- A
The router's WAN interface is configured with the wrong subnet mask
Why wrong: If the WAN interface were misconfigured, the router likely could not ping the ISP gateway at all.
- B
The default route is missing or has an incorrect next-hop IP
The router can reach the ISP's gateway IP (192.0.2.1), but the default route points to 192.0.2.2, which is not the correct next-hop. This prevents internet traffic from being forwarded properly.
- C
NAT is not configured on the router
Why wrong: While NAT is often required for internet access, the symptom (ping to the ISP works but default route points to wrong IP) points to a routing issue first.
- D
A firewall on the router is blocking outbound traffic
Why wrong: If a firewall were blocking, the ping to the ISP would likely also fail; the issue is specifically with the default route.
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 at a remote branch office cannot access internet resources. The branch's edge router shows that the WAN interface is up. The default route is configured to point to next-hop 192.0.2.2, but the admin can successfully ping 192.0.2.1 from the router. 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 default route is missing or has an incorrect next-hop IP
The correct answer is B because the admin can ping 192.0.2.1 (the WAN interface IP) but not reach 192.0.2.2 (the next-hop), indicating that the default route is either missing or misconfigured. Since the WAN interface is up and the local IP is reachable, the issue is with the routing table entry pointing to the next-hop, not with the interface or subnet mask. Without a valid default route, the router cannot forward traffic destined for the internet.
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 router's WAN interface is configured with the wrong subnet mask
Why it's wrong here
If the WAN interface were misconfigured, the router likely could not ping the ISP gateway at all.
- ✓
The default route is missing or has an incorrect next-hop IP
Why this is correct
The router can reach the ISP's gateway IP (192.0.2.1), but the default route points to 192.0.2.2, which is not the correct next-hop. This prevents internet traffic from being forwarded properly.
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.
- ✗
NAT is not configured on the router
Why it's wrong here
While NAT is often required for internet access, the symptom (ping to the ISP works but default route points to wrong IP) points to a routing issue first.
- ✗
A firewall on the router is blocking outbound traffic
Why it's wrong here
If a firewall were blocking, the ping to the ISP would likely also fail; the issue is specifically with the default route.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful ping to the WAN interface IP (192.0.2.1) means the WAN link is fully functional, but they overlook that the default route's next-hop (192.0.2.2) is a different address that must also be reachable for internet traffic to be forwarded.
Detailed technical explanation
How to think about this question
The router uses the routing table to determine the next-hop for destination traffic; a default route (0.0.0.0/0) with next-hop 192.0.2.2 must be present and reachable. The successful ping to 192.0.2.1 confirms Layer 3 connectivity on the WAN interface, but if the next-hop 192.0.2.2 is not responding or the route is missing, the router will drop packets destined outside the local subnet. In real-world scenarios, this often occurs after a routing protocol failure or a static route misconfiguration, and can be verified with 'show ip route' or 'traceroute' commands.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Network Troubleshooting — study guide chapter
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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 default route is missing or has an incorrect next-hop IP — The correct answer is B because the admin can ping 192.0.2.1 (the WAN interface IP) but not reach 192.0.2.2 (the next-hop), indicating that the default route is either missing or misconfigured. Since the WAN interface is up and the local IP is reachable, the issue is with the routing table entry pointing to the next-hop, not with the interface or subnet mask. Without a valid default route, the router cannot forward traffic destined for the internet.
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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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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