- A
The server's default gateway is misconfigured
If the server's default gateway is not the router that forwarded the request, the server can receive packets but cannot reply properly, causing a one-way communication failure.
- B
The user's workstation has a firewall blocking port 80
Why wrong: If a workstation firewall blocked port 80, the user would likely not be able to browse the internet either, and the router ping test is irrelevant.
- C
The router has a missing route to the server's network
Why wrong: The technician successfully pinged the server from the router, so a route exists; a missing route would have caused the ping to fail.
- D
The server's subnet mask is incorrect
Why wrong: An incorrect subnet mask on the server would affect local connectivity but would not explain why the router can reach it while the user cannot.
Quick Answer
The answer is a misconfigured server default gateway, as this creates an asymmetric routing issue where the server receives traffic but cannot send replies back to the correct subnet. When a user can access the internet but not an internal web server at 10.10.10.100, and the technician can ping that server from the router acting as the user’s default gateway, the router clearly has a valid route to the server’s network. The problem is that the server’s default gateway is misconfigured—it lacks a return path to the user’s subnet, so the TCP handshake fails because the SYN-ACK never reaches the user. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of routing fundamentals and asymmetric routing, often appearing as a trap where students assume the server is down or the router is misconfigured. A common memory tip: “If the server can receive but not reply, check its gateway—it’s a one-way street.”
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 that they can access the internet but cannot access the internal web server at 10.10.10.100. The technician can ping the server's IP from the router that serves as the user's default gateway. Which of the following 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 server's default gateway is misconfigured
The user can reach the internet but not the internal web server at 10.10.10.100, while the technician can ping that server from the router (the default gateway). This indicates that the router has a valid route to the server's network and the server is reachable from the router's perspective. The most likely cause is that the server's default gateway is misconfigured: the server does not know how to send return traffic back to the user's subnet, so the TCP handshake fails (the SYN-ACK never reaches the user).
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 server's default gateway is misconfigured
Why this is correct
If the server's default gateway is not the router that forwarded the request, the server can receive packets but cannot reply properly, causing a one-way communication failure.
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 user's workstation has a firewall blocking port 80
Why it's wrong here
If a workstation firewall blocked port 80, the user would likely not be able to browse the internet either, and the router ping test is irrelevant.
- ✗
The router has a missing route to the server's network
Why it's wrong here
The technician successfully pinged the server from the router, so a route exists; a missing route would have caused the ping to fail.
- ✗
The server's subnet mask is incorrect
Why it's wrong here
An incorrect subnet mask on the server would affect local connectivity but would not explain why the router can reach it while the user cannot.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful ping from the router to the server means end-to-end connectivity is fine, but they overlook the fact that the server's return path to the user's subnet requires a correctly configured default gateway on the server itself.
Detailed technical explanation
How to think about this question
When a server receives a request from a client on a different subnet, it must send its reply to its configured default gateway. If that gateway is incorrect or missing, the server will either drop the packet or send it to the wrong next-hop, causing asymmetric routing and connection timeouts. This is a classic 'can ping out but not in' scenario, often verified by checking the server's routing table with `ip route` or `route print` and ensuring the default gateway points to the router's interface IP on the server's VLAN.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 server's default gateway is misconfigured — The user can reach the internet but not the internal web server at 10.10.10.100, while the technician can ping that server from the router (the default gateway). This indicates that the router has a valid route to the server's network and the server is reachable from the router's perspective. The most likely cause is that the server's default gateway is misconfigured: the server does not know how to send return traffic back to the user's subnet, so the TCP handshake fails (the SYN-ACK never reaches the user).
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
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