- A
Layer 1
Why wrong: Layer 1 devices like hubs and repeaters do not make forwarding decisions based on MAC addresses. They only regenerate signals on all ports.
- B
Layer 2
This describes a switch, which operates at the Data Link layer (Layer 2). It uses MAC addresses to forward frames and floods unknown unicast frames.
- C
Layer 3
Why wrong: Layer 3 devices like routers use IP addresses to make forwarding decisions and can modify packets (e.g., TTL). They do not operate primarily on MAC addresses.
- D
Layer 4
Why wrong: Layer 4 (Transport layer) handles end-to-end communication and segmentation. Devices at this layer include firewalls that filter based on ports, but they do not forward based on MAC addresses.
Question 323 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.
A network device receives a frame and forwards it based on the destination MAC address. The device does not modify the frame and only floods unknown unicast frames. At which layer of the OSI model does this device operate?
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
This device operates at Layer 2 (Data Link Layer) because it forwards frames based on the destination MAC address, does not modify the frame, and floods unknown unicast frames. These behaviors are characteristic of a transparent bridge or switch, which uses a MAC address table to make forwarding decisions without examining IP addresses or modifying the frame. Layer 2 devices do not perform routing or alter the frame's content, distinguishing them from Layer 3 routers.
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
Why it's wrong here
Layer 1 devices like hubs and repeaters do not make forwarding decisions based on MAC addresses. They only regenerate signals on all ports.
When this WOULD be correct
This option would be correct if the question described a device that regenerates electrical signals without inspecting any frame headers, such as a hub or repeater, and asked at which OSI layer it operates.
- ✓
Layer 2
Why this is correct
This describes a switch, which operates at the Data Link layer (Layer 2). It uses MAC addresses to forward frames and floods unknown unicast frames.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Layer 3
Why it's wrong here
Layer 3 devices like routers use IP addresses to make forwarding decisions and can modify packets (e.g., TTL). They do not operate primarily on MAC addresses.
When this WOULD be correct
A question that describes a device forwarding based on destination IP address, performing routing decisions, and modifying the frame (e.g., decrementing TTL) would make Layer 3 the correct answer.
- ✗
Layer 4
Why it's wrong here
Layer 4 (Transport layer) handles end-to-end communication and segmentation. Devices at this layer include firewalls that filter based on ports, but they do not forward based on MAC addresses.
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 2Correct answer▾
Why this is correct
This describes a switch, which operates at the Data Link layer (Layer 2). It uses MAC addresses to forward frames and floods unknown unicast frames.
✗Layer 1Wrong answer — click to see why▾
Why this is wrong here
The device forwards based on MAC addresses and floods unknown unicasts, which are Layer 2 functions. Layer 1 devices (e.g., repeaters, hubs) do not examine MAC addresses and simply regenerate signals.
★ When this WOULD be the correct answer
This option would be correct if the question described a device that regenerates electrical signals without inspecting any frame headers, such as a hub or repeater, and asked at which OSI layer it operates.
Why candidates choose this
Candidates may confuse the physical transmission of frames with the switching logic, thinking that any device handling frames operates at Layer 1 because it deals with bits.
✗Layer 3Wrong answer — click to see why▾
Why this is wrong here
Layer 3 devices (routers) forward based on destination IP address, not MAC address, and they modify the frame by decrementing TTL and recalculating checksums. This device forwards by MAC address and does not modify frames, which is Layer 2 switching.
★ When this WOULD be the correct answer
A question that describes a device forwarding based on destination IP address, performing routing decisions, and modifying the frame (e.g., decrementing TTL) would make Layer 3 the correct answer.
Why candidates choose this
Candidates may confuse MAC address forwarding with IP forwarding, or think that any forwarding device operates at Layer 3, overlooking the specific behavior of switches at Layer 2.
✗Layer 4Wrong answer — click to see why▾
Why this is wrong here
Layer 4 (Transport) handles end-to-end communication, segmentation, and flow control using ports, not MAC address forwarding. The device described operates at Layer 2 (Data Link) because it forwards based on MAC addresses and floods unknown unicasts.
★ When this WOULD be the correct answer
A question asking: 'Which OSI layer is responsible for reliable data transfer between hosts, including segmentation and error recovery?' would make Layer 4 correct, as it describes TCP/UDP functions.
Why candidates choose this
Candidates may confuse the device's forwarding behavior with higher-layer processing, thinking that any intelligent forwarding implies Layer 4, or they may misremember that switches operate at Layer 2 and routers at Layer 3, leading to Layer 4 as a guess.
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
The N10-009 exam often tests the distinction between Layer 2 switching and Layer 3 routing by describing a device that forwards based on MAC addresses but does not modify frames, leading candidates to mistakenly think of a router (Layer 3) because they associate 'forwarding' with routing, when in fact the key clue is the lack of frame modification and the flooding of unknown unicasts.
Detailed technical explanation
How to think about this question
Under the hood, a Layer 2 switch builds its MAC address table by learning the source MAC address of incoming frames and associating it with the ingress port. When an unknown unicast frame arrives (destination MAC not in the table), the switch floods it out all ports except the receiving port, a process defined in IEEE 802.1D for transparent bridging. In real-world scenarios, this flooding behavior can cause unnecessary traffic in large VLANs, which is why features like MAC address table aging and port security are critical for performance and security.
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.
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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 — This device operates at Layer 2 (Data Link Layer) because it forwards frames based on the destination MAC address, does not modify the frame, and floods unknown unicast frames. These behaviors are characteristic of a transparent bridge or switch, which uses a MAC address table to make forwarding decisions without examining IP addresses or modifying the frame. Layer 2 devices do not perform routing or alter the frame's content, distinguishing them from Layer 3 routers.
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.
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Last reviewed: Jun 11, 2026
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