200-201 Security Monitoring Practice Question
A threat hunter reviews Cisco Umbrella DNS logs and notices repeated queries for randomly generated subdomains under a single parent domain, each resolved by a different authoritative name server. The hunter suspects DNS tunneling. Which additional artifact would most directly confirm command-and-control activity rather than legitimate DNS behavior?
⚠ Common exam trap
The trap here is treating generic DNS anomalies such as short TTLs or NXDOMAIN spikes as proof of tunneling, when only encoded payload content in responses confirms data transfer.
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
✓
TXT record responses containing long base64-encoded strings
DNS tunneling moves data inside DNS queries and responses, most commonly using TXT records because they support larger payloads. Long base64-encoded strings in TXT responses, paired with random subdomains and rotating authoritative servers, show that the DNS channel is carrying encoded command-and-control or exfiltration data. This artifact distinguishes malicious tunneling from ordinary DNS resolution patterns.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
High volume of A records with short TTL values
Why it's wrong here
Short TTLs are common in content delivery networks, dynamic DNS, and load-balanced services, so they are not specific to tunneling. While malware authors sometimes use low TTLs to rotate infrastructure quickly, legitimate services do the same. This artifact alone does not distinguish command-and-control from normal high-availability DNS design. The hunter needs evidence of encoded data transfer or a known malicious destination, not just cache timing characteristics that many benign domains share.
- ✗
NXDOMAIN responses for nonexistent subdomains
Why it's wrong here
NXDOMAIN responses occur constantly in legitimate networks due to typos, stale caches, and search domain suffixes. While some malware uses domain generation algorithms that produce many NXDOMAIN results, that pattern indicates failed resolution attempts, not successful data transfer. The scenario describes subdomains that resolve successfully through different name servers, so NXDOMAIN is not the confirming artifact. The hunter needs evidence of encoded content in successful responses, not failed lookups.
- ✓
TXT record responses containing long base64-encoded strings
Why this is correct
DNS tunneling frequently uses TXT records because they can carry arbitrary data and are often permitted through firewalls. Long base64-encoded strings in TXT responses indicate that the DNS channel is transporting encoded payloads, which is a strong signal of command-and-control or exfiltration. Combined with the random subdomain pattern, this artifact directly confirms that data is being moved over DNS rather than merely resolved. Legitimate TXT records, such as SPF or DKIM, have structured formats and predictable lengths.
- ✗
Queries originating from multiple internal VLANs
Why it's wrong here
Multiple VLANs generating DNS queries is normal in an enterprise where each subnet has its own resolver or forwarder. This pattern could simply reflect broad user activity or a misconfigured client, and it does not demonstrate encoded data transfer. The hunter is looking for evidence of tunneling, which requires inspecting the content and structure of the DNS payloads. Source subnet diversity is a contextual detail, not a confirming artifact of command-and-control over DNS.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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.