- A
The SPAN destination port is configured with spanning-tree bpduguard enable, and a BPDU from the connected switch triggers errdisable.
BPDU guard on a SPAN destination port causes errdisable upon BPDU reception, despite SPAN disabling STP on that port.
- B
The SPAN source VLAN includes the native VLAN, causing BPDUs to be forwarded to the destination port.
Why wrong: SPAN does not forward BPDUs from the source VLAN to the destination port; BPDUs are handled by the supervisor.
- C
The SPAN destination port is in the same VLAN as the source, causing a loop that triggers BPDU guard.
Why wrong: SPAN destination ports are not part of the source VLAN; they are dedicated monitor ports.
- D
The switch has PortFast enabled on the SPAN destination port, which automatically enables BPDU guard.
Why wrong: PortFast does not automatically enable BPDU guard; it must be explicitly configured or enabled globally with BPDU guard.
Quick Answer
The answer is that the SPAN destination port is configured with spanning-tree bpduguard enable, and a BPDU from the connected switch triggers errdisable. This occurs because BPDU guard operates independently of spanning-tree participation; even though a SPAN destination port does not run Spanning Tree Protocol, the switch still monitors incoming BPDUs on that port. If BPDU guard is enabled globally or per interface, any received BPDU—such as from a switch connected for monitoring—immediately errdisables the port. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that BPDU guard is a security feature that overrides port roles, and a common trap is assuming SPAN destination ports are immune to it. Remember the memory tip: “SPAN destination + BPDU = shutdown,” meaning the port is for copying traffic, not for receiving BPDUs, so guard still bites.
300-410 SPAN, RSPAN, and ERSPAN Practice Question
This 300-410 practice question tests your understanding of span, rspan, and erspan. 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.
An engineer configures SPAN on a Cisco switch to monitor traffic from a source VLAN. Unexpectedly, BPDU guard shuts down the monitoring port when a switch is connected to it. Which is the most likely explanation?
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
The SPAN destination port is configured with spanning-tree bpduguard enable, and a BPDU from the connected switch triggers errdisable.
SPAN destination ports do not participate in spanning tree, but BPDU guard still operates on them if configured globally or per interface. When a BPDU is received on a SPAN destination port, BPDU guard errdisables the port, even though the port is not forwarding traffic.
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 SPAN destination port is configured with spanning-tree bpduguard enable, and a BPDU from the connected switch triggers errdisable.
Why this is correct
BPDU guard on a SPAN destination port causes errdisable upon BPDU reception, despite SPAN disabling STP on that port.
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.
- ✗
The SPAN source VLAN includes the native VLAN, causing BPDUs to be forwarded to the destination port.
Why it's wrong here
SPAN does not forward BPDUs from the source VLAN to the destination port; BPDUs are handled by the supervisor.
- ✗
The SPAN destination port is in the same VLAN as the source, causing a loop that triggers BPDU guard.
Why it's wrong here
SPAN destination ports are not part of the source VLAN; they are dedicated monitor ports.
- ✗
The switch has PortFast enabled on the SPAN destination port, which automatically enables BPDU guard.
Why it's wrong here
PortFast does not automatically enable BPDU guard; it must be explicitly configured or enabled globally with BPDU guard.
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 300-410 questions on switching, trunking, and access-port configuration.
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SPAN, RSPAN, and ERSPAN — study guide chapter
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FAQ
Questions learners often ask
What does this 300-410 question test?
SPAN, RSPAN, and ERSPAN — This question tests SPAN, RSPAN, and ERSPAN — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The SPAN destination port is configured with spanning-tree bpduguard enable, and a BPDU from the connected switch triggers errdisable. — SPAN destination ports do not participate in spanning tree, but BPDU guard still operates on them if configured globally or per interface. When a BPDU is received on a SPAN destination port, BPDU guard errdisables the port, even though the port is not forwarding traffic.
What should I do if I get this 300-410 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 300-410 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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Last reviewed: Jun 19, 2026
This 300-410 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 300-410 exam.
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