CCNA Switching and Network Access Practice Question
Network Topology
You are connected to SW1 via the console. The network uses Rapid-PVST+ and you need to ensure that SW1 becomes the root bridge for VLAN 10 and VLAN 20. Additionally, configure PortFast and BPDU Guard on interface GigabitEthernet0/1, which connects to a workstation. After configuration, the workstation is moved and the port goes err-disabled. Diagnose the cause and recover the port without reloading the switch.
⚠ Common exam trap
Do not confuse 'root primary' with a guaranteed root election; always check for lower priorities. Also, remember that err-disabled ports require manual intervention (shutdown/no shutdown) unless you configure errdisable recovery. BPDU Guard err-disables the port; simply disabling BPDU Guard does not recover it.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure spanning-tree vlan 10 priority 4096 and spanning-tree vlan 20 priority 4096. Then on interface GigabitEthernet0/1, configure spanning-tree portfast and spanning-tree bpduguard enable. After removing the BPDU source, use 'shutdown' and 'no shutdown' to recover the port.
SW1 is currently the root for VLAN 10 but not for VLAN 20. To become root for both VLANs, set the spanning-tree priority to a lower value (e.g., 4096) for each VLAN. The port Gi0/1 went err-disabled because it received a BPDU, which is unexpected on a PortFast edge port with BPDU Guard enabled. To recover, first identify and remove the BPDU source (likely another switch connected to that port), then use 'shutdown' followed by 'no shutdown' on the interface to bring it back up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure spanning-tree vlan 10 priority 4096 and spanning-tree vlan 20 priority 4096. Then on interface GigabitEthernet0/1, configure spanning-tree portfast and spanning-tree bpduguard enable. After removing the BPDU source, use 'shutdown' and 'no shutdown' to recover the port.
Why this is correct
Setting the priority for each VLAN individually ensures SW1 becomes the root bridge for both. Enabling PortFast and BPDU Guard on the access port protects against loops and disables the port if a BPDU is received. The err-disabled state requires manual reset with shutdown/no shutdown after removing the BPDU source.
- ✗
Configure spanning-tree vlan 10,20 root primary and spanning-tree portfast on Gi0/1; then use 'errdisable recovery cause bpduguard' to automatically recover the port.
Why it's wrong here
The 'root primary' command sets priority to 24576, which may not be low enough if another switch has a lower priority. Also, automatic recovery via 'errdisable recovery' is not the recommended manual recovery method described in the question; the question asks to recover without reloading, but automatic recovery is an alternative, not the direct action.
- ✗
Configure spanning-tree vlan 10,20 priority 0 and spanning-tree bpduguard enable on Gi0/1; then use 'no spanning-tree bpduguard' to recover the port.
Why it's wrong here
Setting priority to 0 is valid but extreme and may cause issues if other switches also use 0. More importantly, disabling BPDU Guard does not recover the port; the port remains err-disabled until you issue 'shutdown' and 'no shutdown'.
- ✗
Configure spanning-tree vlan 10,20 priority 4096 and spanning-tree portfast on Gi0/1; then use 'clear spanning-tree detected-protocols' to recover the port.
Why it's wrong here
While the spanning-tree configuration is correct, the recovery command is wrong. 'clear spanning-tree detected-protocols' is used to re-run the spanning-tree algorithm, not to recover an err-disabled port. The correct recovery is 'shutdown' and 'no shutdown'.
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.
✓Configure spanning-tree vlan 10 priority 4096 and spanning-tree vlan 20 priority 4096. Then on interface GigabitEthernet0/1, configure spanning-tree portfast and spanning-tree bpduguard enable. After removing the BPDU source, use 'shutdown' and 'no shutdown' to recover the port.Correct answer▾
Why this is correct
Setting the priority for each VLAN individually ensures SW1 becomes the root bridge for both. Enabling PortFast and BPDU Guard on the access port protects against loops and disables the port if a BPDU is received. The err-disabled state requires manual reset with shutdown/no shutdown after removing the BPDU source.
✗Configure spanning-tree vlan 10,20 root primary and spanning-tree portfast on Gi0/1; then use 'errdisable recovery cause bpduguard' to automatically recover the port.Wrong answer — click to see why▾
Why this is wrong here
The 'root primary' command does not guarantee root status if another switch has a priority lower than 24576. The question expects manual recovery, not automatic.
Why candidates choose this
Candidates may think 'root primary' is a guaranteed method and that 'errdisable recovery' is the standard way to recover err-disabled ports.
✗Configure spanning-tree vlan 10,20 priority 0 and spanning-tree bpduguard enable on Gi0/1; then use 'no spanning-tree bpduguard' to recover the port.Wrong answer — click to see why▾
Why this is wrong here
Priority 0 is not incorrect but is not the standard recommendation. The recovery method is wrong: disabling BPDU Guard does not clear the err-disabled state.
Why candidates choose this
Candidates might think that setting the lowest priority (0) is best and that removing the guard will fix the issue.
✗Configure spanning-tree vlan 10,20 priority 4096 and spanning-tree portfast on Gi0/1; then use 'clear spanning-tree detected-protocols' to recover the port.Wrong answer — click to see why▾
Why this is wrong here
The command 'clear spanning-tree detected-protocols' does not clear the err-disabled state; it only resets the port's protocol state.
Why candidates choose this
Candidates may confuse this command with recovery commands or think it resets the port's error condition.
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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
Root bridge
The root bridge is the central reference point in a Spanning Tree Protocol (STP) network, serving as the logical root of the spanning tree topology.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.