Cisco Systems 78-11741-02 manual Using Cisco IOS Software, Understanding Command Modes, Xxxix

Using Cisco IOS Software

This chapter provides helpful tips for understanding and configuring Cisco IOS software using the command-line interface (CLI). It contains the following sections:

•Understanding Command Modes

•Getting Help

•Using the no and default Forms of Commands

•Saving Configuration Changes

•Filtering Output from the show and more Commands

•Identifying Supported Platforms

For an overview of Cisco IOS software configuration, refer to the Cisco IOS Configuration

Fundamentals Configuration Guide.

For information on the conventions used in the Cisco IOS software documentation set, see the chapter “About Cisco IOS Software Documentation” located at the beginning of this book.

Understanding Command Modes

You use the CLI to access Cisco IOS software. Because the CLI is divided into many different modes, the commands available to you at any given time depend on the mode you are currently in. Entering a question mark (?) at the CLI prompt allows you to obtain a list of commands available for each command mode.

When you log in to the CLI, you are in user EXEC mode. User EXEC mode contains only a limited subset of commands. To have access to all commands, you must enter privileged EXEC mode, normally by using a password. From privileged EXEC mode you can issue any EXEC command—user or privileged mode—or you can enter global configuration mode. Most EXEC commands are one-time commands. For example, show commands show important status information, and clear commands clear counters or interfaces. The EXEC commands are not saved when the software reboots.

Configuration modes allow you to make changes to the running configuration. If you later save the running configuration to the startup configuration, these changed commands are stored when the software is rebooted. To enter specific configuration modes, you must start at global configuration mode. From global configuration mode, you can enter interface configuration mode and a variety of other modes, such as protocol-specific modes.

ROM monitor mode is a separate mode used when the Cisco IOS software cannot load properly. If a valid software image is not found when the software boots or if the configuration file is corrupted at startup, the software might enter ROM monitor mode.

Cisco IOS IP Configuration Guide

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