ISC2 CC Network Security Practice Question
A security analyst notices an unusually high number of incomplete TCP connection requests. Which type of attack is most likely occurring?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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SYN flood
SYN flood attacks exploit the TCP three-way handshake by sending many SYN packets without completing the handshake, exhausting server resources.
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 flood
Why this is correct
A SYN flood overwhelms a target by sending numerous TCP SYN packets without completing the three-way handshake, leaving connections half-open. This precisely matches the stem's observation of abnormally high incomplete TCP connection requests, exhausting the backlog queue and preventing legitimate connections from being established.
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Smurf attack
Why it's wrong here
A Smurf attack sends ICMP echo requests to a broadcast address with a spoofed source, generating ICMP replies, not TCP handshakes. Incomplete TCP connection requests indicate a SYN flood exhausting the backlog. Smurf is tempting as a spoofed-source amplification attack, but it operates at ICMP layer, not TCP.
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ARP spoofing
Why it's wrong here
ARP spoofing poisons the IP-to-MAC mapping cache to intercept or redirect traffic between hosts; it does not generate half-open TCP connections. The incomplete handshakes described indicate a SYN flood exhausting the backlog. ARP spoofing would be the answer for a scenario involving duplicated MAC addresses or man-in-the-middle redirection on a LAN.
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DNS amplification
Why it's wrong here
DNS amplification floods a target with large responses from open resolvers over UDP; it produces no TCP handshake state at all. A SYN flood leaves many half-open TCP connections. DNS amplification is tempting because it is a volumetric denial-of-service technique, but it does not generate incomplete TCP requests.
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Related to this question
Key term
TCP
TCP is a connection-oriented transport layer protocol that ensures reliable, ordered, and error-checked delivery of data between applications over IP networks.
Key term
Denial-of-service
A Denial-of-service (DoS) attack is an attempt to make a computer, network, or online service unavailable to its intended users by overwhelming it with fake traffic or requests.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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