Briefly describe the ROM Monitor mode.

What will be an ideal response?

ROM Monitor mode is actually the bootstrap program that is built into the firmware of the router. In addition to initializing the hardware and loading the IOS, ROM Monitor can be used to perform other tasks such as diagnostics and recovering passwords. You can set the router to enter ROM Monitor mode during the boot process by modifying the configuration register. The router will also enter ROM Monitor mode if it cannot find an IOS image during the boot process. The prompt for ROM Monitor mode on the Cisco 1003, 1600, 2600, 3600, 4500, 7200, and 7500 routers is some variation of rommon>.

To configure your system to enter ROM Monitor mode, you can enter the following command at the global configuration prompt:
router(config)#config-register 0x2100