This FC0-U61 practice question tests your understanding of infrastructure. 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 is trying to access a website but receives a 'DNS server not responding' error. 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.
DHCP server is down
Why wrong: DHCP issues would cause IP address problems.
DNS server is unreachable
The error explicitly mentions DNS server.
Firewall is blocking the website
Why wrong: Firewall would give a different error.
Modem is disconnected
Why wrong: Modem failure would cause no connectivity at all.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DNS server is unreachable
The 'DNS server not responding' error indicates that the client cannot reach the DNS server to resolve the domain name into an IP address. This is most commonly caused by the DNS server being unreachable due to network connectivity issues, server downtime, or incorrect DNS server configuration. Without DNS resolution, the browser cannot translate the website's URL into an IP address, even if the network and web server are functional.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DHCP server is down
Why it's wrong here
DHCP issues would cause IP address problems.
DNS server is unreachable
Why this is correct
The error explicitly mentions DNS server.
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.
Firewall is blocking the website
Why it's wrong here
Firewall would give a different error.
Modem is disconnected
Why it's wrong here
Modem failure would cause no connectivity at all.
Common exam traps
The trap here is that candidates often confuse DNS resolution failures with network connectivity issues or firewall blocks, but the specific error message points directly to the DNS server being unreachable, not to general network or application-layer problems.
Detailed technical explanation
DNS resolution typically uses UDP port 53 for queries, and the client sends a recursive query to the configured DNS server. If the DNS server is unreachable, the client's resolver will fail after a timeout (usually 5-10 seconds) and return the 'DNS server not responding' error. In enterprise environments, this can occur if the DNS server's IP address is misconfigured in the network adapter settings or if a router along the path drops UDP packets to port 53.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the FC0-U61 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Infrastructure — This question tests Infrastructure — Read the scenario before looking for a memorised answer..
The correct answer is: DNS server is unreachable — The 'DNS server not responding' error indicates that the client cannot reach the DNS server to resolve the domain name into an IP address. This is most commonly caused by the DNS server being unreachable due to network connectivity issues, server downtime, or incorrect DNS server configuration. Without DNS resolution, the browser cannot translate the website's URL into an IP address, even if the network and web server are functional.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This FC0-U61 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 FC0-U61 exam.
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