CCNA Switching and Network Access Practice Question
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?
⚠ Common exam trap
Remember, BPDU Guard is about protection, not ignoring or processing BPDUs. It disables the port to prevent loops.
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
✓
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.
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.
- ✗
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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
STP
STP (Spanning Tree Protocol) is a network protocol that prevents loops in Ethernet networks by creating a loop-free logical topology.
Key term
STP
Shielded Twisted Pair (STP) is a copper cable that wraps each twisted pair in foil or braid to block electromagnetic interference.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.