The data link layer or layer 2 is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN)

The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer.

Layer 2 devices deliver frames using unique hardware addresses. A frame's header contains source and destination addresses that indicate which device originated the frame and which device is expected to receive and process it. In contrast to the hierarchical and routable addresses of the network layer, layer-2 addresses are flat, meaning that no part of the address can be used to identify the logical or physical group to which the address belongs.

The data link thus provides data transfer across the physical link. That transfer can be reliable or unreliable

The data link layer provides error-detection and error-correction by implementing redundancy check algorithms such as CRC and LRC. The calculation of CRC and LRC is done by processing the data to be sent bit by bit. After calculating, the obtained checksum is added to the trailer of the data frame to be sent.