ISC2 CC Network Security Practice Question
A security administrator is configuring a network device that monitors traffic and generates alerts when suspicious patterns are detected. The device does not block traffic. Which type of system is being deployed?
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
✓
Intrusion Detection System (IDS)
An IDS (Intrusion Detection System) is passive and only alerts, while an IPS actively blocks.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Web Application Firewall (WAF)
Why it's wrong here
A WAF inspects HTTP/HTTPS application-layer requests and can actively block them, so it neither matches the stated non-blocking behaviour nor the generic traffic-monitoring scope. It is tempting because WAFs do generate alerts on suspicious web patterns, and would be correct if the requirement were protecting a specific web application from injection or cross-site attacks.
- ✓
Intrusion Detection System (IDS)
Why this is correct
An IDS passively inspects network traffic, matching signatures or anomalies to raise alerts without dropping packets. Because the stem specifies the device monitors and alerts but does not block, an Intrusion Detection System satisfies that non-preventive constraint; an IPS would actively block traffic inline.
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Intrusion Prevention System (IPS)
Why it's wrong here
An IPS sits inline and drops or resets malicious traffic, directly contradicting the requirement that the device does not block traffic. It is tempting because an IPS performs the same signature and anomaly detection as an IDS, and would be the correct choice if the scenario demanded automatic prevention rather than alert-only monitoring.
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Next-Generation Firewall (NGFW)
Why it's wrong here
An NGFW enforces policy by permitting or denying flows, so it blocks traffic rather than merely alerting. It is tempting because NGFWs include intrusion detection signatures and application awareness, and would be correct if the requirement were inline enforcement at a network perimeter rather than passive detection.
Go deeper
Related to this question
Learn chapter
Network Security Components and Controls
Key term
IDS
An IDS is a security system that monitors network or system traffic for suspicious activity and alerts administrators to potential threats, but does not actively block them.
Key term
Intrusion Detection System
An Intrusion Detection System (IDS) is a security tool that monitors network traffic or system activities for malicious actions or policy violations and sends alerts to administrators.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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