The answer is that an overly aggressive IPS signature set is the most likely cause of blocking legitimate web traffic. This happens because an inline IPS actively inspects every packet against its signature database, and when signatures are tuned too broadly or contain known false positives, they will match benign traffic patterns that resemble malicious activity. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your understanding of the trade-off between security and availability—a common trap is confusing a false positive with a false negative, where the latter would miss real attacks. Remember that after deployment, users reporting blocked legitimate traffic points directly to signature sensitivity, not to a network misconfiguration or a missing update. Memory tip: “Aggressive signatures block the good guys first.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network 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.
An organization has implemented a network-based intrusion prevention system (IPS) in inline mode. After deployment, users report that legitimate web traffic is being blocked. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
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
✓
The IPS signature set is too aggressive or includes false positives.
An inline IPS actively inspects and can block traffic based on its signature database. If the signature set is too aggressive or contains false positives, legitimate traffic matching those signatures will be incorrectly blocked. This is the most direct cause of blocking legitimate web traffic after deployment.
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.
✗
The IPS is not receiving traffic due to a tap failure.
Why it's wrong here
Tap failure would result in no traffic, not just blocking.
✗
The IPS is placed behind the firewall instead of in front.
Why it's wrong here
Placement does not directly cause blocking of legitimate traffic.
✗
The IPS is configured in promiscuous mode.
Why it's wrong here
Promiscuous mode is passive and does not block traffic.
✓
The IPS signature set is too aggressive or includes false positives.
Why this is correct
Aggressive signatures can flag legitimate traffic as malicious, causing blocks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between inline and promiscuous modes, where candidates mistakenly think promiscuous mode can block traffic, but only inline mode allows active blocking.
Detailed technical explanation
How to think about this question
IPS signatures can be tuned with thresholds and exceptions to reduce false positives. For example, a signature for SQL injection might trigger on a common parameter name like 'id' in a URL, blocking legitimate requests. Real-world deployments often require initial tuning in monitor-only mode before enabling blocking to avoid disrupting business operations.
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 SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
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: The IPS signature set is too aggressive or includes false positives. — An inline IPS actively inspects and can block traffic based on its signature database. If the signature set is too aggressive or contains false positives, legitimate traffic matching those signatures will be incorrectly blocked. This is the most direct cause of blocking legitimate web traffic after deployment.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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