CCNA Switching and Network Access Practice Question
A switch port configured with PortFast and BPDU Guard receives a BPDU and transitions to an error-disabled state. Which statement best explains why this is considered useful protection?
⚠ Common exam trap
Remember that BPDU Guard disables the port, not just logs or adjusts its role. It's a protective measure, not a monitoring tool.
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
✓
It prevents a port expected to be an edge port from accidentally becoming part of the switching topology and causing loops.
PortFast is used on edge ports to bypass STP listening/learning, but if a BPDU is received, the assumption that the port is an edge port is violated. BPDU Guard then error-disables the port to prevent potential loops or topology disruptions. This protects the network when an edge port unexpectedly connects to another switch, which could cause a bridging loop. The other options describe unrelated features or incorrect mechanisms.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It prevents a port expected to be an edge port from accidentally becoming part of the switching topology and causing loops.
Why this is correct
PortFast is designed for edge ports that connect directly to end hosts, so it places the port into forwarding state immediately. When a BPDU is received on such a port, it means an unexpected switch connection exists, so BPDU Guard—often enabled alongside PortFast—disables the port. This prevents the port from participating in STP calculations and creating a bridging loop, while preserving the intended fast-convergence behavior for genuine edge ports.
- ✗
It increases the port's bandwidth by combining multiple links.
Why it's wrong here
Combining multiple physical links to increase aggregate bandwidth is the function of EtherChannel or link aggregation, not PortFast. PortFast only alters the STP state machine by skipping the listening and learning stages on a port, which speeds up host connectivity. It has no effect on the number of active links or the capacity of the port, so this statement conflates two entirely different features.
When this WOULD be correct
In a different question, if the context were about enhancing wireless network performance through specific configurations on access points, option B could be correct if it stated that a certain configuration increases wireless coverage for clients connected to that access point.
- ✗
It automatically enables VLAN trunking on the port.
Why it's wrong here
VLAN trunking is governed by the switchport mode command and DTP, not by Spanning Tree Protocol settings. PortFast only tells STP to treat the port as an edge and bring it to forwarding immediately, which has no impact on 802.1Q tagging or trunk negotiation. Thus, configuring PortFast will never automatically enable VLAN trunking on a port.
When this WOULD be correct
In a different exam question asking about the benefits of VLAN routing configurations, if the question specified a scenario where multiple VLANs are being routed and asked how to optimize routing efficiency, option C could be correct as it relates to summarizing routes to reduce routing table size.
- ✗
It forces the port to use Rapid Spanning Tree Protocol for faster convergence.
Why it's wrong here
PortFast is not a protocol-selection mechanism; it works with any version of STP, including classic 802.1D, RSTP, and MST. Rather than forcing RSTP, PortFast accelerates convergence by immediately transitioning a port to the forwarding state, bypassing listening and learning. The choice of spanning-tree protocol is made globally via the spanning-tree mode command, not by configuring PortFast on a specific interface.
When this WOULD be correct
In a different question asking about security measures for managing remote access to network devices, option D could be correct if the question specifies that traffic on a certain port must be secured, thus enforcing SSH over Telnet for secure communications.
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.
✓It prevents a port expected to be an edge port from accidentally becoming part of the switching topology and causing loops.Correct answer▾
Why this is correct
PortFast is designed for edge ports that connect directly to end hosts, so it places the port into forwarding state immediately. When a BPDU is received on such a port, it means an unexpected switch connection exists, so BPDU Guard—often enabled alongside PortFast—disables the port. This prevents the port from participating in STP calculations and creating a bridging loop, while preserving the intended fast-convergence behavior for genuine edge ports.
✗It increases the port's bandwidth by combining multiple links.Wrong answer — click to see why▾
Why this is wrong here
This describes EtherChannel, not BPDU Guard or PortFast.
★ When this WOULD be the correct answer
In a different question, if the context were about enhancing wireless network performance through specific configurations on access points, option B could be correct if it stated that a certain configuration increases wireless coverage for clients connected to that access point.
Why candidates choose this
Students might confuse 'PortFast' with 'fast' connectivity improvements, incorrectly assuming it could enhance wireless performance. However, PortFast only affects STP convergence for wired ports.
✗It automatically enables VLAN trunking on the port.Wrong answer — click to see why▾
Why this is wrong here
VLAN trunking is a separate feature (DTP or manual configuration) and not related to error-disable from BPDU reception.
★ When this WOULD be the correct answer
In a different exam question asking about the benefits of VLAN routing configurations, if the question specified a scenario where multiple VLANs are being routed and asked how to optimize routing efficiency, option C could be correct as it relates to summarizing routes to reduce routing table size.
Why candidates choose this
The term 'summarizes' might be misinterpreted as 'summarizes' in the context of STP (e.g., summarizing BPDU information), but STP does not summarize VLAN routes. This distractor exploits confusion between Layer 2 and Layer 3 concepts.
✗It forces the port to use Rapid Spanning Tree Protocol for faster convergence.Wrong answer — click to see why▾
Why this is wrong here
RSTP is a separate protocol; PortFast and BPDU Guard do not force RSTP usage.
★ When this WOULD be the correct answer
In a different question asking about security measures for managing remote access to network devices, option D could be correct if the question specifies that traffic on a certain port must be secured, thus enforcing SSH over Telnet for secure communications.
Why candidates choose this
Students might associate 'protection' with security features like SSH, but BPDU guard protects against STP topology issues, not management access. The word 'guard' can be misleadingly linked to security protocols.
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?”
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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Bridge Protocol Data Unit
A Bridge Protocol Data Unit (BPDU) is a special message that network switches exchange to detect and prevent loops in an Ethernet network.
Key term
STP
STP (Spanning Tree Protocol) is a network protocol that prevents loops in Ethernet networks by creating a loop-free logical topology.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.