Quick Answer
The answer is the TCP connect scan (-sT). This is correct because a SYN scan (-sS) only sends a SYN packet and waits for a SYN-ACK, which a spoofing security appliance can fake for every port, making all 1000 TCP ports appear open. In contrast, a TCP connect scan completes the full three-way handshake by sending an ACK; if the port is actually closed, the target’s operating system will respond with a RST packet, overriding the appliance’s deceptive SYN-ACK. On the CEH exam, this scenario tests your understanding of how stateful firewalls and intrusion prevention systems can manipulate half-open scans, and it often appears as a trap where testers mistakenly choose the faster SYN scan. A key memory tip: think of the TCP connect scan as “finishing the conversation”—if the other side hangs up with a RST, the port is closed; if it stays connected, it’s truly open.
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. 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.
A penetration tester observes that an Nmap SYN scan shows all 1000 TCP ports as open. The tester suspects the target is using a security appliance that responds with SYN-ACK to all connection attempts, regardless of the actual port state. Which type of Nmap scan would be MOST effective in determining the true state of the ports?
UDP scan (-sU)
Why wrong: UDP scan is for UDP ports and may also be affected by spoofed responses.
Ping sweep (-sn)
Why wrong: Ping sweep only checks host availability, not port states.
TCP connect scan (-sT)
-sT completes the handshake; if the port is closed, a RST is received after the ACK, revealing the true state even if SYN-ACKs are spoofed.
Idle scan (-sI)
Why wrong: Idle scan uses a zombie host and may not address SYN-ACK spoofing.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
TCP connect scan (-sT)
Option C is correct because a TCP connect scan (-sT) completes the full three-way handshake, which forces the target to respond with a RST if the port is actually closed, even if a security appliance initially sends SYN-ACK to all ports. This distinguishes between ports that are truly open (where the handshake completes) and those that are falsely reported as open by the appliance (where the handshake fails or a RST is received).
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.
UDP scan (-sU)
Why it's wrong here
UDP scan is for UDP ports and may also be affected by spoofed responses.
Ping sweep (-sn)
Why it's wrong here
Ping sweep only checks host availability, not port states.
TCP connect scan (-sT)
Why this is correct
-sT completes the handshake; if the port is closed, a RST is received after the ACK, revealing the true state even if SYN-ACKs are spoofed.
Related concept
Read the scenario before looking for a memorised answer.
Idle scan (-sI)
Why it's wrong here
Idle scan uses a zombie host and may not address SYN-ACK spoofing.
Common exam traps
The trap here is that candidates assume a SYN scan (-sS) is always superior due to stealth, but they overlook that a security appliance can spoof SYN-ACKs, making the full handshake of -sT necessary to bypass the deception.
Detailed technical explanation
Under the hood, a security appliance that responds with SYN-ACK to all TCP SYN packets is effectively performing SYN-ACK spoofing, which tricks half-open scans (-sS) into marking all ports as open. The TCP connect scan (-sT) uses the connect() system call, which completes the handshake; if the port is actually closed, the target kernel sends a RST after receiving the ACK, revealing the true state. In real-world scenarios, such appliances are often used in load balancers or firewalls with 'TCP intercept' or 'SYN proxy' features, making -sT a reliable countermeasure.
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
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
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise CEH questions linked to Footprinting, Reconnaissance and Scanning.
Practise CEH questions linked to Enumeration and System Hacking.
Practise CEH questions linked to Malware, Social Engineering and Network Attacks.
Practise CEH questions linked to Web Application and Injection Attacks.
Practise CEH questions linked to Introduction to Ethical Hacking.
Practise CEH questions linked to Scanning Networks and Enumeration.
Practise CEH questions linked to Vulnerability Analysis and System Hacking.
Practise CEH questions linked to Advanced Topics: Wireless, Cloud, IoT, Cryptography.
Practise CEH questions linked to Footprinting and Reconnaissance.
Practise CEH questions linked to Network and Web Application Attacks.
Practise CEH questions linked to Wireless, IoT and Cloud Security.
Practise CEH questions linked to Cryptography and Malware Analysis.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: TCP connect scan (-sT) — Option C is correct because a TCP connect scan (-sT) completes the full three-way handshake, which forces the target to respond with a RST if the port is actually closed, even if a security appliance initially sends SYN-ACK to all ports. This distinguishes between ports that are truly open (where the handshake completes) and those that are falsely reported as open by the appliance (where the handshake fails or a RST is received).
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.
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.