Question 228 of 520

Network Troubleshooting →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the server's firewall is blocking inbound connections to port 8080. This is the most likely cause because a successful ping only confirms ICMP-level reachability to the server’s IP address, while the 'connection refused' error indicates that the TCP handshake on port 8080 is being actively rejected—typically by a firewall rule that permits ICMP echo requests but drops TCP SYN packets to that specific port. Since the web application service is confirmed running, the firewall is the only component that can selectively block traffic at the transport layer while allowing ICMP. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to differentiate between network-layer reachability (ping) and application-layer connectivity, a common trap where candidates mistakenly blame the service or routing. Remember the memory tip: "Ping passes, port refuses—firewall rules are the culprit."

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 network technician is troubleshooting a user's inability to access a specific internal web application hosted on a server at 10.10.10.15:8080. The user can ping the server's IP address successfully, but the web browser displays 'connection refused'. The technician verifies that the web application service is running on the server. What is the most likely cause of the issue?

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.

Question 1mediummultiple choice

Full question →

A
The server's firewall is blocking inbound connections to port 8080.
Connection refused often indicates that a firewall is blocking the specific port. Since the server is reachable via ping, the issue is at the port level. Checking the server firewall rules for port 8080 is the next step.
B
The web application is listening on a different port than 8080.
Why wrong: The technician verified the service is running, but if it were on a different port, the connection would still be refused. However, the most likely first cause to check is the firewall. Also, the question says 'connection refused', which is a response from the server, not a timeout; if the service were on a different port, the firewall might still allow the connection but the service wouldn't respond; depending on configuration, this could also give 'connection refused' if the port is closed. But firewall is more common.
C
The user's web browser is configured to use an incorrect proxy server.
Why wrong: A proxy misconfiguration would typically result in a proxy error message (e.g., 'proxy server not responding') rather than 'connection refused' directly to the server IP.
D
The DNS resolution is failing for the server's hostname.
Why wrong: The user is accessing the server via IP address (10.10.10.15), so DNS is not involved. Ping to the IP succeeded, so network connectivity is fine.

Full breakdown with real-world context →

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 firewall is blocking inbound connections to port 8080.

Since the user can ping the server (ICMP success) but receives 'connection refused' on port 8080, and the service is confirmed running, the most likely cause is that the server's firewall is blocking inbound TCP connections to port 8080. A firewall rule can permit ICMP echo requests while denying TCP SYN packets to specific ports, resulting in a successful ping but a TCP RST or no response at the application layer, which manifests as 'connection refused' in the browser.

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 firewall is blocking inbound connections to port 8080.
Why this is correct
Connection refused often indicates that a firewall is blocking the specific port. Since the server is reachable via ping, the issue is at the port level. Checking the server firewall rules for port 8080 is the next step.
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 web application is listening on a different port than 8080.
Why it's wrong here
The technician verified the service is running, but if it were on a different port, the connection would still be refused. However, the most likely first cause to check is the firewall. Also, the question says 'connection refused', which is a response from the server, not a timeout; if the service were on a different port, the firewall might still allow the connection but the service wouldn't respond; depending on configuration, this could also give 'connection refused' if the port is closed. But firewall is more common.
✗
The user's web browser is configured to use an incorrect proxy server.
Why it's wrong here
A proxy misconfiguration would typically result in a proxy error message (e.g., 'proxy server not responding') rather than 'connection refused' directly to the server IP.
✗
The DNS resolution is failing for the server's hostname.
Why it's wrong here
The user is accessing the server via IP address (10.10.10.15), so DNS is not involved. Ping to the IP succeeded, so network connectivity is fine.

Common exam traps

Common exam trap: answer the scenario, not the keyword

CompTIA often tests the distinction between ICMP reachability (ping) and TCP port accessibility, trapping candidates into thinking a successful ping means all network connectivity is fine, when in fact firewalls can selectively block specific ports while allowing ICMP.

Detailed technical explanation

How to think about this question

The 'connection refused' error is triggered when the client's TCP SYN packet receives a TCP RST (reset) from the server, typically because no process is listening on that port or a firewall explicitly rejects the connection. In this scenario, the service is running, so a firewall rule using a stateful packet inspection (SPI) or access control list (ACL) is likely dropping the SYN packet or sending a RST, while ICMP (ping) is permitted. Real-world examples include Windows Firewall or iptables rules that allow ICMP but block specific TCP ports, often misconfigured during server hardening.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

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 server's firewall is blocking inbound connections to port 8080. — Since the user can ping the server (ICMP success) but receives 'connection refused' on port 8080, and the service is confirmed running, the most likely cause is that the server's firewall is blocking inbound TCP connections to port 8080. A firewall rule can permit ICMP echo requests while denying TCP SYN packets to specific ports, resulting in a successful ping but a TCP RST or no response at the application layer, which manifests as 'connection refused' in the browser.

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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