N10-009 Network Troubleshooting Practice Question
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?
⚠ Common exam trap
Many 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.
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).
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
The problem states the user can access the internet but not the internal web server, yet the router can ping the server. This implies the server can *receive* traffic from the router and, by extension, from the user. However, if the server's default gateway is incorrect, it will attempt to send its *reply* packets to the wrong router or an unreachable address. This results in a one-way communication where the server gets the request but the client never receives the response, manifesting as an inability to access the internal web.
- ✗
The user's workstation has a firewall blocking port 80
Why it's wrong here
If the user's workstation firewall were blocking outbound port 80 traffic, the user would be unable to access *any* web content, including the internet. The problem explicitly states the user *can* access the internet, which fundamentally relies on port 80 (or 443 for HTTPS) for web browsing. Therefore, a local firewall blocking port 80 on the user's machine is inconsistent with the ability to browse the internet successfully.
When this WOULD be correct
A user reports they cannot access a specific website (e.g., https://example.com) but can access other websites. The technician verifies the user's firewall is enabled and blocking outbound port 443. In this case, the workstation firewall blocking the port would be the most likely cause.
- ✗
The router has a missing route to the server's network
Why it's wrong here
If the router were missing a route to the server's network, the router would not know how to forward packets destined for the server. Consequently, any attempt to ping the server *from* the router would fail, as the router would drop the packets or return an unreachable message. The problem explicitly states that the technician *successfully pinged* the server from the router, which directly contradicts the premise of a missing route and confirms the router knows how to reach the server.
When this WOULD be correct
This option would be correct if the technician could not ping the server from the router, indicating that the router lacks a route to the server's subnet, or if the server is on a different network segment not directly connected to the router.
- ✗
The server's subnet mask is incorrect
Why it's wrong here
An incorrect subnet mask on the server would primarily impact its ability to determine if a destination IP address is on the local network or requires routing. If the subnet mask were severely misconfigured, the server might struggle to communicate even with its default gateway, potentially preventing the router from pinging it successfully. Since the router *can* ping the server, its basic network configuration, including the subnet mask, is likely correct enough for local communication within its subnet.
When this WOULD be correct
In a scenario where a user cannot reach a server at all (no ping, no access), and the technician finds that the server's IP address is in a different subnet than expected due to a subnet mask error, then an incorrect subnet mask would be the cause. For example, if the server is configured with /24 instead of /16, it may not communicate with hosts outside its perceived subnet.
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 default gateway is misconfiguredCorrect answer▾
Why this is correct
The problem states the user can access the internet but not the internal web server, yet the router can ping the server. This implies the server can *receive* traffic from the router and, by extension, from the user. However, if the server's default gateway is incorrect, it will attempt to send its *reply* packets to the wrong router or an unreachable address. This results in a one-way communication where the server gets the request but the client never receives the response, manifesting as an inability to access the internal web.
✗The user's workstation has a firewall blocking port 80Wrong answer — click to see why▾
Why this is wrong here
The user can access the internet, indicating general connectivity works. The technician can ping the server from the router, so the router has a route. A workstation firewall blocking port 80 would not explain why the server is unreachable from the user's perspective if the server itself is reachable via ping from the router.
★ When this WOULD be the correct answer
A user reports they cannot access a specific website (e.g., https://example.com) but can access other websites. The technician verifies the user's firewall is enabled and blocking outbound port 443. In this case, the workstation firewall blocking the port would be the most likely cause.
Why candidates choose this
Candidates often assume client-side firewall issues are common and may overlook that the problem is server-side, especially when symptoms involve a single inaccessible server.
✗The router has a missing route to the server's networkWrong answer — click to see why▾
Why this is wrong here
The technician can ping the server's IP from the router, which means the router has a route to the server's network. A missing route would prevent the router from reaching the server, contradicting the given information.
★ When this WOULD be the correct answer
This option would be correct if the technician could not ping the server from the router, indicating that the router lacks a route to the server's subnet, or if the server is on a different network segment not directly connected to the router.
Why candidates choose this
Candidates may assume that any connectivity issue between different subnets is due to a missing route, overlooking that the router's successful ping proves the route exists.
✗The server's subnet mask is incorrectWrong answer — click to see why▾
Why this is wrong here
An incorrect subnet mask on the server would prevent it from communicating with devices on other subnets, but the technician can ping the server from the router, indicating the server's IP configuration is reachable. The issue is that the user cannot access the web server, which suggests the server cannot reply to the user because its default gateway is misconfigured, not its subnet mask.
★ When this WOULD be the correct answer
In a scenario where a user cannot reach a server at all (no ping, no access), and the technician finds that the server's IP address is in a different subnet than expected due to a subnet mask error, then an incorrect subnet mask would be the cause. For example, if the server is configured with /24 instead of /16, it may not communicate with hosts outside its perceived subnet.
Why candidates choose this
Candidates may confuse subnet mask issues with default gateway issues, thinking that an incorrect subnet mask could prevent the server from sending replies to the user, but in this case the server is reachable from the router, ruling out a subnet mask problem.
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
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Related to this question
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Troubleshoot: Network Connectivity
Key term
Default gateway
A default gateway is a network device, typically a router, that acts as the exit point for traffic from a local network to other networks, including the internet.
Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
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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.