Quick Answer
The answer is that the RST/ACK response indicates port 80 is closed. This occurs because, per TCP RFC 793, when a SYN packet reaches a closed port, the target kernel immediately rejects the connection attempt by sending a packet with both the Reset (RST) and Acknowledgment (ACK) flags set. The RST/ACK tells the sender that the host is reachable and the packet was acknowledged, but no service is listening on that port, so the connection is refused. On the Certified Ethical Hacker CEH exam, this concept tests your ability to distinguish between open ports (which respond with SYN/ACK) and filtered ports (which may drop the packet or respond with ICMP unreachable). A common trap is confusing RST/ACK with a firewall block—remember, a clean RST/ACK means the port is closed, not filtered. Memory tip: “RST/ACK means the door is locked, not guarded.”
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 security analyst runs the following command: hping3 -S -p 80 -c 1 192.168.1.1. The response received is an RST/ACK packet. What does this indicate about port 80 on the target?
The port is open and listening
Why wrong: An open port would respond with SYN/ACK.
The port is filtered by a firewall
Why wrong: A filtered port typically drops the packet or responds with no reply or ICMP unreachable.
The port is closed
RST/ACK indicates the port is closed.
The port is in a TIME_WAIT state
Why wrong: TIME_WAIT is a TCP state that would not produce an RST/ACK from a scanning perspective.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The port is closed
Option C is correct because when hping3 sends a SYN packet to a closed port, the target responds with an RST/ACK packet per TCP RFC 793. This indicates that the port is reachable but no service is listening on it, hence the immediate reset.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The port is open and listening
Why it's wrong here
An open port would respond with SYN/ACK.
The port is filtered by a firewall
Why it's wrong here
A filtered port typically drops the packet or responds with no reply or ICMP unreachable.
The port is closed
Why this is correct
RST/ACK indicates the port is closed.
Related concept
Read the scenario before looking for a memorised answer.
The port is in a TIME_WAIT state
Why it's wrong here
TIME_WAIT is a TCP state that would not produce an RST/ACK from a scanning perspective.
Common exam traps
The trap here is that candidates often confuse a RST/ACK response with a filtered port or assume it indicates a firewall blocking the port, but in TCP, a closed port actively sends RST/ACK, whereas a firewall typically drops the packet silently.
Detailed technical explanation
The RST/ACK response is the standard TCP behavior for a closed port when it receives an unsolicited SYN. In real-world scanning, this helps distinguish closed ports from filtered ones; firewalls often drop packets without any response, while a closed port actively rejects the connection. This is the basis for TCP connect scans and half-open scans in tools like Nmap.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
The correct answer is: The port is closed — Option C is correct because when hping3 sends a SYN packet to a closed port, the target responds with an RST/ACK packet per TCP RFC 793. This indicates that the port is reachable but no service is listening on it, hence the immediate reset.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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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.
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