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Managing Configuration Registers

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The last information given from this command is the value of the config-

uration register. In this example, the value is 0x2102, which is the default
setting. The configuration register setting of 0x2102 tells the router to look
in NVRAM for the boot sequence.

Notice the

show

version

command also provides the IOS version, and in

the example above, it shows the IOS version as 12.0(3)T3.

The

show

version

command will display system hardware configuration infor-

mation, software version, and the names and sources of configuration files

and boot images on a router.

Changing the Configuration Register

You can change the configuration register value to modify how the router
boots and runs, as follows:

Force the system into the ROM monitor mode

Select a boot source and default boot filename

Enable or disable the

Break

function

Control broadcast addresses

Set the console terminal baud rate

Load operating software from ROM

Enable booting from a TFTP (Trivial File Transfer Protocol) server

Before you change the configuration register, make sure you know the cur-

rent configuration register value. Use the

show

version

command to get this

information.

You can change the configuration register by using the config-register

command. For example, the following commands tell the router to boot a
small IOS from ROM monitor mode and then show the current configura-
tion register value:

Router(config)#config-register 0x101

Router(config)#^Z

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