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200-201 A SOC analyst for a school district Practice Question
You are a SOC analyst for a school district. The district uses a Cisco Firepower NGFW for traffic inspection and a SIEM for log aggregation. A teacher reports that her workstation is slow and unresponsive. You check the SIEM and see that the workstation (IP 10.1.2.10) has been generating thousands of DNS queries to a domain 'badstuff.example.com' over the past hour. The firewall logs show that the workstation also made many outbound connections to IP 203.0.113.50 on port 80. The DNS queries are for various random subdomains of 'badstuff.example.com'. The school's web filter has no policy for this domain. The user is not technical and cannot explain the behavior. What is the most likely cause and the appropriate first action?
⚠ Common exam trap
Cisco often tests the principle that containment (isolation) is the first priority in an active compromise, not remediation (scanning) or policy updates, and that DNS tunneling is a real exfiltration technique, not a false positive.
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
✓
Isolate the workstation from the network and add the domain to the block list
The workstation is generating thousands of DNS queries for random subdomains of 'badstuff.example.com' and making outbound connections to IP 203.0.113.50 on port 80. This behavior is classic DNS tunneling, where an infected host encodes data in DNS queries to bypass security controls. Isolating the workstation stops the immediate threat and data exfiltration, while adding the domain to the block list prevents further communication from other hosts. A full antivirus scan is insufficient because DNS tunneling malware often evades signature-based detection and requires network containment first.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run a full antivirus scan on the workstation
Why it's wrong here
A scan is important but should be done after isolation to avoid ongoing data theft.
- ✓
Isolate the workstation from the network and add the domain to the block list
Why this is correct
Isolation stops the DNS tunneling immediately; blocking the domain prevents future connections.
- ✗
Update the web filter to block the domain and continue monitoring
Why it's wrong here
Updating the filter does not remediate the already compromised workstation.
- ✗
Ignore the alert because DNS tunneling is not a real threat
Why it's wrong here
DNS tunneling is a known exfiltration technique and should be treated seriously.
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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.