The answer is to implement DNSSEC, restrict recursive queries, and use DNS filtering. DNSSEC (Domain Name System Security Extensions) works by digitally signing DNS records, allowing resolvers to verify that the response came from the authoritative source and was not tampered with during transit, directly preventing the injection of forged data. Restricting recursive queries to trusted internal clients stops attackers from using your server as an open resolver to cache malicious responses, a primary vector for DNS poisoning. On the Certified Ethical Hacker CEH exam, this topic tests your understanding of network-layer defenses and common attack vectors like cache poisoning; a frequent trap is confusing DNS filtering with encryption—filtering blocks known bad domains but does not verify data integrity like DNSSEC does. Remember the mnemonic “DRF” for DNSSEC, Restrict recursion, and Filter—three layers that lock down the DNS pipeline.
CEH Network and Web Application Attacks Practice Question
This CEH practice question tests your understanding of network and web application attacks. 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 effective countermeasures against DNS poisoning attacks? (Select exactly 3)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Restrict recursive queries to trusted sources
Option B is correct because restricting recursive queries to trusted sources prevents attackers from using your DNS server as an open resolver to cache forged responses. By limiting recursion to authorized clients only, the server will not accept and cache DNS data from external, potentially malicious queries, which is a primary vector for DNS cache poisoning.
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.
✗
Use a single DNS server for all queries
Why it's wrong here
Single server is a single point of failure.
✓
Restrict recursive queries to trusted sources
Why this is correct
Limiting recursion prevents unauthorized use.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable DNS caching
Why it's wrong here
Disabling caching reduces performance and does not prevent poisoning.
Read the scenario before looking for a memorised answer.
✓
Implement DNSSEC
Why this is correct
DNSSEC digitally signs DNS records to ensure authenticity.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think disabling DNS caching (Option C) is a valid countermeasure, but CEH expects you to recognize that it is not a security best practice and that DNSSEC, split DNS, and restricting recursion are the standard, effective defenses.
Detailed technical explanation
How to think about this question
DNS cache poisoning exploits the lack of authentication in DNS responses, allowing an attacker to inject false A or NS records into a resolver's cache. DNSSEC (Option E) mitigates this by digitally signing DNS records using RRSIG and DNSKEY records, enabling resolvers to verify authenticity. Split DNS (Option D) separates internal and external DNS zones, preventing external attackers from poisoning internal resolution paths, often implemented with separate authoritative servers and views in BIND.
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 CEH 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Network and Web Application Attacks — This question tests Network and Web Application Attacks — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Restrict recursive queries to trusted sources — Option B is correct because restricting recursive queries to trusted sources prevents attackers from using your DNS server as an open resolver to cache forged responses. By limiting recursion to authorized clients only, the server will not accept and cache DNS data from external, potentially malicious queries, which is a primary vector for DNS cache poisoning.
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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