The answer is that the IDS signature is incorrectly configured, because an ICMP Echo payload of exactly 65535 bytes is technically impossible under normal network operation. The total ICMP packet size is limited to 65535 bytes, but this includes the mandatory IP header (20 bytes) and ICMP header (8 bytes), so the actual data payload can never exceed 65507 bytes. A payload of exactly 65535 bytes would require the entire packet to exceed the maximum IP datagram size, making it a clear false positive rather than a genuine Ping of Death attack. On the Cisco CyberOps Associate 200-201 exam, this question tests your ability to distinguish between signature misconfiguration and actual overflow attacks, a common trap where analysts assume any large ICMP packet is malicious. The trusted internal server source IP further supports misconfiguration over an attack. Memory tip: remember the 65535 limit applies to the whole packet, not just the payload—subtract 28 for headers to find the real maximum.
200-201 Network Intrusion Analysis Practice Question
This 200-201 practice question tests your understanding of network intrusion analysis. 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 intrusion analyst is analyzing a series of alerts from a network-based IDS. The alerts are triggered by the signature 'OVERFLOW-ICMP-ECHO' with a payload size of 65535 bytes. The source IP is a trusted internal server. What is the most likely explanation?
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 IDS signature is incorrectly configured
The ICMP Echo (ping) payload size is limited to 65535 bytes, but the actual data portion of an ICMP packet cannot exceed 65535 minus the IP and ICMP header sizes (typically 20 + 8 = 28 bytes), making a payload of exactly 65535 bytes impossible under normal operation. Since the source IP is a trusted internal server, the most plausible cause is that the IDS signature is misconfigured—likely with an incorrect payload size threshold or a false positive trigger—rather than an actual overflow attempt.
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.
There is a network error causing packet fragmentation
Why it's wrong here
Fragmentation would not create a payload larger than the limit.
✓
The IDS signature is incorrectly configured
Why this is correct
The payload size exceeds the maximum possible, so it's a false positive.
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.
✗
The server is under a DDoS attack
Why it's wrong here
DDoS would not cause an impossible payload size.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a large ICMP payload must indicate an attack (like a Ping of Death or DDoS), but Cisco tests the understanding that a payload of exactly 65535 bytes is impossible in a single unfragmented ICMP packet, pointing to a signature misconfiguration rather than a real threat.
Detailed technical explanation
How to think about this question
ICMP Echo Request packets (Type 8) have a maximum payload size of 65535 bytes minus the IP header (20 bytes minimum) and ICMP header (8 bytes), yielding a theoretical maximum data payload of 65507 bytes. An IDS signature that matches a payload of exactly 65535 bytes is likely using a static threshold that doesn't account for header overhead, or it's a legacy signature from a time when such values were used in buffer overflow exploits (e.g., the 'Ping of Death' attack, which used fragmented ICMP packets to bypass size checks). In practice, modern operating systems reject or reassemble such packets, so a single oversized ICMP from a trusted host is almost certainly a false positive.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: The IDS signature is incorrectly configured — The ICMP Echo (ping) payload size is limited to 65535 bytes, but the actual data portion of an ICMP packet cannot exceed 65535 minus the IP and ICMP header sizes (typically 20 + 8 = 28 bytes), making a payload of exactly 65535 bytes impossible under normal operation. Since the source IP is a trusted internal server, the most plausible cause is that the IDS signature is misconfigured—likely with an incorrect payload size threshold or a false positive trigger—rather than an actual overflow attempt.
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.
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.
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. During a PCAP analysis, an analyst sees an ICMP echo reply packet that is larger than usual (2000 bytes). What is this likely indicating?
medium
A.ICMP flood
B.Fragmented packet
C.Smurf attack
✓ D.Ping of death attempt
Why D: A standard ICMP echo reply packet has a payload of 56 bytes (or 64 bytes including the ICMP header) for a total IP packet size of 84 bytes. A 2000-byte ICMP echo reply exceeds the maximum allowed size for an ICMP packet (65535 bytes for IPv4, but typical implementations limit the data portion to much smaller values). This oversized packet is characteristic of a Ping of Death attack, where the attacker sends a malformed ICMP packet that, when reassembled, causes a buffer overflow on the target system, leading to a crash or denial of service.
Last reviewed: Jun 25, 2026
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