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Ethernet

Ethernet is a Layer 2 protocol operating across the physical and data link layers of the OSI model, and it remains the dominant wired networking technology in homes and enterprise environments. This coverage examines its IEEE standards, sublayer architecture, and the role MAC addresses play in frame-level communication.

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About this video

Ethernet is the most widely deployed Layer 2 networking protocol in use today, found in virtually every home network and enterprise environment. It operates across both the physical and data link layers of the OSI model and interfaces directly with Layer 3, the network layer, making it a foundational component of end-to-end network communication. The data link layer itself is split into two distinct sublayers: the Logical Link Control sublayer, defined by IEEE 802.2, and the Media Access Control sublayer, defined along with the physical layer by the IEEE 802.3 standard. The IEEE 802.3 standard is not a single specification but a family of standards, each identified by an alphanumeric suffix that defines a specific combination of speed and media type. These standards range from early 10 Mbps copper-based specifications through 100 Mbps, 1 Gbps, 10 Gbps, and 40 Gbps variants, covering both copper and fiber implementations. Each standard precisely defines the signaling behavior and physical characteristics required for that medium and speed, providing a comprehensive framework for interoperable Ethernet networking across a broad range of environments. MAC addresses are the addressing mechanism Ethernet uses to identify devices at the data link layer. Expressed in hexadecimal, a MAC address is permanently assigned to a network interface card at the time of manufacture, a value referred to as a burned-in address. When an Ethernet frame is transmitted, it carries both a source MAC address identifying the sending interface and a destination MAC address identifying the intended recipient. Although MAC addresses can be overridden through software in some cases, the burned-in address remains the default identifier for any given network interface and is fundamental to how Ethernet manages device-to-device communication on a local network segment.

What you'll learn

What's covered

Ethernet Protocol

Aligned to

CompTIA Network+
1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.
2.2 Given a scenario, configure switching technologies and features.
Cisco CCNA
1.13 Describe switching concepts
Cisco CCST Networking
1.1 Identify the fundamental conceptual building blocks of networks
4.5 Explain basic switching concepts
Cisco CCST Cybersecurity
2.2 Explain how network addresses impact network security

Key terms

Open Systems Interconnection Model
OSI
A conceptual framework that standardizes network communication into seven distinct layers.
Physical Layer
Layer 1 of the OSI model, responsible for the transmission of raw bits over a physical medium.
Data Link Layer
Layer 2 of the OSI model responsible for node-to-node data transfer and error detection on a single network segment.
Media Access Control
MAC
A sublayer of the Data Link layer that controls how devices on a network gain access to a medium and transmit data.
Media Access Control
MAC
A sublayer of the Data Link layer that controls how devices on a network gain access to a medium and transmit data.
Network Interface Card
NIC
A hardware component that connects a computer to a network.
Logical Link Control
LLC
The upper sublayer of the OSI Data Link layer (Layer 2) that provides flow control, error notification, and an interface to the Network layer. LLC is defined in IEEE 802.2 and identifies the network layer protocol encapsulated within a frame.
IEEE 802.3
The IEEE standard that defines the MAC sublayer and physical layer specifications for Ethernet networks, covering signaling, speeds, and media types.

Transcript

Ethernet is a layer 2 protocol that operates and is widely used, and it is most likely what is operating in your home and if you work for a company. So it is very prevalent out there, and so we are going to spend quite a bit of time taking a look at Ethernet.

Layers And Sublayers

Ethernet is considered to run off of both the physical and data link layers. We can see it interfaces with layer three of the OSI model, which would be the network layer, but it runs within the physical and data link layer.

The data link layer actually has two different sublayers: an LLC sublayer and a MAC sublayer. The LLC sublayer is defined by IEEE 802.2, whereas both the MAC sublayer and the physical layer are actually defined by 802.3.

The 802.3 Standards

We can see these with these different standards that are out there. They all start with 802.3, and then there are different iterations of this. So here is the i, the u, the ab, the ae, the bq. You can imagine there is everything in between these, there is more after these, there is more before these. But this gives you kind of a range of some of the different standards that are out there.

This 10 represents 10 megabits per second, versus a 100 megabits per second, versus a thousand megabits per second, or gigabits per second, one gigabit per second. There is a 10 gigabit, there is a 40 gigabit. Some of these represent the copper lines, the standard for how copper lines communicate, while others of these are fiber. So we see a whole different range of different speeds within here, and it defines how the signaling happens and defines all of the intricacies of each one of those standards out there. So that is the sublayers over here, and then how these are defined using the IEEE standards.

MAC Addresses

There is a lot to be said around MAC addresses and what MAC addresses look like. This is not the time we are going to fully discuss what a MAC address is. We are just going to take a glimpse into what it is.

There are these numbers right here and a few letters in there. That is because it is hexadecimal. These are actually MAC addresses, and you will see a lot of different varying MAC addresses that are out here.

They come on the hardware itself. So if I were to buy a computer, or if I were to buy a laptop, then it has some sort of network interface card, or NIC. Usually it is built into the motherboard nowadays, but you have some sort of NIC that is on the machine, and each one of those interfaces comes with what is called a burned-in address, or an address that is hardcoded onto that machine. There are some ways to override that, so as you send out frames it will have a different MAC address, but for the most part, whatever frame is coming out of that NIC has a source address of whatever MAC address is burned into or assigned to that network interface.

So MAC addresses are a way to address network interface cards. As information is sent out of that card, it leaves destined for another MAC address. So you have a source MAC address that it is coming from and a destination MAC address that it is heading to. And that is how MAC addresses are used.

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