- A
Configure the 'spanning-tree vlan vlan-id root primary' command on the intended distribution switch.
Correct because this command sets the switch priority to 24576 (or lower if needed) to ensure it becomes the root bridge without manual configuration.
- B
Set the priority of the access switch to 0 using the 'spanning-tree vlan vlan-id priority 0' command.
Why wrong: Incorrect because setting the access switch priority to 0 would make it the root bridge, not the distribution switch.
- C
Increase the priority of the distribution switch to 61440 using the 'spanning-tree vlan vlan-id priority 61440' command.
Why wrong: Incorrect because increasing the priority makes the switch less likely to become root; the engineer wants the distribution switch to become root.
- D
Disable STP on the distribution switch and manually configure it as the root bridge.
Why wrong: Incorrect because disabling STP can cause loops and is not a recommended practice; the root bridge is elected dynamically via BPDUs.
350-401 Spanning Tree Protocol Practice Question
This 350-401 practice question tests your understanding of spanning tree protocol. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting an STP issue in a switched network. The network has two distribution switches connected via a trunk, and each distribution switch connects to the same access switch. The engineer notices that the root bridge is not the intended distribution switch. Upon checking, the engineer sees that the access switch has a higher priority than the distribution switches. The engineer needs to ensure that the intended distribution switch becomes the root bridge without causing a temporary loop. What should the engineer do?
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
Configure the 'spanning-tree vlan vlan-id root primary' command on the intended distribution switch.
Option A is correct because the 'spanning-tree vlan vlan-id root primary' command dynamically sets the switch's bridge priority to 24576 (or 4096 if the current root has a priority lower than 24576) and ensures the switch becomes the root bridge without manual priority miscalculation. This command also adjusts the priority of neighboring switches if needed, preventing temporary loops by avoiding the need to disable or reset STP. It is the safest and most efficient method to force a specific switch to become the root bridge in a live network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the 'spanning-tree vlan vlan-id root primary' command on the intended distribution switch.
Why this is correct
Correct because this command sets the switch priority to 24576 (or lower if needed) to ensure it becomes the root bridge without manual configuration.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set the priority of the access switch to 0 using the 'spanning-tree vlan vlan-id priority 0' command.
Why it's wrong here
Incorrect because setting the access switch priority to 0 would make it the root bridge, not the distribution switch.
- ✗
Increase the priority of the distribution switch to 61440 using the 'spanning-tree vlan vlan-id priority 61440' command.
Why it's wrong here
Incorrect because increasing the priority makes the switch less likely to become root; the engineer wants the distribution switch to become root.
- ✗
Disable STP on the distribution switch and manually configure it as the root bridge.
Why it's wrong here
Incorrect because disabling STP can cause loops and is not a recommended practice; the root bridge is elected dynamically via BPDUs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that increasing a switch's priority (making it numerically higher) helps it become root, when in fact the root bridge is elected based on the lowest bridge priority value.
Detailed technical explanation
How to think about this question
The 'spanning-tree vlan vlan-id root primary' command is a macro that internally sets the bridge priority to 24576 by default, but if the current root bridge has a priority lower than 24576, it sets the priority to 4096 to ensure election. This command also adjusts the port cost and path cost on downstream switches to maintain optimal topology, and it does not require manual calculation of priority values, reducing human error. In real-world scenarios, this command is preferred over manual priority configuration because it automatically handles edge cases, such as when another switch already has a very low priority.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 350-401 question test?
Spanning Tree Protocol — This question tests Spanning Tree Protocol — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure the 'spanning-tree vlan vlan-id root primary' command on the intended distribution switch. — Option A is correct because the 'spanning-tree vlan vlan-id root primary' command dynamically sets the switch's bridge priority to 24576 (or 4096 if the current root has a priority lower than 24576) and ensures the switch becomes the root bridge without manual priority miscalculation. This command also adjusts the priority of neighboring switches if needed, preventing temporary loops by avoiding the need to disable or reset STP. It is the safest and most efficient method to force a specific switch to become the root bridge in a live network.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jun 24, 2026
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