N10-009 Network Troubleshooting Practice Question
Users in a remote office are experiencing slow file transfers to the data center. The network technician runs a traceroute and discovers high latency on a specific hop. The technician pings that hop and gets replies with varying latency. The technician also checks the interface error counters on the router at that hop and finds no errors. What is the most likely cause?
⚠ Common exam trap
The trap here is that candidates see 'no errors' on the interface and assume the problem must be at a higher layer, but CompTIA often tests that CPU overload can cause latency without any interface errors, misleading those who think clean counters always mean a healthy router.
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
✓
CPU overload on the router
High latency with varying values (jitter) combined with clean interface error counters points to a router that is overwhelmed by processing demands. When a router's CPU is overloaded, it queues packets for processing, introducing variable delays even though the physical layer shows no errors. This matches the symptom of a specific hop showing latency spikes without CRC or framing errors.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Duplex mismatch
Why it's wrong here
A duplex mismatch occurs when one side of a link operates in full-duplex mode while the other operates in half-duplex. This common misconfiguration leads to severe performance degradation characterized by a high number of late collisions, runts, and Cyclic Redundancy Check (CRC) errors on the half-duplex side, and input errors/discards on the full-duplex side. These specific error counters would be clearly visible on the interface statistics, which are not indicated as present.
When this WOULD be correct
A question describes intermittent connectivity or slow performance between two directly connected devices, and the interface error counters show CRC errors or runts. In that scenario, duplex mismatch is a common cause.
- ✗
Incorrect MTU
Why it's wrong here
An incorrect Maximum Transmission Unit (MTU) setting between two devices or across a path typically leads to either excessive fragmentation, which increases overhead, or outright packet drops if the "Don't Fragment" bit is set. While this can degrade performance, the primary symptom would be consistent packet loss or very specific application failures, not general slow file transfers with variable latency where basic connectivity (ping) is still functional.
When this WOULD be correct
Incorrect MTU would be correct if users report that large file transfers fail or are slow, while small transfers work fine, and the traceroute shows no response or 'fragmentation needed' messages at a specific hop, with no latency variation.
- ✗
Route flapping
Why it's wrong here
Route flapping describes a situation where a route to a destination repeatedly appears and disappears from the routing table due to instability in the network or routing protocol. This rapid change in routing information would manifest as intermittent connectivity, complete unreachability for certain periods, or sudden path changes, rather than a consistent pattern of slow file transfers with variable latency. Users would experience connection drops or timeouts, not just slowness.
When this WOULD be correct
A question describes intermittent connectivity to a remote site, with traceroute showing the route changing between different paths and the route appearing and disappearing in the routing table. The correct answer would be route flapping.
- ✓
CPU overload on the router
Why this is correct
When a router's CPU is overloaded, it struggles to process packets efficiently, leading to increased queue depths for incoming traffic. This results in significant packet processing delays and variable latency, directly impacting file transfer speeds without necessarily generating interface errors like discards or input errors. The router simply cannot keep up with the forwarding, routing table lookups, and other management plane tasks.
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 N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓CPU overload on the routerCorrect answer▾
Why this is correct
When a router's CPU is overloaded, it struggles to process packets efficiently, leading to increased queue depths for incoming traffic. This results in significant packet processing delays and variable latency, directly impacting file transfer speeds without necessarily generating interface errors like discards or input errors. The router simply cannot keep up with the forwarding, routing table lookups, and other management plane tasks.
✗Duplex mismatchWrong answer — click to see why▾
Why this is wrong here
Duplex mismatch typically causes CRC errors and frame check sequence failures, which would appear in interface error counters. Since the technician checked and found no errors, duplex mismatch is unlikely.
★ When this WOULD be the correct answer
A question describes intermittent connectivity or slow performance between two directly connected devices, and the interface error counters show CRC errors or runts. In that scenario, duplex mismatch is a common cause.
Why candidates choose this
Candidates often associate high latency with layer 1 or 2 issues like duplex mismatch, but they overlook that duplex mismatch usually produces visible errors on the interface counters.
✗Incorrect MTUWrong answer — click to see why▾
Why this is wrong here
Incorrect MTU typically causes packet fragmentation or drops, not varying latency with no interface errors. The symptoms of high and varying latency without errors point to CPU overload, not MTU issues.
★ When this WOULD be the correct answer
Incorrect MTU would be correct if users report that large file transfers fail or are slow, while small transfers work fine, and the traceroute shows no response or 'fragmentation needed' messages at a specific hop, with no latency variation.
Why candidates choose this
Candidates may confuse MTU issues with latency problems because both can affect file transfer performance, and MTU misconfiguration is a common cause of network slowdowns in remote office scenarios.
✗Route flappingWrong answer — click to see why▾
Why this is wrong here
Route flapping typically causes intermittent connectivity and routing table instability, not consistently high latency with varying ping responses and no interface errors.
★ When this WOULD be the correct answer
A question describes intermittent connectivity to a remote site, with traceroute showing the route changing between different paths and the route appearing and disappearing in the routing table. The correct answer would be route flapping.
Why candidates choose this
Candidates may associate any routing issue with 'flapping' and confuse high latency with route instability, especially when traceroute shows a problematic hop.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
Troubleshoot: Cable and Physical Layer
Key term
ICMP
ICMP is a network-layer protocol used by network devices to send error messages and operational information about network connectivity.
Key term
Latency
Latency is the time delay between a request being sent over a network and the response being received, often measured in milliseconds.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.