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300-410 Practice Question: An engineer configures SPAN on a Cisco switch to…
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?
Answer choices
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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.
Answer analysis
Option-by-option breakdown
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- ✓
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.
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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.
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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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.