The answer is interface congestion causing queuing delays. When you see high latency on one hop with varying response times and no interface errors, the most likely cause is that the router at that hop is experiencing congestion, forcing packets into a buffer queue before they can be transmitted. This queuing delay directly increases and varies the round-trip time, which is the classic signature of a bottleneck at the egress interface. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate congestion from physical-layer faults—a common trap is to assume a bad cable or CRC errors, but the absence of errors here rules that out. Remember the key clue: variable latency without errors equals queue buildup. For a quick memory tip, think “No errors, varying RTT = Congestion queue.”
N10-009 Network Troubleshooting Practice Question
This N10-009 practice question tests your understanding of network troubleshooting. 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.
Users in a branch office report that file transfers to the data center are slow. A technician runs a traceroute and sees consistently high latency on hop 5. The technician then pings hop 5 and gets replies with varying response times. There are no errors reported on the interface. 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
✓
Interface congestion causing queuing delays.
High latency on hop 5 with varying response times and no interface errors indicates that the router at hop 5 is experiencing congestion, causing packets to be queued before transmission. This queuing delay results in increased and variable round-trip times (RTT), which is a classic symptom of interface congestion. The absence of errors rules out physical-layer issues, and the consistent latency on that specific hop points to a bottleneck at that router's egress interface.
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.
✗
Routing loop causing packets to be dropped.
Why it's wrong here
A routing loop would cause TTL expiry and timeouts, not consistently high latency without errors.
✓
Interface congestion causing queuing delays.
Why this is correct
Congestion leads to packet queuing, resulting in high and variable latency. This is a common cause of performance degradation.
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.
✗
DNS server misconfiguration causing lookup delays.
Why it's wrong here
DNS issues would cause name resolution failures, not high latency on a traceroute hop, which operates at layer 3.
✗
Firewall inspecting traffic and adding latency.
Why it's wrong here
Firewalls typically add some consistent latency, but variable response times suggest queuing due to congestion rather than inspection.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between latency caused by congestion (queuing delay) versus packet loss or routing loops, and the trap here is that candidates may assume high latency always indicates a routing loop or firewall inspection, but the varying response times with no errors point specifically to interface congestion.
Detailed technical explanation
How to think about this question
When an interface is congested, packets are placed into a transmit queue (e.g., FIFO, WFQ, or CBWFQ) and experience queuing delay proportional to the queue depth. Traceroute uses ICMP echo requests or UDP probes with increasing TTL values; the varying RTTs on hop 5 reflect the fluctuating queue lengths at that router's egress interface. In real-world scenarios, this is often caused by bandwidth oversubscription, such as a branch office link being saturated by multiple file transfers, and can be confirmed by checking interface statistics like 'show interfaces' for output queue drops or 'show buffers' for buffer misses.
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 Troubleshooting — This question tests Network Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Interface congestion causing queuing delays. — High latency on hop 5 with varying response times and no interface errors indicates that the router at hop 5 is experiencing congestion, causing packets to be queued before transmission. This queuing delay results in increased and variable round-trip times (RTT), which is a classic symptom of interface congestion. The absence of errors rules out physical-layer issues, and the consistent latency on that specific hop points to a bottleneck at that router's egress interface.
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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