- A
Root Guard: Prevents a switch from becoming root bridge due to rogue BPDUs
BPDU Guard is designed to prevent loops caused by rogue switches by disabling a PortFast-enabled port if a BPDU is received, thus preventing unauthorized switch connections.
- B
BPDU Guard: Prevents loops by disabling ports that receive BPDUs on access ports
This is incorrect because Root Guard prevents an unwanted root bridge election by ensuring a designated port remains designated, but it does not directly prevent loops from rogue switches.
- C
Loop Guard: Prevents alternate/root ports from becoming designated due to BPDU loss
This is incorrect because Loop Guard prevents loops caused by unidirectional links by placing a port into an inconsistent state if BPDUs are not received, but it does not address rogue switches.
- D
UDLD: Detects unidirectional links to prevent loops
This is incorrect because UDLD detects unidirectional links and can shut down the port, but it does not prevent loops caused by rogue switches.
Quick Answer
The answer is UDLD, which detects unidirectional links to prevent loops. This is correct because a unidirectional link allows traffic to flow in only one direction, causing a switch to believe the link is operational when it is not, which can lead to bridging loops that STP cannot resolve on its own. On the CCNA 200-301 v2 exam, you will often be asked to match each STP protection feature to its specific problem, testing your ability to distinguish between Root Guard, BPDU Guard, Loop Guard, and UDLD. A common trap is confusing UDLD with Loop Guard—remember that Loop Guard handles BPDU loss on bidirectional links, while UDLD actively sends probes to verify two-way communication. For a quick memory tip: think “U for Unidirectional, D for Detection.”
CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: portFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.. 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.
Match each STP or switch protection feature to the problem it is mainly designed to prevent.
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: Prevents a switch from becoming root bridge due to rogue BPDUs
STP protection features prevent specific problems: Root Guard protects root bridge election, BPDU Guard prevents loops on access ports, Loop Guard handles BPDU loss, UDLD detects unidirectional links, and PortFast speeds up port transition.
Key principle: PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Root Guard: Prevents a switch from becoming root bridge due to rogue BPDUs
Why this is correct
BPDU Guard is designed to prevent loops caused by rogue switches by disabling a PortFast-enabled port if a BPDU is received, thus preventing unauthorized switch connections.
Related concept
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
- ✓
BPDU Guard: Prevents loops by disabling ports that receive BPDUs on access ports
Why this is correct
This is incorrect because Root Guard prevents an unwanted root bridge election by ensuring a designated port remains designated, but it does not directly prevent loops from rogue switches.
Related concept
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
- ✓
Loop Guard: Prevents alternate/root ports from becoming designated due to BPDU loss
Why this is correct
This is incorrect because Loop Guard prevents loops caused by unidirectional links by placing a port into an inconsistent state if BPDUs are not received, but it does not address rogue switches.
Related concept
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
- ✓
UDLD: Detects unidirectional links to prevent loops
Why this is correct
This is incorrect because UDLD detects unidirectional links and can shut down the port, but it does not prevent loops caused by rogue switches.
Related concept
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The exam trap is confusing BPDU Guard with Root Guard or Loop Guard. Remember that BPDU Guard specifically protects against rogue switches by shutting down the port if a BPDU is received on a PortFast port.
Detailed technical explanation
How to think about this question
Spanning Tree Protocol (STP) is essential for preventing Layer 2 loops in Ethernet networks by electing a root bridge and selectively blocking redundant paths. Cisco switches implement several STP-related protection features to enhance network stability and prevent common problems at the access layer. PortFast allows ports connected to end devices to bypass the usual STP listening and learning states, immediately transitioning to forwarding. This reduces host connection delays but risks loops if misapplied to switch-to-switch links. BPDU Guard complements PortFast by shutting down any PortFast-enabled port that receives a BPDU, which indicates a switch is connected where it shouldn't be. Root Guard protects the root bridge election process by blocking ports that receive superior BPDUs, preventing rogue switches from becoming the root bridge and destabilizing the topology. Loop Guard addresses a different issue: it prevents ports that should be blocking from transitioning to forwarding if BPDUs stop arriving, which can happen due to unidirectional link failures, thus avoiding Layer 2 loops. A common exam trap is confusing the purpose of these features or misapplying them. For example, enabling PortFast on switch-to-switch links can cause loops, and relying solely on BPDU Guard without Root Guard can allow rogue root bridges. Loop Guard is often overlooked but is critical in environments with unstable links. Understanding the distinct role each feature plays in STP protection helps avoid misconfiguration and ensures a stable, loop-free network topology in Cisco environments.
KKey Concepts to Remember
- PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
- BPDU Guard disables a PortFast-enabled port if it receives a Bridge Protocol Data Unit (BPDU), preventing potential loops caused by unauthorized switches.
- Root Guard protects the STP root bridge election by blocking ports that receive superior BPDUs, thus preventing unexpected root bridge changes.
- Loop Guard prevents a non-designated port from erroneously transitioning to the forwarding state when BPDUs stop arriving, avoiding Layer 2 loops.
- STP uses BPDUs to maintain a loop-free Layer 2 topology by electing a root bridge and blocking redundant paths.
- PortFast should only be enabled on ports connected to end devices, never on ports connecting to other switches, to avoid STP topology issues.
- BPDU Guard and Root Guard are complementary STP protection features that enforce network stability by controlling BPDU reception and root bridge placement.
- Loop Guard helps maintain STP stability during unidirectional link failures by preventing ports from incorrectly forwarding traffic.
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
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review portFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this 200-301 question test?
Switching and Network Access — This question tests Switching and Network Access — PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts..
What is the correct answer to this question?
The correct answer is: Root Guard: Prevents a switch from becoming root bridge due to rogue BPDUs — STP protection features prevent specific problems: Root Guard protects root bridge election, BPDU Guard prevents loops on access ports, Loop Guard handles BPDU loss, UDLD detects unidirectional links, and PortFast speeds up port transition.
What should I do if I get this 200-301 question wrong?
Review portFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
PortFast enables immediate transition of a switch port to the forwarding state, preventing delays when connecting end devices like hosts.
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Last reviewed: May 17, 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.
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