200-201 Network Intrusion Analysis Practice Question
An analyst detects traffic from an internal host that periodically sends small DNS queries to a domain with high entropy subdomains (e.g., 'a3k9f2.example.com'). The domain is not on any blocklist, and the query intervals are consistent every 60 seconds. Which technique is most likely being used?
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
✓
DNS tunnelling for C2 communication
DNS tunnelling encodes data in subdomain queries, and periodic beaconing is common for C2. High entropy subdomains and regular intervals suggest DNS tunnelling for C2.
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 tunnelling for C2 communication
Why this is correct
High-entropy subdomains carrying small queries at fixed 60-second intervals indicate data encoded into DNS labels and exfiltrated or commanded through recursive resolvers. The absence from blocklists and regular beaconing fit DNS tunnelling used for command-and-control rather than normal resolution.
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DNS amplification attack
Why it's wrong here
Amplification floods a victim with large responses to spoofed queries; here the host sends small queries at fixed intervals, which is beaconing, not reflection. It is tempting because both abuse DNS, and amplification would be correct if the traffic were large responses aimed at a third party.
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Normal DNS resolution for a dynamic DNS service
Why it's wrong here
Dynamic DNS clients update a provider at long intervals with stable, low-entropy names, not fresh high-entropy subdomains every 60 seconds. It is tempting because periodic DNS traffic resembles legitimate updates, and dynamic DNS would be correct for a host publishing a changing address under one consistent name.
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DNS cache poisoning attempt
Why it's wrong here
Cache poisoning corrupts resolver records so victims are redirected to attacker infrastructure; it does not generate recurring high-entropy queries from an internal host. The periodic 60-second beaconing with random subdomains points to DNS tunnelling or command-and-control exfiltration. Poisoning would be the answer if the scenario described forged responses injected into a resolver's cache.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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