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Difficulty: EasySpanning Tree Protocol Operations

A network technician connects four switches into a redundant topology. All four switches retain their default Spanning Tree Protocol (STP) bridge priority of 32768. The switches have the following MAC addresses:
- Switch A: 00:11:22:AA:BB:CC
- Switch B: 00:11:22:11:22:33
- Switch C: 00:11:22:FF:EE:DD
- Switch D: 00:11:22:44:55:66

Which switch will be elected as the STP root bridge?

  1. Switch BAnswer
  2. B
    Switch C
  3. C
    Switch A
  4. D
    Switch D

Answer

Switch B will be elected as the STP root bridge because it possesses the lowest MAC address among all switches sharing the same default priority.
In Spanning Tree Protocol (STP), the root bridge is selected based on the lowest Bridge ID (BID), which consists of the Bridge Priority and the MAC address. Because all switches share the default priority of 32768, the switch with the lowest MAC address (Switch B, with 00:11:22:11:22:33) wins the root bridge election.

Step-by-Step Solution

1
Compare the STP bridge priority values of all switches.
All switches have an identical priority of 32768.
Since bridge priorities are equal, the tiebreaker process must evaluate the MAC address portion of the Bridge ID (BID).
2
Compare the MAC addresses of each switch to find the lowest numerical value.
Switch B (00:11:22:11:22:33) is lower than Switch D (00:11:22:44:55:66), Switch A (00:11:22:AA:BB:CC), and Switch C (00:11:22:FF:EE:DD).
STP elects the switch with the lowest Bridge ID (Priority + MAC address) as the Root Bridge.

Key Concept

STP Root Bridge Election Process
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Topics

Spanning Tree Protocol Operations

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