The correct answer is that a firewall is likely blocking the scan probes to port 3389, preventing Nmap from determining whether the port is open. This is because an Nmap filtered port state means the scan received no response or an ICMP unreachable error from the target, indicating that a packet filter, firewall, or other network obstacle is obstructing the probes. On the Certified Ethical Hacker CEH exam, this concept tests your ability to interpret Nmap output accurately—a common trap is assuming a filtered port is simply closed, when in fact Nmap cannot confirm its status. Remember that filtered does not mean open or closed; it means the scan was blocked. A useful memory tip: think of a “filter” as a coffee filter—it blocks the grounds (probes) from passing through, so you cannot see what is on the other side.
CEH Scanning Networks and Enumeration Practice Question
This CEH practice question tests your understanding of scanning networks and enumeration. 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.
Exhibit
Refer to the exhibit.
```
$ sudo nmap -sS -sV -O -p 1-1000 192.168.1.10
Starting Nmap 7.93 ( https://nmap.org )
Nmap scan report for 192.168.1.10
Host is up (0.0012s latency).
Not shown: 995 closed ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 8.9p1 Ubuntu 3ubuntu0.1 (Ubuntu Linux; protocol 2.0)
80/tcp open http Apache httpd 2.4.52
443/tcp open ssl/http Apache httpd 2.4.52
3389/tcp filtered ms-wbt-server
8080/tcp open http-proxy Apache httpd 2.4.52
Device type: general purpose
Running: Linux 5.X
OS CPE: cpe:/o:linux:linux_kernel:5
OS details: Linux 5.0 - 5.14
Network Distance: 1 hop
```
Refer to the exhibit. A penetration tester runs the above Nmap scan. Which of the following statements is most accurate regarding the state of port 3389?
Refer to the exhibit.
```
$ sudo nmap -sS -sV -O -p 1-1000 192.168.1.10
Starting Nmap 7.93 ( https://nmap.org )
Nmap scan report for 192.168.1.10
Host is up (0.0012s latency).
Not shown: 995 closed ports
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 8.9p1 Ubuntu 3ubuntu0.1 (Ubuntu Linux; protocol 2.0)
80/tcp open http Apache httpd 2.4.52
443/tcp open ssl/http Apache httpd 2.4.52
3389/tcp filtered ms-wbt-server
8080/tcp open http-proxy Apache httpd 2.4.52
Device type: general purpose
Running: Linux 5.X
OS CPE: cpe:/o:linux:linux_kernel:5
OS details: Linux 5.0 - 5.14
Network Distance: 1 hop
```
A
Port 3389 is open and running a Remote Desktop service, but the service version could not be identified.
Why wrong: A filtered port does not indicate the service is open; it only shows that Nmap cannot probe it.
B
Port 3389 is closed and the target is ignoring the probe.
Why wrong: A closed port would show as 'closed' in Nmap output, not 'filtered'.
C
The target is likely a honeypot designed to simulate a Windows machine.
Why wrong: There is no indication of a honeypot; the filtered state is typical of a firewall.
D
A firewall is likely blocking the scan probes to port 3389, preventing Nmap from determining whether the port is open.
The 'filtered' state means Nmap could not determine if the port is open or closed, usually due to packet filtering.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A firewall is likely blocking the scan probes to port 3389, preventing Nmap from determining whether the port is open.
The Nmap scan output shows port 3389 in a 'filtered' state, which means Nmap received no response or an ICMP unreachable error from the target. This typically indicates a firewall is blocking the probes, preventing Nmap from determining whether the port is actually open or closed. A filtered state does not confirm the port is open or closed, only that access is being obstructed.
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.
✗
Port 3389 is open and running a Remote Desktop service, but the service version could not be identified.
Why it's wrong here
A filtered port does not indicate the service is open; it only shows that Nmap cannot probe it.
✗
Port 3389 is closed and the target is ignoring the probe.
Why it's wrong here
A closed port would show as 'closed' in Nmap output, not 'filtered'.
✗
The target is likely a honeypot designed to simulate a Windows machine.
Why it's wrong here
There is no indication of a honeypot; the filtered state is typical of a firewall.
✓
A firewall is likely blocking the scan probes to port 3389, preventing Nmap from determining whether the port is open.
Why this is correct
The 'filtered' state means Nmap could not determine if the port is open or closed, usually due to packet filtering.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'filtered' with 'closed' or 'open', failing to recognize that Nmap's port states (open, closed, filtered) have distinct meanings based on the type of response received, and that a firewall can cause a filtered state without revealing whether the service is actually running.
Trap categories for this question
Command / output trap
A filtered port does not indicate the service is open; it only shows that Nmap cannot probe it.
Detailed technical explanation
How to think about this question
When Nmap sends a SYN probe to a filtered port, it either receives no response (timeout) or an ICMP Type 3 Code 13 (Destination Unreachable: Communication Administratively Prohibited) packet. This contrasts with an open port, which responds with SYN/ACK, and a closed port, which responds with RST. In real-world scenarios, stateful firewalls or host-based firewalls like Windows Defender Firewall often cause filtered results for RDP (port 3389) unless an exception is configured.
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.
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: A firewall is likely blocking the scan probes to port 3389, preventing Nmap from determining whether the port is open. — The Nmap scan output shows port 3389 in a 'filtered' state, which means Nmap received no response or an ICMP unreachable error from the target. This typically indicates a firewall is blocking the probes, preventing Nmap from determining whether the port is actually open or closed. A filtered state does not confirm the port is open or closed, only that access is being obstructed.
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.
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