The answer is a faulty transceiver, as interface flapping caused by a physical-layer issue is most commonly traced back to a failing SFP or GBIC module. When a transceiver degrades, it produces intermittent signal loss or corrupted link synchronization, causing the router’s interface to detect a carrier drop, bring the link down, and then re-establish it once the signal briefly returns—creating the repeated up/down cycle that defines flapping. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to distinguish hardware faults from software misconfigurations like duplex mismatches or STP loops; a common trap is to blame the cable first, but transceivers fail more frequently due to heat or age. Remember the mnemonic “Flapping? Check the SFP first—it’s the physical link’s weak link.”
N10-009 Network Operations Practice Question
This N10-009 practice question tests your understanding of network operations. 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.
A network monitoring system alerts that a specific router interface has been flapping (repeatedly going up and down) for the past hour. Which of the following is the MOST likely cause of this behavior?
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
✓
Faulty transceiver
A faulty transceiver is the most likely cause of interface flapping because physical-layer issues, such as a failing SFP or GBIC, can cause intermittent loss of signal or link synchronization. The router's interface detects the loss of carrier and brings the link down, then re-establishes it when the signal returns, creating a repeated up/down cycle. This is a common hardware failure mode distinct from software or configuration problems.
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.
✓
Faulty transceiver
Why this is correct
A faulty SFP or GBIC can cause the interface to lose link sporadically, resulting in flapping.
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.
✗
High CPU utilization on the router
Why it's wrong here
High CPU can cause performance issues but typically does not cause the interface to physically go up and down.
✗
Incorrect SNMP community string
Why it's wrong here
SNMP configuration issues would affect monitoring, not the interface state.
✗
Routing protocol misconfiguration
Why it's wrong here
Routing protocol issues can cause route flapping but not physical interface flapping.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'route flapping' (caused by routing protocol issues) with 'interface flapping' (a physical-layer problem), leading them to incorrectly select routing protocol misconfiguration.
Detailed technical explanation
How to think about this question
Interface flapping is often detected by the router's line protocol state machine, which monitors carrier detect (CD) signals from the transceiver. A faulty transceiver may produce intermittent electrical or optical signals, causing the router to log 'line protocol is up/down' messages. In real-world scenarios, swapping the suspect SFP with a known-good one is a standard first step to isolate the issue before escalating to cable or port-level troubleshooting.
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 practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Operations — This question tests Network Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Faulty transceiver — A faulty transceiver is the most likely cause of interface flapping because physical-layer issues, such as a failing SFP or GBIC, can cause intermittent loss of signal or link synchronization. The router's interface detects the loss of carrier and brings the link down, then re-establishes it when the signal returns, creating a repeated up/down cycle. This is a common hardware failure mode distinct from software or configuration problems.
What should I do if I get this N10-009 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.
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Question Discussion
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