PT0-002 Practice Question: TCP SYN scan sends only the initial SYN packet.
This PT0-002 practice question tests your understanding of tools and code analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: tCP SYN scan sends only the initial SYN packet.. 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 analyzing a Python script that uses the 'scapy' library. The script contains the line: `packet = IP(dst='10.0.0.1')/TCP(dport=80, flags='S')`. The tester then uses `sr1(packet, timeout=2)`. What is the primary purpose of this code?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Perform a TCP SYN scan to determine if port 80 is open
The SYN packet is sent; if a SYN-ACK is received, the port is open. This is a stealthy port scan technique.
B
Perform a DNS resolution for the target IP
Why wrong: DNS resolution is not performed with TCP SYN packets; it uses UDP or TCP on port 53.
C
Send a TCP ACK packet to test firewall rules
Why wrong: The flags are set to 'S' (SYN), not 'A' (ACK), so this is not an ACK scan.
D
Complete a full TCP three-way handshake
Why wrong: A three-way handshake requires sending SYN, receiving SYN-ACK, and then sending ACK. This script only sends SYN and receives a response; it does not complete the handshake.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Perform a TCP SYN scan to determine if port 80 is open
The code constructs an IP packet with destination 10.0.0.1 and a TCP segment with destination port 80 and the SYN flag set (flags='S'). The sr1() function sends this packet and waits for a response (up to 2 seconds). This is the classic technique for a TCP SYN scan: if a SYN-ACK is received, the port is open; if an RST is received, the port is closed. The primary purpose is therefore to probe whether port 80 on the target is open.
Key principle: TCP SYN scan sends only the initial SYN packet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Perform a TCP SYN scan to determine if port 80 is open
Why this is correct
The SYN packet is sent; if a SYN-ACK is received, the port is open. This is a stealthy port scan technique.
Clue confirmation
The clue word "primary" in the question point toward this answer.
DNS resolution is not performed with TCP SYN packets; it uses UDP or TCP on port 53.
✗
Send a TCP ACK packet to test firewall rules
Why it's wrong here
The flags are set to 'S' (SYN), not 'A' (ACK), so this is not an ACK scan.
✗
Complete a full TCP three-way handshake
Why it's wrong here
A three-way handshake requires sending SYN, receiving SYN-ACK, and then sending ACK. This script only sends SYN and receives a response; it does not complete the handshake.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing the flags in a TCP header: candidates may mistakenly think 'S' stands for 'send' or 'scan' rather than 'SYN', or they may conflate SYN scans with ACK scans, which serve different purposes in firewall rule detection.
Detailed technical explanation
How to think about this question
In scapy, the '/' operator layers protocols; here IP/TCP creates a complete packet. The sr1() function sends the packet at layer 3 and returns the first response. A SYN scan is stealthier than a full TCP connect scan because it never completes the three-way handshake, reducing the chance of being logged by the target. The timeout=2 parameter prevents indefinite blocking if no response is received.
KKey Concepts to Remember
TCP SYN scan sends only the initial SYN packet.
An open port responds to a SYN with a SYN-ACK packet.
SYN scans are considered 'stealthy' as they don't complete the handshake.
Scapy allows crafting raw packets to control TCP flags.
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
TCP SYN scan sends only the initial SYN packet.
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.
Tools and Code Analysis — This question tests Tools and Code Analysis — TCP SYN scan sends only the initial SYN packet..
What is the correct answer to this question?
The correct answer is: Perform a TCP SYN scan to determine if port 80 is open — The code constructs an IP packet with destination 10.0.0.1 and a TCP segment with destination port 80 and the SYN flag set (flags='S'). The sr1() function sends this packet and waits for a response (up to 2 seconds). This is the classic technique for a TCP SYN scan: if a SYN-ACK is received, the port is open; if an RST is received, the port is closed. The primary purpose is therefore to probe whether port 80 on the target is open.
What should I do if I get this PT0-002 question wrong?
Review tCP SYN scan sends only the initial SYN packet., then practise related PT0-002 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
TCP SYN scan sends only the initial SYN packet.
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