N10-009 - Networking Concepts (23% of the exam) - Section 1.1

Explain concepts related to the Open Systems Interconnection (OSI) reference model and map common protocols and devices to each layer.

Identify the seven OSI layers - physical, data link, network, transport, session, presentation, and application - and explain the data unit and addressing each layer uses. Map common devices and protocols to their layer (a switch and MAC frames at Layer 2, a router and IP packets at Layer 3) and trace encapsulation as data moves down the stack.

OSI modelEncapsulationLayer 2 vs Layer 3Protocol data units

Practice question for this objective

Free sampleNetworking Conceptseasy

As a host encapsulates outgoing data, the Network layer and the Data Link layer each add addressing. Which statement correctly matches each address type to the layer that adds it?

AThe Data Link layer adds source and destination IP addresses, while the Network layer adds source and destination MAC addresses.
BThe Network layer adds source and destination IP addresses, while the Data Link layer adds source and destination MAC addresses. Correct
CThe Network layer adds source and destination port numbers, while the Data Link layer adds IP addresses.
DThe Transport layer adds source and destination MAC addresses, while the Network layer adds port numbers.

Encapsulation adds logical IP addresses at the Network layer and physical MAC addresses at the Data Link layer. Different layers add different addressing during encapsulation: the Network layer places logical source and destination IP addresses in the packet header, and the Data Link layer places physical source and destination MAC addresses in the frame header for delivery across the local link.

Why A is wrong: This inverts the two layers: IP addressing is a Network-layer function and MAC addressing is a Data Link function, not the reverse.

Why B is correct: The Network layer (Layer 3) writes IP addresses into the packet header and the Data Link layer (Layer 2) writes MAC addresses into the frame header during encapsulation.

Why C is wrong: Port numbers are added by the Transport layer, and IP addresses are added by the Network layer, so both assignments here sit at the wrong layer.

Why D is wrong: MAC addresses are a Data Link function and port numbers are a Transport function, so neither pairing in this option is correct.

See more N10-009 practice questions, answers explained.

Exam traps in Networking Concepts

Answers that look right on this material and are not. Each one is a distractor from a different question in the N10-009 bank for this domain.

Layer 1, the physical layer
Why it is wrong: A hub works at the physical layer and just regenerates signals, so this looks tempting, but a device that reads MAC addresses to forward frames is a switch operating at Layer 2.
A frame, because the Transport layer attaches source and destination MAC addresses before passing the unit down.
Why it is wrong: A frame is a real PDU name, but it is the Data Link layer (Layer 2) unit that carries MAC addresses, not anything the Transport layer produces.
It becomes a frame.
Why it is wrong: A frame is the data-link PDU formed when a packet is later wrapped with a MAC header and trailer, one step lower than the encapsulation described here.

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