Root Bridge Election by Lowest MAC When Priorities Are Equal (SW4)

200-301 By islever Editorial Last updated

Interpret basic operations of Rapid PVST+ Spanning Tree Protocol

Short answer

D All switches share the same bridge priority, so the lowest MAC elects the root; SW4 (0C:0A:05:22:05:97) is the lowest, making it root.

Question

Refer to the exhibit. Which switch in this configuration will be elected as the root bridge? - Exhibit: Root Bridge Election by Lowest MAC When Priorities Are Equal (SW4)
  1. SW1: 0C:4A:82.:65:62:72
  2. SW2: 0C:0A:A8:1A:3C:9D
  3. SW3: 0C:0A:18:81:B3:19
  4. SW4: 0C:0A:05:22:05:97 Correct Answer

Key Takeaways

When priorities are equal, the election is decided purely by the lowest MAC address — the classic reason an old switch with a small MAC can take over as root.

With identical bridge priorities across the switches, STP elects the root by the lowest MAC address. SW4's MAC (0C:0A:05:22:05:97) is the lowest of the four, so SW4 becomes the root bridge.

Common mistake: Picking SW3 or SW2 by reading the MACs out of order; compare byte-by-byte from the left — 0C:0A:05 is lower than 0C:0A:18 and 0C:0A:A8.

Expert Analysis

Why the Answer Is Correct

D (SW4) is correct. Because every switch has the same bridge priority, the root is chosen by the lowest MAC address. SW4 (0C:0A:05:22:05:97) is lower than SW3 (0C:0A:18:81:B3:19), SW2 (0C:0A:A8:1A:3C:9D), and SW1 (0C:4A:82:65:62:72), so SW4 is root.

Why the Other Options Are Wrong

A (SW1), B (SW2), and C (SW3) all have higher MAC addresses than SW4 once priority is tied, so they cannot be root.

Community Comment Notes

The vote is D (100). Commenters confirm: first lowest priority, then lowest MAC, and SW4 has the lowest MAC.

Official Reference

https://learningnetwork.cisco.com/s/ccna-exam-topics

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Community Votes

D
100%

100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. exiledwl 👍 2
    D) SW4 is correct, to determine root bridge first check lowest priority then lowest mac add
  2. f2bdbb0 👍 3
    the correct answer is sw 2
  3. 379c9f6 👍 2
    correct
  4. vvk964278 👍 1 Answered D
    D is correct

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