Question 520 of 520

Network Troubleshooting →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the client’s DNS server lacks an A record for the internal hostname, which is the most likely cause of the failure. When nslookup returns “Non-existent domain” for intranet.company.local, it means the DNS server configured on the client cannot resolve that fully qualified domain name, even though the server’s IP address is reachable via ping. This scenario tests your understanding of the DNS resolution process for the CompTIA Network+ N10-009 exam, specifically how internal name resolution differs from external internet access. A common trap is assuming a ping success means name resolution is working, but ping uses IP addresses directly, while browsers rely on DNS to translate hostnames. Remember the key distinction: connectivity does not equal resolution. Memory tip: “Ping proves the path, DNS proves the name.”

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 user reports that they can access the internet but cannot access the company's internal web application at https://intranet.company.local. The technician can ping the server's IP address (192.168.10.50) successfully from the user's workstation. However, when the technician runs 'nslookup intranet.company.local', it returns 'Non-existent domain'. 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.

Question 1mediummultiple choice

Full question →

A
The web server is not running on port 443.
Why wrong: While that could cause a connection failure after DNS resolves, the primary symptom is DNS resolution failure; nslookup returns NXDOMAIN, so the hostname is not resolved at all.
B
The client's DNS server does not have a record for the internal domain.
A 'Non-existent domain' response from nslookup means the DNS server cannot find the A or CNAME record for that hostname, which is the most likely cause.
C
A firewall is blocking traffic to the internal web server.
Why wrong: If DNS resolution fails, the browser never attempts to connect to the server, so a firewall block would not be the primary cause; the user wouldn't even get to the point of a TCP connection.
D
The hostname is misspelled in the browser.
Why wrong: The technician also ran nslookup and got NXDOMAIN, which rules out user typo; the issue is on the DNS server side.

Full breakdown with real-world context →

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

✓

The client's DNS server does not have a record for the internal domain.

The user can access the internet and ping the server's IP address, which confirms Layer 3 connectivity and that the web server is reachable. However, 'nslookup intranet.company.local' returns 'Non-existent domain', indicating that the DNS server used by the client does not have an A or CNAME record for that internal hostname. Since the browser relies on DNS resolution to translate the FQDN to an IP address, the failure to resolve the name prevents the web application from loading, even though the server itself is online and reachable.

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 web server is not running on port 443.
Why it's wrong here
While that could cause a connection failure after DNS resolves, the primary symptom is DNS resolution failure; nslookup returns NXDOMAIN, so the hostname is not resolved at all.
✓
The client's DNS server does not have a record for the internal domain.
Why this is correct
A 'Non-existent domain' response from nslookup means the DNS server cannot find the A or CNAME record for that hostname, which is the most likely cause.
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.
✗
A firewall is blocking traffic to the internal web server.
Why it's wrong here
If DNS resolution fails, the browser never attempts to connect to the server, so a firewall block would not be the primary cause; the user wouldn't even get to the point of a TCP connection.
✗
The hostname is misspelled in the browser.
Why it's wrong here
The technician also ran nslookup and got NXDOMAIN, which rules out user typo; the issue is on the DNS server side.

Common exam traps

Common exam trap: answer the scenario, not the keyword

CompTIA often tests the distinction between connectivity (ping) and name resolution (nslookup), trapping candidates who assume that successful ping to an IP means the web application should work, ignoring that DNS failure prevents the browser from even initiating the HTTP request.

Detailed technical explanation

How to think about this question

DNS resolution for internal domains often relies on split-brain DNS or a dedicated internal DNS server that hosts private zones (e.g., company.local). The 'Non-existent domain' response (NXDOMAIN) indicates that the DNS server authoritative for the queried zone has no record for that name, or the client's configured DNS server does not have a forwarder or stub zone for the internal domain. In real-world scenarios, misconfigured DNS search suffixes or missing delegation can cause this, while the server remains fully functional at the IP level.

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 practitioner preparing for the N10-009 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

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?

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 client's DNS server does not have a record for the internal domain. — The user can access the internet and ping the server's IP address, which confirms Layer 3 connectivity and that the web server is reachable. However, 'nslookup intranet.company.local' returns 'Non-existent domain', indicating that the DNS server used by the client does not have an A or CNAME record for that internal hostname. Since the browser relies on DNS resolution to translate the FQDN to an IP address, the failure to resolve the name prevents the web application from loading, even though the server itself is online and reachable.

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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Same concept, more angles

2 more ways this is tested on N10-009

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A user reports that they cannot access a web server by its URL but can access it by IP address. A technician checks the DNS server and finds it is reachable. What is the most likely cause?

medium

A.Incorrect default gateway
✓ B.DNS resolution failure for that specific record
C.Firewall blocking port 80
D.IP conflict on the user's workstation

Why B: The user can access the web server by IP address but not by URL, which indicates that the name-to-IP resolution is failing. Since the DNS server is reachable, the issue is not with network connectivity to the DNS server but rather with the specific DNS record for that web server. This is a classic DNS resolution failure for that specific record, often due to a missing or incorrect A or AAAA record.

Variation 2. 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?

easy

✓ A.A) DNS resolution failure
B.B) Incorrect default gateway
C.C) Duplicate IP address
D.D) Corrupted TCP/IP stack

Why A: 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.

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