- A
Layer 4
SYN flood is a Layer 4 (Transport) attack exploiting TCP connection handling.
- B
Layer 2
Why wrong: Layer 2 attacks include ARP spoofing, MAC flooding, etc., not SYN flood.
- C
Layer 7
Why wrong: Layer 7 attacks target application protocols like HTTP, DNS, etc.
- D
Layer 3
Why wrong: Layer 3 attacks include IP spoofing, routing attacks, etc., not SYN flood.
Question 502 of 1,000
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and 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.
An attacker sends a flood of SYN packets to a server, consuming its resources and preventing legitimate connections. Which OSI layer is this attack targeting?
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
✓
Layer 4
A SYN flood attack targets the TCP three-way handshake at the transport layer (Layer 4). By sending a high volume of SYN packets without completing the handshake, the attacker exhausts the server's connection queue, preventing legitimate TCP connections from being established. This directly exploits the stateful nature of TCP, which is a Layer 4 protocol.
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.
- ✓
Layer 4
Why this is correct
SYN flood is a Layer 4 (Transport) attack exploiting TCP connection handling.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Layer 2
Why it's wrong here
Layer 2 attacks include ARP spoofing, MAC flooding, etc., not SYN flood.
- ✗
Layer 7
- ✗
Layer 3
Why it's wrong here
Layer 3 attacks include IP spoofing, routing attacks, etc., not SYN flood.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing the network layer (Layer 3) with the transport layer (Layer 4), because IP addresses are involved in routing the packets, but the attack specifically targets TCP's connection management at Layer 4.
Detailed technical explanation
How to think about this question
The attack leverages the TCP backlog queue (defined by the `tcp_max_syn_backlog` kernel parameter in Linux). Each half-open connection consumes a slot in this queue; once full, the server drops new SYN packets. 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 handshake completes.
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 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.
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Communication and Network Security — study guide chapter
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FAQ
Questions learners often ask
What does this CISSP question test?
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Layer 4 — A SYN flood attack targets the TCP three-way handshake at the transport layer (Layer 4). By sending a high volume of SYN packets without completing the handshake, the attacker exhausts the server's connection queue, preventing legitimate TCP connections from being established. This directly exploits the stateful nature of TCP, which is a Layer 4 protocol.
What should I do if I get this CISSP 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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Last reviewed: Jul 4, 2026
This CISSP 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 CISSP exam.
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