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Networking Fundamentals · Foundational

Data Link Layer (L2)

OSI Layer 2, which delivers frames between nodes on the same local network using physical (MAC) addresses.

Definition

The Data Link layer frames packets, adds source and destination MAC addresses, performs error detection with a frame check sequence, and controls access to the medium. IEEE splits it into the Logical Link Control (802.2) and Media Access Control sublayers. Switches, bridges and NICs operate at Layer 2.

Example

An Ethernet switch forwards a frame based on its destination MAC address.

Exam tip

The Layer 2 PDU is the frame and the Layer 2 address is the MAC address; do not confuse it with the Layer 3 packet and IP address.

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