- A
Layer 4 – Transport
Why wrong: Transport layer protocols are TCP/UDP; ARP is not at this layer.
- B
Layer 3 – Network
Why wrong: IP operates at Layer 3, but ARP is Layer 2.
- C
Layer 1 – Physical
Why wrong: Physical layer deals with raw bit transmission, not ARP messages.
- D
Layer 2 – Data Link
ARP is a Layer 2 protocol used for MAC address resolution; ARP spoofing directly targets this layer.
Question 754 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.
A security analyst notices that an attacker is sending forged ARP messages onto a local area network, linking the attacker's MAC address with the IP address of the default gateway. This allows the attacker to intercept traffic destined for the gateway. Which OSI layer is directly targeted by this attack?
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 2 – Data Link
ARP spoofing (or ARP poisoning) operates at Layer 2 (Data Link) because ARP messages are encapsulated directly within Ethernet frames and rely on MAC addresses, not IP routing. By forging ARP replies, the attacker corrupts the IP-to-MAC mapping in the victim's ARP cache, causing frames destined for the default gateway to be sent to the attacker's MAC address instead. This attack exploits the lack of authentication in the ARP protocol (RFC 826) and directly targets the Data Link layer's addressing and frame delivery mechanism.
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 – Transport
- ✗
Layer 3 – Network
Why it's wrong here
IP operates at Layer 3, but ARP is Layer 2.
- ✗
Layer 1 – Physical
Why it's wrong here
Physical layer deals with raw bit transmission, not ARP messages.
- ✓
Layer 2 – Data Link
Why this is correct
ARP is a Layer 2 protocol used for MAC address resolution; ARP spoofing directly targets this layer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse ARP's role in resolving IP addresses (Layer 3) with the layer at which the attack actually occurs, mistakenly choosing Layer 3 instead of recognizing that ARP operates at Layer 2 and exploits the Data Link layer's addressing scheme.
Detailed technical explanation
How to think about this question
Under the hood, ARP spoofing works by sending gratuitous ARP replies (or unsolicited ARP announcements) that update the target's ARP cache without a prior request. In a real-world scenario, an attacker on the same broadcast domain can use tools like `arpspoof` (from the dsniff suite) to continuously send forged ARP packets, effectively becoming a man-in-the-middle for all traffic between the victim and the gateway. This attack is mitigated by dynamic ARP inspection (DAI) on managed switches, which validates ARP packets against a trusted DHCP snooping binding database.
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.
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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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 2 – Data Link — ARP spoofing (or ARP poisoning) operates at Layer 2 (Data Link) because ARP messages are encapsulated directly within Ethernet frames and rely on MAC addresses, not IP routing. By forging ARP replies, the attacker corrupts the IP-to-MAC mapping in the victim's ARP cache, causing frames destined for the default gateway to be sent to the attacker's MAC address instead. This attack exploits the lack of authentication in the ARP protocol (RFC 826) and directly targets the Data Link layer's addressing and frame delivery mechanism.
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.
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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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