How to reset Cisco Router as factory default

This method uses the config-register 0x2102 command in global configuration mode.

1. Check the configuration register on the router by issuing the show version command.
   The configuration register setting is displayed in the last line of the show version command output and should be set to 0x2102. If this is not the case, enter the config-register 0x2102 command once in global configuration mode.
   

   router#configure terminal
   router(config)#config-register 0x2102
   router(config)#end
   router#

   If the show version command is issued again, the same line in the command output will have '(will be 0x2102 at next reload)' appended to the current register setting.
2. Erase the current start-up configuration on the router with the write erase command.
3. Reload the router with the reload command. When prompted to save the configuration, DO NOT save.
   

   router#reload
   System configuration has been modified. Save? [yes/no]: n
   Proceed with reload? [confirm]

   Once the router reloads, the System Configuration Dialog appears.
   

            --- System Configuration Dialog ---
   Would you like to enter the initial configuration dialog? [yes/no]:

   The router is now reset to the original factory defaults.