Content

| 1.4 |  | Basic Configuration of the Switch |
| 1.4.4 |  | Clearing a configuration |

Cisco routers run the Cisco Internetwork Operating System (IOS) and the command-line interface (CLI) embedded in the Cisco IOS software should be familiar by now. Some Cisco Catalyst switches such as the 2950 and 3550 series use an IOS-like operating system. A hybrid OS that evolved from Cisco’s acquisition of Kalpana in 1994. This Catalyst switch OS is normally referred to as command-based or IOS-based. The term command-based comes from the fact that hundreds of commands in various modes are used to configure a variety of technologies.

On Cisco Catalyst IOS-based switches, the CLI supports two basic modes of operation that are password-protected and similar to the Cisco routers. The Normal mode equates to a router's User EXEC mode, allowing most switch parameters to be viewed. No configuration changes are permitted. Changes can only be entered in PRIVILEGED mode. The privileged mode functionally equates to the router PRIVILEGED EXEC mode. In the privileged mode, configuration files can be viewed as with a router. Configuration changes can also be made. Also similar to a router, the switch privileged mode is entered with the enable command. Figure describes the main command modes, how to access each one, the prompt for that mode, and how to exit the mode.

Just as with Cisco routers, IOS-based Catalyst switches have a basic and extended configuration dialog that can be used for initial switch set up. A prompt to enter the System Configuration Dialog will automatically appear upon power up when no configuration exists in the NVRAM of the switch. To exit and enter the CLI operating mode, respond “No” to the prompt when asked to continue with the configuration dialog.

The switch CLI can be accessed through the console interface or through a Telnet session after an IP address has been assigned. Similar to a router, commands in a switch are additive. This means that adding configuration statements to an existing file will not completely overwrite the existing operating or running configuration. The only way to replace the running configuration with a configuration from NVRAM is to reboot the switch.

To clear both the running configuration and startup configuration, enter the erase startup-config command, then reboot the switch with the reload command or power cycle the switch. The configuration can be erased with any of the access methods. If the switch is rebooted during a Telnet session, the connection can be lost because the switch interface is shut down.

On the 2950 and 3550 switches, the erase startup-config command erases the configuration that is stored in NVRAM, but this does not erase the VLAN information. In order to erase the VLAN information, use the delete flash:vlan.dat command. To ensure absolutely no residual configurations, it is a good idea to erase the startup configuration, vlan database, then reboot the switch.

As addressed previously, Cisco IOS-based switch uses the enable command to access privileged mode where extensive configuration parameters can be viewed. However, the switch still cannot be configured in this mode. To configure the switch, enter the global configuration mode by using the configure command. The configure command puts the switch in global configuration mode, where switch configuration is possible.

Configuring the switch through the console port and through Telnet permits commands to be entered in real time, but only one at a time. The Cisco IOS-based switch does not immediately store commands in NVRAM. The command copy running-configuration startup-configuration, similar to the Cisco IOS router command, must be used. As with a router, a series of commands can be reversed with a reload command, provided the running configuration was not saved to NVRAM.