Introduction
Welcome to Video 3 of our free CompTIA Network+ training series.
In this video, we explore the Data Link Layer (Layer 2) of the OSI Model, a foundational component for local network communication. This layer is crucial in ensuring that data frames are delivered accurately from one device to another within the Local Area Network (LAN).
You’ll learn how MAC addresses are used to identify devices, the role of Layer 2 switches, how frames operate in a network, and the difference between logical and physical topology. This lesson also covers key concepts such as the MAC address table (CAM table) and how intermediate devices like switches and wireless access points facilitate network traffic.
If you’re preparing for the Network+ exam or looking to build strong foundational networking knowledge, this lesson is a must-watch!
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🧠 What is the Data Link Layer?
The Data Link Layer (Layer 2) of the OSI Model is responsible for node-to-node delivery of data within the same local network. It handles framing, error detection, addressing, and media access control.
🔄 PDU: Protocol Data Units
At Layer 2, the data is encapsulated into frames, the Protocol Data Units (PDUs) for this layer. These frames contain control information such as source and destination MAC addresses.
📡 Local Communication & MAC Addressing
Layer 2 works over the LAN (Local Area Network). Devices use MAC addresses (physical/hardware addresses) to communicate within the same network segment. These addresses are embedded in the Network Interface Cards (NICs) of the devices.
For example, if Computer A wants to send data to Computer B on the same LAN, it uses the MAC address of Computer B to ensure proper delivery.
🔌 Role of Layer 2 Devices
- Switches operate at Layer 2.
- They maintain a MAC address table (CAM table) to map connected devices to specific ports.
- If the destination MAC is unknown, switches broadcast the frame to learn it.
🗺️ Topologies
- Physical topology refers to how cables and devices are physically connected.
- Logical topology defines how data flows through the network.
🌐 End Systems & Intermediate Systems
- End systems: Computers, servers, mobile devices.
- Intermediate systems: Switches, hubs, wireless access points (APs).
Wireless access points bridge wired and wireless networks, enabling communication across mediums at Layer 2.