- A
Layer 1 – Physical
Why wrong: The Physical layer transmits raw bits over the medium but does not create frames or add MAC addresses.
- B
Layer 2 – Data Link
The Data Link layer creates frames, adds MAC addresses, and provides error detection. It is the correct layer for this function.
- C
Layer 3 – Network
Why wrong: The Network layer handles logical addressing (IP) and routing decisions, not MAC addressing.
- D
Layer 4 – Transport
Why wrong: The Transport layer segments data and provides reliable delivery, but it does not use MAC addresses.
Question 44 of 520
N10-009 Networking Concepts Practice Question
This N10-009 practice question tests your understanding of networking concepts. 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.
At which layer of the OSI model does a network device encapsulate data into frames and add source and destination MAC addresses?
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
The Data Link layer (Layer 2) is responsible for node-to-node communication and encapsulates packets from the Network layer into frames. It adds a header containing the source and destination MAC addresses, which are used for delivery within the same local network segment. This process is defined by IEEE 802 standards such as Ethernet (802.3) and Wi-Fi (802.11).
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 1 – Physical
Why it's wrong here
The Physical layer transmits raw bits over the medium but does not create frames or add MAC addresses.
When this WOULD be correct
A question asking which layer defines electrical signals, cable types, or bit rates (e.g., 'At which layer are voltage levels and connector types defined?') would have Layer 1 as the correct answer.
- ✓
Layer 2 – Data Link
Why this is correct
The Data Link layer creates frames, adds MAC addresses, and provides error detection. It is the correct layer for this function.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Layer 3 – Network
Why it's wrong here
The Network layer handles logical addressing (IP) and routing decisions, not MAC addressing.
When this WOULD be correct
A question asking 'At which OSI layer does a router operate based on IP addresses?' or 'Which layer adds source and destination IP addresses to packets?' would have Layer 3 as the correct answer.
- ✗
Layer 4 – Transport
Why it's wrong here
The Transport layer segments data and provides reliable delivery, but it does not use MAC addresses.
When this WOULD be correct
A question asking: 'At which layer does TCP segment data and add port numbers?' would make Layer 4 correct, as TCP operates at the Transport layer.
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.
✓Layer 2 – Data LinkCorrect answer▾
Why this is correct
The Data Link layer creates frames, adds MAC addresses, and provides error detection. It is the correct layer for this function.
✗Layer 1 – PhysicalWrong answer — click to see why▾
Why this is wrong here
Frames and MAC addresses are data link layer (Layer 2) concepts; Layer 1 handles raw bit transmission without framing or addressing.
★ When this WOULD be the correct answer
A question asking which layer defines electrical signals, cable types, or bit rates (e.g., 'At which layer are voltage levels and connector types defined?') would have Layer 1 as the correct answer.
Why candidates choose this
Candidates may confuse physical transmission of bits with the framing and addressing that occurs at Layer 2, or they may think MAC addresses are part of the physical hardware.
✗Layer 3 – NetworkWrong answer — click to see why▾
Why this is wrong here
Layer 3 (Network) handles logical addressing (e.g., IP addresses) and routing, not frame encapsulation or MAC addresses. Frames and MAC addresses are specific to Layer 2 (Data Link).
★ When this WOULD be the correct answer
A question asking 'At which OSI layer does a router operate based on IP addresses?' or 'Which layer adds source and destination IP addresses to packets?' would have Layer 3 as the correct answer.
Why candidates choose this
Candidates may confuse MAC addresses with IP addresses or think that network devices like switches (Layer 2) and routers (Layer 3) both deal with addressing, leading them to incorrectly select Layer 3.
✗Layer 4 – TransportWrong answer — click to see why▾
Why this is wrong here
Layer 4 (Transport) handles end-to-end communication, segmentation, and reassembly, not frame encapsulation or MAC addressing. Frames and MAC addresses are specific to Layer 2 (Data Link).
★ When this WOULD be the correct answer
A question asking: 'At which layer does TCP segment data and add port numbers?' would make Layer 4 correct, as TCP operates at the Transport layer.
Why candidates choose this
Candidates may confuse the encapsulation process, thinking that adding headers (like TCP headers) is similar to adding MAC addresses, or they may not clearly distinguish between layers.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between MAC addresses (Layer 2) and IP addresses (Layer 3), and the trap here is that candidates may confuse the encapsulation process and incorrectly associate MAC addressing with the Network layer due to familiarity with IP addressing.
Detailed technical explanation
How to think about this question
Framing at Layer 2 includes not only MAC addresses but also a preamble, start frame delimiter (SFD), and a frame check sequence (FCS) for error detection. In Ethernet, the minimum frame size is 64 bytes (including the FCS) to ensure proper collision detection in half-duplex environments. A real-world scenario where this matters is when a switch learns MAC addresses by examining the source MAC in incoming frames to build its MAC address table, which is critical for efficient forwarding.
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 practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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 N10-009 question test?
Networking Concepts — This question tests Networking Concepts — 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 — The Data Link layer (Layer 2) is responsible for node-to-node communication and encapsulates packets from the Network layer into frames. It adds a header containing the source and destination MAC addresses, which are used for delivery within the same local network segment. This process is defined by IEEE 802 standards such as Ethernet (802.3) and Wi-Fi (802.11).
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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Last reviewed: Jun 30, 2026
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.
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