 and preventing VLAN 10 traffic from being forwarded. The other options do not explain the specific PVID_Inc error.
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.
- ✗
Configure spanning-tree portfast on SW1's Gi0/3 interface.
Why it's wrong here
PortFast is used to immediately transition a port to forwarding state for end hosts, but it does not resolve PVID inconsistencies.
- ✓
Configure the same native VLAN on both ends of the trunk link between SW1 and SW3.
Why this is correct
The PVID_Inc error indicates a native VLAN mismatch. Ensuring the native VLAN ID matches on both sides of the trunk will resolve the inconsistency and allow STP to bring the port to a forwarding state.
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.
- ✗
Remove the BPDU Guard configuration from SW1's Gi0/3 interface.
Why it's wrong here
BPDU Guard would cause an err-disable state, not a BKN state with a PVID_Inc flag.
- ✗
Change the STP mode from Rapid PVST+ to PVST+ on SW1.
Why it's wrong here
Changing the STP mode does not fix a native VLAN mismatch and would not affect the PVID inconsistency error.
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.
✓Configure the same native VLAN on both ends of the trunk link between SW1 and SW3.Correct answer▾
Why this is correct
The PVID_Inc error indicates a native VLAN mismatch. Ensuring the native VLAN ID matches on both sides of the trunk will resolve the inconsistency and allow STP to bring the port to a forwarding state.
✗Configure spanning-tree portfast on SW1's Gi0/3 interface.Wrong answer — click to see why▾
Why this is wrong here
The issue is a native VLAN mismatch, not a delay in port state transition.
✗Remove the BPDU Guard configuration from SW1's Gi0/3 interface.Wrong answer — click to see why▾
Why this is wrong here
The exhibit shows the port is in a BKN state, not err-disabled, and the flag is PVID_Inc, not BPDU Guard related.
✗Change the STP mode from Rapid PVST+ to PVST+ on SW1.Wrong answer — click to see why▾
Why this is wrong here
The problem is a layer 2 configuration mismatch, not a protocol compatibility issue.
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.
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: Configure the same native VLAN on both ends of the trunk link between SW1 and SW3. — The output shows that interface Gi0/3 is in a BKN (broken) state due to a PVID inconsistency (PVID_Inc). This occurs when the native VLAN on one end of a trunk does not match the native VLAN on the other end. In this case, the native VLAN configured on SW1's Gi0/3 is not the same as the native VLAN configured on the corresponding interface of SW3. This causes STP to block the port to prevent a bridging loop, effectively isolating SW3 and preventing VLAN 10 traffic from being forwarded. The other options do not explain the specific PVID_Inc error.
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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