The answer is that a firewall blocking the port and ICMP echo requests being blocked are the two most common causes for Nmap reporting a filtered port. When Nmap sends probes to a target port and receives no response or an ICMP unreachable message (such as type 3, code 13), it classifies the port as filtered because it cannot determine whether the port is open or closed. This typically occurs when a host-based or network firewall silently drops the packets or when the target system blocks ICMP echo requests, preventing Nmap from performing its host discovery phase and forcing it to treat all ports as filtered. On the CompTIA PenTest+ PT0-002 exam, this concept tests your understanding of how Nmap’s scan logic interacts with firewall rules and ICMP filtering—a common trap is confusing filtered with closed, but remember that closed ports send a TCP RST, while filtered ports produce no response or an ICMP error. A useful memory tip: “Filtered means firewalled or ICMP-foiled.”
PT0-002 Practice Question: Information Gathering and Vulnerability Scanning
This PT0-002 practice question tests your understanding of information gathering and vulnerability 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.
During a vulnerability scan of a Linux server, the tester notices that the NMAP scan reports port 22 as filtered. Which of the following could be causing this result? (Select TWO).
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Firewall blocking the port
Options A and E are correct. A firewall blocking the port and ICMP echo request blocking both contribute to Nmap reporting filtered. Option B would show closed; Option C would show host down; Option D is unlikely.
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.
✓
Firewall blocking the port
Why this is correct
A firewall can return a filtered state if it drops packets without rejection.
Related concept
Read the scenario before looking for a memorised answer.
✓
ICMP echo requests being blocked
Why this is correct
If Nmap uses ICMP for host discovery and it is blocked, it may mark ports as filtered.
Related concept
Read the scenario before looking for a memorised answer.
✗
SSH service not running
Why it's wrong here
If SSH is not running, the port would typically show as closed (RST).
✗
Host is down
Why it's wrong here
If the host is down, Nmap would report no response, not filtered.
✗
Network congestion
Why it's wrong here
Congestion may cause packet loss but not consistently filtered state.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
If SSH is not running, the port would typically show as closed (RST).
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
Identify which PT0-002 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Information Gathering and Vulnerability Scanning — This question tests Information Gathering and Vulnerability Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Firewall blocking the port — Options A and E are correct. A firewall blocking the port and ICMP echo request blocking both contribute to Nmap reporting filtered. Option B would show closed; Option C would show host down; Option D is unlikely.
What should I do if I get this PT0-002 question wrong?
Identify which PT0-002 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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