This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 security team observes repeated Nmap scans from an external IP address. The scans show fragmented IP packets. Which evasion technique is the attacker using?
Fragmentation
Fragmentation splits packets to evade detection.
Decoy scan
Why wrong: Decoy scan uses fake source IPs.
ACK scan
Why wrong: ACK scan maps firewall rules, not evasion via fragmentation.
Idle scan
Why wrong: Idle scan uses a zombie host to spoof the scan source.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Fragmentation
The attacker is using fragmentation to evade detection by splitting the Nmap probe packets into smaller fragments. This technique bypasses simple packet filters and intrusion detection systems (IDS) that lack IP fragment reassembly capabilities, as the fragments are typically allowed through individually. Nmap's `-f` flag or `--mtu` option is used to send fragmented IP packets, making the scan less conspicuous.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Fragmentation
Why this is correct
Fragmentation splits packets to evade detection.
Related concept
Read the scenario before looking for a memorised answer.
Decoy scan
Why it's wrong here
Decoy scan uses fake source IPs.
ACK scan
Why it's wrong here
ACK scan maps firewall rules, not evasion via fragmentation.
Idle scan
Why it's wrong here
Idle scan uses a zombie host to spoof the scan source.
Common exam traps
EC-Council often tests the distinction between fragmentation and decoy scans, as candidates may confuse 'splitting packets' with 'spoofing IPs' due to both being evasion techniques.
Detailed technical explanation
Fragmentation works by splitting the TCP header across multiple IP fragments, so that the destination port number may appear in a later fragment, evading stateful inspection firewalls that only check the first fragment. Nmap's `-f` option sets the fragment size to 8 bytes (or 16 with `-ff`), forcing the IP layer to create small fragments. Some older IDS/IPS systems reassemble fragments in a linear fashion, but attackers can use overlapping fragments (e.g., with `--send-eth` and custom MTU) to cause reassembly confusion.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CEH 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
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FAQ
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
The correct answer is: Fragmentation — The attacker is using fragmentation to evade detection by splitting the Nmap probe packets into smaller fragments. This technique bypasses simple packet filters and intrusion detection systems (IDS) that lack IP fragment reassembly capabilities, as the fragments are typically allowed through individually. Nmap's `-f` flag or `--mtu` option is used to send fragmented IP packets, making the scan less conspicuous.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This CEH practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CEH exam.
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