LPIC-2 DNS, Web and Mail Services Practice Question
A company uses BIND9 as the authoritative name server for its public zone example.com. External users report that they cannot resolve the MX record for the domain, but internal users can. What is the most likely cause?
⚠ Common exam trap
Many candidates confuse allow-query (which controls who can send queries) with allow-transfer (zone transfers) or recursion settings, or they assume a missing record is the cause when the symptom is selective failure based on client location.
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 allow-query ACL restricts queries to the internal network.
The allow-query ACL in BIND9 restricts which source IP addresses are permitted to send queries to the server. If it is set to allow only the internal network (e.g., 192.168.0.0/16), external users' queries are rejected, causing resolution failures for MX records and all other records. Internal users succeed because their IPs match the ACL, while external users receive a REFUSED response or no answer.
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 zone file lacks an MX record.
Why it's wrong here
An absent MX record would cause failure for both internal and external users.
- ✓
The allow-query ACL restricts queries to the internal network.
Why this is correct
If allow-query limits to internal IPs, external queries are rejected, causing resolution failures for external users.
- ✗
The server is behind a firewall that blocks UDP port 53.
Why it's wrong here
A firewall blocking port 53 would affect both internal and external users equally.
- ✗
The recursion is set to no.
Why it's wrong here
Disabling recursion is normal for authoritative servers and does not block queries; it only prevents recursive lookups.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.