Network interface cards have a DLC address that identifies each card; for instance, Ethernet and other types of cards have a 48-bit MAC address built into the cards' firmware when they are manufactured.

The Logical Link Control (LLC) data communication protocol layer is the upper sublayer of the Data Link Layer specified in the seven-layer OSI model (layer 2). It provides multiplexing and flow control mechanisms that make it possible for several network protocols (IP, IPX) to coexist within a multipoint network and to be transported over the same network media.

The LLC sub-layer acts as an interface between the Media Access Control (MAC) sublayer and the network layer. It is the same for the various physical media (such as Ethernet, token ring, and WLAN).


The LLC sublayer is primarily concerned with:
Multiplexing protocols transmitted over the MAC layer (when transmitting) and decoding them (when receiving).
Providing flow and error control
The protocol used for LLC in IEEE 802 networks and in some non-IEEE 802 networks such as FDDI is specified by the IEEE 802.2 standard.
Some non-IEEE 802 protocols can be thought of as being split into MAC and LLC layers. For example, while HDLC specifies both MAC functions (framing of packets) and LLC functions (protocol multiplexing, flow control, detection, and error control through a retransmission of dropped packets when indicated), some protocols such as Cisco HDLC can use HDLC-like packet framing and their own LLC protocol.
Another example of a Data Link Layer which is split between LLC (for flow and error control) and MAC (for multiple access) is the ITU-T G.hn standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables).
An LLC header tells the Data Link layer what to do with a packet once a frame is received. It works like this: A host will receive a frame and look in the LLC header to find out where the packet is destined for - for example, the IP protocol at the Network layer or IPX.
LLC also does ciphering and deciphering of SN-PDU (SNDCP) packets.
Virtual Circuit Multiplexing (VC-MUX)
Subnetwork Access Protocol (SNAP)
LLC