GCIH Network and Log Investigations Practice Question
An incident handler is examining a packet capture from a compromised workstation and observes a series of DNS queries for domains like 'a1b2c3d4e5.exfil.example.com', each followed by a large TXT response. The queries are sent at regular 30-second intervals, and the subdomains contain random-looking alphanumeric strings. Which of the following techniques is MOST likely being used by the attacker?
⚠ Common exam trap
It's easy for candidates to confuse DNS tunneling with DGA, but DGA typically results in failed queries, while tunneling involves successful data exchange.
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 tunneling for data exfiltration
The correct answer is DNS tunneling for data exfiltration. The combination of regular intervals, random subdomains, and large TXT responses is a hallmark of DNS tunneling, where attackers encode data in DNS queries and responses to bypass network filters. This allows stealthy exfiltration even when other protocols are blocked. Fast-flux, cache poisoning, and DGA do not involve such data transfer 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.
- ✗
DNS cache poisoning to redirect traffic
Why it's wrong here
Cache poisoning aims to inject false DNS records into a resolver's cache, redirecting users to malicious sites. It does not generate a series of queries with random subdomains and large TXT responses from a single workstation. The behavior indicates data exfiltration, not poisoning. Thus, this is not the most likely technique.
- ✓
DNS tunneling for data exfiltration
Why this is correct
The regular intervals, random subdomains, and large TXT responses are classic signs of DNS tunneling. Attackers encode stolen data in DNS queries or responses to bypass firewalls that allow DNS. The consistent timing and high volume of TXT records indicate automated exfiltration, not normal DNS behavior. This scenario matches the pattern of tools like iodine or dnscat2.
- ✗
Fast-flux DNS for resilience
Why it's wrong here
Fast-flux involves rapidly changing DNS A records to multiple IP addresses, often for botnet resilience. It does not typically involve large TXT responses or random subdomains with encoded data. The observed pattern focuses on data transfer via TXT records, not IP address rotation. Therefore, fast-flux is not the primary technique here.
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Domain generation algorithm (DGA) for C2
Why it's wrong here
DGAs generate many domain names for command-and-control, but they typically result in failed DNS queries (NXDOMAIN) as the botnet tries to find an active server. Here, the queries receive large TXT responses, suggesting successful data transfer. DGA is about resilience, not exfiltration. Therefore, DGA is not the best fit.
About these practice questions
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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 GIAC exam blueprint
This GCIH practice question is part of Courseiva's free GIAC 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 GCIH exam.