The answer is to increase the packet size threshold. This tuning action directly addresses the root cause of false positives by raising the minimum packet size that triggers the signature, ensuring that legitimate large ICMP traffic is ignored while still capturing true oversized attack packets, such as those exceeding 65,535 bytes in a fragmented ICMP echo attack. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your understanding of IPS signature tuning to reduce false positives without sacrificing detection—a common trap is choosing to disable the rule entirely or lower the threshold, which either eliminates detection or worsens noise. Remember the memory tip: “Raise the size, lower the noise” to keep detection sharp while filtering out benign traffic.
200-201 Network Intrusion Analysis Practice Question
This 200-201 practice question tests your understanding of network intrusion analysis. 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 Cisco Firepower sensor is generating a high number of false positives from a rule that triggers on large ICMP packets. The analyst suspects the rule threshold is too low. Which tuning action most effectively reduces false positives while maintaining detection of actual attacks?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the packet size threshold.
Increasing the packet size threshold (Option D) directly addresses the root cause of the false positives: the rule is triggering on legitimate large ICMP packets that are below the actual attack size. By raising the threshold to a value that still captures known attack vectors (e.g., ICMP echo requests exceeding 65,535 bytes in a fragmented attack), the sensor reduces noise while preserving detection of true malicious oversized packets. This is the most effective tuning action because it adjusts the detection parameter without disabling or bypassing the rule.
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.
✗
Change the rule action from alert to drop.
Why it's wrong here
Changing action does not reduce false positives; it still triggers.
✗
Disable the rule entirely.
Why it's wrong here
Disabling the rule removes detection capability.
✗
Add an exception for trusted source IPs.
Why it's wrong here
Exceptions help but are less systematic than adjusting the threshold.
✓
Increase the packet size threshold.
Why this is correct
This directly addresses the cause of false positives without disabling detection.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that changing the rule action (e.g., to drop) or adding exceptions is the best way to reduce false positives, when in fact the most precise and effective method is to adjust the detection threshold parameter that is causing the false positives.
Detailed technical explanation
How to think about this question
ICMP packet size thresholds are typically configured in bytes, and the Cisco Firepower intrusion policy uses the 'size' keyword in Snort rules (e.g., 'dsize:>1024') to match packets exceeding a certain length. In real-world scenarios, legitimate applications like path MTU discovery or VPN keepalives may send ICMP packets up to 1500 bytes, while actual attacks often use fragmented ICMP packets that exceed the IP maximum transmission unit (MTU) when reassembled. Tuning the threshold requires analyzing baseline traffic patterns to set a value that avoids normal traffic while still catching anomalies like the 'ping of death' (ICMP echo request > 65,535 bytes) or 'ICMP flood' with large payloads.
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 practitioner preparing for the 200-201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the packet size threshold. — Increasing the packet size threshold (Option D) directly addresses the root cause of the false positives: the rule is triggering on legitimate large ICMP packets that are below the actual attack size. By raising the threshold to a value that still captures known attack vectors (e.g., ICMP echo requests exceeding 65,535 bytes in a fragmented attack), the sensor reduces noise while preserving detection of true malicious oversized packets. This is the most effective tuning action because it adjusts the detection parameter without disabling or bypassing the rule.
What should I do if I get this 200-201 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An IPS sensor is configured inline and drops traffic that triggers the signature 'OVERFLOW-ICMP-ECHO', which triggers on ICMP packets with size > 1024 bytes. A network administrator reports that legitimate network monitoring tools using large ICMP packets are being blocked. What is the best course of action?
hard
A.Increase the threshold to 2048
✓ B.Create a whitelist for the monitoring tool's source IP
C.Disable the signature entirely
D.Change the sensor mode to IDS for that signature
Why B: Option B is correct because creating a whitelist for the monitoring tool's source IP allows the IPS to continue dropping malicious oversized ICMP packets while permitting legitimate traffic from known, trusted sources. This maintains security for the rest of the network without disabling the signature or changing its mode, which would reduce protection.
Variation 2. Which THREE factors should be considered when tuning an IPS signature? (Choose three.)
hard
A.Time of day
✓ B.Application protocol
✓ C.Source and destination IPs
✓ D.Signature severity
E.Packet length
Why B: Application protocol (B) is critical because IPS signatures are protocol-aware and must match the specific protocol context (e.g., HTTP, SMTP, DNS) to avoid false positives. Tuning based on the protocol ensures the signature only inspects traffic where the vulnerability or exploit is relevant, such as applying a SQL injection signature only to HTTP traffic.
Last reviewed: Jun 25, 2026
Question Discussion
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