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 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 loops, and BPDU Guard on PortFast-enabled GigabitEthernet0/3. After configuration, a superior BPDU arrives on G0/1, blocking the port; verify the Root Guard state and ensure BPDU Guard triggers err-disable on G0/3.
R1# show running-config | section interface
interface GigabitEthernet0/0
description Management
ip address 192.168.1.1 255.255.255.0
!
interface GigabitEthernet0/1
description Link to Access Switch
switchport mode access
switchport access vlan 10
spanning-tree portfast
!
interface GigabitEthernet0/2
description Uplink to Core
switchport mode trunk
!
interface GigabitEthernet0/3
description End-Device Port
switchport mode access
switchport access vlan 10
spanning-tree portfast
!
interface Vlan10
ip address 10.0.0.1 255.255.255.0
!
A
G0/1 is in root-inconsistent state; G0/3 is in err-disabled state.
Root Guard transitions a port to root-inconsistent (blocking) when a superior BPDU is received, protecting the root bridge. BPDU Guard on a PortFast port puts the port in err-disabled state upon BPDU reception. These are the expected outcomes.
B
G0/1 is in blocking state; G0/3 is in err-disabled state.
Why wrong: This is incorrect because Root Guard does not put a port into the standard blocking state; it uses the root-inconsistent state. The standard blocking state is used by STP for alternate or backup ports, not by Root Guard.
C
G0/1 is in root-inconsistent state; G0/3 is in blocking state.
Why wrong: This is incorrect because BPDU Guard on a PortFast-enabled port causes err-disable, not blocking. The port becomes operationally down and must be manually re-enabled or recovered via errdisable recovery.
D
G0/1 is in err-disabled state; G0/3 is in root-inconsistent state.
Why wrong: This is incorrect because Root Guard does not cause err-disable; it causes root-inconsistent. BPDU Guard causes err-disable. The states are swapped in this option.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
G0/1 is in root-inconsistent state; G0/3 is in err-disabled state.
Root Guard is needed on the designated port (G0/1) to prevent an unauthorized switch from becoming root by sending superior BPDUs. Loop Guard on the uplink (G0/2) prevents loops if BPDUs stop arriving. BPDU Guard on PortFast ports (G0/3) immediately err-disables them upon BPDU reception. The configuration uses 'spanning-tree guard root' on G0/1, 'spanning-tree guard loop' on G0/2, and 'spanning-tree bpduguard enable' on G0/3. Verification shows G0/1 blocked by root-inconsistent state and G0/3 in err-disabled state.
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.
✓
G0/1 is in root-inconsistent state; G0/3 is in err-disabled state.
Why this is correct
Root Guard transitions a port to root-inconsistent (blocking) when a superior BPDU is received, protecting the root bridge. BPDU Guard on a PortFast port puts the port in err-disabled state upon BPDU reception. These are the expected outcomes.
Related concept
Access ports place end devices into a single VLAN.
✗
G0/1 is in blocking state; G0/3 is in err-disabled state.
Why it's wrong here
This is incorrect because Root Guard does not put a port into the standard blocking state; it uses the root-inconsistent state. The standard blocking state is used by STP for alternate or backup ports, not by Root Guard.
✗
G0/1 is in root-inconsistent state; G0/3 is in blocking state.
Why it's wrong here
This is incorrect because BPDU Guard on a PortFast-enabled port causes err-disable, not blocking. The port becomes operationally down and must be manually re-enabled or recovered via errdisable recovery.
✗
G0/1 is in err-disabled state; G0/3 is in root-inconsistent state.
Why it's wrong here
This is incorrect because Root Guard does not cause err-disable; it causes root-inconsistent. BPDU Guard causes err-disable. The states are swapped in this option.
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.
✓G0/1 is in root-inconsistent state; G0/3 is in err-disabled state.Correct answer▾
Why this is correct
Root Guard transitions a port to root-inconsistent (blocking) when a superior BPDU is received, protecting the root bridge. BPDU Guard on a PortFast port puts the port in err-disabled state upon BPDU reception. These are the expected outcomes.
✗G0/1 is in blocking state; G0/3 is in err-disabled state.Wrong answer — click to see why▾
Why this is wrong here
Root Guard uses a specific 'root-inconsistent' state, not the generic 'blocking' state.
Why candidates choose this
Candidates may confuse the root-inconsistent state with the standard STP blocking state, as both prevent traffic forwarding.
✗G0/1 is in root-inconsistent state; G0/3 is in blocking state.Wrong answer — click to see why▾
Why this is wrong here
BPDU Guard triggers err-disable, not blocking. Blocking is an STP state, not an error state.
Why candidates choose this
Candidates might think BPDU Guard puts the port into a non-forwarding STP state like blocking, but it actually disables the port entirely.
✗G0/1 is in err-disabled state; G0/3 is in root-inconsistent state.Wrong answer — click to see why▾
Why this is wrong here
Root Guard and BPDU Guard have different effects: root-inconsistent vs. err-disable. Mixing them up is a common error.
Why candidates choose this
Candidates may confuse the two guard features, especially since both are STP protection mechanisms.
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: G0/1 is in root-inconsistent state; G0/3 is in err-disabled state. — Root Guard is needed on the designated port (G0/1) to prevent an unauthorized switch from becoming root by sending superior BPDUs. Loop Guard on the uplink (G0/2) prevents loops if BPDUs stop arriving. BPDU Guard on PortFast ports (G0/3) immediately err-disables them upon BPDU reception. The configuration uses 'spanning-tree guard root' on G0/1, 'spanning-tree guard loop' on G0/2, and 'spanning-tree bpduguard enable' on G0/3. Verification shows G0/1 blocked by root-inconsistent state and G0/3 in err-disabled state.
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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