There are following primary modes of operation in IOS.

Setup Mode

In router or switches, all configurations are saved in NVRAM.
If there is no any router’s configuration saved in NVRAM means NVRAM is blank then it shows a message given below:

Continue with configuration dialog [yes/no]:

To enter in setup mode, type “y” for yes.

If initial configurations are saved in NVRAM, then you can’t enter in the setup mode.

It is the primary mode when you log in router or switch.
By default, you can access this mode directly (without password).
It consists of device hostname followed by greater than (>) sign.
For router default hostname is Router. For switch default hostname is Switch.

Router>
Switch>

To see list of commands available in User exec mode, type command “Router>?”

This mode allows you to execute all available exec commands.
To see list of commands available in Privileged exec mode, use the command “Router#?”

It is used to configure the device globally.
Type configure terminal command at privilege mode to access global configuration mode.
It allows you to make changes in the running configuration.
By default, it consists device name followed by (config)#.

To see all commands used in global configuration mode, you can use “Router(config)?”

This mode is used to configure interfaces like Serial interface port (s0/0/0, s0/0/1, so on), and Fast Ethernet interface port (f0/0, f0/1, so on).
We provide IP addresses to each interface through which the device is connected.

To see all commands used in interface configuration mode, you can use “Router(config-if)?” Command.

If you want to move back to the Global configuration mode, use “exit” command.

This mode is used for diagnostic purpose.
By default, the router does not enter in rommon mode.
To manually enter in this mode, type reload command at privileged exec mode and then press CTRL+C key to enter in rommon mode.

Mode	Purpose	Prompt	Command to enter	Command to exit
Setup	Router use setup mode to create an initial configuration, if the running configuration is not present	Parameter[Parameter: Value]:	Router will automatically Insert in this mode if running Configuration is not present.	Press Ctrl+C Command to exit.
User EXEC	It allows you to connect remote devices, and allow authorized users to configure and manage the router or switches.	Router >	Default mode after booting. Login with the password, if configured.	Use exit command
Privileged EXEC	It includes high-level testing and list of commands like show, copy, and debug.	Router#	Use enable command at user exec mode	Use exit command
Global Configuration	It allows users to modify the running system configuration.	Router(config)#	Use configure terminalcommand at privileged exec mode.	Use exit command
Interface Configuration	It allows users to modify the Operation of an interface.	Router(config-if)#	Use interface type number command at global configuration mode.	Use the exit command to return in global configuration mode.
ROMMON	It allows you to Perform low- Level Diagnostics.	ROMMON>	Enter reload command at Privileged exec Mode.	Use exit Command.

Getting familiar with the IOS modes