CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: bPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.. 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
interface GigabitEthernet1/0/9
switchport mode access
spanning-tree portfast
spanning-tree bpduguard enable
Event:
%SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on PortFast enabled port. Disabling interface.
A network administrator notices that a switchport in access mode with PortFast enabled has transitioned to an err-disabled state. What is the most likely cause?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
BPDU Guard disabled the PortFast-enabled access port after it received a BPDU.
The strongest reason is a BPDU Guard violation on a PortFast-enabled access port. In practical terms, the port was expected to face an end host, not a switching device that emits BPDUs. When BPDUs appeared, the switch treated that as a topology-policy violation and error-disabled the interface to protect the network.
This is one of the most classic access-layer protection patterns on the CCNA exam.
Key principle: BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.
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 disabled the PortFast-enabled access port after it received a BPDU.
Why this is correct
This is correct because the event message explicitly identifies a BPDU Guard violation.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.
✗
Port security shut down the port because the VLAN was wrong.
Why it's wrong here
This is wrong because the event shown is about BPDUs, not MAC-based port security.
When this WOULD be correct
In a different question setup, if the scenario described a switchport configured with port security that was set to restrict access to a specific VLAN, and a device attempted to connect using an incorrect VLAN, then this option would be correct as it would lead to the port being shut down due to a security violation.
✗
DHCP snooping disabled the interface because a host requested an address.
Why it's wrong here
This is wrong because DHCP snooping does not produce this spanning-tree error.
When this WOULD be correct
In a different question setup, if the scenario described a switchport that was configured with DHCP snooping and a rogue DHCP server was detected, causing the switch to disable the interface, then this option would be correct.
✗
EtherChannel suspended the interface because the bundle was incomplete.
If the question asked about a situation where an EtherChannel was configured but one of the member links was down or misconfigured, leading to an incomplete bundle, then this option would be correct. In that case, the interface would go into a suspended state due to the EtherChannel configuration issue.
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.
✓BPDU Guard disabled the PortFast-enabled access port after it received a BPDU.Correct answer▾
Why this is correct
This is correct because the event message explicitly identifies a BPDU Guard violation.
✗Port security shut down the port because the VLAN was wrong.Wrong answer — click to see why▾
Why this is wrong here
Port security restricts access based on MAC addresses, not VLANs, and the event message explicitly mentions BPDU Guard, not port security. The exhibit shows a spanning-tree BPDU Guard error, not a port security violation.
★ When this WOULD be the correct answer
In a different question setup, if the scenario described a switchport configured with port security that was set to restrict access to a specific VLAN, and a device attempted to connect using an incorrect VLAN, then this option would be correct as it would lead to the port being shut down due to a security violation.
Why candidates choose this
Students may confuse port security with BPDU Guard because both can place a port in err-disabled state, but they serve different purposes: port security controls MAC addresses, while BPDU Guard prevents rogue switch connections.
✗DHCP snooping disabled the interface because a host requested an address.Wrong answer — click to see why▾
Why this is wrong here
DHCP snooping does not cause err-disabled state due to BPDU reception; it filters DHCP messages and can disable ports for DHCP attacks, but the exhibit clearly shows a spanning-tree BPDU Guard event.
★ When this WOULD be the correct answer
In a different question setup, if the scenario described a switchport that was configured with DHCP snooping and a rogue DHCP server was detected, causing the switch to disable the interface, then this option would be correct.
Why candidates choose this
DHCP snooping is another security feature that can err-disable ports, leading students to mistakenly attribute the BPDU Guard error to DHCP snooping if they overlook the specific syslog message.
✗EtherChannel suspended the interface because the bundle was incomplete.Wrong answer — click to see why▾
Why this is wrong here
EtherChannel suspension occurs due to configuration mismatches or link failures, not BPDU reception. The exhibit's syslog message explicitly identifies BPDU Guard, not EtherChannel issues.
