Ethernet LAN Technology

Study Notes

Ethernet is the most widely used LAN technology today.
It is defined in the IEEE 802.2 and 802.3 standards.
Ethernet supports data bandwidths of 10 Mb/s, 100 Mb/s, 1000 Mb/s (1 Gb/s), 10,000 Mb/s (10 Gb/s), 40,000 Mb/s (40 Gb/s), and 100,000 Mb/s (100 Gb/s).

Ethernet operates in the data link layer and the physical layer.
It relies on the two separate sublayers of the data link layer: the Logical Link Control (LLC) and the MAC sublayers.
The LLC sublayer handles communication between the upper layers and the lower layers, and is implemented in software.
The MAC sublayer constitutes the lower sublayer of the data link layer, is implemented by hardware, and has two primary responsibilities: data encapsulation and media access control.

Data encapsulation provides three primary functions: frame delimiting, addressing, and error detection.
The MAC sublayer is responsible for the placement of frames on the media and the removal of frames from the media.

Ethernet standards have evolved since 1973, specifying faster and more flexible versions of the technology.
Early versions of Ethernet were relatively slow at 10 Mbps, while the latest versions operate at 10 Gigabits per second and faster.

The minimum Ethernet frame size is 64 bytes, and the maximum is 1518 bytes.
Frames less than 64 bytes are called a “collision fragment” or “runt frame” and are automatically discarded by receiving stations.
Frames greater than 1500 bytes of data are considered “jumbo” or “baby giant frames”.
If the size of a transmitted frame is less than the minimum or greater than the maximum, the receiving device drops the frame.

An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits (4 bits per hexadecimal digit).
Hexadecimal is used to represent Ethernet MAC addresses and IP Version 6 addresses.
Hexadecimal is a base sixteen system using the numbers 0 to 9 and the letters A to F.
MAC addresses are used to identify the actual source and destination, and are established by IEEE.
The IEEE assigns the vendor a 3-byte (24-bit) code, called the Organizationally Unique Identifier (OUI).

The MAC address is often referred to as a burned-in address (BIA), meaning the address is encoded into the ROM chip permanently.
The MAC address can be identified using the ipconfig /all command on a Windows host, or the ifconfig command on a MAC or Linux host.
Depending on the device and operating system, various representations of MAC addresses may be seen.

A unicast MAC address is the unique address used when a frame is sent from a single transmitting device to a single destination device.
A broadcast MAC address is used when many network protocols, such as DHCP and ARP, use broadcasts.
A broadcast packet contains a destination IPv4 address that has all ones (1s) in the host portion, indicating that all hosts on that local network will receive and process the packet.