This is part of the CCNA1 Introduction to Networks course. This page will be updated with texts in the future… for now, please refer to my lecture on my YouTube channel.

• The data link layer of the OSI model (Layer 2) prepares network data for the physical network.
• The data link layer is responsible for network interface card (NIC) to network interface card communications.
• The IEEE 802 LAN/MAN data link layer consists of the following two sublayers: LLC and MAC.
• The two types of topologies used in LAN and WAN networks are physical and logical.
• Three common types of physical WAN topologies are: point-to-point, hub and spoke, and mesh.
• Half-duplex communications exchange data in one direction at a time. Full-duplex sends and receives data simultaneously.
• In contention-based multi-access networks, all nodes are operating in half-duplex.
• Examples of contention-based access methods include: CSMA/CD for bus-topology Ethernet LANs and CSMA/CA for WLANs.
• The data link frame has three basic parts: header, data, and trailer.
• Frame fields include: frame start and stop indicator flags, addressing, type, control, data, and error detection.
• Data link addresses are also known as physical addresses.
• Data link addresses are only used for link local delivery of frames.