SYN Flood Attack: Detection and Mitigation
A security analyst discovers that an attacker is sending large numbers of incomplete TCP connection requests to a server, causing the server to run out of resources and stop responding to legitimate requests. Which type of attack is this, and which mitigation should be implemented?
Quick Answer
This is a SYN flood because the attacker is deliberately exploiting the incomplete state of the TCP three-way handshake: normally a connection only becomes established after SYN, SYN-ACK, and a final ACK, but here the attacker sends a flood of SYN packets and never completes that last step, leaving the server holding a huge number of half-open connections. Each of those half-open connections consumes a slot in the server's connection queue, and once that queue fills up, the server can no longer accept new connection attempts from legitimate clients, which is why it stops responding. TCP intercept and SYN cookies solve this by changing how the server handles the handshake itself: rather than committing resources for every incoming SYN, the server can validate that a client is genuinely willing to complete the handshake before it allocates a full connection state, which prevents an attacker from tying up resources with connections that were never going to be finished anyway. This is different from mitigations aimed at completed-connection floods or application-layer attacks, since SYN flood defenses specifically target the handshake stage. Whenever a scenario describes a server exhausted by incomplete TCP connections rather than a high volume of legitimate-looking traffic, that half-open connection pattern points to a SYN flood and the fix of validating handshakes before allocating resources.
⚠ Common exam trap
Many candidates confuse a SYN flood with a ping flood or Smurf attack because all involve flooding, but only SYN floods target the TCP three-way handshake state table.
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
✓
SYN flood; enable TCP intercept or SYN cookies
This is a SYN flood attack, where the attacker sends a high volume of TCP SYN packets without completing the three-way handshake, exhausting the server's connection queue. Enabling TCP intercept (on Cisco devices) or SYN cookies (RFC 4987) allows the server to validate handshakes before allocating resources, mitigating the attack.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
SYN flood; enable TCP intercept or SYN cookies
Why this is correct
The attack is a SYN flood. TCP intercept (or SYN cookies) allows the server to manage half-open connections and mitigate resource exhaustion.
- ✗
Ping flood; implement rate limiting
Why it's wrong here
Ping floods use ICMP echo requests, not incomplete TCP connections.
When this WOULD be correct
A ping flood attack would be the correct answer if the question described an attacker sending a high volume of ICMP echo request packets to overwhelm a target's network bandwidth or CPU, and the mitigation would be implementing rate limiting on ICMP traffic.
- ✗
Smurf attack; disable IP-directed broadcasts
Why it's wrong here
A Smurf attack sends ICMP echo requests to broadcast addresses with spoofed source IPs, causing amplification, not incomplete TCP handshakes.
When this WOULD be correct
A Smurf attack would be correct if the question described an attacker sending ICMP echo requests to a network broadcast address, using a spoofed source IP of the victim, causing all hosts on the network to reply to the victim, overwhelming it with ICMP traffic.
- ✗
ARP poisoning; enable dynamic ARP inspection
Why it's wrong here
ARP poisoning involves sending forged ARP replies to associate IPs with attacker MACs, not exhausting TCP resources.
When this WOULD be correct
This option would be correct in a question describing an attacker sending forged ARP messages to associate their MAC address with the IP of a legitimate device, causing traffic interception or denial of service. The mitigation would be Dynamic ARP Inspection (DAI) to validate ARP packets.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓SYN flood; enable TCP intercept or SYN cookiesCorrect answer▾
Why this is correct
The attack is a SYN flood. TCP intercept (or SYN cookies) allows the server to manage half-open connections and mitigate resource exhaustion.
✗Ping flood; implement rate limitingWrong answer — click to see why▾
Why this is wrong here
The attack described involves incomplete TCP connection requests exhausting server resources, which is a SYN flood, not a ping flood. Ping floods use ICMP echo requests, not TCP connections, and rate limiting is a mitigation for ICMP-based floods, not for SYN floods.
