The answer is to check if the DNS service is listening on UDP port 53. This is the correct first step because a DNS server that is running and has network connectivity can still fail to resolve queries if its daemon is not actually bound to the default query port defined in RFC 1035. Without a listener on UDP 53, incoming client requests are silently dropped, even though the server process appears active. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding that service status and network connectivity are not sufficient—you must verify that the service is actively accepting traffic on the correct port. A common trap is to immediately check client-side resolv.conf or restart the server, but the most efficient diagnostic is running `ss -ulpn | grep :53` to confirm the listener. Remember the memory tip: “Running isn’t listening”—a process can be alive without being reachable on its designated port.
XK0-005 Troubleshooting Practice Question
This XK0-005 practice question tests your understanding of 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 newly configured DNS server is unable to resolve any queries from clients. The server is running and network connectivity is verified. What should the administrator check first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check if the DNS service is listening on UDP port 53
The most common reason a DNS server fails to resolve queries despite being running and having network connectivity is that the DNS service is not listening on UDP port 53, which is the default port for DNS queries per RFC 1035. Checking this with a command like `ss -ulpn | grep :53` or `netstat -uan | grep :53` directly verifies whether the service is actually accepting incoming queries. This is the first logical step before investigating client-side configurations or rebooting.
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.
✗
Check /etc/resolv.conf on clients
Why it's wrong here
Client configuration is not the cause if the server is new.
✗
Check if DNS service is bound to the loopback address
Why it's wrong here
While possible, checking listening sockets is more fundamental.
✓
Check if the DNS service is listening on UDP port 53
Why this is correct
If the service is not listening, queries cannot be answered.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Reboot the DNS server
Why it's wrong here
Rebooting is a last resort, not a first diagnostic step.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often jump to checking client-side resolv.conf or rebooting the server, overlooking the simple verification of whether the DNS service is actually listening on the correct port and protocol (UDP 53) as the first logical troubleshooting step.
Detailed technical explanation
How to think about this question
DNS servers typically listen on UDP port 53 for standard queries and TCP port 53 for zone transfers and responses exceeding 512 bytes. The `ss -tuln` or `netstat -tuln` commands can show listening sockets; if the DNS service (e.g., named, systemd-resolved, dnsmasq) is not listed on port 53, it may be misconfigured, not started, or blocked by a firewall. In real-world scenarios, a common subtlety is that the DNS service might be bound only to IPv6 (::1) or a specific interface, causing queries from other subnets to fail silently.
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 XK0-005 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check if the DNS service is listening on UDP port 53 — The most common reason a DNS server fails to resolve queries despite being running and having network connectivity is that the DNS service is not listening on UDP port 53, which is the default port for DNS queries per RFC 1035. Checking this with a command like `ss -ulpn | grep :53` or `netstat -uan | grep :53` directly verifies whether the service is actually accepting incoming queries. This is the first logical step before investigating client-side configurations or rebooting.
What should I do if I get this XK0-005 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: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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