Which OSI layer adds the source MAC address to a PDU during encapsulation?

• A. Data Link Layer
• B. Application Layer
• C. Network Layer
• D. Presentation Layer

Answer: (A)

Layer 2 handles framing and MAC addressing. When a network-layer packet arrives for sending, the Data Link layer encapsulates it by forming a frame and adding a header that carries the source and destination MAC addresses. This enables local delivery on the same LAN, as switches use these MAC addresses to forward frames to the next hop or destination device. The higher layers don’t deal with physical or MAC addressing—Application handles user data, Network handles IP addressing and routing, and Presentation handles data formatting. So the Data Link layer is responsible for adding the source MAC address during encapsulation.