★ When this WOULD be the correct answer
A ping flood attack would be the correct answer if the question described an attacker sending a high volume of ICMP echo request packets to overwhelm a target's network bandwidth or CPU, and the mitigation would be implementing rate limiting on ICMP traffic.
Why candidates choose this
Candidates may confuse 'flood' attacks and assume any overwhelming traffic is a ping flood, or they may not distinguish between TCP-based and ICMP-based attacks, leading them to choose a familiar mitigation like rate limiting.
✗Smurf attack; disable IP-directed broadcastsWrong answer — click to see why▾
Why this is wrong here
The question describes incomplete TCP connection requests exhausting server resources, which is a SYN flood, not a Smurf attack. A Smurf attack uses ICMP echo requests sent to a network's broadcast address with a spoofed source IP, causing amplification and targeting the victim with ICMP replies.
★ When this WOULD be the correct answer
A Smurf attack would be correct if the question described an attacker sending ICMP echo requests to a network broadcast address, using a spoofed source IP of the victim, causing all hosts on the network to reply to the victim, overwhelming it with ICMP traffic.
Why candidates choose this
Candidates may confuse any attack that consumes resources with a Smurf attack, especially if they remember that Smurf attacks cause resource exhaustion via amplification, but they overlook the specific protocol (ICMP vs. TCP) and the mechanism (broadcast vs. incomplete handshake).
✗ARP poisoning; enable dynamic ARP inspectionWrong answer — click to see why▾
Why this is wrong here
ARP poisoning targets the Address Resolution Protocol to intercept traffic on a local network, not to exhaust server resources via incomplete TCP connections. The described attack is a SYN flood, which exploits the TCP three-way handshake.
★ When this WOULD be the correct answer
This option would be correct in a question describing an attacker sending forged ARP messages to associate their MAC address with the IP of a legitimate device, causing traffic interception or denial of service. The mitigation would be Dynamic ARP Inspection (DAI) to validate ARP packets.
Why candidates choose this
Candidates may confuse network-layer attacks or think that any resource exhaustion attack involves poisoning, or they may recall ARP poisoning as a common attack without carefully matching the symptoms described.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
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Related to this question
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Wireless Security Protocols
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
TCP
TCP (Transmission Control Protocol) is a core internet protocol that ensures data is sent reliably and in order between devices over a network.
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Same concept, more angles
2 more ways this is tested on N10-009
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network administrator reviews firewall logs and sees thousands of SYN packets coming from various source IP addresses to a single internal web server. No ACK or RST packets are observed from these sources. Which type of attack is most likely occurring?
hard- A.DNS amplification attack
- ✓ B.SYN flood attack
- C.ARP spoofing attack
- D.Man-in-the-middle attack
Why B: A SYN flood attack exploits the TCP three-way handshake by sending a high volume of SYN packets to a target server without completing the handshake (no ACK or RST). This exhausts the server's connection table resources, preventing legitimate connections. The observed pattern of many SYN packets from various sources with no subsequent ACK or RST is the hallmark of a SYN flood.
Variation 2. A security analyst is investigating a network anomaly. The analyst notices that the company's web server is receiving a large number of TCP SYN packets from random source IP addresses, all destined for port 80. The web server is responding with SYN-ACK packets, but the connections are never completed. This is causing the server's connection table to fill up, degrading performance for legitimate users. Which type of attack is being described?
hard- A.Ping of death
- B.Smurf attack
- ✓ C.SYN flood
- D.DNS amplification
Why C: The attack described is a SYN flood, a type of denial-of-service (DoS) attack that exploits the TCP three-way handshake. The attacker sends a high volume of TCP SYN packets with spoofed source IP addresses to the server's port 80. The server responds with SYN-ACK packets to each spoofed source and waits for the final ACK, which never arrives, causing the server's half-open connection table (backlog queue) to fill up and exhaust resources, degrading performance for legitimate users.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA 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 N10-009 exam.