The correct answer is to isolate the workstation from the network and add the domain to the block list. This is the appropriate first action because the behavior—thousands of DNS queries for random subdomains of 'badstuff.example.com' combined with outbound HTTP connections to a separate IP—is a textbook example of DNS tunneling detection and response, where an infected host encodes exfiltrated data within DNS queries to bypass security controls. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your ability to recognize command-and-control (C2) exfiltration techniques and prioritize containment over remediation; a common trap is choosing a full antivirus scan first, which fails because tunneling malware often evades signature-based detection. Remember the priority order: contain before clean. A useful memory tip is "DNS Dump: Disconnect, Name-block, Scan later."
200-201 Security Monitoring Practice Question
This 200-201 practice question tests your understanding of security monitoring. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Clue confirmation
The clue words "first", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
DNS tunneling works by encoding data into DNS query names (e.g., base64-encoded chunks as subdomains) and receiving responses via DNS records, allowing covert communication over UDP port 53. The outbound connections to IP 203.0.113.50 on port 80 suggest a secondary command-and-control channel or data exfiltration over HTTP, which is typical for multi-stage malware. In a school district environment, the lack of a web filter policy for the domain indicates it was likely registered recently or uses domain-generation algorithms (DGAs) to evade static block lists.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Monitoring — This question tests Security Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first", "most likely". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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