Cisco IOS Software employs a structured system of modes organized hierarchically. The user EXEC mode is at the top, followed by the privileged EXEC mode. You can move from the privileged EXEC mode to the global configuration mode and from there to more specialized configuration modes, such as interface configuration mode and router configuration mode.
As you can see in the image above, you can only enter a lower-level mode from a higher-level one because of the hierarchy. For instance, to enter global configuration mode, you must first be in privileged EXEC mode and enter from user EXEC mode.
Each mode supports a unique set of commands customized to that mode's function and is responsible for configuring certain tasks. For example, interface-specific configuration commands are only available in the interface configuration mode, and any commands entered there affect only the chosen device interface.
To get a better understanding of the features and functionalities of each mode, here are more details for each mode:
- User EXEC mode: This is the initial mode you access when logging into a Cisco device. It offers limited access to view basic system information and execute basic commands to perform monitoring and check device status and connectivity.
- Privileged EXEC mode: This mode, often called "enable" mode, grants elevated administrator privileges beyond user EXEC mode. It allows you to execute various configuration and monitoring commands, making it possible to modify device settings and access detailed system information. To enter privileged EXEC mode, enter the “enable” command in user EXEC mode.
- Global configuration mode: The purpose of global configuration mode is to allow you to configure settings that are applied globally and affect the entire device, such as hostnames, routing protocols, and access control lists (ACLs). Also, from this mode, you can enter more specific modes. Enter the “configure terminal” command in privileged EXEC mode to enter global configuration mode.
- Interface configuration mode: This mode allows you to modify and fine-tune the parameters of specific network interfaces on the device, such as Ethernet or serial connections. Users can define essential parameters such as IP addresses, subnets, and duplex settings in this mode, configuring these configurations to each interface's specific needs and goals. To enter interface configuration mode, you must enter the “interface interface-type” command in global configuration mode.
- Router configuration mode: This mode is dedicated to the fine-tuning of routing protocols such as OSPF, EIGRP, or BGP, enabling you to configure routing behavior with precision. To enter router configuration mode, you must enter the “router routing-protocol process-number” command in global configuration mode (the configuration command varies between different routing protocols).
But how can you return from higher-level to lower-level mode? Well, you can use the “exit” command in Cisco IOS to exit the current configuration mode and return to the previous mode. Use the ”end” command (or CTRL + Z) to return directly to the privileged EXEC mode regardless of the mode you are currently in, while the “logout” command logs you out of the current session and disconnects you from the device.
Let's look at the configuration example below to find out how the commands can be used to switch between previously explained modes and how to change the default name of the switch to SW1.
As you can see from the commands above, the hostname was changed to SW1, and then the interface mode of FastEthernet 0/1 was entered, as well as the OSPF router mode, before exiting and returning to user EXEC mode.