Ethernet LANs课件.ppt

Ethernet LANs Chapter 2 Chapter Objectives Describe issues related to increasing traffic on an Ethernet LAN Identify switched LAN technology solutions to Ethernet networking issues Describe the host-to-host packet delivery process through a switch Describe the features and functions of the Cisco IOS Software command-line interface (CLI) Start an access layer switch and use the CLI to configure and monitor the switch Enable physical, access, and port-level security on a switch List the ways in which an Ethernet LAN can be optimized Describe methods of troubleshooting switch issues Understanding the Challenges of Shared LANs LANs are a relatively low-cost means of sharing expensive resources. LANs allow multiple users and devices in a relatively small geographic area to exchange files and messages and to access shared resources such as those provided by file servers. LANs have rapidly evolved into support systems that are critical to communications within an organization. Segment length (the maximum length) is an important consideration when using Ethernet technology in a LAN. A segment is a network connection made by a single unbroken network cable. Ethernet cables and segments can span only a limited physical distance, beyond which transmissions will become degraded because of line noise, reduced signal strength, and failure to follow the carrier sense multiple access collision detect (CSMA/CD) specifications for collision detection. The guidelines for understanding Ethernet cable specifications, using 10BASE-T as an example: 10 refers to the speed supported, in this case 10 Mbps. BASE means it is baseband Ethernet. T means twisted-pair cable, Category 5 or above. For example, 10BASE-FL would be 10 Mbps, baseband, over fiber-optic (FL indicates fiber link). Each type of Ethernet network also has a maximum segment length Table 2-1. Ethernet Segment Distance Limitations Ethernet Specification Description Segment Length 10BASE-T 10-Mbps Ethernet over twisted-