IOS

The IOS stands for Internetwork Operating System. It provides the command line interface to many Cisco Systems brand routers, and being an operating system, also contains command execution and actual routing software. It is very similar in structure to MS-DOS and Linux, as well as other router operating systems.

Command prompt output:

• User Mode: Router>
• Priveledged Exec Mode: Router#

command format:

Commands are single words. Arguments are interpreted when a space seperates the argument from the command. Cisco calls arguments subcommands. Command-line arguments may contain dashes.

• Example: show running-config. (shows the active configuration.)

Autocomplete

Unlike most operating systems, the CIOS has so few commands that it will interpret truncated commands without requiring the user to autocomplete the command. Entering a command that requires an argument without an argument will produce:

%Incomplete Command.

To display arguments use the "?" argument. ("?" is also the help command.)

Command History

Like most operating systems, the CIOS has a command history. It can be accessed using the up and down arrow keys (like other operating systems.)

Mode(s)

Commands will not be shown to users that or do not have sufficient privilege to access them. Commands will fail to execute as if they don't exist. The highest priveledge mode for a user is the "Priveleged Exec" mode. (accessible using the Enable command).

Administrators should also be familiar with the following modes:

• Global Configuration Mode.
• config-mode
• Rxboot mode