Cisco IOS has a Command Line Interface (CLI). CLI is the primary user interface for Cisco router and switches. Command line interface(CLI) supports various command modes. The Cisco router and switch has following different modes.
- User EXEC Mode
- Privileged EXEC Mode
- Global Configuration Mode
- Setup Mode
- ROM Monitor Mode
Furthermore, Global configuration mode has a Specific Configuration Modes. These specific configuration modes will be explained under Global Configuration Mode. Figure 1 Illustrate some specific configuration modes with their prompt.
User Mode is also known is User EXEC mode. This mode is the first mode a user has access to the router after logging in. The user mode can be recognized by the > prompt following the name of the router/switch. Router default name is Router and switch default name is Switch. Default host name can be changed from Global configuration mode by the help of hostname command. Command will be explained in coming articles.
The user mode is usually password protected. You need a valid username and password to access this mode. This mode allows the user to execute only the basic commands, such as those that show the system’s status. The router cannot be configured or restarted from this mode. The figure-2 illustrate the user mode at CLI.
This mode is also known is enable mode or a privileged exec mode. Privileged exec mode is the main exec mode. This mode allows a user to view extensive info about the router’s configuration, and also allows a user to change some of the configuration parameters. The Privileged mode is also password protected. The user should enter the password to access this mode.
In the lab environment, it’s usually unprotected. You can access this mode by executing enable command at user exec mode. We can list all available commands of this mode by entering at command line interface (CLI). Most commands of this mode are one-time commands. Which show the result and current status and clear counters on interfaces respectively. Common commands can be entered both from user exec mode or privileged exec mode. Exec mode commands are not saved across the reboot of the device. The figure-3 illustrate the Privileged mode of the router.
Global Configuration Mode
The config mode is actually only a temporary gateway mode to get to extended configuration modes (specific configuration mode). Very little can be done in the configuration mode. The figure-4 illustrate the global configuration mode. This mode is used to configure device globally, or to enter in the element like interface, protocols specific configuration mode. Use configure terminal command at privileged exec mode to access global configuration mode.
Global configuration mode and extended (specific) configuration mode allowing you to make a change in running configuration. By default running configuration is not stored across the reboot, but you can save the running configuration to preserve it across the reboot. To save running configuration use copy running-config startup-config from privileged EXEC mode commands. To return in privileged exec mode from global configuration mode or specific configuration mode we have used three commands.
- Ctrl + Z
Ctrl+Z key combination will work in all mode.
exit command only works in global configuration mode.
end command is the safest way to exit from global configuration mode or interface specific mode.
Some of the extended configuration or specific configuration modes are listed below in figue-4 with their prompt.
As I described in the previous article that when a Cisco router is powered up, it will first run a POST test to ensure all hardware is working fine, and then router tries to locate running configuration. If the router finds the configuration it would load that. If it fails to locate configuration, it would initiate the setup mode. The setup mode is a step-by-step process which helps you configure basic aspects of the router. In this mode, the router will ask you questions about the initial settings in a sequence for basic configuration values. Depending on answers provided by you, the router will automatically build initial configuration.
This mode is also called ROM Monitor Mode. During the boot process, if the router does not find a valid IOS image and failed to load IOS in RAM, it would enter in ROMMON mode. This mode also accessible manually. This mode is the diagnostic mode just like safe mode in windows. By default, the router does not enter in this mode unless it fails to locate the IOS image. To enter manually in ROMMON mode, execute reload command from privileged exec mode and then press CTRL + C key combination or break during the first 60 seconds of startup. This mode can also be used for password recovery. Prompt for this mode is rommon>