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200-201 Practice Question: A host is infected with malware that uses DNS…
A host is infected with malware that uses DNS tunneling to exfiltrate data. Which type of analysis would best detect this activity?
⚠ Common exam trap
Cisco often tests the misconception that firewall logs or NetFlow are sufficient for detecting application-layer tunneling, when in fact only DNS-specific logs provide the granularity to see the encoded payloads within DNS queries.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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DNS log analysis
DNS tunneling encodes exfiltrated data within DNS queries or responses, often using TXT or A record types to bypass network security controls. DNS log analysis is the most direct detection method because it reveals anomalous patterns such as unusually long domain names, excessive NXDOMAIN responses, or high volumes of DNS traffic to a single external server, which are hallmarks of tunneling activity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DNS log analysis
Why this is correct
DNS log analysis inspects query records for anomalies such as unusually long subdomains, high query volumes, or TXT record abuse, which are hallmarks of DNS tunnelling. Since the malware exfiltrates data through DNS queries, examining these logs directly satisfies the stem's requirement to detect the tunnelling activity.
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Windows event log analysis
Why it's wrong here
Windows event logs capture authentication, process and service activity on the host, not DNS query strings leaving the network, so tunnelled data encoded in query names is never recorded. It is tempting because log analysis is the right choice for detecting suspicious process execution, privilege escalation or lateral movement on the endpoint itself.
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Firewall log analysis
Why it's wrong here
Firewall logs record permitted and denied connections by IP address and port; DNS tunnelling travels over allowed port 53 to a legitimate resolver, so the queries appear normal. It is tempting because firewall logs are the correct choice for detecting blocked inbound scans or connections to known malicious IP addresses.
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NetFlow analysis
Why it's wrong here
NetFlow records IP headers, ports and byte counts, not DNS query names or payload contents, so tunnelled exfiltration hidden inside DNS queries stays invisible. It is tempting because flow analysis excels at spotting volumetric anomalies and beaconing to unfamiliar external hosts, which is where it would be the correct choice.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.