N10-009 Network Troubleshooting Practice Question
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?
⚠ Common exam trap
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.
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.
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.
- ✗
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.
When this WOULD be correct
In a scenario where a user cannot access a web application and the technician finds the service is not listening on the expected port (e.g., configured to port 9090 instead of 8080), the most likely cause is the application listening on a different port. This would result in a 'connection refused' error if no other service is on that port.
- ✗
The user's web browser is configured to use an incorrect proxy server.
Why it's wrong here
A misconfigured proxy server would typically manifest as an error indicating the browser's inability to connect to or authenticate with the proxy itself, such as 'Proxy Server Not Responding' or 'Unable to connect to proxy server.' The 'connection refused' message, in this context, directly originates from the target server (10.10.10.15) after the browser successfully established a network path to its IP address. This indicates the issue lies with the destination server's handling of the connection attempt, not an intermediary proxy.
When this WOULD be correct
This option would be correct if the user could not access any external websites, but internal resources were reachable, and the browser was configured with a proxy server that is down or misconfigured for external traffic. For example, a question where a user can access internal sites but not the internet, and the proxy settings are incorrect.
- ✗
The DNS resolution is failing for the server's hostname.
Why it's wrong here
DNS resolution is the process of translating human-readable hostnames into numerical IP addresses. Since the user is explicitly attempting to connect to the server using its IP address, 10.10.10.15, the DNS resolution process is entirely bypassed. Therefore, any failure in DNS would not prevent a direct IP-based connection attempt. The successful ping to the IP address further confirms that basic network layer connectivity to the server is functional, eliminating DNS as a potential cause.
When this WOULD be correct
A user reports being unable to access a website by its domain name (e.g., www.example.com) but can access it by its IP address. The technician confirms that other users can access the site by domain name. In this scenario, DNS resolution failure for the specific user would be the likely cause.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓The server's firewall is blocking inbound connections to port 8080.Correct answer▾
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.
✗The web application is listening on a different port than 8080.Wrong answer — click to see why▾
Why this is wrong here
The technician verified the web application service is running, so it is listening on some port. If it were listening on a different port, the browser would not get 'connection refused' but rather a timeout or no response, unless that port is also blocked. The 'connection refused' error indicates the server actively rejected the connection, which is typical of a firewall blocking the specific port.
★ When this WOULD be the correct answer
In a scenario where a user cannot access a web application and the technician finds the service is not listening on the expected port (e.g., configured to port 9090 instead of 8080), the most likely cause is the application listening on a different port. This would result in a 'connection refused' error if no other service is on that port.
Why candidates choose this
Candidates may think that if the service is running, it must be on the expected port, but misconfiguration is common. They overlook that 'connection refused' specifically indicates the port is reachable but no service is listening, which could be due to a different port or firewall, but the firewall is more likely given the service is confirmed running.
✗The user's web browser is configured to use an incorrect proxy server.Wrong answer — click to see why▾
Why this is wrong here
The user can successfully ping the server, indicating network connectivity and DNS resolution are working. The 'connection refused' error suggests the server is actively rejecting the connection, which points to a firewall blocking port 8080, not a proxy misconfiguration.
★ When this WOULD be the correct answer
This option would be correct if the user could not access any external websites, but internal resources were reachable, and the browser was configured with a proxy server that is down or misconfigured for external traffic. For example, a question where a user can access internal sites but not the internet, and the proxy settings are incorrect.
Why candidates choose this
Candidates may confuse 'connection refused' with proxy-related errors like 'proxy server refusing connection', or they might overthink the issue and assume a proxy is involved even when direct connectivity is confirmed.
✗The DNS resolution is failing for the server's hostname.Wrong answer — click to see why▾
Why this is wrong here
The user can successfully ping the server's IP address (10.10.10.15), indicating that network connectivity and IP-level communication are working. DNS resolution is not involved because the user is accessing the server by IP address, not by hostname. Therefore, a DNS failure cannot be the cause.
★ When this WOULD be the correct answer
A user reports being unable to access a website by its domain name (e.g., www.example.com) but can access it by its IP address. The technician confirms that other users can access the site by domain name. In this scenario, DNS resolution failure for the specific user would be the likely cause.
Why candidates choose this
Candidates may confuse general web access issues with DNS problems, assuming that 'connection refused' could stem from name resolution failure, even though the question explicitly states the user is using an IP address.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
Go deeper
Related to this question
Learn chapter
Troubleshooting Methodology
Key term
TCP
TCP (Transmission Control Protocol) is a core internet protocol that ensures data is sent reliably and in order between devices over a network.
Key term
Firewall
A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predetermined security rules to protect trusted internal networks from untrusted external networks.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.