CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: portFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.. 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 switch port connected to an end host is configured with both PortFast and BPDU Guard. What is the most likely outcome if a small switch is connected there and starts sending BPDUs?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The port is error-disabled by BPDU Guard.
BPDU Guard places the port into an error-disabled state upon receiving a BPDU, because PortFast defines the port as an edge port that should never receive BPDUs. Option B is incorrect because receiving a BPDU does not automatically make a port a root port; root port selection depends on bridge ID and path cost, and BPDU Guard prevents further STP processing by disabling the port. Option C is incorrect because a port cannot convert to a trunk solely by receiving a BPDU; trunking requires manual configuration or Dynamic Trunking Protocol (DTP). Option D is incorrect because PortFast does not disable STP entirely; it only speeds up initial convergence, and BPDU Guard actively responds to BPDUs by error-disabling the port.
Key principle: PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.
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 error-disabled by BPDU Guard.
Why this is correct
This is correct because BPDU Guard disables the edge port when a BPDU is received.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.
✗
The port automatically becomes the root port.
Why it's wrong here
This is wrong because BPDU Guard does not promote the port into root-port status.
When this WOULD be correct
In a different scenario where a switch is configured without BPDU Guard and a port is set to participate in STP, if it receives BPDUs from a connected switch, it could potentially become the root port if it has the lowest bridge ID and path cost.
✗
The port converts into a trunk for the attached switch.
Why it's wrong here
This is wrong because BPDU Guard does not negotiate trunking in response to BPDUs.
When this WOULD be correct
In a different scenario where a switch port is configured to allow trunking and is connected to another switch that is sending BPDUs, the port could be set to automatically negotiate trunking, making it a trunk port. The question would need to specify that trunking is enabled and that BPDUs are expected as part of the configuration.
✗
The port ignores the BPDU because PortFast disables STP entirely.
Why it's wrong here
This is wrong because PortFast does not eliminate BPDU Guard protection or all STP awareness.
When this WOULD be correct
In a different scenario where a switch is configured to disable STP entirely on a specific port, a question might ask what happens when a BPDU is received on that port. In that case, the correct answer could be that the port ignores the BPDU since STP is completely disabled.
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 port is error-disabled by BPDU Guard.Correct answer▾
Why this is correct
This is correct because BPDU Guard disables the edge port when a BPDU is received.
✗The port automatically becomes the root port.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a port configured with PortFast and BPDU Guard will not automatically become the root port when it receives BPDUs; instead, it will be error-disabled due to BPDU Guard's protective mechanism.
★ When this WOULD be the correct answer
In a different scenario where a switch is configured without BPDU Guard and a port is set to participate in STP, if it receives BPDUs from a connected switch, it could potentially become the root port if it has the lowest bridge ID and path cost.
Why candidates choose this
Candidates may find this option tempting because they might confuse the behavior of STP with PortFast configurations, thinking that any BPDU received would lead to a re-evaluation of the port's role in the STP topology.
✗The port converts into a trunk for the attached switch.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because a port configured with PortFast and BPDU Guard does not convert to a trunk when receiving BPDUs; instead, BPDU Guard will disable the port to prevent potential loops.
★ When this WOULD be the correct answer
In a different scenario where a switch port is configured to allow trunking and is connected to another switch that is sending BPDUs, the port could be set to automatically negotiate trunking, making it a trunk port. The question would need to specify that trunking is enabled and that BPDUs are expected as part of the configuration.
Why candidates choose this
Candidates might be tempted by this option due to a misunderstanding of how switch port configurations work, particularly the interaction between PortFast and trunking, leading them to incorrectly assume that receiving BPDUs would trigger trunking.
✗The port ignores the BPDU because PortFast disables STP entirely.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because PortFast does not disable Spanning Tree Protocol (STP) entirely; it only allows the port to transition to the forwarding state immediately without waiting for STP convergence. BPDU Guard will still take effect if BPDUs are received on a PortFast-enabled port.
★ When this WOULD be the correct answer
In a different scenario where a switch is configured to disable STP entirely on a specific port, a question might ask what happens when a BPDU is received on that port. In that case, the correct answer could be that the port ignores the BPDU since STP is completely disabled.
Why candidates choose this
Candidates may find this option tempting because they might confuse PortFast's functionality with STP being entirely disabled, leading them to believe that no BPDUs would be processed at all.
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
Remember, BPDU Guard is about protection, not ignoring or processing BPDUs. It disables the port to prevent loops.
Detailed technical explanation
How to think about this question
PortFast is a Cisco feature that expedites the transition of a switch port into the forwarding state by skipping the usual Spanning Tree Protocol (STP) listening and learning phases. This feature is designed for ports connected directly to end devices such as PCs or servers, where no STP topology changes are expected. However, PortFast does not disable STP entirely; the port still participates in STP and can receive BPDUs if they arrive.
BPDU Guard complements PortFast by adding a layer of protection against accidental topology loops. When BPDU Guard is enabled on a PortFast port, it continuously monitors for incoming BPDUs. If a BPDU is detected, which indicates that another switch or STP device is connected, BPDU Guard immediately places the port into an error-disabled state. This action prevents potential Layer 2 loops and topology instability by shutting down the port until manual or automatic recovery is performed.
A common exam trap is misunderstanding the interaction between PortFast and BPDU Guard. Some might incorrectly assume that PortFast disables STP or that the port will ignore BPDUs. In reality, PortFast only accelerates port state transitions, and BPDU Guard enforces strict topology protection by disabling the port upon BPDU receipt. Practically, this means connecting a switch to a PortFast and BPDU Guard enabled port will cause the port to shut down, preventing network loops and preserving STP integrity.
KKey Concepts to Remember
PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.
BPDU Guard monitors PortFast-enabled ports and places a port into an error-disabled state if any Bridge Protocol Data Units (BPDUs) are received, protecting the network topology.
Switch ports configured with PortFast are intended for end devices and should not receive BPDUs, which are normally sent by switches participating in STP.
When BPDU Guard detects a BPDU on a PortFast port, it disables the port to prevent potential Layer 2 loops caused by unexpected switches connected to edge ports.
PortFast does not disable STP entirely; it only accelerates port transition states but still allows BPDU Guard to enforce topology protection.
The error-disabled state caused by BPDU Guard requires manual or automatic recovery to re-enable the port after a BPDU violation.
BPDU Guard is a critical feature in STP topology protection, especially in environments where edge ports connect to end hosts rather than other switches.
Connecting a switch to a PortFast and BPDU Guard enabled port violates the assumption of an edge port and triggers BPDU Guard to err-disable the port.
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
PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.
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.
Review portFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity..
What is the correct answer to this question?
The correct answer is: The port is error-disabled by BPDU Guard. — BPDU Guard places the port into an error-disabled state upon receiving a BPDU, because PortFast defines the port as an edge port that should never receive BPDUs. Option B is incorrect because receiving a BPDU does not automatically make a port a root port; root port selection depends on bridge ID and path cost, and BPDU Guard prevents further STP processing by disabling the port. Option C is incorrect because a port cannot convert to a trunk solely by receiving a BPDU; trunking requires manual configuration or Dynamic Trunking Protocol (DTP). Option D is incorrect because PortFast does not disable STP entirely; it only speeds up initial convergence, and BPDU Guard actively responds to BPDUs by error-disabling the port.
What should I do if I get this 200-301 question wrong?
Review portFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity., then practise related 200-301 questions on the same topic to reinforce the concept.
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?
PortFast immediately transitions a switch port into the forwarding state, bypassing the usual STP listening and learning states to speed up host connectivity.
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