The answer is a Network-based Intrusion Detection System (NIDS). This is the correct choice because a NIDS passively monitors network traffic and generates alerts when suspicious patterns are detected, but it operates out-of-band and cannot drop packets, meaning it poses zero risk of blocking legitimate traffic. In contrast, a Network-based Intrusion Prevention System (NIPS) sits inline and can actively block traffic, which introduces the very risk the organization wants to avoid. On the ISC2 Certified in Cybersecurity CC exam, this question tests your understanding of the fundamental difference between detection and prevention systems—a common trap is confusing NIDS with NIPS when the scenario emphasizes “no blocking.” Remember the keyword “detect without blocking” directly points to NIDS. For a quick memory tip: think of the “D” in NIDS as “Detect only, no Drop,” while the “P” in NIPS stands for “Prevent and possibly block.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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.
An organization wants to detect and alert on potential network intrusions but does not want to risk blocking legitimate traffic. Which system should they deploy?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Network-based Intrusion Detection System (NIDS)
A Network-based Intrusion Detection System (NIDS) passively monitors network traffic and generates alerts when suspicious patterns are detected, but it does not take any inline action to block traffic. This makes it the correct choice for an organization that wants to detect and alert on potential intrusions without any risk of blocking legitimate traffic, as the NIDS operates out-of-band and cannot drop packets.
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.
✓
Network-based Intrusion Detection System (NIDS)
Why this is correct
A NIDS is passive and only alerts on potential intrusions without blocking traffic, avoiding false positives that block legitimate traffic.
Related concept
Read the scenario before looking for a memorised answer.
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Unified Threat Management (UTM) appliance
Why it's wrong here
UTM includes multiple functions often including blocking, which may block legitimate traffic.
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Firewall with deep packet inspection
Why it's wrong here
A firewall with DPI can block traffic, presenting a risk of blocking legitimate traffic.
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Network-based Intrusion Prevention System (NIPS)
Why it's wrong here
A NIPS blocks traffic inline, which could block legitimate traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between detection (IDS) and prevention (IPS) by emphasizing that an IDS is passive and out-of-band, while an IPS is inline and can block traffic, so the trap here is confusing the alert-only capability of NIDS with the active blocking of NIPS or UTM appliances.
Detailed technical explanation
How to think about this question
A NIDS typically uses a network tap or SPAN port to receive a copy of traffic, allowing it to analyze packets without being in the forwarding path. This out-of-band deployment ensures zero latency impact and no single point of failure for traffic flow, but it also means the NIDS cannot prevent an attack in real time—it can only alert after the fact. In contrast, a NIPS uses inline mode with specialized ASICs to enforce signatures at wire speed, which can cause false positives that drop legitimate traffic.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Network-based Intrusion Detection System (NIDS) — A Network-based Intrusion Detection System (NIDS) passively monitors network traffic and generates alerts when suspicious patterns are detected, but it does not take any inline action to block traffic. This makes it the correct choice for an organization that wants to detect and alert on potential intrusions without any risk of blocking legitimate traffic, as the NIDS operates out-of-band and cannot drop packets.
What should I do if I get this CC 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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