Summary

Summary
This page summarizes the topics discussed in this module.


The Cisco IOS is embedded in all Cisco routers. The purpose of the Cisco IOS software is to provide basic routing and switching functions, to give the network scalability, and to provide a reliable and secure way to access the network resources.

The Cisco IOS software uses a command-line interface accessed through a console session or by using a dial-up connection through a modem connected to the router AUX port. A Telnet session to the router can be established remotely if at least one interface is configured with an IP address.

Cisco IOS software provides a command interpreter service known as the command EXEC. After each command is entered, the EXEC validates and executes the command.

There are two access levels available for added security. The user EXEC mode, which is identified by a > prompt, provides basic monitoring commands. From user EXEC mode, a user can run basic commands. For example, the user can view router properties or make temporary changes to the terminal settings. No password is required to access the user EXEC mode.

The privileged EXEC mode, which is identified by a # prompt, is the global configuration and management mode. This mode allows access to all router commands. Within privileged EXEC mode, a user can configure the router interfaces, connect to external sources, load protocols, and move or delete files.

The enable command is used to access privileged EXEC mode. Privileged EXEC mode can also be configured with user name and password for more security.

Enter ? to view a list of available commands in a given mode. If the system detects any errors in a command, a carat symbol (^) will display as a marker. In addition, the enhanced editing mode provides a set of editing key functions that allows the user to edit a command line as it is being typed.

Compatibility issues with the router flash and RAM memory are major considerations before a newer release of the Cisco IOS software can be installed. Use the show version command to check current resources and available memory. Newer releases with more features will typically require more memory. The show flash command is used to verify that the system has sufficient memory to load a new Cisco IOS image. Use of the Cisco Software Advisor provides the most current information and allows the selection of options that meet network requirements.