Password Recovery and Factory Default a Cisco 1921 Router

If you have lost or don’t know the credentials for a Cisco 1921 router, there is a way around it to perform a factory reset

This is a bit involved but has been proven to work.

First, remove the cover by taking the rack ears off and removing the four Torx screws. The lid then slides off taking the greeny blue Cisco cover with it. This can be quite stiff. It has been known to need putting on the floor and glancing kick on the lid to get it off.

Once inside you will see a small daughter board mounted in the middle of the motherboard. Remove the retaining screw and pull the board straight up to disconnect it. You have now removed the flash so the router will have no choice but to boot into the ROMMON recovery mode.

Plug in a console cable and power up the switch. It may boot a few times complaining it can’t see the USB flash but it eventually drops you into the recovery mode.

It will say rommon>1

At this point carefully replace the flash and replace the retaining screw. Bear in mind the unit is powered up so has mains and logic voltages present.

At this point the old config with the unknown password is still saved on the flash so we want the router to ignore this config at it’s next boot. In the console type:

confreg 0x2142

This config register sets the BIOS to ignore the saved configuration and it will now tell you that you need to restart the router for this to take effect. Type:

reset

Once the router has booted again you will get a prompt asking Would you like to enter the initial configuration dialogue? [yes/no]
Type no

You are now in the unconfigured router. You can now do a very basic setup allowing enough working elements to get your configuration into the switch. Normally this would be setting up an interface with an IP address so you can TFTP a config onto the router.

Once you have your config on board you are almost ready to go. However if we restarted the router now it is still set to ignore the configuration. Go back into conf t and type:

config-register 0x2102

You are now ready to restart the router.

If you do this from the console using the reload command, you will be asked if you want to save the configuration. Say no, otherwise you will save a blank config over the top of your newly transferred on.