350-401 · Question #311
350-401 Question #311: Real Exam Question with Answer & Explanation
The correct answer is B: Configure root guard and portfast on all access switch ports.. To designate a switch as the root bridge and prevent other switches from taking over its role, configure the chosen root bridge with a low priority and enable root guard on all its downstream ports and other access switches' ports.
Question
In a traditional 3 tier topology, an engineer must explicitly configure a switch as the root bridge and exclude it from any further election process for the spanning-tree domain. Which action accomplishes this task?
Options
- AConfigure the spanning-tree priority to 32768
- BConfigure root guard and portfast on all access switch ports.
- CConfigure BPDU guard in all switch-to-switch connections.
- DConfigure the spanning-tree priority equal to 0.
Explanation
To designate a switch as the root bridge and prevent other switches from taking over its role, configure the chosen root bridge with a low priority and enable root guard on all its downstream ports and other access switches' ports.
Common mistakes.
- A. Configuring the spanning-tree priority to 32768 sets it to the default priority, which does not guarantee it will become the root or protect its root status.
- C. Configuring BPDU guard on switch-to-switch connections is a misconfiguration as it would shut down these critical links upon receiving BPDUs, breaking STP functionality.
- D. Configuring the spanning-tree priority equal to 0 makes a switch the root bridge by giving it the lowest possible priority, but it does not actively prevent other switches from attempting to become root through superior BPDUs; root guard provides this protective mechanism.
Concept tested. Spanning Tree Protocol (STP) Root Guard
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