An IOS mode is a collection of commands used to customize a set of related features or to manage a specific area of the device. IOS modes are also referred to as IOS access modes and IOS command modes. There are five IOS modes: global configuration mode, privileged EXEC mode, user EXEC mode, setup mode, and ROM Monitor mode. The first three modes are used to configure new settings, edit existing settings, and view the current settings. The following two modes are used, respectively, to configure the device initially and troubleshoot it in an emergency.
Cisco IOS modes navigation:
- The CLI can be switched between the user EXEC mode and the privileged EXEC mode using the enable and disable commands, respectively.
- Use the enable command to get to the privileged EXEC mode. The enable mode is another name for the privileged EXEC mode.
- The enable command is entered using the syntax: router > enable
- There is no requirement for a keyword or argument to perform this command. The prompt becomes: after pressing the Enter key: Router#
- The switch is now in privileged EXEC mode, as indicated by the # at the end of the prompt.
- The IOS asks for the password if password authentication is set up for the privileged EXEC mode.
For instance: router > enable Password: Router#
- To switch back to user EXEC mode from the privileged EXEC mode, use the disable command.
For instance: Disable Router # Router>
User EXEC Mode:
- You have a limited amount and selection of commands accessible to you in User EXEC. For instance, the majority of display commands are accessible at this level of the IOS hierarchy, since their use has no negative effects on the router or the switch.
- Additionally, you can use ping to check the IP connectivity of other devices and use Telnet to troubleshoot down to Layer 7 or remotely manage other devices. The larger symbol (>) that follows the hostname of the Cisco device designates the User EXEC Cisco IOS prompt.
- So, the prompt Router> greater-than symbol (>) signifies that the router is at the user EXEC level. There are no commands at the user EXEC level that could reload or configure the router’s configuration, for example. Type “?” To display a list of the user EXEC level commands. The Router> command prompt. (This capability is known as context-sensitive help.)
- List the available user EXEC commands.
Privileged EXEC Mode:
- The next level of the IOS is called Privileged EXEC, and it offers the same commands as User EXEC, as well as some additional ones that can change how the Cisco device functions.
- Type the command enable from User EXEC to obtain access to Privileged EXEC. The prompt switches from > to # once you press Enter, indicating that you are now in Privileged EXEC mode. Type the command enable from User EXEC to obtain access to Privileged EXEC. The prompt switches from > to # once you press Enter, indicating that you are now in Privileged EXEC mode.
- Other brand-new and potentially harmful commands in Privileged EXEC include to name a few, delete, clear, erase, configure, copy, and reload (reboots the device) except show and debug commands.
- Perform the operations on Router1 to gain access to and list the privileged EXEC commands:
- Enter the privileged EXEC mode
- List of privileged EXEC commands
Global configuration mode:
- Configuration is one of the commands that Privileged EXEC gives you access to. This implies that in order to update any Cisco device configuration, we must access yet another level of the Cisco IOS.
- You can instruct the Cisco IOS to configure the Cisco device using your terminal window by issuing the configure terminal command.
- Global Configuration is the name of the new level that you enter after completing this operation.
- You can use the “end” or “exit” commands to leave this mode. Additionally, you can press CTRL + Z on your keyboard.
- Most commands are available in this mode out of all modes that are available. This mode divides related commands into sub-configuration modes to manage these commands.
- IOS-specific sub-configuration modes exist. Cisco produces IOS software in a variety of versions. A sub-configuration mode that is present in one flavor of IOS might or might not be present in others.
- The most popular sub-configuration settings that are accessible across all IOS variants are listed in the table below.
| Sub-configuration mode | Contains commands that are used to: – |
|---|---|
| Interface configuration mode | Configure a physical interface of the device |
| Sub-interface configuration mode | Configure virtual interfaces |
| Routing protocol configuration mode | Configure a routing protocol |
| IP access list configuration mode | Configure the in-built security feature of the IOS |
| Line configuration mode | Configure access modes of the IOS |
- As implied by the name, any configuration made at this level affects the Cisco router or switch globally. We can change the hostname of the router or switch, create a login banner, create a password to prompt users attempting to access Privileged EXEC, and many more configuration chores here.
