N10-009 Network Troubleshooting Practice Question
A user reports that they cannot access a web server at 10.0.1.200. The user can ping the server's IP address but cannot open the web page. The web server is known to be running and accessible from other users on the same subnet. What is the most likely cause?
⚠ Common exam trap
A common mix-up: candidates assume a successful ping means full network connectivity, but ICMP and TCP are separate protocols that can be filtered independently by ACLs, so ping working does not guarantee web access.
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
✓
ACL blocking port 80 or 443
The user can ping the server (ICMP works) but cannot access the web page, which indicates Layer 3 connectivity is fine but the specific TCP ports (80 for HTTP or 443 for HTTPS) are being blocked. An ACL applied on the server, a switch, or a router between the user and the server is the most likely cause, as it would permit ICMP echo requests while denying HTTP/HTTPS traffic. Other users on the same subnet can access the server, ruling out server-side or subnet-wide issues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Default gateway is misconfigured
Why it's wrong here
The default gateway is essential for routing traffic to destinations outside the local subnet. However, if the user and the web server at 10.0.1.200 are on the same local network segment (e.g., 10.0.1.0/24), communication between them occurs directly using MAC addresses resolved via ARP. A misconfigured default gateway would only prevent access to resources beyond the local subnet, not direct IP communication within it, and ping would still function.
- ✓
ACL blocking port 80 or 443
Why this is correct
An Access Control List (ACL) is a set of rules configured on a network device, such as a router or firewall, to filter network traffic. The ability to successfully ping the web server indicates basic Layer 3 (IP) connectivity is established, as ping utilizes ICMP. However, the inability to access web services specifically suggests that TCP traffic destined for ports 80 (HTTP) or 443 (HTTPS) is being explicitly denied by an ACL, a common security measure.
- ✗
DNS resolution failure
Why it's wrong here
The Domain Name System (DNS) is responsible for translating human-readable domain names into numerical IP addresses. In this scenario, the user is attempting to access the web server directly by its IP address, 10.0.1.200. Therefore, DNS resolution is entirely bypassed and not required for this connection attempt, meaning a DNS failure would have no impact on the ability to reach the server via its IP.
When this WOULD be correct
A user reports they cannot access a website by its domain name (e.g., www.example.com) but can access it by IP address. Other users on the same subnet can access the site by name. DNS resolution failure would be the most likely cause.
- ✗
Duplicate IP address
Why it's wrong here
A duplicate IP address occurs when two or more devices on the same network are assigned the identical IP address. This conflict typically leads to severe and intermittent connectivity problems for all affected devices, as ARP requests receive conflicting responses. If a duplicate IP were the root cause, the user would likely experience intermittent or complete failure when attempting to ping the server, not just a specific inability to access web services.
When this WOULD be correct
A user reports intermittent connectivity to a server; pinging the server sometimes fails and sometimes succeeds, and other users on the same subnet also experience similar issues. This scenario suggests an IP address conflict.
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.
✓ACL blocking port 80 or 443Correct answer▾
Why this is correct
An Access Control List (ACL) is a set of rules configured on a network device, such as a router or firewall, to filter network traffic. The ability to successfully ping the web server indicates basic Layer 3 (IP) connectivity is established, as ping utilizes ICMP. However, the inability to access web services specifically suggests that TCP traffic destined for ports 80 (HTTP) or 443 (HTTPS) is being explicitly denied by an ACL, a common security measure.
✗DNS resolution failureWrong answer — click to see why▾
Why this is wrong here
DNS resolution failure would prevent the user from resolving a hostname to an IP address, but the user can ping the server's IP address (10.0.1.200) directly, indicating that name resolution is not the issue.
★ When this WOULD be the correct answer
A user reports they cannot access a website by its domain name (e.g., www.example.com) but can access it by IP address. Other users on the same subnet can access the site by name. DNS resolution failure would be the most likely cause.
Why candidates choose this
Candidates often associate web access issues with DNS problems, overlooking that the user can successfully ping the IP address, which eliminates DNS as the cause.
✗Duplicate IP addressWrong answer — click to see why▾
Why this is wrong here
A duplicate IP address would cause intermittent connectivity or complete failure for both devices, but the user can ping the server successfully, ruling out an IP conflict.
★ When this WOULD be the correct answer
A user reports intermittent connectivity to a server; pinging the server sometimes fails and sometimes succeeds, and other users on the same subnet also experience similar issues. This scenario suggests an IP address conflict.
Why candidates choose this
Candidates may confuse symptoms of IP conflicts with application-layer issues, or assume that any connectivity problem could be due to duplicate IPs without considering that ping success eliminates that possibility.
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
Learn chapter
Troubleshoot: Cable and Physical Layer
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.
Key term
ICMP
ICMP is a network protocol used by devices to send error messages and operational information about network communication problems.
About these practice questions
Courseiva writes every N10-009 question from scratch — 464 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
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.