Which Cisco IOS command allows you to change the setting of the configuration register?
A.
boot config
B.
configuration-register edit
C.
config-register
D.
edit configuration-register
Explanation:
The config-register command is used to change the setting of the configuration register. The configurationregister has the boot field setting, which specifies the order in which the router should look for bootstrap
information. The router contains a 16-bit software register, which is stored in the non-volatile random access
memory (NVRAM). The config-register command is used to modify the default configuration register. The most
common use of changing this register is to instruct the router to ignore the stored configuration file and boot as
a new router with no configuration. This process is normally used when a router has a password that is not
known and must be reset. For security purposes, this procedure can only be performed from the console
connection, which means it requires physical access to the router.
Normally the setting of this register is 0x2102, which tells the router to look for a configuration file. If the file
exists, it will use it. If none exists, the router will boot into ROM and present the user with a menu-based setup.
This would be the default behavior for a new router as well.
To view the value of the configuration register, use the show version command as displayed below. The
register setting can be seen at the bottom of the output in bold.
Configuration register is 0x2102
To change this setting would require issuing these commands, followed by a restart:
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#config
Router(config)#config-register 0x2142
By setting register to 0x2142, the router will ignore a configuration file at reboot if it exists. The router will then
enter setup mode and prompt for you to enter initial system configuration information, as would happen with a
new router. This enables the user to bypass an unknown password, since the password is contained in the file.
The boot config command is incorrect because this command is used to set the device where the configuration
file is located (flash, slot, etc.) and file name for the configuration file, which helps the router to configure itself
during startup.
The configuration-register edit command and the edit configuration-register commands are incorrect because
they are not valid Cisco IOS commands.Objective:
Infrastructure Management
Sub-Objective:
Perform device maintenanceCisco > Support > Routers > Cisco 10000 Series Routers > Troubleshoot and Alerts > Troubleshooting
TechNotes > Use of the Configuration Register on All Cisco Routers > Document ID: 50421
