Resetting a Cisco IOS device

When you need to reset a Cisco IOS device password/configuration, you need it to boot with the config register set to boot without loading the saved configuration. This register is stored in non-volatile memory. You can set this register in ROMMON or in Enable-privilege config mode in IOS.

Normal boot, read config file: 0x2102
boot without reading config file: 0x2142

ROMMON command to set config register to boot without reading the config file:
rommon 1 > confreg 0x2142

IOS command to set config register to boot normally, reading the config file at bootup:
router# conf t
router(config)# config-register 0x2102