The correct answer is to create a firewall rule blocking traffic from the thermostat’s MAC address to the external IP. This targeted, least-disruptive mitigation stops the suspicious communication without affecting other devices on the IoT VLAN, preserving network functionality while keeping the thermostat online for forensic analysis. On the CEH exam, this scenario tests your ability to apply granular access controls during an IoT suspicious traffic investigation firewall rule implementation, distinguishing it from broader actions like disabling the entire VLAN or blocking all outbound traffic. A common trap is choosing to isolate the device by removing it from the network, which destroys visibility into the threat. Remember the memory tip: “MAC and IP, not VLAN-wide” — always block at the device-address level first to maintain investigative access.
CEH Wireless, IoT and Cloud Security Practice Question
This CEH practice question tests your understanding of wireless, iot and cloud security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A security analyst notices unusual traffic from a smart thermostat to an external IP address. The thermostat is on a separate IoT VLAN. Which action should the analyst take to investigate and mitigate the threat?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a firewall rule to block traffic from the thermostat's MAC address to the external IP.
Option D is correct because creating a firewall rule to block traffic from the thermostat's MAC address to the specific external IP is a targeted, least-disruptive mitigation. It preserves the IoT VLAN's functionality for other devices while stopping the suspicious communication. This approach allows the analyst to investigate further without losing visibility into the threat, as the thermostat remains on the network for forensic analysis.
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.
✗
Disconnect the thermostat from the network.
Why it's wrong here
Disconnecting might be too disruptive without confirming the threat.
✗
Block all outbound traffic from the IoT VLAN.
Why it's wrong here
This would block all IoT devices, not just the suspicious one.
✗
Uninstall the companion app from the user's smartphone.
Why it's wrong here
The app may not be the source; the device itself is communicating.
✓
Create a firewall rule to block traffic from the thermostat's MAC address to the external IP.
Why this is correct
This precisely blocks the suspicious traffic without affecting other devices.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Option A (disconnect) because it seems like an immediate containment step, but CEH emphasizes that disconnecting destroys forensic evidence and prevents further analysis, whereas a targeted firewall rule allows both mitigation and investigation.
Detailed technical explanation
How to think about this question
Under the hood, the firewall rule uses the thermostat's MAC address (Layer 2) to identify the device, combined with the destination IP (Layer 3) to create a granular access control entry (ACE). This leverages stateful inspection to drop packets matching the rule while allowing other traffic. In a real-world scenario, this approach is critical for IoT devices that may have been compromised via a firmware vulnerability (e.g., CVE-2021-27561 in some smart thermostats), where the device initiates outbound connections to a command-and-control (C2) server; blocking only that specific flow preserves the ability to capture packet captures (PCAPs) for threat hunting.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Wireless, IoT and Cloud Security — This question tests Wireless, IoT and Cloud Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a firewall rule to block traffic from the thermostat's MAC address to the external IP. — Option D is correct because creating a firewall rule to block traffic from the thermostat's MAC address to the specific external IP is a targeted, least-disruptive mitigation. It preserves the IoT VLAN's functionality for other devices while stopping the suspicious communication. This approach allows the analyst to investigate further without losing visibility into the threat, as the thermostat remains on the network for forensic analysis.
What should I do if I get this CEH question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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