Learn "configuration Register" In 0,5 Minutes

With "configuration register", we can configure, what the router will do at the next reboot.

To see, what is the actual setting of your routers configuration register, use the command

router#show version

To change the configuration register, use the following command in global config mode:

Router(config)#config-register 0x2142

For CCNA exam, you need to know two configuration register settings. These are:

0x2102 is the factory-default configuration register value. 
0x2142 boots from flash without using NVRAM contents good for password recovery. 

When the config. register is set to 2142, the router will start in setup-mode, 
where you can interactive select some options.
The "normal" config. register is 2102.