Quick Answer
The answer is a port scan using the SYN scan technique. This is correct because a SYN scan, also known as a half-open scan, sends SYN packets to multiple ports to probe for open services; when a target responds with a SYN-ACK, the scanner never sends the final ACK to complete the three-way handshake, leaving the connection half-open. The absence of subsequent ACK packets in the firewall logs is the key indicator that distinguishes this from a legitimate connection attempt or a brute-force attack. On the Systems Security Certified Practitioner SSCP exam, this scenario tests your ability to differentiate reconnaissance techniques from denial-of-service or authentication attacks, often appearing in questions about intrusion detection and log analysis. A common trap is confusing the high volume of SYN packets with a SYN flood DDoS, but the key difference is that a SYN scan targets many ports from a single source without completing handshakes, while a flood overwhelms a single port. Memory tip: think “SYN scan = SYN sent, no ACK back; SYN flood = SYN sent, no SYN-ACK back.”
This SSCP practice question tests your understanding of network and communications 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 network analyst reviews firewall logs and sees multiple SYN packets to various ports from the same external IP in a short time, with no subsequent ACK. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Brute force password attack on SSH
Why wrong: Brute force would target a single port repeatedly.
Distributed denial-of-service (DDoS) attack
Why wrong: DDoS typically uses many sources and may use other protocols.
ICMP ping sweep
Why wrong: Ping sweep uses ICMP Echo requests, not SYN packets.
Port scan using SYN scan technique
SYN scan is a common reconnaissance method.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Port scan using SYN scan technique
A SYN scan sends SYN packets to multiple ports; if a port is open, the target responds with SYN-ACK, but the scanner never completes the handshake (no ACK). The absence of ACK packets after the SYN packets indicates the scanner is not establishing connections, which is characteristic of a SYN scan, not a brute force or DDoS attack.
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.
Brute force password attack on SSH
Why it's wrong here
Brute force would target a single port repeatedly.
Distributed denial-of-service (DDoS) attack
Why it's wrong here
DDoS typically uses many sources and may use other protocols.
ICMP ping sweep
Why it's wrong here
Ping sweep uses ICMP Echo requests, not SYN packets.
Port scan using SYN scan technique
Why this is correct
SYN scan is a common reconnaissance method.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
ISC2 often tests the distinction between a SYN scan and a DDoS attack; the trap is that candidates see 'multiple SYN packets' and immediately think 'SYN flood DDoS,' but a SYN flood typically uses spoofed IPs and aims to exhaust resources, whereas a single IP scanning various ports without ACKs indicates reconnaissance.
Detailed technical explanation
SYN scan (half-open scan) exploits the TCP three-way handshake: the scanner sends a SYN, and if it receives a SYN-ACK, it knows the port is open but sends a RST instead of ACK to avoid completing the connection. This technique is stealthier than a full connect scan because many applications do not log incomplete handshakes. Tools like Nmap use this by default (with root privileges) to map open ports quickly.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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FAQ
Network and Communications Security — This question tests Network and Communications Security — Read the scenario before looking for a memorised answer..
The correct answer is: Port scan using SYN scan technique — A SYN scan sends SYN packets to multiple ports; if a port is open, the target responds with SYN-ACK, but the scanner never completes the handshake (no ACK). The absence of ACK packets after the SYN packets indicates the scanner is not establishing connections, which is characteristic of a SYN scan, not a brute force or DDoS attack.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This SSCP practice question is part of Courseiva's free ISC2 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 SSCP exam.
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