This CS0-003 practice question tests your understanding of security operations. 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 SOC analyst receives an alert about a potential data exfiltration via DNS tunneling. Which of the following tools would best help the analyst investigate the alert?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Endpoint Detection and Response (EDR)
Why wrong: EDR may capture process and network connections but not necessarily the full DNS payload.
Antivirus logs
Why wrong: Antivirus logs do not capture DNS traffic details.
NetFlow
Why wrong: NetFlow provides flow metadata but not the content of DNS queries.
PCAP capture
Full packet capture allows examination of DNS payloads to detect tunneling.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
PCAP capture
PCAP capture (D) is the correct tool because DNS tunneling involves encoding data within DNS queries and responses, which can only be fully analyzed by inspecting the raw packet payloads. PCAP files allow the analyst to examine the actual DNS packet contents, including query names, response records, and timing patterns, which are essential for detecting anomalous DNS traffic indicative of tunneling.
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.
Endpoint Detection and Response (EDR)
Why it's wrong here
EDR may capture process and network connections but not necessarily the full DNS payload.
Antivirus logs
Why it's wrong here
Antivirus logs do not capture DNS traffic details.
NetFlow
Why it's wrong here
NetFlow provides flow metadata but not the content of DNS queries.
PCAP capture
Why this is correct
Full packet capture allows examination of DNS payloads to detect tunneling.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the distinction between metadata-only tools (NetFlow) and full-packet capture (PCAP), expecting candidates to recognize that only PCAP provides the granularity needed for protocol-specific abuse like DNS tunneling.
Detailed technical explanation
DNS tunneling exploits the fact that DNS queries can contain arbitrary data in the domain name field (up to 255 bytes per label, 253 bytes total). Tools like dnscat2 or Iodine encode exfiltrated data as subdomains, and the server responds with encoded data in TXT or CNAME records. PCAP analysis with Wireshark or tshark allows filtering on DNS query lengths, entropy analysis of domain names, and tracking of unusual query volumes per client.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
What to study next
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FAQ
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
The correct answer is: PCAP capture — PCAP capture (D) is the correct tool because DNS tunneling involves encoding data within DNS queries and responses, which can only be fully analyzed by inspecting the raw packet payloads. PCAP files allow the analyst to examine the actual DNS packet contents, including query names, response records, and timing patterns, which are essential for detecting anomalous DNS traffic indicative of tunneling.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This CS0-003 practice question is part of Courseiva's free CompTIA 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 CS0-003 exam.
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