CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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 as the switch with the lowest bridge ID, which combines priority and 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.
Exhibit
SW2# show spanning-tree vlan 10
Root ID Priority 32778
Address 0011.1111.1111
Cost 4
Port 1 (GigabitEthernet0/1)
Bridge ID Priority 32778
Address 00aa.aaaa.aaaa
SW2 receives the following STP details for VLAN 10: The root bridge ID is 32768:0001.0001.0001 (SW1), and SW2's bridge ID is 32768:0002.0002.0002. Its interface Gi0/1 has a path cost of 4 to the root, while Gi0/2 has a path cost of 19. Based on this information, which statement is correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Gi0/1 on SW2 is the root port.
The root bridge has the lowest bridge ID. SW1 is the root because its bridge ID is lower than SW2's local bridge ID. On a non-root switch, the port with the best path toward the root becomes the root port, so Gi0/1 is the root port here.
Key principle: STP elects the root bridge as the switch with the lowest bridge ID, which combines priority and 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.
✗
SW2 is the root bridge for VLAN 10.
Why it's wrong here
The root ID shown is different from SW2's local bridge ID.
When this WOULD be correct
In a different question scenario where the exhibit shows that SW2 has the lowest bridge ID among all switches in the VLAN, candidates would correctly identify that SW2 is the root bridge for VLAN 10, confirming its role in the STP topology.
✓
Gi0/1 on SW2 is the root port.
Why this is correct
The output states that the root is reached through Port 1, which maps to Gi0/1.
Related concept
STP elects the root bridge as the switch with the lowest bridge ID, which combines priority and MAC address.
✗
All SW2 ports in VLAN 10 must be designated ports.
Why it's wrong here
A non-root switch has a root port, and some other ports may be alternate or designated depending on topology.
When this WOULD be correct
In a different scenario where the question states that SW2 is the root bridge for VLAN 10, and all other switches in the topology have designated ports leading to SW2, then this option would be correct. This would imply that SW2's ports are indeed all designated due to its root bridge status.
✗
STP is disabled because the priorities are equal.
Why it's wrong here
Equal priority does not disable STP; the MAC portion breaks the tie.
When this WOULD be correct
In a different exam scenario where the question specifies that all switches in the network have identical bridge priorities and no unique MAC addresses, one could conclude that STP is effectively disabled due to the lack of a definitive root bridge. The question would need to emphasize that no other STP parameters are available to break the tie.
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.
✓Gi0/1 on SW2 is the root port.Correct answer▾
Why this is correct
The output states that the root is reached through Port 1, which maps to Gi0/1.
✗SW2 is the root bridge for VLAN 10.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because the question indicates that SW2 is not the root bridge for VLAN 10, as it is receiving STP details from another switch, implying that another switch has a lower bridge ID.
★ When this WOULD be the correct answer
In a different question scenario where the exhibit shows that SW2 has the lowest bridge ID among all switches in the VLAN, candidates would correctly identify that SW2 is the root bridge for VLAN 10, confirming its role in the STP topology.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of STP roles, mistakenly believing that receiving STP details indicates that the switch is the root bridge, rather than recognizing the importance of bridge IDs in determining the root.
✗All SW2 ports in VLAN 10 must be designated ports.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because not all ports on a switch can be designated ports; at least one port must be a root port or a blocked port based on STP calculations. In the context of the given exhibit, SW2 cannot have all its VLAN 10 ports designated if it is not the root bridge.
★ When this WOULD be the correct answer
In a different scenario where the question states that SW2 is the root bridge for VLAN 10, and all other switches in the topology have designated ports leading to SW2, then this option would be correct. This would imply that SW2's ports are indeed all designated due to its root bridge status.
Why candidates choose this
Candidates may choose this option because they might confuse the roles of ports in STP, thinking that if a switch is functioning properly, all its ports must be designated. This reflects a misunderstanding of STP roles and their requirements.
