Cisco 12406 - Manual (Page 8)

Chapter 4 Troubleshooting the Installation
Performing Other Configuration Tasks
4-8
Cisco 12006 and Cisco 12406 Router Installation and Configuration Guide
OL-11497-03
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.