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 R1, a multilayer switch acting as the STP root for VLAN 10. Configure Root Guard on port GigabitEthernet0/1 (designated port) to protect against superior BPDUs from an unauthorized switch, Loop Guard on uplink GigabitEthernet0/2 to prevent forwarding loops on unidirectional links, and BPDU Guard on PortFast-enabled GigabitEthernet0/3 to shut down the port if a BPDU is received. After configuration, troubleshoot the scenario: a superior BPDU is received on G0/1, causing it to be blocked by Root Guard, and an unauthorized switch sends a BPDU to G0/3, placing it in err-disable state. Verify the final configuration and state.
R1#show running-config interface gigabitEthernet0/1
Building configuration...
Current configuration : 133 bytes
!
interface GigabitEthernet0/1
description Link to Access Switch
switchport mode access
switchport access vlan 10
spanning-tree guard root
end
R1#show running-config interface gigabitEthernet0/2
Building configuration...
Current configuration : 115 bytes
!
interface GigabitEthernet0/2
description Uplink to Core
switchport mode trunk
spanning-tree guard loop
end
R1#show running-config interface gigabitEthernet0/3
Building configuration...
Current configuration : 127 bytes
!
interface GigabitEthernet0/3
description Server Port
switchport mode access
switchport access vlan 10
spanning-tree portfast
spanning-tree bpduguard enable
end
R1#show spanning-tree interface gigabitEthernet0/1 detail
Port 1 (GigabitEthernet0/1) of VLAN0010 is root guard blocked
Port path cost 4, Port priority 128, Port Identifier 128.1.
Designated root has priority 24576, address 0011.2233.4455
Designated bridge has priority 24576, address 0011.2233.4455
Designated port id is 128.1, designated path cost 0
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 1, received 5
R1#show interfaces gigabitEthernet0/3 status
Port Name Status Vlan Duplex Speed Type
Gi0/3 Server Port err-disabled 10 auto auto 10/100/1000BaseTX
R1#show spanning-tree vlan 10
VLAN0010
Spanning tree enabled protocol rstp
Root ID Priority 24576
Address 0011.2233.4455
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24576 (priority 24576 sys-id-ext 10)
Address 0011.2233.4455
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 Desi BLK*4 128.1 P2p *ROOT_Guard
Gi0/2 Desi FWD 4 128.2 P2p *LOOP_Guard
Gi0/3 Desi BLK 4 128.3 P2p *BPDU_Guard
A
[CORRECT] Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.
This option correctly describes the behavior of Root Guard, Loop Guard, and BPDU Guard as per Cisco IOS. Root Guard forces a port to become a designated port and blocks it if a superior BPDU is received, placing it in a root-inconsistent state (BLK*). Loop Guard prevents loops by putting the port into loop-inconsistent state if BPDUs stop. BPDU Guard err-disables a PortFast-enabled port upon BPDU reception. Manual intervention is required to recover from err-disable.
B
Root Guard on G0/1 is incorrectly configured; it should be configured on the root port, not the designated port. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is correctly configured, but the port should automatically recover from err-disable state after a timeout.
Why wrong: This is incorrect because Root Guard is specifically designed to be configured on designated ports to prevent them from becoming root ports. Configuring it on a root port would be ineffective. Also, BPDU Guard does not automatically recover; the port remains err-disabled until manually re-enabled or configured with errdisable recovery.
C
Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is incorrectly configured because Loop Guard should be applied to root ports, not uplink ports. BPDU Guard on G0/3 is correctly configured, but the port should be in a blocking state, not err-disabled.
Why wrong: This is incorrect because Loop Guard can be applied to any port that is a potential root port or alternate port, but it is commonly used on blocked ports or uplinks. The key error is that BPDU Guard causes err-disable, not a blocking state. Also, the statement about Loop Guard being only for root ports is inaccurate.
D
Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is incorrectly configured because BPDU Guard should be applied to trunk ports, not access ports, and the port should be placed in a root-inconsistent state.
Why wrong: This is incorrect because BPDU Guard can be applied to any PortFast-enabled port, regardless of whether it is an access or trunk port. The port is err-disabled, not placed in a root-inconsistent state (which is a Root Guard behavior).
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
[CORRECT] Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.
The scenario demonstrates three STP protection mechanisms. Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.
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.
✓
[CORRECT] Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.
