The data link layer is Layer 2 of the OSI model. It organizes data from the network layer into frames and applies the addressing and transmission rules needed to move those frames across a directly connected network link. Ethernet is a familiar example, but frame formats and link behavior depend on the protocol.
What the data link layer does
Layer 2 sits between the network layer (Layer 3) and the physical layer (Layer 1). It provides an interface between network-layer data and the technology carrying it across a local link. The link might connect a device to a local network or connect network devices to one another; Layer 2 handles delivery over that link, not routing end to end across multiple networks.
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Its protocol takes data from above, places it in a link-layer unit commonly called a frame, and applies the rules needed for that type of link. The frame’s structure and the details of delivery are protocol-specific, so Ethernet frames are an example—not a universal Layer 2 format. IEEE 802.3 specifies Ethernet LAN operation and a common MAC specification: IEEE 802.3-2022.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsFrames and addresses: Ethernet as an example
An Ethernet frame carries network-layer data across an Ethernet link and includes source and destination MAC addresses. These addresses support delivery on the local Ethernet network. They are different from IP addresses: MAC addresses belong to the link layer, while IP addresses belong to the network layer and are used for communication across networks.
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A Layer 2 switch uses link-layer information to forward frames within a LAN. A router instead makes network-layer forwarding decisions to move traffic between networks. The two devices therefore operate at different layers and serve different forwarding roles.
Cisco’s Ethernet overview explains Ethernet in practical terms, while its sample chapter on Ethernet frames illustrates frame handling and Layer 2 switching.
LLC and MAC in IEEE 802 LANs
In IEEE 802 LAN architecture, the data link layer is described as two sublayers:
- Logical Link Control (LLC): The upper sublayer, providing a logical interface with the network layer and identifying protocol information.
- Media Access Control (MAC): The sublayer associated with the particular access method, including medium-specific access functions.
This split describes IEEE 802 architecture; it should not be taken to mean that every link-layer protocol uses sublayers with these names. IEEE’s catalog marks the 1985 edition of IEEE 802.2 as superseded and its 1989 edition as withdrawn. The IEEE 802.2 working-group page says the standard was withdrawn in 2010 and points to ISO/IEC 8802-2 as stabilized. These references provide architectural context, not a claim that those older catalog entries are current editions: IEEE 802.2-1985 and IEEE/ISO 802.2-1989.
Does Layer 2 guarantee reliable delivery?
No single reliability behavior applies to every data-link protocol. Depending on the protocol and service, a link may use acknowledgements, sequencing, flow control, or recovery. Other services provide best-effort, connectionless transfer. Cisco’s explanation of Logical Link Control describes different LLC service types; reliability depends on the service selected rather than being guaranteed by the data link layer in all networks.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How Layer 2 differs from Layer 3
The simplest distinction is scope: Layer 2 carries frames over a link, while Layer 3 handles packets and forwarding across networks. In the Ethernet-and-IP example, Ethernet uses MAC addresses for local frame delivery, whereas IP addresses identify network-layer destinations. Switches forward frames within a LAN; routers forward between networks.
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