- A
The web server service is stopped
Why wrong: If the web server service were stopped, the telnet to port 443 would have failed. Since telnet succeeded, the service is running.
- B
DNS resolution is failing for the FQDN
Why wrong: DNS failure would prevent the browser from resolving the hostname, but the technician used the IP address successfully in ping and telnet. The browser could still fail if it relies on the hostname, but the symptom of 'Unable to connect' typically indicates a connection problem, not name resolution.
- C
The browser is configured to use an incorrect proxy server
If the browser is set to use a proxy server that is unavailable or misconfigured, it will fail to connect to the web server even though network connectivity is fine. Telnet and ping bypass proxy settings, confirming the server is reachable.
- D
A firewall is blocking TCP port 443
Why wrong: If a firewall were blocking port 443, the telnet to that port would have failed. Since telnet succeeded, the firewall is allowing the connection.
Quick Answer
The answer is an incorrect proxy server configuration. This is the most likely cause because the technician confirmed the server is reachable via ping and that the HTTPS service is actively listening on port 443 using telnet, which rules out network connectivity or server-side failures. The browser’s “Unable to connect” error, despite these successful lower-layer tests, points directly to a client-side misconfiguration—specifically, the browser is sending its request to a proxy server that cannot route to the internal application. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate between network-layer reachability and application-layer behavior; a common trap is assuming a failed browser connection means a server or network problem. Remember the memory tip: “Ping and telnet pass, but the browser fails? Check the proxy rails.”
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 cannot access the company's internal web application at https://apps.internal.company.com. The technician can ping the server's IP address (10.10.10.20) successfully and also successfully telnet to 10.10.10.20 on port 443. However, the web browser displays 'Unable to connect'. 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 browser is configured to use an incorrect proxy server
The technician can ping the server IP and telnet to port 443, proving the server is reachable and the HTTPS service is listening. However, the browser fails to load the page, which points to a client-side issue. An incorrect proxy server configuration in the browser would cause the browser to send requests to a proxy that cannot reach the internal server, resulting in 'Unable to connect' despite successful network-level connectivity tests.
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 web server service is stopped
Why it's wrong here
If the web server service were stopped, the telnet to port 443 would have failed. Since telnet succeeded, the service is running.
- ✗
DNS resolution is failing for the FQDN
Why it's wrong here
DNS failure would prevent the browser from resolving the hostname, but the technician used the IP address successfully in ping and telnet. The browser could still fail if it relies on the hostname, but the symptom of 'Unable to connect' typically indicates a connection problem, not name resolution.
- ✓
The browser is configured to use an incorrect proxy server
Why this is correct
If the browser is set to use a proxy server that is unavailable or misconfigured, it will fail to connect to the web server even though network connectivity is fine. Telnet and ping bypass proxy settings, confirming the server is reachable.
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.
- ✗
A firewall is blocking TCP port 443
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume successful telnet to port 443 implies the web application is fully functional, overlooking that the browser may use a proxy server that is not involved in the telnet test, leading them to incorrectly choose a firewall or DNS issue.
Detailed technical explanation
How to think about this question
When a browser is configured with an incorrect proxy, it sends an HTTP CONNECT request to the proxy server for the destination host and port. If the proxy cannot resolve or reach the internal FQDN (e.g., apps.internal.company.com), it returns a connection error to the browser, which displays 'Unable to connect'. This contrasts with direct connectivity tests like telnet, which bypass the proxy and connect directly to the IP, thus succeeding. In real-world scenarios, misconfigured proxy settings are a common cause of browser-only failures, especially in corporate environments with explicit proxy configurations.
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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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 browser is configured to use an incorrect proxy server — The technician can ping the server IP and telnet to port 443, proving the server is reachable and the HTTPS service is listening. However, the browser fails to load the page, which points to a client-side issue. An incorrect proxy server configuration in the browser would cause the browser to send requests to a proxy that cannot reach the internal server, resulting in 'Unable to connect' despite successful network-level connectivity tests.
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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