The answer is to restrict zone transfers to specific IP addresses, disable zone transfers by default, and use TSIG (Transaction Signatures) for authentication. These three methods are correct because DNS zone transfer attacks exploit the lack of access control on TCP port 53, allowing an attacker to request a full copy of the zone file. By limiting transfers to authorized secondary DNS servers via IP whitelisting, disabling zone transfers entirely on primary servers, and signing zone transfer requests with TSIG, you prevent unauthorized disclosure of all DNS records. On the Certified Ethical Hacker CEH exam, this topic tests your understanding of DNS enumeration and reconnaissance techniques, often appearing in questions about network footprinting. A common trap is confusing disabling recursive queries with zone transfer prevention—recursion limits amplification attacks but does not block zone transfers, which use TCP. Remember the mnemonic “RDT” for Restrict, Disable, and TSIG to lock down your DNS zone data.
CEH Footprinting, Reconnaissance and Scanning Practice Question
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which THREE of the following are valid methods to prevent DNS zone transfer attacks? (Select 3)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disable recursive queries for external hosts
Option B is correct because disabling recursive queries for external hosts prevents DNS servers from being used in amplification attacks and also limits the information that can be obtained via zone transfers. Recursive queries are not required for zone transfers (which use TCP port 53), but disabling recursion for external hosts reduces the attack surface by preventing unauthorized users from querying the server for all records in a domain.
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.
✗
Increase the SOA refresh interval
Why it's wrong here
Refresh interval controls how often secondary checks for updates; does not prevent unauthorized transfers.
✓
Disable recursive queries for external hosts
Why this is correct
This prevents external hosts from using the DNS server as a resolver, but indirect benefit.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use TSIG (Transaction Signatures) for authentication
Why this is correct
TSIG ensures only authenticated servers can request zone transfers.
Related concept
Read the scenario before looking for a memorised answer.
✓
Restrict zone transfers to specific IP addresses
Why this is correct
Only allow authorized secondary DNS servers to perform zone transfers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Block all inbound traffic on UDP port 53
Why it's wrong here
Blocking port 53 would also block legitimate DNS queries; not a practical solution.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the roles of UDP and TCP in DNS, incorrectly assuming that blocking UDP port 53 will stop zone transfers, when in fact zone transfers use TCP port 53 and blocking UDP 53 only breaks normal queries.
Detailed technical explanation
How to think about this question
DNS zone transfers (AXFR/IXFR) operate over TCP port 53, not UDP. Restricting zone transfers to specific IP addresses (Option D) is the most direct method, often implemented via allow-transfer directives in BIND or similar ACLs in Windows DNS. TSIG (Option C) uses shared secret keys and HMAC-MD5 (RFC 2845) to authenticate zone transfer requests, ensuring only authorized secondary servers can initiate transfers. Disabling recursion for external hosts (Option B) is a best practice to prevent DNS cache poisoning and reconnaissance, but it does not directly block zone transfers; however, it limits the data an attacker can gather via other query types.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Disable recursive queries for external hosts — Option B is correct because disabling recursive queries for external hosts prevents DNS servers from being used in amplification attacks and also limits the information that can be obtained via zone transfers. Recursive queries are not required for zone transfers (which use TCP port 53), but disabling recursion for external hosts reduces the attack surface by preventing unauthorized users from querying the server for all records in a domain.
What should I do if I get this CEH 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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