20+ practice questions focused on Spanning Tree Protocol — one of the most tested topics on the ENCOR 350-401 exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start Spanning Tree Protocol PracticeA network engineer is troubleshooting an STP issue in a switched network. The network has two distribution switches connected via a trunk, and each distribution switch connects to the same access switch. The engineer notices that the root bridge is not the intended distribution switch. Upon checking, the engineer sees that the access switch has a higher priority than the distribution switches. The engineer needs to ensure that the intended distribution switch becomes the root bridge without causing a temporary loop. What should the engineer do?
Explanation: Option A is correct because the 'spanning-tree vlan vlan-id root primary' command dynamically sets the switch's bridge priority to 24576 (or 4096 if the current root has a priority lower than 24576) and ensures the switch becomes the root bridge without manual priority miscalculation. This command also adjusts the priority of neighboring switches if needed, preventing temporary loops by avoiding the need to disable or reset STP. It is the safest and most efficient method to force a specific switch to become the root bridge in a live network.
An engineer is designing a redundant Layer 2 network with multiple VLANs. The network uses Rapid PVST+ for STP. The engineer wants to ensure that different VLANs have different root bridges to optimize traffic flow. The distribution switches are Cisco Catalyst 9300s. The engineer has configured one distribution switch as the root for VLANs 10 and 20, and the other as the root for VLANs 30 and 40. However, after implementation, the engineer notices that all VLANs have the same root bridge. What is the most likely cause?
Explanation: The 'spanning-tree root primary' command without specifying a VLAN sets the bridge priority to 24576 for all VLANs on the switch, making it the root for every VLAN. Since the engineer intended different root bridges per VLAN, this command overrides any per-VLAN priority settings and causes all VLANs to elect the same root bridge.
A network engineer is troubleshooting a Layer 2 loop issue. The network consists of three switches: SW1, SW2, and SW3, all connected in a triangle. The engineer notices that SW1 is the root bridge. After a link failure between SW1 and SW2, the network experiences a temporary loop. The engineer wants to prevent such loops in the future by enabling a feature that provides faster convergence and prevents temporary loops during topology changes. The engineer is using Rapid PVST+. Which feature should the engineer enable?
Explanation: When a link fails in a triangle topology with Rapid PVST+, the switch that lost its root port may temporarily transition a blocked alternate port to forwarding before the new root port is fully synchronized, causing a loop. Enabling Loop Guard on all switch ports prevents this by keeping a port in a blocking state if BPDUs are not received, ensuring that a port does not erroneously transition to forwarding during a topology change. This provides faster convergence without temporary loops by enforcing BPDU-based loop prevention.
An engineer is configuring a new access switch that connects to two distribution switches via trunk links. The distribution switches are configured with Rapid PVST+ and are both running as root bridges for different VLANs. The engineer wants to ensure that the access switch does not become the root bridge for any VLAN, even if the distribution switches fail. The engineer also wants to prevent any unauthorized switch from becoming root. What configuration should the engineer apply on the access switch?
Explanation: Option A is correct because setting the spanning-tree priority to 61440 (the highest possible value) ensures the access switch will never become the root bridge, even if the current root bridges fail. Enabling Root Guard on the uplink ports prevents any unauthorized switch from becoming root by placing the port into a root-inconsistent state if a superior BPDU is received, thus protecting the root bridge election.
A network engineer is troubleshooting a connectivity issue in a switched network. The network uses Rapid PVST+ with multiple VLANs. The engineer notices that a host connected to an access port on SW1 cannot communicate with the default gateway, which is on a distribution switch. The access port is configured with PortFast and BPDU Guard. The engineer checks the switch logs and sees that the port went into errdisable state. What is the most likely cause of the errdisable state?
Explanation: The access port is configured with PortFast and BPDU Guard. PortFast immediately transitions the port to forwarding, but BPDU Guard monitors for incoming BPDUs. When another switch is connected to this access port, it sends BPDUs, triggering BPDU Guard to error-disable the port to prevent a potential bridging loop. This matches the log entry showing the port went into errdisable state.
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Practice all Spanning Tree Protocol questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of Spanning Tree Protocol. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
Spanning Tree Protocol questions on the 350-401 frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. Spanning Tree Protocol is tested as part of the ENCOR 350-401 blueprint. Practicing with targeted Spanning Tree Protocol questions ensures you can handle any format or difficulty that appears.
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Difficulty is subjective, but Spanning Tree Protocol is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
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