Software Configuration Register

This appendix describes the router software configuration register, the factory default settings, and the procedures for changing those settings.

Software Configuration Register Settings

The router has a 16-bit software register, which is written into the nonvolatile memory. Use the processor configuration register information contained in this appendix to do the following:

• Change software configuration register settings

• Setting and displaying the configuration register value

• Force the system into the bootstrap monitor

• 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 TFTP server

Table B-1 lists the meaning of each of the software configuration memory bits, and Table B-2 defines the boot field names.

Changing Configuration Register Settings

To change software configuration register settings when the operating system is running, use the config-register command following and restart the server. Configuration register changes take effect only when the server restarts: that is, when you switch the power off and on or when you issue a reload command from the console.

In order to issue the configure or reload commands, you must first enable the privileged mode of operation. At the router> prompt, enter enable. The system will prompt you for the privileged password. After you enter the password, the prompt will change to a pound sign (router#). Enter the user configuration dialogue with the config-terminal command.

To set the contents of the configuration register, use the config-register value configuration command. Value is a hexadecimal number preceded by 0x. The software configuration register is stored in nonvolatile memory. For example, the default switch register contents can be set with the command config-register 0x1. To exit the user configuration dialogue, press the Ctrl-Z key combination. To exit the privileged mode, enter disable at the prompt.

The new value settings will be saved to memory; however, the new settings do not take effect until the system software is reloaded.

To display the configuration register value currently in effect and the value that will be used at the next reload, if the two values are different, use the show version command.

The lowest four bits of the processor configuration register (bits 3, 2, 1, and 0) form the boot field. (See Table B-2.) The boot field specifies a number in binary. If you set the boot field value to 0, you must boot the operating system manually by entering the b command at the bootstrap prompt. If you set the boot field value to 1 (the factory default), the router boots using the default ROM software. If you set the boot field to any other bit pattern, the router uses the resulting number to form a default boot filename for netbooting. (See Table B-3.)

The server creates a boot filename as part of the automatic configuration processes. To form the boot filename, the server starts with cisco and links the octal equivalent of the boot field number, a dash, and the processor-type name. Table B-3 lists the default boot filenames or actions for the processor.

Bit 10 controls the host portion of the Internet broadcast address. Setting bit 10 causes the processor to use all zeros; clearing bit 10 (the factory default) causes the processor to use all ones. Bit 10 interacts with bit 14, which controls the network and subnet portions of the broadcast address. Table B-4 shows the combined effect of bits 10 and 14.

Bits 11 and 12 in the configuration register determine the baud rate of the console terminal. Table B-5 shows the bit settings for the four available baud rates. (The factory-set default baud rate is 9600.)

config
conf 0x010F