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Question 701 of 1,052
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CCNA Practice Question: A network administrator has configured Rapid…
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
SwitchA# show interfaces GigabitEthernet0/1 status Port Name Status Vlan Duplex Speed Type Gi0/1 err-disabled 1 auto auto 10/100/1000BaseTX SwitchA# show running-config interface GigabitEthernet0/1 Building configuration... Current configuration : 150 bytes ! interface GigabitEthernet0/1 switchport mode trunk spanning-tree guard root spanning-tree bpduguard enable end SwitchA# show spanning-tree interface GigabitEthernet0/1 detail Port 1 (GigabitEthernet0/1) of VLAN0001 is root blocking Port path cost 4, Port priority 128, Port Identifier 128.1. Designated root has priority 8193, address 0001.0001.0001 Designated bridge has priority 32769, address aaaa.aaaa.aaaa Designated port id is 128.1, designated path cost 4 Timers: message age 2, forward delay 15, hold 0 Number of transitions to forwarding state: 1 BPDU: sent 3, received 102 The port is not in the portfast mode Root guard is enabled on the port BPDU guard is enabled on the port
A network administrator has configured Rapid PVST+ on all switches. After connecting a new access switch to an existing distribution switch, the distribution switch interface goes into err-disabled state. The new switch is configured with PortFast on its uplink port. 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.
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 the distribution switch interface
The err-disabled state is caused by the combination of Root Guard and BPDU Guard on the distribution switch's trunk port. When the new access switch sends a superior BPDU (in this case, the new switch is incorrectly configured with a lower bridge priority), Root Guard places the port in root-inconsistent state, which then triggers BPDU Guard to err-disable the port because BPDU Guard was also configured. The correct solution is to remove BPDU Guard from the trunk port; Root Guard alone would prevent the port from becoming a root port without err-disable. Option B is correct because BPDU Guard should not be enabled on trunk ports expecting BPDUs. Option A is incorrect because disabling Root Guard would allow the unwanted root bridge. Option C is incorrect because PortFast on the access switch does not cause err-disable on the distribution switch. Option D is incorrect because the port is not a trunk in the sense of the issue; the problem is the guard features.
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.
- ✗
Disable Root Guard on the distribution switch interface
Why it's wrong here
Root Guard is correctly configured to prevent the new switch from becoming root. Disabling it would allow the new switch to become root, causing network instability.
- ✓
Disable BPDU Guard on the distribution switch interface
Why this is correct
BPDU Guard err-disables a PortFast-enabled port upon receiving any BPDU. Since this is a trunk port expecting BPDUs, BPDU Guard should not be enabled. Removing it allows the port to stay up while Root Guard still protects against an unwanted root bridge.
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 PortFast from the new access switch uplink interface
Why it's wrong here
PortFast on the access switch does not cause err-disable on the distribution switch. PortFast only speeds up the transition to forwarding on the access switch, and it is not the source of the problem.
- ✗
Configure the interface as an access port instead of trunk
Why it's wrong here
Changing the port mode does not address the root cause. The err-disable is due to BPDU Guard reacting to a BPDU, not due to trunking issues.
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 the distribution switch interfaceCorrect answer▾
Why this is correct
BPDU Guard err-disables a PortFast-enabled port upon receiving any BPDU. Since this is a trunk port expecting BPDUs, BPDU Guard should not be enabled. Removing it allows the port to stay up while Root Guard still protects against an unwanted root bridge.
✗Disable Root Guard on the distribution switch interfaceWrong answer — click to see why▾
Why this is wrong here
Root Guard is not the cause of err-disable; it is BPDU Guard that err-disables the port.
✗Remove PortFast from the new access switch uplink interfaceWrong answer — click to see why▾
Why this is wrong here
PortFast on one switch does not affect the other switch's interface status directly.
✗Configure the interface as an access port instead of trunkWrong answer — click to see why▾
Why this is wrong here
The port mode is not relevant to the BPDU Guard err-disable condition.
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: Disable BPDU Guard on the distribution switch interface — The err-disabled state is caused by the combination of Root Guard and BPDU Guard on the distribution switch's trunk port. When the new access switch sends a superior BPDU (in this case, the new switch is incorrectly configured with a lower bridge priority), Root Guard places the port in root-inconsistent state, which then triggers BPDU Guard to err-disable the port because BPDU Guard was also configured. The correct solution is to remove BPDU Guard from the trunk port; Root Guard alone would prevent the port from becoming a root port without err-disable. Option B is correct because BPDU Guard should not be enabled on trunk ports expecting BPDUs. Option A is incorrect because disabling Root Guard would allow the unwanted root bridge. Option C is incorrect because PortFast on the access switch does not cause err-disable on the distribution switch. Option D is incorrect because the port is not a trunk in the sense of the issue; the problem is the guard features.
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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