Cisco Systems Cisco 12406, Cisco 12006 manual Bits in the Software Configuration Register

Chapter 4 Troubleshooting the Installation

Performing Other Configuration Tasks

Bits in the Software Configuration Register

This section provides more detailed descriptions of the significance of the bits in the software configuration register and how they interact during the boot process.

As described in the “Boot Field Settings” section on page 4-4, the boot field setting determines the source of the Cisco IOS software image that is used to boot the router. If you set the boot field value to 0 (0x0000), you must boot the operating system manually by entering the boot command at the ROM monitor prompt (rommon>) on the system console.

If you set the boot field value to 0x2 through 0xF and a valid boot system command is stored in the configuration file, the router boots the Cisco IOS software image as directed by that value. If no boot system command is present in the configuration file, the router forms a default boot filename and attempts to acquire that file from a network TFTP server.

In the following example, the software configuration register is set to boot the router from the Flash memory SIMM on the RP and to ignore the Break function at the next reboot of the system:

Router# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)# config-register 0x0102

Router(config)# boot system flash filename

Ctrl-Z

Router#

With the configuration register set to 0x0102, the system computes a default boot filename. In forming this filename, the system starts with cisco and appends the octal equivalent of the boot field number, a hyphen, and the processor type (grp or prp).

Table 4-3 lists the range of possible computed default filenames for booting over the network. However, a valid boot system configuration command stored in the NVRAM configuration file overrides any computed default filename for booting over the network.

	Cisco 12006 and Cisco 12406 Router Installation and Configuration Guide
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