This module returns to some of the roots of modern Ethernet LANs with a discussion of the evolution of Ethernet/802.3, the most commonly deployed LAN architecture. A look at the historical context of LAN development and various networking devices that can be utilized at Layer 1, Layer 2, and Layer 3 of the OSI model will help provide a solid understanding of the reasons why network devices have evolved as they have.

Until recently, most Ethernet networks were built using repeaters. When the performance of these networks began to suffer because too many devices shared the same segment, network engineers added bridges to create multiple collision domains. As networks grew in size and complexity, the bridge evolved into the modern switch, allowing microsegmentation of the network. Today’s networks typically are built using switches and routers, often with the routing and switching function in the same device.

Many modern switches are capable of performing varied and complex tasks in the network. This module will provide an introduction to network segmentation and will describe the basics of switch operation.

Switches and bridges perform much of the heavy work in a LAN, making nearly instantaneous decisions when frames are received. This module describes in detail how frames are transmitted by switches, how frames are filtered, and how switches learn the physical addresses of all network nodes. As an introduction to the use of bridges and switches in LAN design, the principles of LAN segmentation and collision domains are also covered.

Switches are Layer 2 devices that are used to increase available bandwidth and reduce network congestion. A switch can segment a LAN into microsegments, which are segments with only a single host. Microsegmentation creates multiple collision-free domains from one larger domain. As a Layer 2 device, the LAN switch increases the number of collision domains, but all hosts connected to the switch are still part of the same broadcast domain.

Students completing this module should be able to:

• Describe the history and function of shared, half-duplex Ethernet
• Define collision as it relates to Ethernet networks
• Define microsegmentation
• Define CSMA/CD
• Describe some of the key elements affecting network performance
• Describe the function of repeaters
• Define network latency
• Define transmission time
• Describe the basic function of Fast Ethernet
• Define network segmentation using routers, switches, and bridges
• Describe the basic operations of a switch
• Define Ethernet switch latency
• Explain the differences between Layer 2 and Layer 3 switching
• Define symmetric and asymmetric switching
• Define memory buffering
• Compare and contrast store-and-forward and cut-through switching
• Understand the differences between hubs, bridges, and switches
• Describe the main functions of switches
• List the major switch frame transmission modes
• Describe the process by which switches learn addresses
• Identify and define forwarding modes
• Define LAN segmentation
• Define microsegmentation using switching
• Describe the frame-filtering process
• Compare and contrast collision and broadcast domains
• Identify the cables needed to connect switches to workstations
• Identify the cables needed to connect switches to switches