The answer is a SYN flood attack, mitigated by enabling TCP intercept or SYN cookies. This attack overwhelms a server by sending a high volume of TCP SYN packets without completing the three-way handshake, exhausting the server’s connection queue and causing it to drop legitimate requests. TCP intercept (on Cisco devices) or SYN cookies (RFC 4987) validate handshakes before allocating resources, preventing queue exhaustion. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of denial-of-service attack types and their countermeasures; a common trap is confusing SYN floods with ICMP floods or ping of death. Remember the key: the attacker never sends the final ACK, so the server is left holding half-open connections. Memory tip: “SYN sent, ACK missing—queue is glistening.”
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 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?
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.
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.
✓
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
Ping flood; implement rate limiting
Why it's wrong here
Ping floods use ICMP echo requests, not incomplete TCP connections.
✗
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.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that 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.
Detailed technical explanation
How to think about this question
Under the hood, a SYN flood exploits the TCP backlog queue (typically 1024 entries on Linux) by sending spoofed SYN packets; the server responds with SYN-ACK and waits for an ACK that never arrives, eventually filling the queue. SYN cookies work by encoding connection state in the initial sequence number, allowing the server to avoid storing state until the handshake completes, as defined in RFC 4987. In real-world scenarios, attackers often use botnets to generate millions of SYN packets per second, overwhelming even large servers without mitigation.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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: 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.
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.
About these practice questions
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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.
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Question Discussion
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