LFCS Networking Practice Question
A Linux server is unable to resolve the hostname 'app.internal.example.com' but can resolve other names. The /etc/nsswitch.conf file contains: hosts: files mdns4_minimal [NOTFOUND=return] dns. The /etc/hosts file does not list the hostname. Which configuration change would most likely resolve the issue?
⚠ Common exam trap
It's easy for candidates to assume the issue is with DNS configuration or order, but the real problem is the [NOTFOUND=return] action on mdns4_minimal, which prematurely terminates the resolution chain for non-.local hostnames.
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
✓
Remove the mdns4_minimal entry or change it to 'mdns4' without the NOTFOUND=return
The issue is that mdns4_minimal with [NOTFOUND=return] causes the resolver to stop after a failed mDNS query, preventing it from falling back to DNS. Since the hostname is not in /etc/hosts and not reachable via mDNS, the resolver returns 'not found' immediately without querying DNS. Removing the mdns4_minimal entry or changing it to 'mdns4' (without the NOTFOUND=return) allows the resolver to proceed to DNS if mDNS fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the hosts line to: hosts: dns files mdns4_minimal
Why it's wrong here
Reordering to dns files mdns4_minimal still leaves mdns4_minimal's [NOTFOUND=return] action able to terminate the lookup before completion, and it changes precedence for every hostname. The fault is the return action, not module order; removing or amending that action lets dns be queried.
- ✗
Configure /etc/resolv.conf to use a different DNS server
Why it's wrong here
Other names already resolve, proving the configured DNS servers work; the [NOTFOUND=return] action on mdns4_minimal stops the lookup before dns is consulted for this name. Changing resolv.conf servers leaves that nsswitch short-circuit intact, so the failure persists.
- ✓
Remove the mdns4_minimal entry or change it to 'mdns4' without the NOTFOUND=return
Why this is correct
Removing `mdns4_minimal` or dropping its `[NOTFOUND=return]` action stops the resolver aborting the lookup when multicast DNS returns nothing. With that action present, the `dns` source is never consulted for names mDNS cannot answer, so `app.internal.example.com` fails despite DNS being reachable.
- ✗
Add the hostname to the local multicast DNS configuration
Why it's wrong here
Multicast DNS resolves only .local names via mdns4_minimal; app.internal.example.com is a unicast DNS name, so adding it to mDNS configuration cannot resolve it. It is tempting because mdns4_minimal appears in the nsswitch hosts line, but that module handles local-link discovery, not internal DNS zones.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.