This LFCS practice question tests your understanding of networking. 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 Linux system administrator is troubleshooting a DNS resolution issue on a Ubuntu 20.04 server. The server is configured with a static IP address on interface eth0 via /etc/netplan/01-netcfg.yaml. The administrator set the DNS servers to 8.8.8.8 and 8.8.4.4 in the cloud-config file. After applying the netplan configuration, the server can resolve hostnames correctly. However, after a few days, users report that the server can no longer resolve external hostnames. The administrator checks /etc/resolv.conf and sees that it contains only a local DNS server (127.0.0.53) and no references to the public DNS servers. The administrator wants to ensure that the public DNS servers are always used and that local DNS is bypassed. What is the best course of action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Modify the netplan configuration to set dns servers and set 'dhcp4-overrides: {use-dns: false}' then apply.
Option A is correct because in Ubuntu 20.04, netplan uses systemd-resolved by default, which listens on 127.0.0.53. Setting 'dhcp4-overrides: {use-dns: false}' in the netplan configuration prevents DHCP from overriding the manually specified DNS servers, ensuring that only the public DNS servers (8.8.8.8 and 8.8.4.4) are used for resolution. After applying with 'netplan apply', systemd-resolved will forward queries to those public servers, bypassing the local stub resolver.
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.
✓
Modify the netplan configuration to set dns servers and set 'dhcp4-overrides: {use-dns: false}' then apply.
Why this is correct
This ensures netplan configures systemd-resolved to use the specified DNS servers.
Clue confirmation
The clue words "best", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Directly edit /etc/resolv.conf to add the public DNS servers and make it immutable using chattr +i.
Why it's wrong here
systemd-resolved will still overwrite or ignore the file.
✗
Use the 'host' command to force DNS queries to use a specific server.
Why it's wrong here
The 'host' command is a diagnostic tool, not a persistent fix.
✗
Stop and disable the systemd-resolved service using systemctl.
Why it's wrong here
Disabling systemd-resolved may cause other DNS resolution issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think directly editing /etc/resolv.conf or disabling systemd-resolved is a valid fix, but they fail to understand that netplan and systemd-resolved work together to manage DNS, and the proper way to bypass the local stub is to configure the upstream servers correctly in netplan with DHCP overrides disabled.
Trap categories for this question
Command / output trap
The 'host' command is a diagnostic tool, not a persistent fix.
Detailed technical explanation
How to think about this question
Ubuntu 20.04 uses systemd-resolved as the DNS stub resolver, which listens on 127.0.0.53 and manages /etc/resolv.conf as a symlink to /run/systemd/resolve/stub-resolv.conf. When netplan applies DNS servers, it configures systemd-resolved's upstream servers, but if DHCP overrides are not explicitly disabled, DHCP-provided DNS servers can replace the static ones. The 'dhcp4-overrides: {use-dns: false}' directive ensures that DHCP options (like option 6 for DNS) are ignored, preserving the static 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 practitioner preparing for the LFCS 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.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Modify the netplan configuration to set dns servers and set 'dhcp4-overrides: {use-dns: false}' then apply. — Option A is correct because in Ubuntu 20.04, netplan uses systemd-resolved by default, which listens on 127.0.0.53. Setting 'dhcp4-overrides: {use-dns: false}' in the netplan configuration prevents DHCP from overriding the manually specified DNS servers, ensuring that only the public DNS servers (8.8.8.8 and 8.8.4.4) are used for resolution. After applying with 'netplan apply', systemd-resolved will forward queries to those public servers, bypassing the local stub resolver.
What should I do if I get this LFCS 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: "best", "always". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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