The answer is the lowest bridge ID, with priority considered first. This is correct because the Spanning Tree Protocol (STP) root bridge election uses lowest bridge ID, priority first, meaning the switch with the numerically smallest priority value wins the election. If two switches share the same priority, the tie is broken by comparing their MAC addresses, and the lower MAC address becomes the root. On the CCNA 200-301 v2 exam, this concept tests your understanding of the bridge ID structure and the election process, often appearing in multiple-choice questions that ask which value is evaluated first. A common trap is assuming the MAC address is the primary factor, but the priority always takes precedence. To remember this, think of the mnemonic "Priority Paves the Path" — priority is the first gatekeeper, and only if priorities tie does the MAC address step in as the tiebreaker.
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: sTP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
When spanning tree elects a root bridge, which value is considered first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Lowest bridge ID, which begins with priority
The root bridge is the switch with the lowest bridge ID. The bridge ID is made up of priority and MAC address, so priority is considered first, then MAC address if priorities tie.
Key principle: STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Lowest MAC address only
Why it's wrong here
MAC address matters only if the bridge priorities are equal.
When this WOULD be correct
In a different question that asks specifically about the criteria for selecting a root bridge when multiple bridges have the same priority, the lowest MAC address would be the deciding factor. For example, if the question specifies that all bridges have the same priority, then the lowest MAC address would be the correct answer.
✗
Lowest bridge priority only
Why it's wrong here
Priority alone is not the entire comparison value; the full bridge ID is used.
When this WOULD be correct
In a different question that asks specifically for the criteria used to determine the root bridge when only considering priority values, option B could be correct if the question states that all bridges have the same MAC address, thus making the lowest bridge priority the deciding factor.
✓
Lowest bridge ID, which begins with priority
Why this is correct
Correct. STP compares the bridge ID, and priority is the leading field in that comparison.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.
✗
Highest interface bandwidth
Why it's wrong here
Interface bandwidth affects path cost, not root bridge election.
When this WOULD be correct
In a different question that asks about factors influencing network performance or path selection in a Layer 2 network, the highest interface bandwidth could be relevant. For example, a question might ask which attribute affects the best path selection for data traffic in a network topology.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Lowest bridge ID, which begins with priorityCorrect answer▾
Why this is correct
Correct. STP compares the bridge ID, and priority is the leading field in that comparison.
✗Lowest MAC address onlyWrong answer — click to see why▾
Why this is wrong here
The MAC address is only used as a tiebreaker when bridge priorities are equal. It is not the first value considered in root bridge election.
★ When this WOULD be the correct answer
In a different question that asks specifically about the criteria for selecting a root bridge when multiple bridges have the same priority, the lowest MAC address would be the deciding factor. For example, if the question specifies that all bridges have the same priority, then the lowest MAC address would be the correct answer.
Why candidates choose this
Students may confuse the role of MAC address in bridge ID with it being the primary criterion, especially since MAC addresses are unique and often used in other networking decisions.
✗Lowest bridge priority onlyWrong answer — click to see why▾
Why this is wrong here
The bridge priority is only the first part of the bridge ID; the full bridge ID (priority + MAC address) is compared. If priorities are equal, the MAC address is used as a tiebreaker.
★ When this WOULD be the correct answer
In a different question that asks specifically for the criteria used to determine the root bridge when only considering priority values, option B could be correct if the question states that all bridges have the same MAC address, thus making the lowest bridge priority the deciding factor.
Why candidates choose this
It is tempting because priority is the most significant field in the bridge ID, leading some to think it alone determines the root bridge, but the MAC address is also part of the comparison.
✗Highest interface bandwidthWrong answer — click to see why▾
Why this is wrong here
Interface bandwidth is used to calculate path cost, which influences port roles (root port, designated port) but does not affect root bridge election. Root bridge election is based solely on bridge ID.
★ When this WOULD be the correct answer
In a different question that asks about factors influencing network performance or path selection in a Layer 2 network, the highest interface bandwidth could be relevant. For example, a question might ask which attribute affects the best path selection for data traffic in a network topology.
Why candidates choose this
Students may think higher bandwidth is better and assume it influences root bridge selection, confusing path cost metrics with the bridge ID comparison.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Remember that the bridge priority is evaluated before the MAC address in the root bridge election process.
Detailed technical explanation
How to think about this question
Spanning Tree Protocol (STP) is a Layer 2 network protocol designed to prevent loops in Ethernet networks by electing a single root bridge. The root bridge acts as the logical center of the network topology, and all path calculations for forwarding frames are made relative to it. The election process is fundamental to STP operation and ensures a loop-free topology by blocking redundant paths.
The root bridge election process uses the Bridge ID (BID) as the deciding factor. The BID is a composite value consisting of a configurable bridge priority (default 32768) and the switch’s MAC address. STP compares the BIDs of all switches in the network, first by priority and then by MAC address if priorities are equal. The switch with the lowest BID becomes the root bridge. This hierarchical comparison ensures a deterministic and consistent root bridge selection.
A common exam trap is misunderstanding that the MAC address alone or priority alone determines the root bridge. While the MAC address is part of the BID, it is only considered if two switches have the same priority. Also, interface bandwidth or path cost influences port roles and forwarding decisions but does not affect root bridge election. Practically, network engineers can manipulate root bridge election by adjusting bridge priority values to control which switch becomes root, ensuring optimal traffic flow and redundancy.
KKey Concepts to Remember
STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.
The bridge priority is the first field compared in the bridge ID during root bridge election, with lower values preferred.
If two switches have the same priority, STP compares their MAC addresses to determine the root bridge, selecting the lowest MAC address.
Interface bandwidth and path cost influence port roles and forwarding decisions but do not affect root bridge election.
The root bridge serves as the logical center of the STP topology, and all path calculations are made relative to it.
Network engineers can influence root bridge election by adjusting the bridge priority to ensure optimal network design.
STP prevents Layer 2 loops by blocking redundant paths based on root bridge election and port roles.
The bridge ID comparison process ensures a deterministic and consistent root bridge selection across all switches.
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.
Key takeaway
STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.
Real-world example
How this comes up in practice
A practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review sTP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address..
What is the correct answer to this question?
The correct answer is: Lowest bridge ID, which begins with priority — The root bridge is the switch with the lowest bridge ID. The bridge ID is made up of priority and MAC address, so priority is considered first, then MAC address if priorities tie.
What should I do if I get this 200-301 question wrong?
Review sTP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
STP elects the root bridge by comparing the bridge ID, which consists of a configurable priority and the switch’s MAC address.
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