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Question 550 of 1,052
hardmultiple choiceObjective-mapped
CCNA Practice Question: Receives a call that users in VLAN 10 on Switch B…
This 200-301 practice question tests your understanding of 200-301 exam topics. 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.
Exhibit
SwitchA# show spanning-tree interface gigabitEthernet 0/1 detail Port 1 (GigabitEthernet0/1) of VLAN0010 is root INCONSISTENT Port path cost 4, Port priority 128, Port Identifier 128.1. Designated root has priority 32768, address aaaa.bbbb.cccc Designated bridge has priority 32768, address aaaa.bbbb.cccc Designated port id is 128.1, designated path cost 0 Timers: message age 0, forward delay 0, hold 0 Number of transitions to forwarding state: 0 The port is not in the portfast mode Root guard is enabled on the port BPDU guard is disabled Loop guard is disabled Link type is point-to-point (auto) BPDU: sent 3, received 2
A network engineer receives a call that users in VLAN 10 on Switch B cannot ping the default gateway, which is a router on a stick connected to Switch A. The engineer checks the interface connecting Switch A to Switch B (GigabitEthernet0/1) and finds it is down. Which command output best explains the cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"which command"Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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
✓
Root guard is enabled and the port received a superior BPDU, causing it to become root-inconsistent.
The output shows that the port is in a 'root INCONSISTENT' state because root guard is enabled. Root guard prevents a port from becoming a root port; if a superior BPDU is received, the port is placed into a root-inconsistent state (effectively blocking). This explains why the link between the switches is down, causing hosts in VLAN 10 to lose connectivity to the default gateway. The solution is to disable root guard on the interface or ensure that the port is not receiving superior BPDUs.
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.
- ✗
The interface is in err-disable state due to BPDU guard.
Why it's wrong here
BPDU guard would place the port in err-disable if a BPDU is received on a PortFast-enabled port.
- ✓
Root guard is enabled and the port received a superior BPDU, causing it to become root-inconsistent.
Why this is correct
Root guard on the interface caused the port to be placed in root-inconsistent state when a superior BPDU was received, blocking the port.
Clue confirmation
The clue words "best", "which command" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
- ✗
Loop guard is enabled and the port is in a blocking state due to missing BPDUs.
Why it's wrong here
Loop guard would place the port in a loop-inconsistent state if BPDUs stop being received, not root-inconsistent.
- ✗
The port is in a forwarding state but the VLAN is misconfigured.
Why it's wrong here
The output clearly shows the port is not forwarding; it is in root-inconsistent state.
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.
✓Root guard is enabled and the port received a superior BPDU, causing it to become root-inconsistent.Correct answer▾
Why this is correct
Root guard on the interface caused the port to be placed in root-inconsistent state when a superior BPDU was received, blocking the port.
✗The interface is in err-disable state due to BPDU guard.Wrong answer — click to see why▾
Why this is wrong here
The output shows BPDU guard is disabled, and the port is in root-inconsistent, not err-disable.
✗Loop guard is enabled and the port is in a blocking state due to missing BPDUs.Wrong answer — click to see why▾
Why this is wrong here
The output shows loop guard is disabled, and the state is root-inconsistent, not loop-inconsistent.
✗The port is in a forwarding state but the VLAN is misconfigured.Wrong answer — click to see why▾
Why this is wrong here
The port is not forwarding; it is root-inconsistent, which blocks traffic.
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 output clearly shows the port is not forwarding; it is in root-inconsistent state.
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.
What to study next
Got this wrong? Here's your next step.
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.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Access ports place end devices into a single VLAN.
What is the correct answer to this question?
The correct answer is: Root guard is enabled and the port received a superior BPDU, causing it to become root-inconsistent. — The output shows that the port is in a 'root INCONSISTENT' state because root guard is enabled. Root guard prevents a port from becoming a root port; if a superior BPDU is received, the port is placed into a root-inconsistent state (effectively blocking). This explains why the link between the switches is down, causing hosts in VLAN 10 to lose connectivity to the default gateway. The solution is to disable root guard on the interface or ensure that the port is not receiving superior BPDUs.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best", "which command". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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