200-201 Security Monitoring Practice Question
An analyst captures traffic and sees a high number of DNS queries for random subdomains under a single domain, all returning NXDOMAIN. This pattern is typical of which malicious activity?
⚠ Common exam trap
Cisco often tests the distinction between DGA activity and DNS tunneling by emphasizing that DGA generates random, unresolvable subdomains (NXDOMAIN), while tunneling uses structured subdomains that typically receive valid responses (e.g., TXT records) to exfiltrate data.
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
✓
Domain generation algorithm (DGA) activity
D is correct because a high volume of DNS queries for random subdomains under a single domain, all returning NXDOMAIN, is a classic indicator of Domain Generation Algorithm (DGA) activity. Malware uses DGA to generate thousands of pseudo-random domain names to contact a command-and-control (C2) server; the NXDOMAIN responses indicate that the generated domains are not yet registered or have been sinkholed.
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 cache poisoning
Why it's wrong here
Cache poising corrupts DNS records, not generates random queries.
- ✗
DNS amplification attack
Why it's wrong here
Amplification uses spoofed source IPs to amplify traffic, not random subdomains.
- ✗
DNS tunneling
Why it's wrong here
DNS tunneling encodes data in DNS queries, but usually uses fewer, longer queries.
- ✓
Domain generation algorithm (DGA) activity
Why this is correct
DGA malware generates many random subdomains to bypass domain blacklists.
Go deeper
Related to this question
About these practice questions
This 200-201 question is part of Courseiva's 979-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
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.