The answer is a DNS server misconfiguration. This is the most likely cause because the client can ping external IP addresses and the default gateway, confirming that IP connectivity, routing, and physical networking are all functional; the failure to resolve hostnames while successfully pinging by IP isolates the problem squarely to the name resolution process. On the CompTIA Network+ N10-009 exam, this scenario tests your ability to distinguish between Layer 3 connectivity issues and application-layer DNS failures—a common trap is to suspect a faulty DHCP server or a routing problem, but since the client received an IP and can reach external IPs, DHCP and routing are working. Remember the key diagnostic: if you can ping IPs but not names, the issue is always DNS, not connectivity. A useful memory tip is "Ping by IP, not by name? DNS is to blame."
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.
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.
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.
✓
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.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
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.
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