CAS-004 Security Architecture Practice Question
A company is adopting a defense-in-depth strategy. Which of the following is an example of a preventive control at the network layer?
⚠ Common exam trap
Test-takers frequently confuse detective controls (IDS, SIEM) with preventive controls; candidates often assume that monitoring tools prevent attacks, but they only detect and alert.
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
✓
Network segmentation
Network segmentation is a preventive control because it proactively restricts lateral movement by dividing the network into isolated segments using firewalls, VLANs, or subnets. This limits an attacker's ability to move freely after compromising a host, thereby preventing the spread of an attack. It operates at the network layer (Layer 3) and enforces access control policies between segments, making it a classic example of a preventive control in a defense-in-depth strategy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Intrusion Detection System (IDS)
Why it's wrong here
An IDS detects and alerts on malicious traffic but does not block it, so it is detective, not preventive. Detection is tempting because it operates at the network layer, and an IDS would be the right answer if the question asked for a detective control at that layer.
- ✗
Security Information and Event Management (SIEM)
Why it's wrong here
SIEM aggregates and correlates logs to detect and alert on events; it is detective, not preventive, and it does not block traffic at the network layer. It is tempting because SIEM is central to defence in depth, but it would be the correct choice for a monitoring or detection control, not prevention.
- ✓
Network segmentation
Why this is correct
Network segmentation restricts lateral movement by dividing the network into isolated zones with enforced access rules, blocking traffic before it reaches targets. This preventive, network-layer control satisfies the defense-in-depth requirement by stopping intrusion attempts rather than merely detecting them.
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Penetration testing
Why it's wrong here
Penetration testing validates existing controls by simulating attacks; it is an assessment activity, not a preventive network-layer control, and it blocks nothing. It is tempting because it strengthens defence in depth, but it would be correct when the question asks how controls are verified, not how traffic is prevented.
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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 CompTIA exam blueprint
This CAS-005 practice question is part of Courseiva's free CompTIA 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 CAS-005 exam.