- Additionally, you can enter a variety of sub-configuration modes at this level of the Cisco IOS hierarchy to apply certain configurations for things like interfaces, routing protocols, and EXEC lines.
- Features that have an impact on the entire system are subject to global configuration instructions. You can switch into global configuration mode by using the configure privileged EXEC command.
- When the global configuration mode is selected, Router(config)# appears as the router prompt. Then utilize the help system to show the global commands accessible. Follow these instructions to gain access to and list the router’s global configuration commands:
- At the terminal, from the privileged EXEC mode, enter global configuration mode.
- List the global configuration commands.
Interface configuration mode:
- You can define interface-specific instructions that only apply to the interfaces listed in the configuration directly from Global Configuration.
- The interfaces can now be enabled, IP addresses assigned, speeds specified, and other interface instructions configured.
- Again, the IOS commands available at this sub-configuration level are inapplicable at Global Configuration, Privileged EXEC, or User EXEC.
- The operation of an interface, such as an Ethernet, Token Ring, or serial port, can be changed via interface configuration commands. You must enter interface configuration mode by typing the interface type port number command in order to configure a specific interface from global configuration mode. By typing interface serial 0, you can access interface configuration mode on the serial 0 interface. You are in interface configuration mode, according to the Router(config-if)# command-line prompt. To view the commands available in interface configuration mode, consult the help system.
- Enter the exit command to leave interface configuration mode and return to global configuration mode.
- Follow these instructions to access and list the interface configuration commands:
- From global configuration mode, enter interface configuration mode for the Serial 0 interface.
- List the interface configuration commands.
- From interface configuration mode, return to global configuration mode.
Router configuration mode:
- By configuring a routing protocol using the router routing protocol command, router configuration mode is accessed from global configuration mode. The router is in router setup mode when a routing protocol is configured.
- Use the router rip command in global configuration mode to set up Routing Information Protocol (RIP) on the router. You are in router configuration mode, as indicated by the Router(config-router)# prompt. After that, utilize the help system to see a list of the commands that can be used in router configuration mode.
- Enter the exit command to quit router configuration mode and go back to global configuration mode.
- Follow these instructions to access and list the router configuration commands:
- From global configuration mode, enter router configuration mode.
- List the router configuration commands.
- From router configuration mode, return to global configuration mode.
Line configuration mode:
- Line configurations are particular to those EXEC lines through which a user can access the Cisco device and are also accessed from Global Configuration. With regard to the console and auxiliary ports, the 5 vty (virtual teletype) Telnet lines, and the User EXEC access to a router or switch, you can specify parameters such as logins and passwords. You must use the keyword line from Global Configuration, then the EXEC line you want to customize. For instance, you might type line console 0 from Global Configuration to define console-specific instructions. Regardless of the line you are specifying, the prompt changes to Router (config-line)#.
- Performing the actions will allow you to access and list the console port, auxiliary port, physical terminal (if present), and virtual terminal line configuration commands:
- From global configuration mode, configure a range of five vty lines from 0 to 4.
- List the line configuration commands.
- From line configuration mode, return to privileged EXEC mode.
- From privileged EXEC mode, exit the EXEC completely.
Setup Mode:
- The IOS looks for the device configuration when we turn on an IOS-operated device. The user is put in this mode if a valid configuration cannot be found.
- The user can customize the device’s initial settings in this mode.
- This mode displays a text-based wizard that queries the user about the sequence’s starting parameters.
- The initial configuration is automatically created by the IOS based on the user’s responses.
Mode ROMMON:
- During the boot process, the IOS image file is loaded into the RAM.
- This mode is automatically entered by the device if the IOS image file is corrupt or missing.
- The user can debug the IOS in this mode.
- In this mode, the user has the option of loading a new IOS image file from the TFTP server or choosing a different IOS image file to boot the device.
- If there is no functional IOS, ROMMON> launches immediately.
- To begin manually, hold down the CTRL and C keys for the first 60 seconds of booting.
- Exit should be used.
- The graphic below depicts how all IOS modes interact with one another.