Why this is correct
This option correctly describes the behavior of Root Guard, Loop Guard, and BPDU Guard as per Cisco IOS. Root Guard forces a port to become a designated port and blocks it if a superior BPDU is received, placing it in a root-inconsistent state (BLK*). Loop Guard prevents loops by putting the port into loop-inconsistent state if BPDUs stop. BPDU Guard err-disables a PortFast-enabled port upon BPDU reception. Manual intervention is required to recover from err-disable.
Related concept
Access ports place end devices into a single VLAN.
✗
Root Guard on G0/1 is incorrectly configured; it should be configured on the root port, not the designated port. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is correctly configured, but the port should automatically recover from err-disable state after a timeout.
Why it's wrong here
This is incorrect because Root Guard is specifically designed to be configured on designated ports to prevent them from becoming root ports. Configuring it on a root port would be ineffective. Also, BPDU Guard does not automatically recover; the port remains err-disabled until manually re-enabled or configured with errdisable recovery.
✗
Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is incorrectly configured because Loop Guard should be applied to root ports, not uplink ports. BPDU Guard on G0/3 is correctly configured, but the port should be in a blocking state, not err-disabled.
Why it's wrong here
This is incorrect because Loop Guard can be applied to any port that is a potential root port or alternate port, but it is commonly used on blocked ports or uplinks. The key error is that BPDU Guard causes err-disable, not a blocking state. Also, the statement about Loop Guard being only for root ports is inaccurate.
✗
Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is incorrectly configured because BPDU Guard should be applied to trunk ports, not access ports, and the port should be placed in a root-inconsistent state.
Why it's wrong here
This is incorrect because BPDU Guard can be applied to any PortFast-enabled port, regardless of whether it is an access or trunk port. The port is err-disabled, not placed in a root-inconsistent state (which is a Root Guard behavior).
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.
✓[CORRECT] Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.Correct answer▾
Why this is correct
This option correctly describes the behavior of Root Guard, Loop Guard, and BPDU Guard as per Cisco IOS. Root Guard forces a port to become a designated port and blocks it if a superior BPDU is received, placing it in a root-inconsistent state (BLK*). Loop Guard prevents loops by putting the port into loop-inconsistent state if BPDUs stop. BPDU Guard err-disables a PortFast-enabled port upon BPDU reception. Manual intervention is required to recover from err-disable.
✗Root Guard on G0/1 is incorrectly configured; it should be configured on the root port, not the designated port. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is correctly configured, but the port should automatically recover from err-disable state after a timeout.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: Root Guard is applied to designated ports, not root ports. BPDU Guard does not auto-recover by default.
Why candidates choose this
Candidates may confuse Root Guard with Root Guard placement or assume BPDU Guard has automatic recovery similar to UDLD.
✗Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is incorrectly configured because Loop Guard should be applied to root ports, not uplink ports. BPDU Guard on G0/3 is correctly configured, but the port should be in a blocking state, not err-disabled.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: Loop Guard is not restricted to root ports; it can be used on any port where BPDUs are expected. BPDU Guard results in err-disable, not blocking.
Why candidates choose this
Candidates may think Loop Guard is only for root ports because it is often used there, or confuse BPDU Guard's action with normal STP blocking.
✗Root Guard on G0/1 is correctly configured. Loop Guard on G0/2 is correctly configured. BPDU Guard on G0/3 is incorrectly configured because BPDU Guard should be applied to trunk ports, not access ports, and the port should be placed in a root-inconsistent state.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: BPDU Guard is not limited to access ports; it works on any PortFast-enabled port. The state is err-disable, not root-inconsistent.
Why candidates choose this
Candidates may associate BPDU Guard with access ports only, or confuse the err-disable state with root-inconsistent state from Root Guard.
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: [CORRECT] Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior. — The scenario demonstrates three STP protection mechanisms. Root Guard on G0/1 is correctly configured; when a superior BPDU is received, the port is placed into a root-inconsistent state (BKN* in show spanning-tree) to prevent the switch from becoming root. Loop Guard on G0/2 prevents loops if BPDUs stop arriving due to a unidirectional link. BPDU Guard on G0/3, combined with PortFast, err-disables the port upon receiving any BPDU, as shown by the err-disabled status. To recover, the administrator must manually re-enable the interface after removing the offending device. No additional configuration is required; the existing commands are correct and produce the expected behavior.
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
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.