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Cisco uBR924 Software Configuration Guide
OL-0337-05 (8/2002)
Appendix A Using Cisco IOS Software
Understanding the Command-Line Interface
Understanding the Command-Line Interface
The Cisco IOS command-line interface (CLI) is a text-based interface available on every Cisco router
that uses the Cisco IOS software. This allows a network administrator to quickly configure any of
Cisco’s many different models of routers without having to learn a unique interface for each.
The following guidelines apply to the CLI:
• The CLI is case-insensitive—for example, you can enter either SHOW VERSION or show version
to display the Cisco uBR924 router’s software revision.
• You can abbreviate commands and keywords to the minimum number of characters that define a
unique abbreviation. For example, you can abbreviate the show command to sh (but you cannot
abbreviate the show command to just s because several other commands also start with the letter s).
• If you enter an unrecognized command, the router assumes the command is actually the host name
of a PC or other router and tries to open a Telnet connection to it. If the router cannot find that host,
the connection will eventually time out and the CLI prompt will be redisplayed.
• By default, if a command displays more than one screen of data, it pauses the screen and displays
--More-- at the bottom of the screen. You can advance one line at a time by pressing the Return key,
advance one screen at a time by pressing the spacebar, or quit by pressing q.
• As a general rule, every configuration command can be disabled by prefixing the command with the
keyword no. For example, IP routing is enabled with the ip routing command; IP routing is disabled
with the no ip routing command.
• The CLI on the Cisco uBR924 router can be accessed either through a Telnet connection or through
a serial connection with its console port. (Web browser access to the CLI is not supported on the
Cisco uBR924 router when the Cable Monitor is active.)
These additional topics are covered in the sections that follow:
• The CLI contains many different command modes that allow access to different areas of the
Cisco uBR924 router’s configuration. Certain commands are available only in a specific command
mode. See “Command Modes” section on page A-3.
• The question mark character (?) displays a list of the available commands and can be used to display
help about a specific command. See “Context-Sensitive Help” section on page A-6.
• You can use the command history feature to quickly recall and edit previous commands. See
“Command History Features” section on page A-7.
• When commands produce long displays, you can use output modifiers to select which parts of the
display you want to see. See “Using Output Modifiers” section on page A-8.
Command Modes
The Cisco IOS software has many different modes of operation—each mode contains its own set of
commands that either display or configure a particular aspect of the Cisco uBR924 router’s
configuration. When you initially log in to the Cisco uBR924 router, you enter user EXEC mode, which
provides a limited number of commands that can only display information about the router; you cannot
change the router’s configuration in user EXEC mode.
To change the router’s configuration, you must enter privileged EXEC mode or one of the other
configuration modes. Each command mode has a unique prompt so that you can easily see which mode
you are in.
Table A-1 shows the most common modes that are used on the Cisco uBR924 router: