Understanding Command Modes

This section describes the Cisco IOS command mode structure. Each command mode supports specific Cisco IOS commands. For example, you can use the interface type number command only from global configuration mode.

The following Cisco IOS command modes are hierarchical. When you begin a router session, you are in user EXEC mode.

•  User EXEC

•  Privileged EXEC

•  Global configuration

Table lists the command modes that are used in this guide, how to access each mode, the prompt you see in that mode, and how to exit to a mode or enter the next mode. Because each mode configures different router elements, you might need to enter and exit modes frequently. You can see a list of available commands for a particular mode by entering a question mark (?) at the prompt. For a description of each command, including syntax, see the Cisco IOS 12.2 documentation set.

Enable Secret and Enable Passwords

By default, the router ships without password protection. Because many privileged EXEC commands are used to set operating parameters, you should password-protect these commands to prevent unauthorized use.

You can use two commands to do this:

•   enable secret password (a very secure, encrypted password)

•   enable password (a less secure, unencrypted password)

You must enter an enable secret password to gain access to privileged EXEC mode commands.

For maximum security, the passwords should be different. If you enter the same password for both during the setup process, your router accepts the passwords, but warns you that they should be different.

An enable secret password can contain from 1 to 25 uppercase and lowercase alphanumeric characters. An enable password can contain any number of uppercase and lowercase alphanumeric characters. In both cases, a number cannot be the first character. Spaces are also valid password characters; for example, two words is a valid password. Leading spaces are ignored; trailing spaces are recognized.

Entering Global Configuration Mode

To make any configuration changes to your router, you must be in global configuration mode. This section describes how to enter global configuration mode while using a terminal or PC that is connected to your router console port.

To enter global configuration mode:

Step 1 After your router boots up, answer no when the following question displays:

Would you like to enter the initial configuration dialog [yes]: no

Step 2 Enter the enable command:

router> enable

Step 3 If you have configured your router with an enable password, enter it when you are prompted.

The enable password does not show on the screen when you enter it. This example shows how to enter privileged EXEC mode:

Password: enable_password

router#

Enable mode is indicated by the # in the prompt. You can now make changes to your router configuration.

Step 4 Enter the configure terminal command to enter global configuration mode, indicated by (config)# in the prompt:

router# configure terminal

router (config)#

You can now make changes to your router configuration.

Using Commands

This section provides some tips about entering Cisco IOS commands at the command-line interface (CLI).

Abbreviating Commands

You only have to enter enough characters for the router to recognize the command as unique. This example shows how to enter the show version command:

router # sh v

Undoing Commands

If you want to disable a feature or undo a command you entered, you can enter the keyword no before most commands; for example, no ip routing.

Command-Line Error Messages

Table  lists some error messages that you might encounter while using the CLI to configure your router.

% Ambiguous command:
"show con"

% Incomplete command.

% Invalid input detected at
`^' marker.

Saving Configuration Changes

You need to enter the copy running-config startup-config command to save your configuration changes to nonvolatile RAM (NVRAM) so that they are not lost if there is a system reload or power outage. This example shows how to use this command to save your changes:

router # copy running-config startup-config

Destination filename [startup-config]?

Press Return to accept the default destination filename startup-config, or enter your desired destination filename and press Return.

It might take a minute or two to save the configuration to NVRAM. After the configuration has been saved, the following message appears:

Building configuration...

router #

• Pin It
• Share
• Tweet

Be Sociable, Share!

• 

Related posts:

1. How to Configure Line Console and Executive Mode Password in Cisco Router
2. How to Remove IP address from Router Ethernet Interface
3. commands and configuration of CISCO Router’s
4. Cisco 2500 Router’s Password Recovery
5. IS-IS protocol Configuration on Cisco routers

Tagged as: Abbreviating Commands, Command Modes, Command-Line Error Messages, Common CLI Error Messages, Enable Secret and Enable Passwords, Entering Global Configuration Mode, Global configuration, Privileged EXEC, Router Command Modes, Saving Configuration Changes, To enter global configuration mode:, Understanding Command Modes, Undoing Commands, User EXEC, Using Commands, Using router Commands