The correct answer is to disable BPDU Guard on the distribution switch interface. This is because BPDU Guard, when enabled globally, immediately err-disables any port that receives a Bridge Protocol Data Unit, even if that BPDU comes from a legitimate new access switch. The distribution switch interface entered the err-disabled state because it received a BPDU from the new switch’s PortFast-enabled uplink, which still sends BPDUs; BPDU Guard treats any incoming BPDU as a potential loop threat and shuts the port down. On the CCNA 200-301 v2 exam, this scenario tests your understanding that PortFast does not automatically enable BPDU Guard—they are separate features, and globally enabling BPDU Guard applies to all PortFast ports unless explicitly disabled per interface. A common trap is assuming PortFast alone prevents BPDU processing, but it only skips the listening/learning states. Remember the mnemonic: “Guard blocks BPDUs, PortFast skips states—never assume one turns on the other.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 and globally enabled BPDU Guard. 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.
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
Disable Root Guard on the distribution switch interface
Why wrong: 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.
B
Disable BPDU Guard on the distribution switch interface
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.
C
Remove PortFast from the new access switch uplink interface
Why wrong: 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.
D
Configure the interface as an access port instead of trunk
Why wrong: 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.
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 distribution switch interface entered err-disabled because it received a BPDU while BPDU Guard was enabled. BPDU Guard is not automatically enabled with PortFast; it must be explicitly turned on, and the scenario assumes it is active. When a BPDU arrives on a BPDU Guard–enabled port, the switch err-disables it to prevent loops. Disabling BPDU Guard on that interface resolves the condition. Disabling Root Guard (option A) would not stop the BPDU Guard trigger; removing PortFast (option C) would not disable the already-enabled BPDU Guard; and changing the port to access mode (option D) is irrelevant to BPDU Guard behavior.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
Read the scenario before looking for a memorised answer.
✗
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 does not cause err-disable; it only prevents the port from becoming a root port. The err-disabled state is triggered by BPDU Guard, not Root Guard.
Why candidates choose this
Students may confuse Root Guard with BPDU Guard, thinking that disabling Root Guard would resolve the err-disable, but Root Guard does not err-disable ports.
✗Remove PortFast from the new access switch uplink interfaceWrong answer — click to see why▾
Why this is wrong here
PortFast on the access switch's uplink does not cause err-disable on the distribution switch. PortFast only affects the access switch's port state, not the distribution switch's interface.
Why candidates choose this
Test-takers might think that PortFast is misconfigured on a trunk port, but PortFast is not the issue here; the problem is BPDU Guard on the distribution switch.
✗Configure the interface as an access port instead of trunkWrong answer — click to see why▾
Why this is wrong here
The err-disable is caused by BPDU Guard, not by trunking misconfiguration. Changing the port mode to access would not resolve the BPDU Guard issue and could disrupt connectivity.
Why candidates choose this
Students might assume that trunk ports should not have PortFast or BPDU Guard, but the real issue is BPDU Guard, not the trunk mode itself.
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: answer the scenario, not the keyword
Many learners incorrectly assume BPDU Guard is enabled by default on PortFast ports; in reality, it requires explicit configuration, so the exam may present a scenario where BPDU Guard is already enabled to test this distinction.
Detailed technical explanation
How to think about this question
BPDU Guard is a security feature that disables a PortFast-enabled port if it receives any BPDU, protecting against accidental loops from misconfigured switches. In Rapid PVST+, BPDUs are sent every 2 seconds by default, and the err-disable state is triggered immediately upon BPDU reception. A real-world scenario is when a new switch is connected to a distribution switch that has PortFast and BPDU Guard enabled on the uplink, causing immediate port shutdown until manually or automatically recovered.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Disable BPDU Guard on the distribution switch interface — The distribution switch interface entered err-disabled because it received a BPDU while BPDU Guard was enabled. BPDU Guard is not automatically enabled with PortFast; it must be explicitly turned on, and the scenario assumes it is active. When a BPDU arrives on a BPDU Guard–enabled port, the switch err-disables it to prevent loops. Disabling BPDU Guard on that interface resolves the condition. Disabling Root Guard (option A) would not stop the BPDU Guard trigger; removing PortFast (option C) would not disable the already-enabled BPDU Guard; and changing the port to access mode (option D) is irrelevant to BPDU Guard behavior.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A switch administrator enters the following commands on interface GigabitEthernet1/0/10:
interface g1/0/10
switchport mode access
switchport access vlan 30
spanning-tree portfast
spanning-tree bpduguard enable
A user connects a small managed switch to this port, and the access port immediately changes to an err-disabled state.
Which feature caused the port to shut down?
medium
A.PortFast
✓ B.BPDU Guard
C.Access VLAN 30 assignment
D.The interface being in access mode
Why B: BPDU Guard is the feature that caused the shutdown. This question is really about separating two features that are often configured together on user-facing ports: PortFast and BPDU Guard. PortFast helps an edge port come up quickly, which is useful for PCs and phones. BPDU Guard adds protection by watching for BPDUs on that same port. If a switch is connected where only an end device should exist, the newly connected switch may send BPDUs. The local switch interprets that as a topology risk and disables the port to protect the Layer 2 network. The clues are the err-disabled state and the fact that another switch was connected. VLAN assignment and access mode are normal here and do not explain the shutdown.
Last reviewed: Jun 11, 2026
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