Understanding Cisco IOS Software Basics
This section describes what you need to know about the Cisco IOS software before you configure the router using the CLI. Understanding these concepts will save time as you begin to use the commands. If you have never used Cisco IOS software or need a refresher, take a few minutes to read this chapter before you proceed to the next chapter.
If you are already familiar with Cisco IOS software, proceed to the Configuring the Host Name and Password section.
This chapter includes the following:
Getting Help
Use the question mark (?) and arrow keys to help you enter commands:
- For a list of available commands, enter a question mark:
Router> ?
- To complete a command, enter a few known characters followed by a question mark (with no space):
Router> s?
- For a list of command variables, enter the command followed by a space and a question mark:
Router> show ?
- To redisplay a command you previously entered, press the Up Arrow key. You can continue to press the Up Arrow key for more commands.
Command Modes
The Cisco IOS user interface is divided into different modes. Each command mode permits you to configure different components on your router. The commands available at any given time depend on which mode you are currently in. Entering a question mark (? ) at the prompt displays a list of commands available for each command mode. The following table lists the most common command modes.
|
Command Mode |
Access Method |
Router Prompt Displayed |
Exit Method |
|---|---|---|---|
|
User EXEC |
Log in. |
Router> |
Use the logout command. |
|
Privileged EXEC |
From user EXEC mode, enter the enable command. |
Router# |
To exit to user EXEC mode, use the disable , exit , or logout command. |
|
Global configuration |
From the privileged EXEC mode, enter the configure terminal command. |
Router (config)# |
To exit to privileged EXEC mode, use the exit or end command, or press Ctrl-Z . |
|
Interface configuration |
From the global configuration mode, enter the GigabitEthernet interface command such as, gigabitethernet0/0 . |
Router (config-if)# |
To exit to global configuration mode, use the exit command. To exit directly to privileged EXEC mode, press Ctrl-Z . |
 Timesaver |
Each command mode restricts you to a subset of commands. If you are having trouble entering a command, check the prompt, and enter the question mark (?) for a list of available commands. You might be in the wrong command mode or be using the wrong syntax. |
In the following example, notice how the prompt changes after each command, to indicate a new command mode for Cisco vg400:
Router> enable
Password: <enable password>
Router# configure terminal
Router(config)# interface gigabitEthernet 0/0/0
Router#
%SYS-5-CONFIG_I: Configured from console by console
The last message is normal and does not indicate an error. Press Return to get the Router# prompt.
 Note |
Press Ctrl-Z in any mode to immediately return to enable mode ( Router# ), instead of entering exit , which returns you to the previous mode. |
Undoing a Command or Feature
If you want to undo a command you entered or disable a feature, enter the keyword no before most commands. For example, no ip routing .
Saving Configuration Changes
Enter the copy running-config startup-config command to save your configuration changes to nonvolatile random-access memory (NVRAM). Doing so ensures that the changes are not lost if there is a system reload or power outage. For example:
Router# copy running-config startup-config
Building configuration...
It might take a minute or two to save the configuration to NVRAM. After the configuration has been saved, the screen displays the following:
[OK]
Router#
Feedback