An Engineers Notebook

How to factory reset a Cisco Router/Switch via Rommon

To reset some Cisco routers and switches, you need to enter ROMMON mode. To get into ROMMON, you can hold down the reset button on the front/back of the device for 5-10 seconds before IOS boots up. You also then need to press the BREAK key. If you don’t have a break key (you may be on laptop) you can send a break key through Putty, Click the menu > Special Command > Break Key. This should get you into Rommon mode. You need to type “confreg 0x142” and then reboot the router. This will cause the rooter to ignore the startup config. You can then boot into the router, do a “copy running-config startup-config” and reboot again. You next need to put confreg back otherwise the router will ignore the new settings you have overwritten. To do this, repeat the same process but set confreg to 0x102, reboot and your router/switch is fully reset. 

 

 

Configuration Register SettingRouter Behavior
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

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