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hardmultiple choiceObjective-mapped

Exhibit

Three-switch STP domain - VLAN 30

Gi0/1Gi0/2Gi0/3SW1 Pri:32798SW2 Pri:28678SW3 Pri:24598

Based on the exhibit, which switch will become the root bridge for VLAN 30?

Question 1hardmultiple choice
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Based on the exhibit, which switch will become the root bridge for VLAN 30?

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Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Best answer

SW3

This is correct because SW3 has the lowest bridge priority and therefore the lowest bridge ID overall.

B

Distractor review

SW2

This is wrong because SW2's priority is lower than SW1's but still higher than SW3's.

C

Distractor review

SW1

This is wrong because SW1 has the highest priority value shown and therefore loses the election.

D

Distractor review

All three because STP elects one root per uplink

This is wrong because STP elects one root bridge per spanning-tree instance, not one per uplink.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A frequent mistake is believing that the switch with the highest priority or the highest MAC address becomes the root bridge. Candidates often confuse the priority comparison order or think multiple switches can be root bridges simultaneously. Another trap is misunderstanding that STP elects one root bridge per uplink rather than per VLAN or spanning-tree instance. This leads to incorrect answers like option D. Remember, STP always selects the single switch with the lowest combined bridge priority and MAC address as the root bridge for each VLAN, which is why SW3 wins here.

Technical deep dive

How to think about this question

Spanning Tree Protocol (STP) is a Layer 2 protocol used to prevent loops in Ethernet networks by electing a single root bridge for each VLAN. The root bridge acts as the logical center of the network topology, and all path calculations for forwarding frames are made relative to this root. Each switch in the STP domain has a unique Bridge ID composed of a configurable priority value and the switch’s MAC address. The election process chooses the switch with the lowest Bridge ID as the root bridge. The root bridge election process first compares the bridge priority values of all switches participating in the VLAN. The switch with the lowest priority value wins the election. If two or more switches have the same priority, the tie is broken by comparing their MAC addresses, with the lowest MAC address winning. In this question, SW3 wins because it has the lowest priority value, making it the root bridge for VLAN 30 without needing to compare MAC addresses. A common exam trap is assuming the highest priority wins or that multiple switches can be root bridges simultaneously. STP elects exactly one root bridge per VLAN or spanning-tree instance, and lower priority values have precedence. Understanding this prevents confusion when analyzing STP topology changes or troubleshooting VLAN-specific root bridge elections in Cisco networks, where default priorities and MAC addresses determine the root bridge role.

KKey Concepts to Remember

  • STP elects a single root bridge per VLAN by comparing bridge IDs composed of priority and MAC address.
  • The switch with the lowest bridge priority value becomes the root bridge in the STP election process.
  • If bridge priorities tie, STP uses the lowest MAC address as a tiebreaker to select the root bridge.
  • STP prevents Layer 2 loops by blocking redundant paths and forwarding frames based on the root bridge topology.
  • Each non-root switch selects one root port as its lowest-cost path back to the root bridge.
  • STP does not elect multiple root bridges per VLAN or per uplink; only one root bridge exists per VLAN.
  • Lower bridge priority values have precedence over higher values in STP root bridge elections.
  • Cisco switches use a default priority of 32768, which can be manually adjusted to influence root bridge selection.

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.

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More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 3

What is the OSPF metric called?

Question 4

A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

STP elects a single root bridge per VLAN by comparing bridge IDs composed of priority and MAC address.

What is the correct answer to this question?

The correct answer is: SW3 — The switch with the lowest bridge ID becomes the root bridge. In practical terms, STP compares bridge priority first, and if needed the MAC address breaks the tie. In this case, SW3 has the lowest priority value, so it wins the election even without needing a MAC-address tie-break. This is a foundational STP election question. The important detail is that lower priority wins, not higher priority.

What should I do if I get this 200-301 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

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