The answer is an Xmas tree scan. This is correct because an Xmas tree scan sends TCP packets with the FIN, PSH, and URG flags all set simultaneously, causing the packet to "light up" like a Christmas tree. According to RFC 793, closed ports should respond with an RST packet, while open ports typically ignore the packet, making this a stealth reconnaissance technique to map firewall rules and port states without completing a full TCP handshake. On the CompTIA Network+ N10-009 exam, this question tests your ability to recognize abnormal TCP flag combinations used in network scanning. A common trap is confusing it with a SYN scan or NULL scan—remember that a NULL scan has no flags set, while an Xmas tree scan has three flags lit. A helpful memory tip: think of a Christmas tree with its three bright lights—FIN, PSH, and URG—all glowing at once.
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. 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 notices a large number of incoming TCP packets to a server with the FIN, PSH, and URG flags set. This pattern is characteristic of which type of network scan?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Xmas tree scan
An Xmas tree scan sends TCP packets with the FIN, PSH, and URG flags set (the packet 'lights up' like a Christmas tree). This is a stealth scan technique used to probe open or closed ports based on RFC 793 behavior: closed ports should respond with an RST packet, while open ports may ignore the packet (or respond differently depending on the OS). The pattern described—FIN, PSH, and URG all set—is the definitive signature of an Xmas tree scan.
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.
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SYN scan
Why it's wrong here
A SYN scan sends packets with only the SYN flag set to initiate connections.
✓
Xmas tree scan
Why this is correct
An Xmas tree scan sets the FIN, PSH, and URG flags. It is a stealthy technique used to probe open/closed ports.
Related concept
Read the scenario before looking for a memorised answer.
✗
Null scan
Why it's wrong here
A Null scan sends a packet with no flags set, which is different from the FIN, PSH, URG combination.
✗
ACK scan
Why it's wrong here
An ACK scan sends packets with only the ACK flag set, used to map firewall rules, not to set FIN, PSH, and URG.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between Xmas tree, Null, and SYN scans by focusing on the specific flag combinations, so the trap here is confusing the FIN/PSH/URG set (Xmas tree) with a Null scan (no flags) or a SYN scan (only SYN).
Detailed technical explanation
How to think about this question
Under the hood, the Xmas tree scan exploits RFC 793's requirement that a closed port must respond with an RST to any incoming segment not containing an RST, regardless of flags. However, many modern operating systems (e.g., Windows, some Linux kernels) do not comply strictly with this RFC, making the scan unreliable against those targets. In real-world penetration testing, this scan is often used to evade simple packet filters that only block SYN packets, but it is easily detected by modern intrusion detection systems (IDS) due to the unusual flag combination.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Xmas tree scan — An Xmas tree scan sends TCP packets with the FIN, PSH, and URG flags set (the packet 'lights up' like a Christmas tree). This is a stealth scan technique used to probe open or closed ports based on RFC 793 behavior: closed ports should respond with an RST packet, while open ports may ignore the packet (or respond differently depending on the OS). The pattern described—FIN, PSH, and URG all set—is the definitive signature of an Xmas tree scan.
What should I do if I get this N10-009 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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Question Discussion
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