✗STP is disabled because the priorities are equal.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because STP cannot be disabled simply due to equal bridge priorities; it requires a tie-breaker based on MAC addresses or port IDs to determine the root bridge. In the context of the question, STP is still operational, and the root bridge is determined by the lowest bridge ID.
★ When this WOULD be the correct answer
In a different exam scenario where the question specifies that all switches in the network have identical bridge priorities and no unique MAC addresses, one could conclude that STP is effectively disabled due to the lack of a definitive root bridge. The question would need to emphasize that no other STP parameters are available to break the tie.
Why candidates choose this
Candidates may find this option tempting because they might misunderstand how STP operates and assume that equal priorities automatically lead to STP being disabled, overlooking the need for a tie-breaking mechanism.
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
A common exam trap is to incorrectly conclude that STP is disabled when bridge priorities are equal. Candidates may mistakenly believe that equal priorities cause STP to fail or not elect a root bridge. However, STP always elects a root bridge by comparing the MAC addresses as a tiebreaker when priorities match. Another trap is assuming all ports on a non-root switch must be designated ports, ignoring the existence of a root port that leads toward the root bridge. Misreading the root port can lead to incorrect answers about port roles and network topology.
Trap categories for this question
Command / output trap
The root ID shown is different from SW2's local bridge ID.
Detailed technical explanation
How to think about this question
Spanning Tree Protocol (STP) is a Layer 2 network protocol that prevents switching loops by electing a root bridge and blocking redundant paths. Each switch in the STP topology has a unique bridge ID composed of a priority value and the switch’s MAC address. The root bridge is the switch with the lowest bridge ID, and all other switches determine their best path to this root. This path is identified by selecting a root port, which is the port with the lowest path cost to the root bridge.
When a switch receives STP information, it compares the root bridge ID in the BPDU with its own bridge ID to determine if it is the root bridge. If it is not the root, the switch selects a root port that provides the best path to the root bridge. This port forwards traffic toward the root. Other ports on the switch may be designated ports or blocked ports depending on the topology and path costs. The root port is unique per switch and is critical for loop-free forwarding.
A common exam trap is assuming that equal priority values disable STP or that all ports on a non-root switch must be designated ports. In reality, STP uses the MAC address portion of the bridge ID to break ties when priorities are equal, ensuring a single root bridge is elected. Additionally, non-root switches always have one root port, which is the port with the best path to the root bridge, while other ports may be designated or blocked. Understanding these distinctions is essential for correctly interpreting STP output and avoiding misconfiguration or misinterpretation during the CCNA exam.
KKey Concepts to Remember
STP elects the root bridge as the switch with the lowest bridge ID, which combines priority and MAC address.
A non-root switch selects one root port as its lowest-cost path back to the root bridge.
The root port on a switch forwards traffic toward the root bridge and is unique per VLAN.
Designated ports are selected on segments to forward traffic away from the root and prevent loops.
STP uses the MAC address to break ties when bridge priorities are equal, ensuring a single root bridge.
Ports on a non-root switch can be root ports, designated ports, or blocked ports depending on topology.
The root bridge does not have a root port because it is the reference point for all path calculations.
STP prevents loops by blocking redundant paths and forwarding only the best path toward the root.
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 as the switch with the lowest bridge ID, which combines priority and MAC address.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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 as the switch with the lowest bridge ID, which combines priority and MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — STP elects the root bridge as the switch with the lowest bridge ID, which combines priority and MAC address..
What is the correct answer to this question?
The correct answer is: Gi0/1 on SW2 is the root port. — The root bridge has the lowest bridge ID. SW1 is the root because its bridge ID is lower than SW2's local bridge ID. On a non-root switch, the port with the best path toward the root becomes the root port, so Gi0/1 is the root port here.
What should I do if I get this 200-301 question wrong?
Review sTP elects the root bridge as the switch with the lowest bridge ID, which combines priority and MAC address., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
STP elects the root bridge as the switch with the lowest bridge ID, which combines priority and MAC address.
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