- A
Perform a TCP connect scan (-sT) on all ports of the subnet to identify open ports and services.
Why wrong: Connect scan completes the three-way handshake, is not stealthy, and generates more traffic.
- B
Perform an Xmas scan (-sX) on all ports of the subnet to evade detection by sending packets with invalid flag combinations.
Why wrong: Xmas scan can be filtered by firewalls and is less reliable for determining open ports.
- C
First, perform a TCP SYN scan (-sS) on the three allowed ports across the subnet. Once a live host is identified, perform a TCP SYN scan (-sS) on all 65535 ports of that host.
TCP SYN scan is stealthy (half-open) and efficient. Scanning only allowed ports first reduces traffic, then full port scan on the live host.
- D
Perform a UDP scan (-sU) on all ports of the subnet because UDP is connectionless and less likely to be logged.
Why wrong: UDP scan is slow, unreliable, and may be blocked by firewall; also not stealthy for TCP services.
Quick Answer
The correct approach is to first perform a TCP SYN scan (-sS) on the three allowed ports across the subnet, then conduct a full TCP SYN scan on all 65535 ports of the identified live host. This is correct because a TCP SYN scan sends only a SYN packet and never completes the three-way handshake, making it inherently stealthy and ideal for evading firewall logging while minimizing packet count. By initially targeting only the permitted ports (80, 443, 8080), you efficiently discover live hosts without triggering alarms, then expand to a full port scan on the most promising target to map all services. On the CEH exam, this scenario tests your understanding of firewall evasion and stealth scanning techniques, often appearing as a multi-step reconnaissance question where the trap is choosing a full connect scan (-sT) or a ping sweep, both of which complete handshakes and generate more noise. Remember the key principle: SYN stealth first, then full sweep—or simply, “SYN first, sweep last.”
CEH Scanning Networks and Enumeration Practice Question
This CEH practice question tests your understanding of scanning networks and enumeration. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
You are a penetration tester for a financial institution. During the reconnaissance phase, you discover that the target network uses a firewall that only allows inbound TCP connections on ports 80, 443, and 8080. You need to identify live hosts and running services on the internal network (192.168.1.0/24) from an external perspective. To avoid detection, you must minimize the number of packets sent and ensure that your scanning technique does not complete the TCP three-way handshake. Additionally, you have limited time and need to scan all 65535 ports on the most promising target. Based on the firewall rules and the need for stealth, which of the following approaches should you take?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
First, perform a TCP SYN scan (-sS) on the three allowed ports across the subnet. Once a live host is identified, perform a TCP SYN scan (-sS) on all 65535 ports of that host.
Option C is correct because a TCP SYN scan (-sS) sends only a SYN packet and does not complete the three-way handshake, making it stealthy. First scanning only the three allowed ports (80, 443, 8080) across the subnet minimizes packets and identifies live hosts. Once a promising target is found, a full SYN scan on all 65535 ports efficiently maps services while evading the firewall's restrictions.
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.
- ✗
Perform a TCP connect scan (-sT) on all ports of the subnet to identify open ports and services.
Why it's wrong here
Connect scan completes the three-way handshake, is not stealthy, and generates more traffic.
- ✗
Perform an Xmas scan (-sX) on all ports of the subnet to evade detection by sending packets with invalid flag combinations.
Why it's wrong here
Xmas scan can be filtered by firewalls and is less reliable for determining open ports.
- ✓
First, perform a TCP SYN scan (-sS) on the three allowed ports across the subnet. Once a live host is identified, perform a TCP SYN scan (-sS) on all 65535 ports of that host.
Why this is correct
TCP SYN scan is stealthy (half-open) and efficient. Scanning only allowed ports first reduces traffic, then full port scan on the live host.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Perform a UDP scan (-sU) on all ports of the subnet because UDP is connectionless and less likely to be logged.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose an Xmas scan (Option B) thinking it is stealthy due to invalid flags, but fail to realize that modern firewalls and IDS systems easily detect and drop such anomalous packets, making it ineffective against port-based allow rules.
Detailed technical explanation
How to think about this question
A TCP SYN scan leverages the fact that a SYN-ACK response indicates an open port, while an RST indicates a closed port, without completing the handshake. Firewalls that allow inbound SYN packets on specific ports (80, 443, 8080) will pass these probes, enabling host discovery even when other ports are filtered. In practice, this technique is often combined with idle scans or decoys to further evade detection in high-security environments.
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.
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FAQ
Questions learners often ask
What does this CEH question test?
Scanning Networks and Enumeration — This question tests Scanning Networks and Enumeration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: First, perform a TCP SYN scan (-sS) on the three allowed ports across the subnet. Once a live host is identified, perform a TCP SYN scan (-sS) on all 65535 ports of that host. — Option C is correct because a TCP SYN scan (-sS) sends only a SYN packet and does not complete the three-way handshake, making it stealthy. First scanning only the three allowed ports (80, 443, 8080) across the subnet minimizes packets and identifies live hosts. Once a promising target is found, a full SYN scan on all 65535 ports efficiently maps services while evading the firewall's restrictions.
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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 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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