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 user reports that they can access a website by its IP address but not by its domain name. Which of the following is most likely 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.
Correct. DNS is responsible for translating domain names to IP addresses; a failure in DNS will cause name resolution to fail while IP-based access works.
B
B) Incorrect default gateway
Why wrong: An incorrect gateway would prevent all outbound traffic, including IP-based access. Since IP access works, this is not the issue.
C
C) Duplicate IP address
Why wrong: A duplicate IP address would cause intermittent connectivity and possibly network errors, but it would not selectively affect name resolution.
D
D) Corrupted TCP/IP stack
Why wrong: A corrupted TCP/IP stack would likely cause issues with all network communication, including IP-based access.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A) DNS resolution failure
Accessing a website by IP address but not by domain name indicates that the client can reach the web server over the network, but the name-to-IP translation process is failing. This is a classic symptom of a DNS resolution failure, where the client cannot query or receive a valid A or AAAA record for the domain from its configured DNS server.
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.
✓
A) DNS resolution failure
Why this is correct
Correct. DNS is responsible for translating domain names to IP addresses; a failure in DNS will cause name resolution to fail while IP-based access works.
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.
✗
B) Incorrect default gateway
Why it's wrong here
An incorrect gateway would prevent all outbound traffic, including IP-based access. Since IP access works, this is not the issue.
✗
C) Duplicate IP address
Why it's wrong here
A duplicate IP address would cause intermittent connectivity and possibly network errors, but it would not selectively affect name resolution.
✗
D) Corrupted TCP/IP stack
Why it's wrong here
A corrupted TCP/IP stack would likely cause issues with all network communication, including IP-based access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse DNS failure with a gateway or routing issue, but the ability to reach the server by IP proves Layer 3 connectivity is working, isolating the problem to the application layer name resolution process.
Detailed technical explanation
How to think about this question
DNS resolution typically uses UDP port 53 for queries and TCP port 53 for zone transfers or large responses. A common subtle cause is a misconfigured DNS suffix search list on the client, which can cause the resolver to append incorrect domains and fail to find the correct FQDN. In real-world scenarios, this issue often arises after a DHCP server change or a firewall rule that blocks outbound DNS queries while permitting HTTP traffic.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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: A) DNS resolution failure — Accessing a website by IP address but not by domain name indicates that the client can reach the web server over the network, but the name-to-IP translation process is failing. This is a classic symptom of a DNS resolution failure, where the client cannot query or receive a valid A or AAAA record for the domain from its configured DNS server.
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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Question Discussion
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