Cisco IOS CLI Modes - Part 1
Cisco IOS CLI Modes - Part 1 of 6
Cisco IOS has a number of command line interface (CLI) modes. The most important modes to be aware of are the two EXEC modes (user and privileged) which are used primarily for verification and troubleshooting commands. The commands available in EXEC mode depend (by default) on the EXEC privilege level which can range from 0 (very few available commands) to 15 (all commands are available). User EXEC mode is privilege level 1 and Privileged EXEC mode is level 15.
You can enter Global Configuration mode from Privileged EXEC mode. Global configuration mode is used to configure your system globally, or to enter specific configuration modes to configure specific elements such as interfaces or protocols. From Global Configuration mode you can enter into any of a slew of subconfiguration modes. The one that youll use the most is Interface Configuration mode.
ROM Monitor Mode (ROMMON) is a separate mode used when the router cannot boot properly. If your device is in ROMMON theres most likely a big problem. You can induce ROMMON mode by changing your configuration register or sending a break character during POST. You should probably play with ROMMON a little in a lab situation so that its not a shock to you when the day comes (and it will come) that you see it in production.