This 350-401 practice question tests your understanding of spanning tree protocol. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
A network engineer runs the following command on Switch SW9:
SW9# show spanning-tree vlan 90
VLAN0090 Spanning tree enabled protocol ieee Root ID Priority 24666 Address aabb.cc00.1000 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24666 (priority 24576 sys-id-ext 90) Address aabb.cc00.1000 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Desg FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p Gi0/4 Desg FWD 4 128.4 P2p
Based on this output, what is the base priority of the root bridge?
24576
Correct. 24576 is the base priority (24666 - 90 = 24576).
24666
Why wrong: Incorrect. 24666 includes the VLAN ID; the base priority is lower.
32768
Why wrong: Incorrect. 32768 is not shown in the output.
32858
Why wrong: Incorrect. There is no such value.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
24576
The root bridge priority is 24666, which includes the system ID extension of 90. The base priority is 24666 - 90 = 24576.
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
For each option: why learners choose it and why it is or isn't the right answer here.
24576
Why this is correct
Correct. 24576 is the base priority (24666 - 90 = 24576).
Related concept
Access ports place end devices into a single VLAN.
24666
Why it's wrong here
Incorrect. 24666 includes the VLAN ID; the base priority is lower.
32768
Why it's wrong here
Incorrect. 32768 is not shown in the output.
32858
Why it's wrong here
Incorrect. There is no such value.
Common exam traps
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.
Trap categories for this question
Command / output trap
Incorrect. 32768 is not shown in the output.
Detailed technical explanation
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.
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
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
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 350-401 questions on switching, trunking, and access-port configuration.
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FAQ
Spanning Tree Protocol — This question tests Spanning Tree Protocol — Access ports place end devices into a single VLAN..
The correct answer is: 24576 — The root bridge priority is 24666, which includes the system ID extension of 90. The base priority is 24666 - 90 = 24576.
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 350-401 questions on switching, trunking, and access-port configuration.
Access ports place end devices into a single VLAN.
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Last reviewed: Jun 18, 2026
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