The answer is closed. In Nmap, a closed port state is determined when the target host responds to a probe with a TCP RST (Reset) packet, which confirms the port is reachable and the host is alive, but no application or service is listening on that port. This directly distinguishes it from a filtered state, where no response or an ICMP unreachable error indicates a firewall or packet filter is blocking the probe. On the Certified Ethical Hacker CEH exam, this concept tests your ability to interpret Nmap scan results and understand network reconnaissance fundamentals; a common trap is confusing closed with filtered, since both may appear inactive, but closed proves connectivity while filtered suggests obstruction. A useful memory tip: think of closed as a door that is reachable but locked with no one inside, whereas filtered is a door you cannot even knock on because a wall (firewall) blocks the path.
CEH Introduction to Ethical Hacking Practice Question
This CEH practice question tests your understanding of introduction to ethical hacking. 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.
```
$ nmap -sS -T4 -p 22,80,443 192.168.1.10
Starting Nmap 7.80 ( https://nmap.org )
Nmap scan report for 192.168.1.10
Host is up (0.0012s latency).
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
443/tcp closed https
Nmap done: 1 IP address (1 host up) scanned in 2.45 seconds
```
Refer to the exhibit. An ethical hacker runs the shown Nmap scan against a target. Which port state indicates that the port is reachable but no service is listening?
Refer to the exhibit.
```
$ nmap -sS -T4 -p 22,80,443 192.168.1.10
Starting Nmap 7.80 ( https://nmap.org )
Nmap scan report for 192.168.1.10
Host is up (0.0012s latency).
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
443/tcp closed https
Nmap done: 1 IP address (1 host up) scanned in 2.45 seconds
```
A
open
Why wrong: Open means a service is listening.
B
closed
Closed means reachable but no service listening.
C
filtered
Why wrong: Filtered means the probe was blocked.
D
unfiltered
Why wrong: Unfiltered is not shown in this output.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
closed
Option B is correct because a 'closed' port in Nmap indicates that the target host responded with a TCP RST (Reset) packet, meaning the port is reachable and the host is alive, but no application is listening on that port. This state confirms the port is accessible (not filtered by a firewall) yet no service is bound to it.
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.
✗
open
Why it's wrong here
Open means a service is listening.
✓
closed
Why this is correct
Closed means reachable but no service listening.
Related concept
Read the scenario before looking for a memorised answer.
✗
filtered
Why it's wrong here
Filtered means the probe was blocked.
✗
unfiltered
Why it's wrong here
Unfiltered is not shown in this output.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'closed' with 'filtered' or 'unfiltered', not realizing that a closed port specifically means the host responded with a TCP RST, proving reachability without a listening service.
Trap categories for this question
Command / output trap
Unfiltered is not shown in this output.
Detailed technical explanation
How to think about this question
Nmap determines port states based on TCP/IP stack responses: a closed port replies with an RST packet per RFC 793, while an open port sends a SYN-ACK. In real-world scenarios, closed ports can be used to detect live hosts during reconnaissance, as a firewall that allows RST responses indicates the host is up and the port is not filtered.
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.
Introduction to Ethical Hacking — This question tests Introduction to Ethical Hacking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: closed — Option B is correct because a 'closed' port in Nmap indicates that the target host responded with a TCP RST (Reset) packet, meaning the port is reachable and the host is alive, but no application is listening on that port. This state confirms the port is accessible (not filtered by a firewall) yet no service is bound to it.
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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