★ When this WOULD be the correct answer
If the question asked about a situation where an EtherChannel was configured but one of the member links was down or misconfigured, leading to an incomplete bundle, then this option would be correct. In that case, the interface would go into a suspended state due to the EtherChannel configuration issue.
Why candidates choose this
EtherChannel can also cause err-disabled state, but the error message in the exhibit is clearly about spanning-tree BPDU Guard, not EtherChannel protocol mismatches.
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
Be careful not to confuse BPDU Guard with other port security features or network issues like duplex mismatches.
Trap categories for this question
Command / output trap
This is wrong because the event shown is about BPDUs, not MAC-based port security.
Detailed technical explanation
How to think about this question
BPDU Guard is a Cisco feature designed to protect the network topology by disabling ports that receive Bridge Protocol Data Units (BPDUs) unexpectedly. It is typically enabled on access ports configured with PortFast, which assumes the port connects directly to an end device rather than another switch. PortFast allows the port to bypass the usual STP listening and learning states, transitioning immediately to forwarding to reduce connection delays for end devices. However, if a BPDU is received on such a port, it indicates a potential topology change or misconfiguration, which could cause loops or instability.
When BPDU Guard detects a BPDU on a PortFast-enabled port, it immediately places the port into an err-disabled state to prevent possible Layer 2 loops. This behavior is a strict enforcement of the network design principle that access ports should not receive BPDUs. The switch logs an event message indicating a BPDU Guard violation, which helps network administrators quickly identify the cause of the shutdown. This mechanism is critical in environments where unauthorized switches or bridging devices might be connected to access ports, potentially disrupting the spanning-tree topology.
A common exam trap is confusing BPDU Guard violations with other security features like port security or DHCP snooping. Port security deals with MAC address violations and does not react to BPDUs, while DHCP snooping protects against rogue DHCP servers and does not interact with spanning-tree events. EtherChannel suspends interfaces due to bundle inconsistencies, not BPDU reception. Understanding the specific triggers and behaviors of BPDU Guard helps avoid misdiagnosing the cause of an err-disabled port and ensures proper troubleshooting and network protection.
KKey Concepts to Remember
BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.
PortFast is configured on access ports to allow immediate transition to the forwarding state, assuming the port connects to an end device, not another switch.
When BPDU Guard detects a BPDU on a PortFast-enabled port, it error-disables the interface to protect the network topology from unexpected switches.
Port security focuses on MAC address violations and does not trigger error-disable states due to BPDU reception or spanning-tree events.
DHCP snooping monitors DHCP messages to prevent rogue DHCP servers but does not interact with spanning-tree or BPDU Guard mechanisms.
EtherChannel bundles multiple physical links into one logical link and suspends interfaces only when bundle consistency fails, unrelated to BPDU Guard events.
Spanning Tree Protocol (STP) uses BPDUs to detect loops and maintain a loop-free topology; unexpected BPDUs on PortFast ports indicate misconfiguration or unauthorized devices.
Error-disabled ports require manual intervention or configured automatic recovery to restore connectivity after BPDU Guard triggers a shutdown.
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
BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.
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 bPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge., then practise related 200-301 questions on the same topic to reinforce the concept.
Switching and Network Access — This question tests Switching and Network Access — BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge..
What is the correct answer to this question?
The correct answer is: BPDU Guard disabled the PortFast-enabled access port after it received a BPDU. — The strongest reason is a BPDU Guard violation on a PortFast-enabled access port. In practical terms, the port was expected to face an end host, not a switching device that emits BPDUs. When BPDUs appeared, the switch treated that as a topology-policy violation and error-disabled the interface to protect the network.
This is one of the most classic access-layer protection patterns on the CCNA exam.
What should I do if I get this 200-301 question wrong?
Review bPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge., then practise related 200-301 questions on the same topic to reinforce the concept.
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?
BPDU Guard disables a PortFast-enabled access port immediately upon receiving a BPDU to prevent potential Layer 2 loops caused by connecting another switch or bridge.
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.