LPIC-2 DNS, Web and Mail Services Practice Question
This LPIC-2 practice question tests your understanding of dns, web and mail services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 DNS server returns SERVFAIL for queries to a zone that is configured as a slave. The master server is reachable. What should the administrator check?
The serial number on the master is greater than on the slave.
Why wrong: Serial number comparison is used to decide whether to transfer, but if transfer fails, the slave may have an old zone and return SERVFAIL, but the root cause is often access control.
B
The zone transfer is allowed from the slave.
If the master does not allow-transfer from the slave IP, the slave cannot obtain the zone and returns SERVFAIL.
C
The slave's allow-query includes the master.
Why wrong: allow-query is for client queries, not for zone transfers.
D
The TSIG key is correct.
Why wrong: TSIG is for authentication; if incorrect, it would cause a transfer error, but SERVFAIL can still occur from other issues.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The zone transfer is allowed from the slave.
When a slave DNS server returns SERVFAIL for a zone it is configured to serve, but the master is reachable, the most common cause is that the master's zone transfer ACL does not include the slave's IP address. Without an explicit 'allow-transfer' directive (or equivalent) on the master permitting the slave, the master will refuse the zone transfer, leaving the slave with no valid zone data and thus returning SERVFAIL. This is a fundamental access control check in BIND and other DNS servers.
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 serial number on the master is greater than on the slave.
Why it's wrong here
Serial number comparison is used to decide whether to transfer, but if transfer fails, the slave may have an old zone and return SERVFAIL, but the root cause is often access control.
✓
The zone transfer is allowed from the slave.
Why this is correct
If the master does not allow-transfer from the slave IP, the slave cannot obtain the zone and returns SERVFAIL.
Related concept
Read the scenario before looking for a memorised answer.
✗
The slave's allow-query includes the master.
Why it's wrong here
allow-query is for client queries, not for zone transfers.
✗
The TSIG key is correct.
Why it's wrong here
TSIG is for authentication; if incorrect, it would cause a transfer error, but SERVFAIL can still occur from other issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on serial numbers or query permissions, but the critical missing piece is the master's transfer authorization, which is a separate ACL from query access.
Detailed technical explanation
How to think about this question
Under the hood, when a slave starts or refreshes, it sends an AXFR or IXFR query to the master. The master checks its 'allow-transfer' ACL (often defined in the zone stanza or global options) before responding. If the slave's IP is not permitted, the master returns a REFUSED or simply drops the connection, leaving the slave without zone data. In BIND, the 'allow-transfer { none; };' default for many distributions can silently block all transfers, leading to SERVFAIL on the slave even though the master is up and the slave configuration appears correct.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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.
DNS, Web and Mail Services — This question tests DNS, Web and Mail Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The zone transfer is allowed from the slave. — When a slave DNS server returns SERVFAIL for a zone it is configured to serve, but the master is reachable, the most common cause is that the master's zone transfer ACL does not include the slave's IP address. Without an explicit 'allow-transfer' directive (or equivalent) on the master permitting the slave, the master will refuse the zone transfer, leaving the slave with no valid zone data and thus returning SERVFAIL. This is a fundamental access control check in BIND and other DNS servers.
What should I do if I get this LPIC-2 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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