Question 1hardmultiple choice
Full question →- A
Idle scan
-sI is the idle scan flag.
- B
SYN scan
Why wrong: SYN scan uses -sS.
- C
Decoy scan
Why wrong: Decoy scan uses -D.
- D
Fragmentation scan
Why wrong: Fragmentation uses -f.
Question 156 of 1,010
Quick Answer
The answer is an idle scan. This is the correct choice because the `-sI` flag in Nmap specifically triggers an idle scan, which uses a zombie host—in this case, 192.168.1.10—as a decoy to probe the target. The technique works by monitoring changes in the zombie’s IP ID sequence; if the target port is open, the zombie’s IP ID increments, revealing the result without exposing the attacker’s own IP address. On the Certified Ethical Hacker CEH exam, this question tests your understanding of stealth scanning methods and the mechanics of IP ID manipulation, often appearing in scenario-based questions where you must identify the scan type from command syntax. A common trap is confusing the idle scan with a decoy scan (`-D`), but remember that only the idle scan requires a zombie host to bounce probes. Memory tip: think of the “I” in `-sI` as standing for “Idle” or “Invisible” because your IP stays hidden.
CEH Footprinting, Reconnaissance and Scanning Practice Question
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 runs `nmap -sI 192.168.1.10 -p 80 10.0.0.1` and receives output indicating port 80 is open. The scan uses a zombie host. Which type of scan is this?
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
✓
Idle scan
The `-sI` flag in Nmap specifies an idle scan, which uses a zombie host (192.168.1.10) to probe the target (10.0.0.1). By observing changes in the zombie's IP ID sequence, the attacker can infer whether a port on the target is open or closed without revealing their own IP address. The output indicating port 80 is open confirms the scan type as an idle scan.
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.
- ✓
Idle scan
Why this is correct
-sI is the idle scan flag.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
SYN scan
Why it's wrong here
SYN scan uses -sS.
- ✗
Decoy scan
Why it's wrong here
Decoy scan uses -D.
- ✗
Fragmentation scan
Why it's wrong here
Fragmentation uses -f.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the `-sI` flag with decoy scans (`-D`) because both involve spoofing, but idle scans uniquely require a zombie host and IP ID analysis, not just multiple decoy IPs.
Detailed technical explanation
How to think about this question
The idle scan exploits the predictable IP ID increment behavior of many operating systems (e.g., Windows, older Linux kernels). The attacker sends a SYN/ACK to the zombie, records its IP ID, then sends a spoofed SYN packet to the target with the zombie's IP as the source; if the target port is open, it sends a SYN/ACK to the zombie, causing the zombie to send a RST and increment its IP ID, which the attacker detects by probing the zombie again. This technique is stealthy but unreliable against modern systems with randomized IP IDs (e.g., Linux kernels 2.6+ with `sysctl net.ipv4.tcp_timestamps` enabled).
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: Idle scan — The `-sI` flag in Nmap specifies an idle scan, which uses a zombie host (192.168.1.10) to probe the target (10.0.0.1). By observing changes in the zombie's IP ID sequence, the attacker can infer whether a port on the target is open or closed without revealing their own IP address. The output indicating port 80 is open confirms the scan type as an idle scan.
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.
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 →
Keep practising
More CEH practice questions
- A penetration tester is analyzing a captured TCP session that includes a successful SQL injection attack. Which TWO of t…
- You are a security consultant for a mid-sized company that recently migrated its customer relationship management (CRM)…
- An organization is implementing a social engineering defense program. Which TWO measures are most effective in reducing…
- An ethical hacker is assessing a Linux web server running Apache. The server is suspected to have a remote file inclusio…
- A penetration tester discovers that a target Windows system has port 445 open and responds to SMB requests. Which tool s…
- Which TWO of the following are effective physical security controls to prevent tailgating?
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.