step 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 0×2102. If this is not the case, enter the config-register 0×2102 command once in global configuration mode
router# configure terminal
router(config)# config-register 0×2102
If the show version command is issued again, the same line in the command output will have ‘(will be 0×2102 at next reload)‘ appended to the current register setting.
Step 2 : Erase the current start-up configuration on the router with the write erase command
Step 3 : Reload the router with the reload command. When prompted to save the configuration, DO NOT save.
router#reloadSystem configuration has been modified. Save? [yes/no]: nProceed with reload? [confirm]
Step 4 : Once the router reloads, the user will be presented with a ‘System Configuration Dialog’ as shown below. The router is now reset back to the original factory defaults.
— System Configuration Dialog —
Would you like to enter the initial configuration dialog? [yes/no]:
This article is not fully entirely made by www.ionhelp.com but partially excerpted from the website www.cisco.com and several other websites.