- A
The IDS is dropping packets with the SYN flag set
IDS can be configured to drop packets based on flags. SYN scans send only SYN, while connect scans send a full handshake; the IDS may allow the latter.
- B
The server is using a firewall that blocks all inbound SYN packets
Why wrong: A firewall blocking all SYN packets would also prevent TCP connect scans, as they also use SYN packets.
- C
The analyst's packets are being fragmented, causing them to be dropped
Why wrong: Fragmentation evasion splits packets; it would affect both SYN and connect scans similarly, not selectively block SYN scans.
- D
The target is using a honeypot that responds to all connection attempts
Why wrong: A honeypot would respond to both scan types, not cause SYN scans to fail while connect scans succeed.
CEH Footprinting, Reconnaissance and Scanning Practice Question
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
During a penetration test, a security analyst observes that Nmap SYN scans to a target server are not returning any results, but TCP connect scans succeed. The server is running an IDS. Which evasion technique is the analyst MOST likely encountering?
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 choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The IDS is dropping packets with the SYN flag set
The IDS is configured to drop packets with only the SYN flag set, which is the hallmark of a SYN scan. This evasion technique forces the attacker to use a full TCP connect scan (which completes the three-way handshake) to bypass the IDS detection. The IDS drops the initial SYN packet, preventing the scan from receiving any response, while a full connect scan is allowed because it mimics legitimate traffic.
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 IDS is dropping packets with the SYN flag set
Why this is correct
IDS can be configured to drop packets based on flags. SYN scans send only SYN, while connect scans send a full handshake; the IDS may allow the latter.
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 using a firewall that blocks all inbound SYN packets
- ✗
The analyst's packets are being fragmented, causing them to be dropped
Why it's wrong here
Fragmentation evasion splits packets; it would affect both SYN and connect scans similarly, not selectively block SYN scans.
- ✗
The target is using a honeypot that responds to all connection attempts
Why it's wrong here
A honeypot would respond to both scan types, not cause SYN scans to fail while connect scans succeed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a firewall is blocking the SYN packets, but the question specifies an IDS is running, and the key distinction is that a firewall would block both scan types, while an IDS can selectively drop only half-open SYN packets to evade detection.
Trap categories for this question
Similar concept trap
Fragmentation evasion splits packets; it would affect both SYN and connect scans similarly, not selectively block SYN scans.
Detailed technical explanation
How to think about this question
SYN scans (half-open scans) send a TCP packet with only the SYN flag set and do not complete the handshake, making them stealthier but easily detected by IDS that monitor for incomplete connections. An IDS can be configured with a rule to drop packets that have the SYN flag set and no other flags (e.g., using iptables `--tcp-flags SYN SYN`), forcing attackers to use full connect scans that complete the three-way handshake. In real-world scenarios, this technique is often combined with rate limiting to further hinder reconnaissance.
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 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
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.
- →
Footprinting, Reconnaissance and Scanning — study guide chapter
Learn the concepts, then practise the questions
- →
Footprinting, Reconnaissance and Scanning practice questions
Targeted practice on this topic area only
- →
All CEH questions
1,010 questions across all exam domains
- →
Certified Ethical Hacker CEH study guide
Full concept coverage aligned to exam objectives
- →
CEH practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related CEH practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Footprinting, Reconnaissance and Scanning practice questions
Practise CEH questions linked to Footprinting, Reconnaissance and Scanning.
Enumeration and System Hacking practice questions
Practise CEH questions linked to Enumeration and System Hacking.
Malware, Social Engineering and Network Attacks practice questions
Practise CEH questions linked to Malware, Social Engineering and Network Attacks.
Web Application and Injection Attacks practice questions
Practise CEH questions linked to Web Application and Injection Attacks.
Introduction to Ethical Hacking practice questions
Practise CEH questions linked to Introduction to Ethical Hacking.
Scanning Networks and Enumeration practice questions
Practise CEH questions linked to Scanning Networks and Enumeration.
Vulnerability Analysis and System Hacking practice questions
Practise CEH questions linked to Vulnerability Analysis and System Hacking.
Advanced Topics: Wireless, Cloud, IoT, Cryptography practice questions
Practise CEH questions linked to Advanced Topics: Wireless, Cloud, IoT, Cryptography.
Footprinting and Reconnaissance practice questions
Practise CEH questions linked to Footprinting and Reconnaissance.
Network and Web Application Attacks practice questions
Practise CEH questions linked to Network and Web Application Attacks.
Wireless, IoT and Cloud Security practice questions
Practise CEH questions linked to Wireless, IoT and Cloud Security.
Cryptography and Malware Analysis practice questions
Practise CEH questions linked to Cryptography and Malware Analysis.
Practice this exam
Start a free CEH practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this CEH question test?
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The IDS is dropping packets with the SYN flag set — The IDS is configured to drop packets with only the SYN flag set, which is the hallmark of a SYN scan. This evasion technique forces the attacker to use a full TCP connect scan (which completes the three-way handshake) to bypass the IDS detection. The IDS drops the initial SYN packet, preventing the scan from receiving any response, while a full connect scan is allowed because it mimics legitimate traffic.
What should I do if I get this CEH 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 →
Last reviewed: Jun 24, 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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.