- A
Incorrect subnet mask
Why wrong: An incorrect subnet mask would affect communication with devices on other subnets, but the client can ping external IPs, so the subnet mask is likely correct.
- B
DNS server misconfiguration
DNS is used for hostname resolution. If the DNS server address is wrong or unreachable, name resolution will fail even though IP connectivity works.
- C
Default gateway not set
Why wrong: The client can ping external IPs, so the default gateway must be set and functioning.
- D
Firewall blocking DNS
Why wrong: A firewall blocking DNS would also likely block other types of traffic, and the client can ping external IPs, so it is not the most likely cause.
Question 105 of 520
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. 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 client obtains an IP address from a DHCP server but cannot resolve hostnames. The client can ping the default gateway and external IP addresses successfully. What 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.
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
✓
DNS server misconfiguration
The client can ping external IP addresses and the default gateway, confirming that IP connectivity and routing are functional. However, the inability to resolve hostnames points directly to a DNS resolution failure, which occurs when the DNS server address is misconfigured or unreachable. Since DHCP provided the IP address, the DNS server setting is likely incorrect or missing in the DHCP scope.
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.
- ✗
Incorrect subnet mask
Why it's wrong here
An incorrect subnet mask would affect communication with devices on other subnets, but the client can ping external IPs, so the subnet mask is likely correct.
When this WOULD be correct
In a scenario where a client obtains an IP address but cannot communicate with any devices outside its local subnet, including the default gateway, an incorrect subnet mask would be the likely cause.
- ✓
DNS server misconfiguration
Why this is correct
DNS is used for hostname resolution. If the DNS server address is wrong or unreachable, name resolution will fail even though IP connectivity 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.
- ✗
Default gateway not set
Why it's wrong here
The client can ping external IPs, so the default gateway must be set and functioning.
When this WOULD be correct
A client obtains an IP address but cannot ping the default gateway or any external IP addresses. The client can only communicate within its own subnet.
- ✗
Firewall blocking DNS
Why it's wrong here
A firewall blocking DNS would also likely block other types of traffic, and the client can ping external IPs, so it is not the most likely cause.
When this WOULD be correct
A firewall blocking DNS would be correct if the client could not ping external IP addresses or the default gateway, but could obtain an IP address via DHCP. For example, if the firewall is configured to allow DHCP but block all other traffic except specific ports, and DNS (port 53) is explicitly blocked.
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.
✓DNS server misconfigurationCorrect answer▾
Why this is correct
DNS is used for hostname resolution. If the DNS server address is wrong or unreachable, name resolution will fail even though IP connectivity works.
✗Incorrect subnet maskWrong answer — click to see why▾
Why this is wrong here
The client can ping external IP addresses successfully, which indicates that the subnet mask is correct; otherwise, routing to external IPs would fail.
★ When this WOULD be the correct answer
In a scenario where a client obtains an IP address but cannot communicate with any devices outside its local subnet, including the default gateway, an incorrect subnet mask would be the likely cause.
Why candidates choose this
Candidates may confuse symptoms of DNS failure with subnet mask issues, or incorrectly assume that an IP address obtained from DHCP implies a correct subnet mask.
✗Default gateway not setWrong answer — click to see why▾
Why this is wrong here
The client can ping the default gateway and external IP addresses, which indicates the default gateway is correctly configured. The issue is name resolution, not routing.
★ When this WOULD be the correct answer
A client obtains an IP address but cannot ping the default gateway or any external IP addresses. The client can only communicate within its own subnet.
Why candidates choose this
Candidates may confuse symptoms of DNS failure with gateway issues, or assume that hostname resolution requires a correctly set gateway.
✗Firewall blocking DNSWrong answer — click to see why▾
Why this is wrong here
The client can ping external IP addresses successfully, indicating that traffic to external networks is not blocked. A firewall blocking DNS would prevent DNS queries but not ICMP pings to external IPs; however, the ability to ping external IPs suggests no general firewall blocking of outbound traffic. The issue is specifically name resolution, not packet filtering.
★ When this WOULD be the correct answer
A firewall blocking DNS would be correct if the client could not ping external IP addresses or the default gateway, but could obtain an IP address via DHCP. For example, if the firewall is configured to allow DHCP but block all other traffic except specific ports, and DNS (port 53) is explicitly blocked.
Why candidates choose this
Candidates may think that if DNS is not working, a firewall must be blocking it, overlooking that successful pings to external IPs indicate general network connectivity is intact. They confuse name resolution failure with a firewall issue without considering the evidence of successful external pings.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The N10-009 exam often tests the distinction between IP connectivity and name resolution, trapping candidates who assume that successful pings to external IPs imply DNS is working, when in fact DNS is a separate service that must be explicitly configured.
Detailed technical explanation
How to think about this question
DNS resolution relies on the client sending queries to the DNS server specified in its DHCP lease (option 6). If the DHCP server provides an invalid or unreachable DNS server IP, or if the client's DNS cache is corrupted, name resolution fails while IP-based communication remains unaffected. Tools like nslookup or dig can isolate whether the issue is with the DNS server or the client's resolver configuration.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Visual reference
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this N10-009 question test?
Networking Concepts — This question tests Networking Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: DNS server misconfiguration — The client can ping external IP addresses and the default gateway, confirming that IP connectivity and routing are functional. However, the inability to resolve hostnames points directly to a DNS resolution failure, which occurs when the DNS server address is misconfigured or unreachable. Since DHCP provided the IP address, the DNS server setting is likely incorrect or missing in the DHCP scope.
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.
About these practice questions
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Last reviewed: Jun 11, 2026
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.
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