The answer is that the website server is blocking ICMP requests. This is the most likely cause because the nslookup successfully returned the correct IP address, confirming that DNS resolution is functioning properly and the workstation can locate the server. However, when a ping to that IP address fails, it indicates that while the server is reachable at the network layer, it is deliberately not responding to ICMP echo requests—a common security configuration to reduce attack surface and prevent network reconnaissance. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of how ICMP blocking can create a false impression of unreachability, often tripping up candidates who assume a failed ping means a dead host. A key trap here is confusing a successful nslookup with end-to-end connectivity; remember that DNS resolution and ICMP responses are separate functions. Memory tip: “Ping fails, DNS sails—ICMP’s in the pail.”
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 technician is troubleshooting a user's inability to reach a specific website. The user can reach other websites without issue. The technician runs nslookup on the user's workstation and receives the correct IP address for the website. However, a ping to that IP address fails. Which of the following 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.
Why wrong: If the default gateway were misconfigured, the user would likely be unable to reach any external websites, not just one.
B
The website server is blocking ICMP requests.
Many servers disable ICMP echo replies for security, but HTTP traffic can still function. Since DNS resolves correctly but ping fails, ICMP is likely blocked.
C
The DNS server is not resolving the domain name.
Why wrong: nslookup returned the correct IP, so DNS is working.
D
The subnet mask is incorrect.
Why wrong: An incorrect subnet mask would likely cause issues reaching all destinations, not just one.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The website server is blocking ICMP requests.
Since nslookup returns the correct IP address, DNS resolution is working. The ping fails despite a valid IP, which indicates that the destination server is reachable at the network layer but is not responding to ICMP echo requests. Many web servers are configured to block ICMP to reduce attack surface or prevent reconnaissance, which is a common security practice.
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 default gateway is misconfigured.
Why it's wrong here
If the default gateway were misconfigured, the user would likely be unable to reach any external websites, not just one.
✓
The website server is blocking ICMP requests.
Why this is correct
Many servers disable ICMP echo replies for security, but HTTP traffic can still function. Since DNS resolves correctly but ping fails, ICMP is likely blocked.
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 DNS server is not resolving the domain name.
Why it's wrong here
nslookup returned the correct IP, so DNS is working.
✗
The subnet mask is incorrect.
Why it's wrong here
An incorrect subnet mask would likely cause issues reaching all destinations, not just one.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a failed ping means the host is unreachable, ignoring that ICMP can be blocked independently of the application traffic the user is trying to access.
Detailed technical explanation
How to think about this question
ICMP is a separate protocol from TCP/UDP and is often filtered at firewalls or host-based security policies without affecting web traffic over port 80/443. Ping uses ICMP Type 8 (Echo Request) and expects Type 0 (Echo Reply); if the server drops these packets, the ping fails even though HTTP/HTTPS connections succeed. This is a common troubleshooting pitfall where a failed ping is misinterpreted as a complete lack of connectivity.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
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 website server is blocking ICMP requests. — Since nslookup returns the correct IP address, DNS resolution is working. The ping fails despite a valid IP, which indicates that the destination server is reachable at the network layer but is not responding to ICMP echo requests. Many web servers are configured to block ICMP to reduce attack surface or prevent reconnaissance, which is a common security practice.
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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