- A
BPDU Guard was incorrectly enabled on a port that should be a trunk link.
Why wrong: BPDU Guard can be enabled on any port, not just access ports. The err-disable occurred because BPDU Guard received a BPDU while PortFast was enabled on an inter-switch link. If the port were a trunk without PortFast, BPDU Guard would not be triggered unless globally forced, but the question states both features were present. The port being an access or trunk does not directly cause the err-disable.
- B
The connected switch is sending BPDUs with a lower bridge priority.
Why wrong: BPDU Guard triggers on any BPDU, regardless of bridge priority or root bridge election. A lower priority simply influences STP topology; it does not cause an err-disable condition. The trigger is the receipt of a BPDU, not its contents.
- C
Spanning-tree PortFast is enabled on a port that connects to another switch.
PortFast skips the listening and learning STP states and is designed for end hosts. When combined with BPDU Guard, the switch was instructed to disable the port upon receiving any BPDU. The downstream switch naturally sends BPDUs, causing BPDU Guard to react and place the port in err-disable. Removing PortFast (and leaving BPDU Guard alone, or disabling BPDU Guard on that link) would resolve the issue.
- D
The port is configured as an access port, but should be a trunk.
Why wrong: An access/trunk mismatch would cause VLAN-related problems, but it would not lead to an err-disable triggered by BPDU Guard. Switches still send BPDUs on access ports by default, so the BPDU Guard reaction is independent of the port mode. The issue here is PortFast, not the switchport mode.
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.
After connecting a new switch to interface GigabitEthernet1/0/1 on a distribution switch, a network engineer notices that the interface is in err-disable state. The engineer checks the configuration and finds that spanning-tree portfast and spanning-tree bpduguard enable are applied to the interface. What is the most likely cause of the err-disable state?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
Spanning-tree PortFast is enabled on a port that connects to another switch.
Option C is correct because PortFast is designed for end-host ports that should not receive BPDUs. When PortFast is enabled on a port connecting to another switch, the switch will immediately transition the port to forwarding state, but if it then receives a BPDU from the connected switch, BPDU Guard will error-disable the port. This is the most common cause of err-disable state when both PortFast and BPDU Guard are configured on an inter-switch link.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
BPDU Guard was incorrectly enabled on a port that should be a trunk link.
Why it's wrong here
BPDU Guard can be enabled on any port, not just access ports. The err-disable occurred because BPDU Guard received a BPDU while PortFast was enabled on an inter-switch link. If the port were a trunk without PortFast, BPDU Guard would not be triggered unless globally forced, but the question states both features were present. The port being an access or trunk does not directly cause the err-disable.
- ✗
The connected switch is sending BPDUs with a lower bridge priority.
Why it's wrong here
BPDU Guard triggers on any BPDU, regardless of bridge priority or root bridge election. A lower priority simply influences STP topology; it does not cause an err-disable condition. The trigger is the receipt of a BPDU, not its contents.
- ✓
Spanning-tree PortFast is enabled on a port that connects to another switch.
Why this is correct
PortFast skips the listening and learning STP states and is designed for end hosts. When combined with BPDU Guard, the switch was instructed to disable the port upon receiving any BPDU. The downstream switch naturally sends BPDUs, causing BPDU Guard to react and place the port in err-disable. Removing PortFast (and leaving BPDU Guard alone, or disabling BPDU Guard on that link) would resolve the issue.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The port is configured as an access port, but should be a trunk.
Why it's wrong here
An access/trunk mismatch would cause VLAN-related problems, but it would not lead to an err-disable triggered by BPDU Guard. Switches still send BPDUs on access ports by default, so the BPDU Guard reaction is independent of the port mode. The issue here is PortFast, not the switchport mode.
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.
✓Spanning-tree PortFast is enabled on a port that connects to another switch.Correct answer▾
Why this is correct
PortFast skips the listening and learning STP states and is designed for end hosts. When combined with BPDU Guard, the switch was instructed to disable the port upon receiving any BPDU. The downstream switch naturally sends BPDUs, causing BPDU Guard to react and place the port in err-disable. Removing PortFast (and leaving BPDU Guard alone, or disabling BPDU Guard on that link) would resolve the issue.
✗BPDU Guard was incorrectly enabled on a port that should be a trunk link.Wrong answer — click to see why▾
Why this is wrong here
Candidates often associate BPDU Guard exclusively with access ports and assume configuring it on a trunk is itself a misconfiguration, overlooking that PortFast is the real culprit.
✗The connected switch is sending BPDUs with a lower bridge priority.Wrong answer — click to see why▾
Why this is wrong here
Students may confuse root bridge placement with BPDU Guard operation, thinking that a BPDU from a superior switch might cause a port to be disabled, when in fact BPDU Guard is content-agnostic.
✗The port is configured as an access port, but should be a trunk.Wrong answer — click to see why▾
Why this is wrong here
Candidates may think that because a link between switches should be a trunk, the access mode misconfiguration is the root cause. However, they miss the fact that BPDU Guard acts on the BPDU regardless of the port mode, and the real misconfiguration is PortFast.
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: answer the scenario, not the keyword
Cisco often tests the misconception that BPDU Guard alone causes err-disable, but the trap here is that PortFast must be enabled for BPDU Guard to trigger err-disable on a port receiving BPDUs from another switch.
Detailed technical explanation
How to think about this question
PortFast bypasses the normal spanning-tree listening and learning states, placing the port into forwarding state immediately. BPDU Guard monitors for incoming BPDUs; if one is received on a PortFast-enabled port, the port is placed into err-disable state to prevent potential loops. In a real-world scenario, this often occurs when an engineer mistakenly enables PortFast on a port connecting to another switch, forgetting that PortFast should only be used on ports connected to end devices like PCs or printers.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Switching and Network Access — study guide chapter
Learn the concepts, then practise the questions
- →
Switching and Network Access practice questions
Targeted practice on this topic area only
- →
All 200-301 questions
1,819 questions across all exam domains
- →
CCNA 200-301 v2 study guide
Full concept coverage aligned to exam objectives
- →
200-301 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Network Infrastructure and Connectivity practice questions
Practise 200-301 questions linked to Network Infrastructure and Connectivity.
Switching and Network Access practice questions
Practise 200-301 questions linked to Switching and Network Access.
IP Routing practice questions
Practise 200-301 questions linked to IP Routing.
Network Services and Security practice questions
Practise 200-301 questions linked to Network Services and Security.
AI and Network Operations practice questions
Practise 200-301 questions linked to AI and Network Operations.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
Practice this exam
Start a free 200-301 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 200-301 question test?
Switching and Network Access — This question tests Switching and Network Access — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Spanning-tree PortFast is enabled on a port that connects to another switch. — Option C is correct because PortFast is designed for end-host ports that should not receive BPDUs. When PortFast is enabled on a port connecting to another switch, the switch will immediately transition the port to forwarding state, but if it then receives a BPDU from the connected switch, BPDU Guard will error-disable the port. This is the most common cause of err-disable state when both PortFast and BPDU Guard are configured on an inter-switch link.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
Last reviewed: Jun 25, 2026
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.