This 200-201 practice question tests your understanding of security concepts. 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.
A security analyst discovers that an attacker exfiltrated data using DNS tunneling. Which TWO controls should be implemented to detect or prevent this? (Select two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Monitor DNS query sizes and frequencies
Option A is correct because DNS tunneling often involves unusually large query sizes (e.g., encoded data in subdomains) and abnormal query frequencies (e.g., thousands of requests per minute). Monitoring these metrics allows analysts to spot deviations from baseline behavior, which is a key detection technique for exfiltration via DNS. Option B is correct because a DNS sinkhole redirects malicious or suspicious DNS queries to a controlled IP address, effectively blocking the resolution of domains used for tunneling and preventing data from reaching the attacker's command-and-control server.
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.
✓
Monitor DNS query sizes and frequencies
Why this is correct
Unusually large or frequent queries may indicate tunneling.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use a DNS sinkhole
Why this is correct
A sinkhole redirects known malicious domains, preventing exfiltration.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable recursive DNS on the internal DNS server
Why it's wrong here
This does not block tunneling through external recursive resolvers.
✗
Implement DNSSEC
Why it's wrong here
DNSSEC ensures DNS data integrity but does not detect tunneling.
✗
Block all DNS queries to external servers
Why it's wrong here
This would prevent legitimate DNS resolution and internet access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that DNSSEC or disabling recursion can stop DNS tunneling, but DNSSEC only signs records and does not inspect payloads, while disabling recursion breaks internal resolution without affecting external tunneling via forwarders.
Detailed technical explanation
How to think about this question
DNS tunneling exploits the fact that DNS queries can carry arbitrary data in the subdomain labels (e.g., base64-encoded payloads). Under the hood, the attacker encodes data into DNS query names, and the response can carry data in TXT or NULL records. Real-world scenarios include using tools like dnscat2 or Iodine, which can create a covert channel over UDP port 53. Monitoring tools like Zeek (Bro) or Security Onion can analyze DNS traffic for entropy spikes, long domain names, or high query rates to detect such activity.
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 200-201 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.
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.
Security Concepts — This question tests Security Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Monitor DNS query sizes and frequencies — Option A is correct because DNS tunneling often involves unusually large query sizes (e.g., encoded data in subdomains) and abnormal query frequencies (e.g., thousands of requests per minute). Monitoring these metrics allows analysts to spot deviations from baseline behavior, which is a key detection technique for exfiltration via DNS. Option B is correct because a DNS sinkhole redirects malicious or suspicious DNS queries to a controlled IP address, effectively blocking the resolution of domains used for tunneling and preventing data from reaching the attacker's command-and-control server.
What should I do if I get this 200-201 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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