Electing the Root Bridge by Lowest Priority Then MAC

Interpret basic operations of Rapid PVST+ Spanning Tree Protocol
Answer Correct answer: C — SW3 is elected root: it holds the lowest bridge priority, and among any ties it wins on the lower MAC address (0C:0A:18... beats SW2's 0C:0A:A8...).

Refer to the exhibit. Which switch in this configuration will be elected as the root bridge? SW1: 0С:0А:05:22:05:97 - SW2: 0C:0A:A8:1A:3C:9D - SW3: 0С:0А:18:81:ВЗ:19 - SW4: 0С:4А:82:56:35:78 - image

  1. SW1
  2. SW2
  3. SW3 Correct Answer
  4. SW4

Community Votes

C
100%

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

Community Insight

Priority is compared before MAC. SW1's MAC is numerically lowest, but its higher default priority (32768) loses to SW3's 8192, so MAC only breaks the tie between the equal-priority switches.

STP elects the root by lowest bridge priority, then lowest MAC. In the exhibit SW2 and SW3 share the lowest priority (8192), lower than SW1/SW4's default 32768; between them SW3's MAC (0C:0A:18:81:B3:19) is lower than SW2's, so SW3 becomes root.

Picking SW1 because its MAC looks lowest, or SW2 without the MAC tiebreaker. Apply priority first, then MAC within the same priority.

Community Discussion (7 comments)

exiledwl 👍 1 Selected: C
Answer definitely C, first check lowest priority then check lowest mac addresss
exiledwl 👍 1
Answer definitely C, first check lowest priority then check lowest mac address
SnowWhiteYeti 👍 2 Selected: C
Lowest Priority then MAC Address.
[Removed] 👍 1 Selected: C
Ref: Spanning Tree Root Bridge Election on Cisco Switches – FlackBox “The Root Bridge Election … You can manipulate the Root Bridge Election by setting Bridge priority on your switches. The default value is 32768, and the lowest number is preferred. In the case of a tie, the switch with the lowest MAC address will be selected. …”
379c9f6 👍 2
Correct Answer is C.
61745b5 👍 2 Selected: C
Answer is C Priority tie leads to comparing MACs (SW3 has a lower MAC)
Rushit23 👍 1
C The MAC address of SW3 (0C:0A:18:81:B3:19) is lower than that of SW2 (0C:0A:A8:1A:3C:9D), so: SW3 will be elected as the root bridge.

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Expert Analysis

Why the Answer Is Correct

C (SW3) is correct. Root election compares priority first: SW2 and SW3 run the lowest priority (8192), beating SW1/SW4's default 32768. With priority tied, the lower MAC wins — SW3 (0C:0A:18:81:B3:19) is lower than SW2 (0C:0A:A8:1A:3C:9D).

Why the Other Options Are Wrong

A (SW1) and D (SW4) have the higher default priority 32768, so they cannot win. B (SW2) loses the MAC tiebreaker to SW3 despite sharing the lowest priority.

Community Comment Notes

The vote is C (100). Commenters state 'lowest priority then MAC' and confirm SW3's MAC is lower than SW2's among the tied-priority switches.

Official Reference

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

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