The answer is to configure spanning-tree vlan 10 priority 4096 and spanning-tree vlan 20 priority 4096, then enable PortFast and BPDU Guard on GigabitEthernet0/1, and recover the errdisabled port with a shutdown/no shutdown cycle after removing the BPDU source. This is correct because setting a lower priority than the default 32768 ensures SW1 becomes the root bridge for both VLANs under Rapid-PVST+, while BPDU Guard errdisable recovery is triggered when a PortFast edge port unexpectedly receives a BPDU—typically from a misconnected switch—causing the interface to error-disable for security. On the CCNA 200-301 v2 exam, this tests your understanding of STP convergence, root bridge election, and the interaction between PortFast, BPDU Guard, and errdisable state; a common trap is forgetting that BPDU Guard only activates on PortFast-enabled ports, or attempting to recover with a reload instead of the interface-level shutdown/no shutdown. Remember the mnemonic: "Lower priority wins the root, BPDU Guard kills the port, and a toggle brings it back."
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
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.
SW1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 32778
Address 0001.0001.0001
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext 10)
Address 0001.0001.0001
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.1 P2p
Gi0/2 Desg FWD 4 128.2 P2p
SW1#show running-config | section interface GigabitEthernet0/1
interface GigabitEthernet0/1
switchport mode access
switchport access vlan 10
spanning-tree portfast
spanning-tree bpduguard enable
SW1#show interfaces status err-disabled
Port Name Status Reason
Gi0/1 err-disabled bpduguard
SW1#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 32788
Address 0002.0002.0002
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 0002.0002.0002
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.1 P2p
Gi0/2 Desg FWD 4 128.2 P2p
A
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.
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.
B
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 wrong: 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.
C
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 wrong: 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'.
D
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 wrong: 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'.
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.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Related concept
Access ports place end devices into a single VLAN.
✗
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?”
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Command / output trap
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.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
Switching and Network Access — This question tests Switching and Network Access — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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