Cisco configuration Register

Im recently graduated from my bachelor degree study. Now im working as Network Engineer at one of biggest cisco gold partner in indonesia. If any of u know Multipolar thats where i make some progress in my career.

Im responsible in managing biggest local bank indonesia network distribution switch, access, wireless, video conference and nexus for SOSA application, and datacenter.  

Below is some note / documentation that maybe useful for u guys.

 

Cisco Configuration Register

All cisco router have  16 bit software register that is written on NVRAM.

By default the configuration register is set to load IOS from flash memory and look for and load startup-config file from NVRAM.

there are many useful of cisco configuration register. One of them is to enter ROM monitor mode to recover cisco password.

first we need to know our cisco configuration register by typing command:

# show version.

Configuration Register is 0x2102     ->  find this line.   ( default setting )

!!to change the configuration register!!

#conf terminal

(config)#config register 0x2142          -> change register 

(config)#end

#wr                                                      -> save config

#reload                                                -> reload router to apply new configuration register.

to recover password on cisco router:

1 boot router

2 while boot perform break to enter router into ROM monitor mode.

3 change register to 0x2142

4 reload router

5 enter privileged mode

6 copy startup-config running-configuration

7 change password

8 reset configuration regiter using default value (0x2102)

9 save and reload

there are other purpose of changing configuration register as:

• select boot source
• control broadcast address
• set terminal baud rate
• enable booting from TFTP server
• disable / enable break button

done.