N10-009 Networking Concepts Practice Question
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?
⚠ Common exam trap
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.
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.
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
The Physical layer, Layer 1, deals with the physical transmission of raw bit streams over a medium. Devices like hubs, repeaters, and network cabling operate at this layer, focusing solely on electrical, optical, or radio signals. These devices are entirely unintelligent; they do not interpret frame headers or MAC addresses, nor do they make any forwarding decisions. Instead, they simply regenerate and propagate incoming signals to all connected ports without discrimination.
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
A network device operating at Layer 2, such as a switch, receives data in the form of frames. It makes forwarding decisions by examining the destination Media Access Control (MAC) address within the frame header. Switches maintain a MAC address table, also known as a Content Addressable Memory (CAM) table, to map MAC addresses to specific ports. If the destination MAC address is unknown, the switch will flood the frame out all ports except the ingress port.
- ✗
Layer 3
Why it's wrong here
Layer 3, the Network layer, is primarily concerned with logical addressing and routing packets across different networks. Devices such as routers make forwarding decisions based on destination IP addresses, consulting their routing tables to determine the optimal path. While routers encapsulate packets into frames for transmission over a local segment, their fundamental forwarding logic is based on IP addresses, not the MAC addresses used for local delivery within a single network segment.
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, the Transport layer, is responsible for end-to-end communication between applications, managing data segmentation, reassembly, and flow control. Devices like advanced firewalls or load balancers operate at this layer, inspecting TCP/UDP port numbers to filter traffic or direct application requests. However, these devices do not directly forward frames based on MAC addresses; their forwarding logic relies on higher-level protocol information after Layer 2 and 3 processing.
When this WOULD be correct
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.
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
A network device operating at Layer 2, such as a switch, receives data in the form of frames. It makes forwarding decisions by examining the destination Media Access Control (MAC) address within the frame header. Switches maintain a MAC address table, also known as a Content Addressable Memory (CAM) table, to map MAC addresses to specific ports. If the destination MAC address is unknown, the switch will flood the frame out all ports except the ingress port.
✗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?”
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 |
Go deeper
Related to this question
Learn chapter
Interior vs Exterior Routing Protocols
Key term
OSI model
The OSI model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers, from physical hardware to application software.
Key term
Frame
A frame is a unit of data at the Data Link layer of networking, containing header, payload, and trailer information for local network delivery.
About these practice questions
This N10-009 question is part of Courseiva's 464-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on N10-009
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 switch forwards frames based on which address?
easy- ✓ A.MAC address
- B.IP address
- C.Port number
- D.Domain name
Why A: A network switch operates at Layer 2 (Data Link Layer) of the OSI model and uses MAC addresses to make forwarding decisions. When a frame arrives, the switch examines the destination MAC address, looks it up in its MAC address table (CAM table), and forwards the frame only to the port associated with that MAC address, reducing collision domains and improving network efficiency.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.