81
OL-4923-01 B0
Bit Meanings
The lowest four bits of the software configuration register (bits 3, 2, 1, and 0) form the boot field. (See
Table 19
.) 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 (>), as follows:
> b [tftp] flash
filename
Definitions of the various b command options follow:
•
b—Boots the default system software from Flash memory
•
b flash—Boots the first file in onboard Flash memory
•
b slot0: filename—Boots the file filename from the Flash memory card in PC Card slot 0
•
b slot1: filename—Boots the file filename from the Flash memory card in PC Card slot 1
•
b filename [host]—Boots from server host using TFTP
•
b bootflash: [filename]—Boots the file filename from onboard Flash memory
If you set the boot field value to 0x2 through 0xF and there is a valid boot system command stored in
the configuration file, then the router boots the system software as directed by that value. If there is no
boot system command, the router forms a default boot filename for booting from a network server. (See
Table 20
for the format of these default filenames.)
In the following example, the software configuration register is set to boot the router from onboard Flash
memory and to ignore the Break function at the next reboot of the router:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# config-register 0x102
Router(config)# boot system flash
[filename]
Router(config)# Ctrl-Z
Router#
The server creates a default boot filename as part of the automatic configuration processes. 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.
Table 20
lists the default boot filenames or actions for the processor.
Note
A boot system configuration command in the router configuration in NVRAM overrides the default
netboot filename.
Table 20
Default Boot Filenames
Action/Filename
Bit 3
Bit 2
Bit 1
Bit 0
Bootstrap mode
0
0
0
0
Default software
0
0
0
1
cisco2-RSP
0
0
1
0
cisco3-RSP
0
0
1
1
cisco4-RSP
0
1
0
0
cisco5-RSP
0
1
0
1
cisco6-RSP
0
1
1
0
