- A
The DNS server is reachable but not responding due to high load.
Correct. If the DNS server is overloaded, it may drop queries intermittently. The user can still ping the server (ICMP is different from DNS), but DNS queries time out.
- B
The default gateway is down.
Why wrong: If the default gateway were down, the user would not be able to ping any external IP addresses. The fact that pinging 8.8.8.8 works rules this out.
- C
The corporate firewall is blocking UDP port 53.
Why wrong: A firewall block on UDP port 53 would cause DNS failures consistently, not intermittently. The user would never be able to resolve domain names.
- D
The user's machine has a corrupted DNS cache.
Why wrong: A corrupted DNS cache typically causes failures for specific cached entries, but the issue is described as intermittent and affects all domain names. Flushing the cache might resolve it, but the intermittent nature points more to server load.
Quick Answer
The answer is a DNS server overload causing intermittent resolution failure, because the user can ping external IP addresses like 8.8.8.8 but cannot resolve domain names such as google.com, which confirms IP connectivity is intact while DNS query processing is failing. This specific symptom—where ICMP echo requests succeed but UDP/53 DNS queries time out—indicates the DNS server is reachable but overwhelmed by high load, dropping or ignoring incoming resolution requests. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate between a network connectivity issue and a DNS service issue; a common trap is assuming a failed ping to the DNS server means it is down, when in fact the server may respond to ICMP but not to DNS queries under load. Remember the memory tip: “Ping works, DNS doesn’t? Think load, not link.”
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.
A user reports intermittent inability to access websites. When the issue occurs, the user can ping external IP addresses (e.g., 8.8.8.8) but cannot ping domain names like google.com. The user's IP configuration shows a DNS server address of 8.8.8.8. 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 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
The DNS server is reachable but not responding due to high load.
The user can ping external IP addresses (e.g., 8.8.8.8) but cannot resolve domain names like google.com, which indicates that IP connectivity is working but DNS resolution is failing. Since the DNS server address is 8.8.8.8 and the user can ping it, the server is reachable; however, intermittent failures suggest the server is overwhelmed and dropping or not responding to queries. This matches the symptom of a reachable but unresponsive DNS server due to high load, where ICMP (ping) succeeds but UDP/53 DNS queries time out.
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.
- ✓
The DNS server is reachable but not responding due to high load.
Why this is correct
Correct. If the DNS server is overloaded, it may drop queries intermittently. The user can still ping the server (ICMP is different from DNS), but DNS queries time out.
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.
- ✗
The default gateway is down.
Why it's wrong here
If the default gateway were down, the user would not be able to ping any external IP addresses. The fact that pinging 8.8.8.8 works rules this out.
- ✗
The corporate firewall is blocking UDP port 53.
- ✗
The user's machine has a corrupted DNS cache.
Why it's wrong here
A corrupted DNS cache typically causes failures for specific cached entries, but the issue is described as intermittent and affects all domain names. Flushing the cache might resolve it, but the intermittent nature points more to server load.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a reachable server (via ping) means all services are working, but Cisco tests the distinction between ICMP reachability and UDP/TCP service availability, especially for DNS where high load can cause intermittent failures.
Detailed technical explanation
How to think about this question
DNS queries use UDP port 53 by default, with a fallback to TCP if the response is truncated or if the query fails. When a DNS server is under high load, it may implement rate limiting or drop incoming UDP packets to maintain stability, causing intermittent timeouts for resolution while still responding to ICMP echo requests. In real-world scenarios, administrators can use tools like `dig` with the `+tcp` flag to test if TCP-based resolution works, which would bypass UDP packet loss and confirm the server is reachable but overloaded.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this N10-009 question test?
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: The DNS server is reachable but not responding due to high load. — The user can ping external IP addresses (e.g., 8.8.8.8) but cannot resolve domain names like google.com, which indicates that IP connectivity is working but DNS resolution is failing. Since the DNS server address is 8.8.8.8 and the user can ping it, the server is reachable; however, intermittent failures suggest the server is overwhelmed and dropping or not responding to queries. This matches the symptom of a reachable but unresponsive DNS server due to high load, where ICMP (ping) succeeds but UDP/53 DNS queries time out.
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.
About these practice questions
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Last reviewed: Jun 11, 2026
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.
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