33
Configuring the Software Configuration Register
78-4339-09
Implementing Additional Configuration and Maintenance Tasks
Step 5
Display the configuration register value currently in effect, which will be used at the next reload by
entering the
show version
EXEC command.
The value is displayed on the last line of the screen display, as in the following example:
Configuration register is 0x141 (will be 0x2102 at next reload)
Step 6
Save your settings.
Configuration register changes take effect only after the system reloads, such as when you issue a
reload
command from the console.
Step 7
Reboot the system. The new configuration register value takes effect with the next system boot.
Configuration Register Bit Meanings
The lowest four bits of the software configuration register (bits 3, 2, 1, and 0) form the
boot field.
(See
Table 10
.) The boot field specifies a number in binary form. 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
0x2
through
0xF
and there is a valid
boot
system
command stored in
the configuration file, theCisco 12000 Series Router boots the system software as directed by that value.
If there is no
boot system
command, the Cisco 12000 Series Router forms a default boot filename for
booting from a network server. (See
Table 11
for the format of these default filenames.)
In the following example, the software configuration register is set to boot the system from onboard
Flash memory and to ignore Break at the next reboot of the system:
Router#
conf term
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#
config-register 0x2102
Router(config)#
boot system flash
[
filename
]
Crtl-z
Router#
The server creates a default boot filename as part of the automatic configuration process. To form the
boot filename, the server starts with the name
cisco
and adds the octal equivalent of the boot field
number, a hyphen, and the processor-type name (
GRP
).
Table 11
lists the default boot filenames. A
boot system
configuration command in the configuration file
in NVRAM overrides the default filename created for booting over the network.
Note
If a bootable Cisco IOS software image exists in a Flash memory card or Flash disk installed in
PCMCIA slot 0 or slot 1, the configuration register setting is overridden, and the bootable Cisco IOS
software image will be booted instead of the default TFTP-bootable Cisco IOS software image
(cisco2-GRP through cisco17-GRP).
Table 11
Default Boot Filenames
Action/File Name
Bit 3
Bit 2
Bit 1
Bit 0
Bootstrap mode
0
0
0
0
Default software
0
0
0
1
cisco2-GRP
0
0
1
0
cisco3-GRP
0
0
1
1
