To factory default a Cisco router, you will need to run a couple commands in “rommon”. Send a break a few times to force the router in to rommon. Do this immediately after powering on the router.
rommon>confreg 0x2142
rommon>reset
The router will reload and the config should be wiped. Once you are back in “enable” mode again, you will need to change the config register back to 0x2102. If you fail to do this, your config changes will not save after a reload or power cycle.
Router(config)#config-register 0x2102
Router(config)#end
Router#write memory
Listed below are other configuration register settings:
0x102
Ignores break
9600 console baud
0x1202
1200 baud rate
0x2101
Boots into bootstrap
Ignores break
Boots into ROM if initial boot fails
9600 console baud rate
0x2102
Ignores break
Boots into ROM if initial boot fails
9600 console baud rate default value for most platforms
0x2120
Boots into ROMmon
19200 console speed
0x2122
Ignores break
Boots into ROM if initial boot fails
19200 console baud rate
0x2124
NetBoot
Ignores break
Boots into ROM if initial boot fails
19200 console speed
0x2142
Ignores break
Boots into ROM if initial boot fails
9600 console baud rate
Ignores the contents of Non-Volatile RAM (NVRAM) (ignores configuration)
0x2902
Ignores break
Boots into ROM if initial boot fails
4800 console baud rate
0x2922
Ignores break
Boots into ROM if initial boot fails
38400 console baud rate
0x3122
Ignores break
Boots into ROM if initial boot fails
57600 console baud rate
0x3902
Ignores break
Boots into ROM if initial boot fails
2400 console baud rate
0x3922
Ignores break
Boots into ROM if initial boot fails
115200 console baud rate