Quick Answer
The correct answer is a SYN flood attack, because the pattern of a TCP SYN packet with no subsequent ACK indicates an incomplete handshake designed to exhaust server resources. In a normal three-way handshake, the client sends a SYN, the server responds with SYN-ACK, and the client completes the connection with an ACK; when that final ACK never arrives, the server is left with half-open connections that consume memory and backlog capacity. On the Cisco CyberOps Associate 200-201 exam, this question tests your ability to recognize denial-of-service attack signatures during network intrusion analysis, often appearing alongside traffic captures or log entries showing repeated SYN packets from spoofed sources. A common trap is confusing this with a SYN scan, but a scan typically involves a single probe per port, whereas a flood shows high volume and no completion. Memory tip: think “SYN sent, ACK absent — half-open, resource spent.”
This 200-201 practice question tests your understanding of network intrusion analysis. 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.
During network intrusion analysis, an analyst observes a TCP connection with the SYN flag set but no subsequent ACK. This pattern is indicative of:
SYN flood attack
Incomplete SYN handshakes are a sign of SYN flood.
DNS resolution
Why wrong: DNS mostly uses UDP, not TCP with SYN.
Normal three-way handshake
Why wrong: Normal handshake includes ACK after SYN.
ICMP echo request
Why wrong: ICMP does not use TCP flags.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SYN flood attack
A SYN flood attack is a type of denial-of-service (DoS) attack where the attacker sends a high volume of TCP SYN packets to a target server but never completes the three-way handshake by sending the final ACK. This leaves the server with half-open connections, consuming resources and potentially exhausting the connection backlog, which prevents legitimate clients from establishing connections.
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.
SYN flood attack
Why this is correct
Incomplete SYN handshakes are a sign of SYN flood.
Related concept
Read the scenario before looking for a memorised answer.
DNS resolution
Normal three-way handshake
Why it's wrong here
Normal handshake includes ACK after SYN.
ICMP echo request
Common exam traps
Cisco often tests the distinction between a normal three-way handshake and an incomplete handshake pattern, where candidates mistakenly think any SYN packet indicates a legitimate connection attempt rather than recognizing the missing ACK as the hallmark of a SYN flood.
Detailed technical explanation
In a SYN flood, the attacker often spoofs the source IP address to prevent the server from sending the SYN-ACK to a real host, which would otherwise send a RST to close the half-open connection. The server's TCP stack maintains a backlog queue (e.g., the listen() backlog parameter in Linux) for these incomplete connections; once full, new connection requests are dropped. Modern mitigations include SYN cookies (RFC 4987), which encode connection state in the SYN-ACK sequence number, allowing the server to avoid storing state until the final ACK arrives.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
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FAQ
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
The correct answer is: SYN flood attack — A SYN flood attack is a type of denial-of-service (DoS) attack where the attacker sends a high volume of TCP SYN packets to a target server but never completes the three-way handshake by sending the final ACK. This leaves the server with half-open connections, consuming resources and potentially exhausting the connection backlog, which prevents legitimate clients from establishing connections.
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 25, 2026
This 200-201 practice question is part of Courseiva's free Cisco 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 200-201 exam.
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