How To Change Config Register On Cisco Switch 3650

What is Configuration Register?

Configuration Register is a special 16 bits value that can be configured in Cisco routers. Information technology is mainly used in three cases;

To determine how the router boots
To determine kicking options
To set console speed

During the boot, router checks its software and the configuration files. To make up one's mind these files, router firstly check Configuration Annals. According to its value, router determines what to do.

Configuration Annals Configuration is particularly used for Router Password Recovery. So, what are the values of this special number?

config-register

Configuration Register 0x2102

The default value of Config Register is 0x2102. With Configuration Register 0x2102 value, the router boots from NVRAM and the normal router precedures works. The configuration stored in NVRAM is the startup configuration. So, if we need to bypass this configuration, we can change the default value. Especially during Router Password Recovery, this uncomplicated configuration is washed.

We can check this value on Cisco routers with "show version" control. At the output of "evidence version" command, Configuration Register value volition exist at the bottom.

Router# prove version

Cisco IOS Software, C800 Software (C800-UNIVERSALK9-M), Version 15.2(4)M4, RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Compiled Thu 20-Jun-13 16:14 by mnguyen

ROM: Organisation Bootstrap, Version fifteen.2(2r)T, RELEASE SOFTWARE (fc1)

Router uptime is 35 minutes, 14 seconds

System returned to ROM by ability-on

Organization image file is "flash:c800-universalk9-mz.SPA.152-four.M4.bin"

…

Configuration annals is 0x2102

config-register-2102-vs2142

Config Register 0x2142

To bypass NVRAM configuration, in other words, to bypass start-up configurataion, we can change Config Annals value. Here, the new value that we will set volition be Configuration Register 0x2142.

How to Change Configuration Annals?

At that place are 2 way to change Config Register on a router. This tin can be done both in Rommon mode and in configuration way.

In Rommon mode, information technology can be modify with "confreg" command. Beneath, we are changing Configuration Register as 0x2142.

rommon > confreg 0x2142

After this configurationi we should reset the router to utilise this new value,or to force the router boot through this config register.

The other style is configuring on configuration mode with "config- register" control.

Router# configure terminal

Router(config)# config-register 0x2142

After configuration, you can check the ne value and be sure about the value.

Router# testify version

Cisco IOS Software, C800 Software (C800-UNIVERSALK9-Grand), Version 15.ii(iv)M4, RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Compiled Thu 20-Jun-13 16:fourteen by mnguyen

ROM: System Bootstrap, Version 15.2(2r)T, RELEASE SOFTWARE (fc1)

Router uptime is 35 minutes, fourteen seconds

System returned to ROM by ability-on

System image file is "flash:c800-universalk9-mz.SPA.152-four.M4.bin"

Configuration register is 0x2102 (will exist 0x2142 at next reload)

Again, nosotros should reload the router for the new config annals to take outcome.

Router# reload

Organization configuration has been modified. Salve? [yes/no]: n

Proceed with reload? [confirm]

You can find the detailed information about Config Register on Cisco Folio.