The answer is a host-based firewall configured to silently drop all incoming traffic. When Nmap reports all ports as filtered, it means the target is reachable—as confirmed by a successful ping—but the probe packets, such as SYN or ACK, are being discarded without any response. A stateful firewall that silently drops unsolicited inbound packets prevents Nmap from receiving either a SYN/ACK (open) or RST (closed) reply, leaving every port in the ambiguous filtered state. On the Certified Ethical Hacker CEH exam, this scenario tests your understanding of how firewalls manipulate TCP handshake responses; a common trap is assuming a dead host, but the key distinction is that a live host responds to ICMP while a firewall blocks TCP probes. Remember the mnemonic: “Ping lives, ports die—firewall’s silent lie.”
CEH Footprinting, Reconnaissance and Scanning Practice Question
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 analyst notices that their Nmap scan results show all ports as 'filtered' despite the target host being alive and responsive to ping. Which of the following is the MOST likely cause?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target has a host-based firewall that drops all incoming traffic silently
When an Nmap scan shows all ports as 'filtered', it indicates that the target is reachable (since ping succeeds) but the probe packets (e.g., SYN, ACK) are being dropped without any response. A host-based firewall configured to silently drop all incoming traffic is the most likely cause, as it prevents Nmap from receiving RST or SYN/ACK replies, leading to the 'filtered' state for every port.
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 analyst's machine has a misconfigured routing table
Why it's wrong here
Routing issues would likely cause host unreachable errors, not filtered ports on a live host.
✓
The target has a host-based firewall that drops all incoming traffic silently
Why this is correct
A stateful firewall dropping packets without sending RST or ICMP unreachable leads to filtered port status.
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 target is running a honeypot that mimics multiple services
Why it's wrong here
Honeypots typically respond to connection attempts, resulting in open ports, not filtered.
✗
The target is an idle host that does not respond to any traffic
Why it's wrong here
If the host were idle, it would still respond to TCP SYN with RST if port is closed; filtered implies a firewall actively dropping.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'filtered' with 'closed' or 'open', or assume a host that responds to ping must have open ports, but a firewall can silently drop all inbound TCP/UDP probes while still allowing ICMP echo requests.
Detailed technical explanation
How to think about this question
Nmap's 'filtered' state occurs when a firewall drops the probe packet (e.g., TCP SYN) and sends no response (no RST, no SYN/ACK), or when an ICMP unreachable (type 3, code 13) is received. Host-based firewalls like iptables (with a default DROP policy) or Windows Defender Firewall (with inbound block rules) can cause this. In real-world scenarios, stealthy firewalls may also rate-limit or drop probes without ICMP feedback, making Nmap treat all ports as filtered even if the host is up.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
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 target has a host-based firewall that drops all incoming traffic silently — When an Nmap scan shows all ports as 'filtered', it indicates that the target is reachable (since ping succeeds) but the probe packets (e.g., SYN, ACK) are being dropped without any response. A host-based firewall configured to silently drop all incoming traffic is the most likely cause, as it prevents Nmap from receiving RST or SYN/ACK replies, leading to the 'filtered' state for every port.
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A security analyst runs `nmap -sS -sV -A 192.168.1.100` and obtains open ports and service versions. However, the analyst suspects the target is behind an IDS/IPS. Which Nmap technique would BEST evade detection while still performing a similar scan?
medium
✓ A.Add -f to fragment IP packets
B.Use -sT instead of -sS to perform a full TCP connect scan
C.Increase timing to -T5 for a faster scan
D.Replace -sV with -sU to scan UDP services
Why A: Option A is correct because using the `-f` flag fragments the IP packets, splitting the TCP header across multiple packets. This helps evade simple IDS/IPS signatures that rely on detecting a complete SYN scan in a single packet, as the fragmented packets may bypass pattern-matching rules or reassembly buffers.
Last reviewed: Jun 24, 2026
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.
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.