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Question 1,335 of 1,052
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CCNA Practice Question: Notices that a new switch, SW3, was connected to…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Exhibit
SW1# show interfaces gigabitEthernet 0/1 status Port Name Status Vlan Duplex Speed Type Gi0/1 err-disabled 1 auto auto 10/100/1000BaseTX SW1# show running-config interface gigabitEthernet 0/1 Building configuration... Current configuration : 109 bytes ! interface GigabitEthernet0/1 switchport mode access spanning-tree bpduguard enable end SW1# show spanning-tree interface gigabitEthernet 0/1 detail Port 1 (GigabitEthernet0/1) of VLAN0001 is broken (BPDU Guard) Port path cost 4, Port priority 128, Port Identifier 128.1. Designated root has priority 32768, address aaaa.bbbb.cccc Designated bridge has priority 32768, address aaaa.bbbb.cccc Designated port id is 128.1, designated path cost 0 Timers: message age 0, forward delay 0, hold 0 BPDU: sent 0, received 3
A network engineer notices that a new switch, SW3, was connected to port GigabitEthernet0/1 on SW1, but the port immediately went into an err-disabled state. The network uses Rapid PVST+ with BPDU Guard enabled globally on all access ports. The engineer checks the logs and sees 'bpduguard error detected' messages. What is the most likely cause of the err-disabled state?
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.
Clue:
"immediately / without restart"Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
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
✓
Disable BPDU Guard on interface GigabitEthernet0/1 because SW3 is an authorized switch.
The port is in err-disabled state because BPDU Guard is enabled on the interface, and the switch received BPDUs on that port. BPDU Guard is designed to protect against rogue switch connections by disabling a port if it receives a BPDU, which is exactly what happened when SW3 was connected. The 'show spanning-tree interface detail' output shows that BPDUs were received (3 received), triggering the error. The correct solution is to disable BPDU Guard on that port if SW3 is an authorized switch. Option A is wrong because the port is not an access port that should receive BPDUs; BPDU Guard is intentionally triggered. Option C is incorrect because Root Guard would not cause an err-disabled state; it would place the port in a root-inconsistent state. Option D is wrong because Loop Guard would put the port in a loop-inconsistent state (blocking), not err-disabled.
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 port is configured as an access port, but BPDU Guard should be disabled on all access ports.
Why it's wrong here
BPDU Guard is typically enabled on access ports to prevent rogue switches; disabling it globally would reduce security.
- ✓
Disable BPDU Guard on interface GigabitEthernet0/1 because SW3 is an authorized switch.
Why this is correct
Disabling BPDU Guard on the specific port allows the authorized switch to connect without being err-disabled.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
Configure Root Guard on the interface to prevent the err-disabled state.
Why it's wrong here
Root Guard prevents a port from becoming a root port, but it does not prevent err-disabled; it causes a root-inconsistent state.
- ✗
Enable Loop Guard on the interface to prevent the err-disabled state.
Why it's wrong here
Loop Guard prevents alternate or root ports from becoming designated when BPDUs are lost, but it does not prevent err-disabled from BPDU Guard.
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.
✓Disable BPDU Guard on interface GigabitEthernet0/1 because SW3 is an authorized switch.Correct answer▾
Why this is correct
Disabling BPDU Guard on the specific port allows the authorized switch to connect without being err-disabled.
✗The port is configured as an access port, but BPDU Guard should be disabled on all access ports.Wrong answer — click to see why▾
Why this is wrong here
BPDU Guard is correctly enabled on access ports; the issue is that an authorized switch was connected, so the guard was triggered unintentionally.
✗Configure Root Guard on the interface to prevent the err-disabled state.Wrong answer — click to see why▾
Why this is wrong here
Root Guard does not address the BPDU reception issue; it only affects root bridge selection.
✗Enable Loop Guard on the interface to prevent the err-disabled state.Wrong answer — click to see why▾
Why this is wrong here
Loop Guard would not have prevented the err-disabled; it is used for different scenarios.
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 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?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: Disable BPDU Guard on interface GigabitEthernet0/1 because SW3 is an authorized switch. — The port is in err-disabled state because BPDU Guard is enabled on the interface, and the switch received BPDUs on that port. BPDU Guard is designed to protect against rogue switch connections by disabling a port if it receives a BPDU, which is exactly what happened when SW3 was connected. The 'show spanning-tree interface detail' output shows that BPDUs were received (3 received), triggering the error. The correct solution is to disable BPDU Guard on that port if SW3 is an authorized switch. Option A is wrong because the port is not an access port that should receive BPDUs; BPDU Guard is intentionally triggered. Option C is incorrect because Root Guard would not cause an err-disabled state; it would place the port in a root-inconsistent state. Option D is wrong because Loop Guard would put the port in a loop-inconsistent state (blocking), not err-disabled.
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", "immediately / without restart". 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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