Content Overview A switch is a Layer 2 network device that acts as the concentration point for the connection of workstations, servers, routers, hubs, and other switches. A hub is an older type of concentration device which also provides multiple ports. However, hubs are inferior to switches because all devices connected to a hub reside in the same bandwidth domain that produces collisions. Another drawback to using hubs is that they only operate in half-duplex mode. In half-duplex mode, the hubs can send or receive data at any given time, but not both at the same time. Switches can operate in full-duplex mode, which means they can send and receive data simultaneously. Switches are multi-port bridges. Switches are the current standard technology for Ethernet LANs that utilize a star topology. A switch provides many dedicated, point-to-point virtual circuits between connected networking devices, so collisions are virtually impossible. Because of their dominant role in modern networks, the ability to understand and configure switches is essential for network support. A new switch will have a preset configuration with factory defaults. This configuration will rarely meet the needs of a network administator. Switches can be configured and managed from a command-line interface (CLI). Increasingly, networking devices can also be configured and managed using a web based interface and a browser. A network administrator must be familiar with many tasks to be effective in managing a network with switches. Some of these tasks are associated with maintaining the switch and its Internetworking Operating System (IOS). Others are associated with managing interfaces and tables for optimal, reliable, and secure operation. Basic switch configuration, upgrading the IOS, and performing password recovery are essential network administrator skills. Students completing this module should be able to:
Content 6.1 Starting the Switch 6.1.1 Physical startup of the Catalyst switch Switches are dedicated, specialized computers, which contain a central processing unit (CPU), random access memory (RAM), and an operating system. As shown in Figure , switches usually have several ports for the purpose of connecting hosts, as well as specialized ports for the purpose of management. A switch can be managed by connecting to the console port to view and make changes to the configuration. Switches typically have no power switch to turn them on and off. They simply connect or disconnect from a power source. Several switches from the Cisco Catalyst 2950 series are shown in Figure .
Content 6.1 Starting the Switch 6.1.2 Switch LED indicators The front panel of a switch has several lights to help monitor system activity and performance. These lights are called light-emitting diodes (LEDs). The front of the switch has the following LEDs: The System LED shows whether the system is receiving power and functioning correctly. The RPS LED indicates whether or not the remote power supply is in use. The Mode LEDs indicate the current state of the Mode button. The modes are used to determine how the Port Status LEDs are interpreted. To select or change the port mode, press the Mode button repeatedly until the Mode LEDs indicate the desired mode. The Port Status LEDs have different meanings, depending on the current value of the Mode LED.
Content 6.1 Starting the Switch 6.1.3 Verifying port LEDs during switch POST Once the power cable is connected, the switch initiates a series of tests called the power-on self test (POST). POST runs automatically to verify that the switch functions correctly. The System LED indicates the success or failure of POST. If the System LED is off but the switch is plugged in, then POST is running. If the System LED is green, then POST was successful. If the System LED is amber, then POST failed. POST failure is considered to be a fatal error. Reliable operation of the switch should not be expected if POST fails. The Port Status LEDs also change during switch POST. The Port Status LEDs turn amber for about 30 seconds as the switch discovers the network topology and searches for loops. If the Port Status LEDs turn green, the switch has established a link between the port and a target, such as a computer. If the Port Status LEDs turn off, the switch has determined that nothing is plugged into the port.
Content 6.1 Starting the Switch 6.1.4 Viewing initial bootup output from the switch In order to configure or check the status of a switch, connect a computer to the switch in order to establish a communication session. Use a rollover cable to connect the console port on the back of the switch to a COM port on the back of the computer. Start HyperTerminal on the computer. A dialog window will be displayed. The connection must first be named when initially configuring the HyperTerminal communication with the switch. Select the COM port to which the switch is connected using the pull-down menu, and click the OK button. A second dialog window will be displayed. Set up the parameters as shown, and click the OK button. Plug the switch into a wall outlet. The initial bootup output from the switch should be displayed on the HyperTerminal screen. This output shows information about the switch, details about POST status, and data about the switch hardware. After the switch has booted and completed POST, prompts for the System Configuration dialog are presented. The switch may be configured manually with or without the assistance of the System Configuration dialog. The System Configuration dialog on the switch is simpler than that on a router.
Content 6.1 Starting the Switch 6.1.5 Examining help in the switch CLI The command-line interface (CLI) for Cisco switches is very similar to the CLI for Cisco routers. The help command is issued by entering a question mark (?). When this command is entered at the system prompt, a list of commands available for the current command mode is displayed. The help command is very flexible. To obtain a list of commands that begin with a particular character sequence, enter those characters followed immediately by the question mark (?). Do not enter a space before the question mark. This form of help is called word help, because it completes a word. To list keywords or arguments that are associated with a particular command, enter one or more words associated with the command, followed by a space and then a question mark (?). This form of help is called command syntax help, because it provides applicable keywords or arguments based on a partial command. Interactive Media Activity Fill in the Blanks: Switches and Collision Domain After completing this activity, the student will be able to identify the role of a switch in preventing collisions and reducing collision domains.
Content 6.1 Starting the Switch 6.1.6 Switch command modes Switches have several command modes. The default mode is User EXEC mode. The User EXEC mode is recognized by its prompt, which ends in a greater-than character (>). The commands available in User EXEC