This 200-201 practice question tests your understanding of network intrusion analysis. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
An analyst is investigating a potential data exfiltration. The logs show a series of DNS queries with subdomains that appear to be base64-encoded strings. Which technique is likely being used?
DNS tunneling
DNS tunneling encapsulates data in DNS queries to exfiltrate information.
DNS amplification
Why wrong: DNS amplification is a DDoS technique, not exfiltration.
Fast flux
Why wrong: Fast flux rapidly changes IP addresses, not encoding.
Domain generation algorithm
Why wrong: DGA creates random domain names, not encoding data.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DNS tunneling
DNS tunneling encodes data (e.g., exfiltrated files) into subdomains of DNS queries, which are then sent to a malicious authoritative DNS server controlled by the attacker. The base64-encoded subdomains in the logs are a classic indicator of this technique, as the attacker uses the DNS protocol to bypass network security controls and covertly transmit data.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DNS tunneling
Why this is correct
DNS tunneling encapsulates data in DNS queries to exfiltrate information.
Related concept
Read the scenario before looking for a memorised answer.
DNS amplification
Why it's wrong here
DNS amplification is a DDoS technique, not exfiltration.
Fast flux
Why it's wrong here
Fast flux rapidly changes IP addresses, not encoding.
Domain generation algorithm
Why it's wrong here
DGA creates random domain names, not encoding data.
Common exam traps
Cisco often tests the distinction between DNS tunneling (data exfiltration via subdomain encoding) and DNS amplification (a volumetric DDoS attack), so candidates must recognize that base64-encoded subdomains point to tunneling, not amplification.
Detailed technical explanation
In DNS tunneling, the attacker typically uses a tool like 'iodine' or 'dnscat2' to encode data into DNS query subdomains (e.g., 'c29tZXRoaW5nLmV4ZS5hdHRhY2tlci5jb20=') and sends them to a malicious DNS server. The server decodes the subdomain, extracts the payload, and may respond with a TXT record containing further commands or acknowledgments. Real-world scenarios often involve high volumes of TXT or NULL record queries to evade detection, as standard DNS monitoring tools may not flag unusual subdomain lengths or entropy.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
The correct answer is: DNS tunneling — DNS tunneling encodes data (e.g., exfiltrated files) into subdomains of DNS queries, which are then sent to a malicious authoritative DNS server controlled by the attacker. The base64-encoded subdomains in the logs are a classic indicator of this technique, as the attacker uses the DNS protocol to bypass network security controls and covertly transmit data.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This 200-201 practice question is part of Courseiva's free Cisco 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 200-201 exam.
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