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 poisoning injects forged records into a resolver's cache so subsequent lookups return attacker-controlled addresses; it does not generate bulk random-subdomain queries returning NXDOMAIN. It is tempting because both involve DNS abuse, but poisoning targets resolver cache integrity, whereas the observed pattern indicates domain generation algorithm activity.
- ✗
DNS amplification attack
Why it's wrong here
Amplification spoofs a victim's source address and sends small queries to open resolvers, producing large responses aimed at the victim; the queries here originate from the analyst's monitored host and return NXDOMAIN. It is tempting because both involve high DNS query volume, but amplification is a reflection attack, not local DGA lookups.
- ✗
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 large volumes of pseudo-random subdomain queries, most of which fail because only a few are pre-registered by the attacker. The NXDOMAIN responses for random subdomains under one domain precisely match this rendezvous technique.
Go deeper
Related to this question
About these practice questions
This 200-201 question is part of Courseiva's 968-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.