The answer is to reconfigure the spanning tree root bridge by setting SW2’s priority to 0 and adjusting MLS1’s priority to 4096, then enabling PortFast and BPDU Guard on MLS1’s GigabitEthernet0/2, with recovery from err-disable via shutdown and no shutdown. This is correct because the root bridge is elected by the lowest bridge priority; setting SW2 to 0 makes it the root, while raising MLS1’s priority to 4096 prevents it from overtaking SW2 after removing the root primary command. On the CCNA 200-301 v2 exam, this tests your ability to manipulate STP root selection and secure access ports—a common trap is forgetting that PortFast alone does not block BPDUs, so BPDU Guard is essential to prevent rogue switch loops. A memory tip: “Zero wins the root, PortFast skips listening, BPDU Guard locks the port—shut/no shut to unlock.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 a multilayer switch MLS1. The network has two other switches SW1 and SW2 forming a triangle topology. Currently, SW1 is the root bridge but it should be SW2. Additionally, configure PortFast and BPDU Guard on interface GigabitEthernet0/2 of MLS1, which connects to a host. Simulate a BPDU violation on that port and then recover the port from err-disabled state.
MLS1# show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 32769
Address 0001.1111.1111
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0002.2222.2222
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0 Desg FWD 4 128.1 P2p
Gi0/1 Desg FWD 4 128.2 P2p
Gi0/2 Desg FWD 4 128.3 P2p Edge
MLS1# show interfaces gigabitEthernet 0/2 status
Port Name Status Vlan Duplex Speed Type
Gi0/2 err-disabled 1 auto auto 10/100/1000BaseTX
MLS1# show running-config | include spanning-tree
spanning-tree mode rapid-pvst
spanning-tree vlan 1 root primary
MLS1# show running-config interface gigabitEthernet 0/2
interface GigabitEthernet0/2
spanning-tree portfast
spanning-tree bpduguard enable
shutdown
A
On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'shutdown' then 'no shutdown'.
This is correct because removing the root primary command and raising MLS1's priority (e.g., 4096) ensures SW2 with lower priority (0) becomes root. PortFast and BPDU Guard are correctly applied to the host-facing port. After err-disable due to BPDU violation, 'no shutdown' re-enables the port.
B
On MLS1, set priority to 0 to make it root; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by removing BPDU Guard.
Why wrong: This is incorrect because setting MLS1 priority to 0 would make it root, but the goal is to make SW2 root. Also, recovering from err-disable requires re-enabling the port, not removing BPDU Guard.
C
On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by reloading MLS1.
Why wrong: This is incorrect because reloading the switch is unnecessary and disruptive. The correct recovery is to re-enable the port with 'no shutdown' after fixing the cause.
D
On MLS1, set priority to 0; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'no shutdown'.
Why wrong: This is incorrect because setting MLS1 priority to 0 makes it root, but SW2 should be root. The priority values are reversed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'shutdown' then 'no shutdown'.
Currently, SW1 is the root bridge per the topology, but the goal is to make SW2 the root. On MLS1, removing the 'spanning-tree vlan 1 root primary' command and setting a higher priority (4096) ensures it does not interfere. On SW2, set priority to 0 to make it root. On MLS1 Gi0/2, configure PortFast and BPDU Guard. If a BPDU is received, the port goes err-disabled; to recover, issue 'shutdown' then 'no shutdown' after resolving the BPDU source.
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.
✓
On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'shutdown' then 'no shutdown'.
Why this is correct
This is correct because removing the root primary command and raising MLS1's priority (e.g., 4096) ensures SW2 with lower priority (0) becomes root. PortFast and BPDU Guard are correctly applied to the host-facing port. After err-disable due to BPDU violation, 'no shutdown' re-enables the port.
Related concept
Access ports place end devices into a single VLAN.
✗
On MLS1, set priority to 0 to make it root; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by removing BPDU Guard.
Why it's wrong here
This is incorrect because setting MLS1 priority to 0 would make it root, but the goal is to make SW2 root. Also, recovering from err-disable requires re-enabling the port, not removing BPDU Guard.
✗
On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by reloading MLS1.
Why it's wrong here
This is incorrect because reloading the switch is unnecessary and disruptive. The correct recovery is to re-enable the port with 'no shutdown' after fixing the cause.
✗
On MLS1, set priority to 0; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'no shutdown'.
Why it's wrong here
This is incorrect because setting MLS1 priority to 0 makes it root, but SW2 should be root. The priority values are reversed.
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.
✓On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'shutdown' then 'no shutdown'.Correct answer▾
Why this is correct
This is correct because removing the root primary command and raising MLS1's priority (e.g., 4096) ensures SW2 with lower priority (0) becomes root. PortFast and BPDU Guard are correctly applied to the host-facing port. After err-disable due to BPDU violation, 'no shutdown' re-enables the port.
✗On MLS1, set priority to 0 to make it root; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by removing BPDU Guard.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: Setting MLS1 priority to 0 makes it root, opposite of the requirement. Removing BPDU Guard does not recover the port; 'no shutdown' is needed.
Why candidates choose this
Candidates might think setting a lower priority always makes a switch root, but they overlook the requirement that SW2 should be root. They may also confuse recovery methods.
