The answer is that ports responding with SYN-ACK are confirmed open. This is correct because the TCP three-way handshake requires a SYN-ACK reply from the target only when the port is actively listening and willing to establish a connection; a closed port would respond with a RST packet, while a filtered port would typically drop the packet or reply with an ICMP unreachable message. On the CompTIA PenTest+ PT0-002 exam, interpreting SYN-ACK responses in active recon tests your understanding of the handshake mechanics and common scanning pitfalls—trap answers often confuse a SYN-ACK with a half-open state or suggest the port is filtered. A solid memory tip is to remember that a SYN-ACK is a direct “yes” from the port: if you send a SYN and get a SYN-ACK back, that port is open and listening, no further interpretation needed.
PT0-002 A SYN-ACK response indicates an open port. Practice Question
This PT0-002 practice question tests your understanding of information gathering and vulnerability scanning. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: a SYN-ACK response indicates an open port.. 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 penetration tester is performing active reconnaissance on a target network. The tester sends TCP SYN packets to a range of ports on a target host. Only a few ports respond with SYN-ACK packets. What does this indicate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ports that responded with SYN-ACK are open.
The TCP three-way handshake begins with a SYN packet; a SYN-ACK response indicates that the target port received the SYN and is willing to establish a connection, meaning the port is open and listening. Only ports that respond with SYN-ACK are confirmed open, while others may be closed or filtered, but the presence of any SYN-ACK replies directly indicates open ports.
Key principle: A SYN-ACK response indicates an open port.
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 host is protected by a firewall that drops all packets.
Why it's wrong here
If all packets were dropped, there would be no SYN-ACK responses at all.
✓
The ports that responded with SYN-ACK are open.
Why this is correct
A SYN-ACK reply indicates that the port is open and the target is willing to establish a connection.
Related concept
A SYN-ACK response indicates an open port.
✗
The host is running a stealthy IDS.
Why it's wrong here
An IDS might log the scan, but it does not affect the TCP handshake responses.
✗
The network is using IPv6.
Why it's wrong here
IP version is not determined by SYN scan responses; the scan is likely IPv4.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing the absence of a response (filtered) with a firewall dropping all packets, but the presence of any SYN-ACK replies proves that not all packets are dropped, and the correct interpretation is that responding ports are open.
Detailed technical explanation
How to think about this question
In TCP, a SYN-ACK response is part of the standard three-way handshake (SYN, SYN-ACK, ACK) defined in RFC 793, confirming the port is in a LISTENING state. During active reconnaissance with tools like Nmap, a SYN scan (-sS) sends raw SYN packets without completing the handshake, and the presence of SYN-ACK replies distinguishes open ports from closed (RST) or filtered (no response or ICMP unreachable) ports. In real-world scenarios, a firewall might permit SYN packets to certain ports while blocking others, explaining why only a few ports respond.
KKey Concepts to Remember
A SYN-ACK response indicates an open port.
SYN scans are 'half-open' because they don't complete the three-way handshake.
SYN scans are less intrusive than full connect scans.
No response or an RST indicates a closed or filtered port.
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
A SYN-ACK response indicates an open port.
Real-world example
How this comes up in practice
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PT0-002 question in full detail.
Information Gathering and Vulnerability Scanning — This question tests Information Gathering and Vulnerability Scanning — A SYN-ACK response indicates an open port..
What is the correct answer to this question?
The correct answer is: The ports that responded with SYN-ACK are open. — The TCP three-way handshake begins with a SYN packet; a SYN-ACK response indicates that the target port received the SYN and is willing to establish a connection, meaning the port is open and listening. Only ports that respond with SYN-ACK are confirmed open, while others may be closed or filtered, but the presence of any SYN-ACK replies directly indicates open ports.
What should I do if I get this PT0-002 question wrong?
Review a SYN-ACK response indicates an open port., then practise related PT0-002 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
A SYN-ACK response indicates an open port.
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