The lowest four
bits of the processor configuration register (bits 3, 2, 1, and 0) form the
boot field.
The table below
provides information about the bits settings:
Table 2 Bits 0–3
Settings Boot
Field
|
Meaning
|
0
|
Stays at
the system bootstrap prompt (ROM monitor) on a reload or power cycle
|
1
|
Boots the
boot helper image as a system image
|
2
|
Full boot
process, which loads the Cisco IOS image into Flash memory
|
2-F
|
Specifies a
default filename for booting over the network from a TFTP server
|
The boot field
specifies a number in binary. If you set the boot field value to 0, you must
have a console port access to boot the operating system manually. Boot the
operating system by entering the
b command at
the bootstrap prompt as follows:
> b [tftp] flash filename
Definitions of the
various command options follow:
b—Boots the
default system software from ROM
b flash—Boots
the first file in Flash memory
b
filename
[host]—Boots over the network using TFTP
b flash
filename—Boots the file (filename) from Flash
memory
If you set the boot
field value to a value of 2 through F, and there is a valid system boot command
stored in the configuration file, the router boots the system software as
directed by that value. (See
Table 2)
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.
If there are no
boot commands in the configuration file, the router attempts to boot the first
file in system Flash memory. If no file is found in system Flash memory, the
router attempts to netboot a default file with a name derived from the value of
the boot field (for example, cisco2-7200). If the netboot attempt fails, the
boot helper image in boot flash memory will boot up.
If
boot commands are in the configuration file, the
router software processes each
boot command in sequence until the process is
successful or the end of the list is reached. If the end of the list is reached
without a file being successfully booted, the router will retry the
netboot commands up to six times if bit 13 of the
configuration register is set, otherwise it will load the operating system
software available in ROMmon. If bit 13 is not set, the router will continue to
netboot images indefinitely. The default setting for bit 13 is 0. If bit 13 is
set, the system boots the boot helper image found in boot flash memory without
any retries.
The server creates
a default 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 image name.
Note |
A
boot system
configuration command in the router configuration in NVRAM overrides
the default netboot filename.
|
The table below
lists the default boot filenames or actions:
Table 3 Default Boot
Filenames
Action/File Name
|
Bit 3
|
Bit 2
|
Bit 1
|
Bit 0
|
Bootstrap
mode
|
0
|
0
|
0
|
0
|
ROM
software
|
0
|
0
|
0
|
1
|
Flash
software
|
0
|
0
|
1
|
0
|
cisco3-<
image-name1>
|
0
|
0
|
1
|
1
|
cisco4-<image-name2>
|
0
|
1
|
0
|
0
|
cisco5-<image-name3>
|
0
|
1
|
0
|
1
|
cisco6-<image-name4>
|
0
|
1
|
1
|
0
|
cisco7-<image-name5>
|
0
|
1
|
1
|
1
|
cisco10-<image-name6>
|
1
|
0
|
0
|
0
|
cisco11-<image-name7>
|
1
|
0
|
0
|
1
|
cisco12-<image-name8>
|
1
|
0
|
1
|
0
|
cisco13-<image-name9>
|
1
|
0
|
1
|
1
|
cisco14-<image-name10>
|
1
|
1
|
0
|
0
|
cisco15-<image-name11>
|
1
|
1
|
0
|
1
|
cisco16-<image-name12>
|
1
|
1
|
1
|
0
|
cisco17-<image-name13>
|
1
|
1
|
1
|
1
|