✗On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover by reloading MLS1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: Reloading the switch is not the standard recovery for an err-disabled port; 'no shutdown' is the proper command.
Why candidates choose this
Candidates might think that a reload clears all errors, but it is overkill and not the recommended practice. They may not know the 'no shutdown' recovery.
✗On MLS1, set priority to 0; on SW2, set priority to 4096. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'no shutdown'.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: MLS1 should have a higher priority (e.g., 4096) and SW2 a lower priority (e.g., 0) to make SW2 root. The option does the opposite.
Why candidates choose this
Candidates may confuse which switch should have the lower priority. They might think the current root should keep a low priority, but the requirement is to change the root to SW2.
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.
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: On MLS1, remove 'spanning-tree vlan 1 root primary' and set priority to 4096; on SW2, set priority to 0. On MLS1 Gi0/2, configure 'spanning-tree portfast' and 'spanning-tree bpduguard enable'. After BPDU violation, recover with 'shutdown' then 'no shutdown'. — Currently, SW1 is the root bridge per the topology, but the goal is to make SW2 the root. On MLS1, removing the 'spanning-tree vlan 1 root primary' command and setting a higher priority (4096) ensures it does not interfere. On SW2, set priority to 0 to make it root. On MLS1 Gi0/2, configure PortFast and BPDU Guard. If a BPDU is received, the port goes err-disabled; to recover, issue 'shutdown' then 'no shutdown' after resolving the BPDU source.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to switch SW1 via console. The network uses Rapid-PVST+ and you need to ensure that SW1 becomes the root bridge for VLANs 10 and 20. Additionally, configure PortFast and BPDU Guard on interface GigabitEthernet0/2, which connects to an end host. Finally, diagnose why interface GigabitEthernet0/3 is in err-disabled state and bring it back operational.
hard
✓ A.Configure SW1 with spanning-tree vlan 10,20 priority 4096, enable PortFast and BPDU Guard on Gi0/2, and recover Gi0/3 by identifying the cause and using shutdown/no shutdown.
B.Set SW1's priority to 0 for VLANs 10 and 20, enable PortFast on Gi0/2, and recover Gi0/3 by reloading the switch.
C.Configure SW1 with spanning-tree vlan 10,20 root primary, enable PortFast and BPDU Guard globally, and recover Gi0/3 by using the 'errdisable recovery cause all' command.
D.Set SW1's priority to 8192 for VLANs 10 and 20, enable PortFast on Gi0/2, and recover Gi0/3 by removing and reinserting the cable.
Why A: To make SW1 the root bridge for VLANs 10 and 20, configure 'spanning-tree vlan 10,20 priority 4096' (a valid multiple of 4096). Interface Gi0/2 connects to an end host, so enable PortFast with 'spanning-tree portfast' and BPDU Guard with 'spanning-tree bpduguard enable' under the interface to protect against accidental BPDU reception. Gi0/3 is in err-disabled state. Common causes include a port-security violation, UDLD misconfiguration, or a loopback detection. To recover, identify the cause with 'show interfaces status err-disabled', then administratively shut and no shut the interface. Option A correctly accomplishes these tasks. Option B uses an invalid priority value (0) and reloading the switch is unnecessary. Option C configures 'root primary', which sets priority to 24576 but not 4096, and globally enabling PortFast and BPDU Guard is not recommended; also 'errdisable recovery cause all' might recover the port automatically but does not address the root cause. Option D uses priority 8192 (too high) and physical cable manipulation is not a valid recovery method.
Variation 2. You are connected to R1, a multilayer switch running Rapid PVST+. The current root bridge for VLAN 10 has priority 24586 and for VLAN 20 has priority 24676. Configure R1 so that it becomes the root bridge for VLAN 10 and VLAN 20. Then enable PortFast and BPDU Guard on interface FastEthernet0/1, which connects to an access switch. Finally, diagnose why interface FastEthernet0/2 has entered an err-disabled state and recover it.
hard
✓ A.Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown then no shutdown.
B.Configure spanning-tree vlan 10,20 root primary; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.
C.Configure spanning-tree vlan 10,20 priority 8192; on Fa0/1: spanning-tree portfast; on Fa0/2: no shutdown.
D.Configure spanning-tree vlan 10,20 priority 4096; on Fa0/1: spanning-tree portfast and spanning-tree bpduguard enable; on Fa0/2: shutdown.
Why A: To become the root bridge, R1’s priority must be lower than the current root’s priority. Setting the priority to 4096 (or any value lower than 24586/24676) accomplishes this. Option A correctly uses `spanning-tree vlan 10,20 priority 4096` (though the actual command per VLAN is `spanning-tree vlan 10 priority 4096` and `spanning-tree vlan 20 priority 4096`). It also enables PortFast and BPDU Guard on Fa0/1 to prevent BPDU reception on an edge port, and recovers the err-disabled Fa0/2 by cycling `shutdown` then `no shutdown`. Options B and C fail because they do not enable BPDU Guard, leaving the interface vulnerable. Option D fails because it only shuts down Fa0/2 without the `no shutdown` command, so the interface remains administratively down.
Last reviewed: Jun 6, 2026
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