Configuration Register Boot Field - Cisco Catalyst 5000 Series Installation And Configuration Note

Functional Description
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Note
Process" section on page 5.
Configuration Register Boot Field
The lowest four bits of the 16-bit configuration register (bits 3, 2, 1, and 0) form the boot field. The
value of the boot field determines if the RSFC loads a system image and where the RSFC searches
for the image:
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For information on changing the configuration register boot field value, see the "Setting the
Configuration Register Boot Field" section on page 20. For more information on the RSFC boot
process, see the "RSFC Boot Process" section on page 5.
BOOTLDR Environment Variable
The BOOTLDR environment variable specifies one or more RSFC boot helper images. When the
BOOTLDR variable is defined, the RSFC boots the specified boot helper image, which in turn boots
a system image from Flash or over the network. If an entry in the BOOTLDR environment variable
list specifies an invalid device or file, the RSFC skips that entry.
For information on changing the BOOTLDR environment variable, see the "Setting the BOOTLDR
Variable" section on page 21. For more information on the RSFC boot process, see the "RSFC Boot
Process" section on page 5.
BOOT Environment Variable
The BOOT environment variable specifies one or more RSFC system images on various devices
(such as bootflash: and tftp:). If the configuration register boot field value is set to any value
between 0x2 and 0xF inclusive, the RSFC checks the contents of the BOOT variable at startup to
determine the location and filename of the image to boot.
If an entry in the BOOT environment variable list does not specify a device, the RSFC assumes the
device is tftp:. If an entry in the BOOT environment variable list specifies an invalid device, the
RSFC skips that entry.
For information on changing the BOOT environment variable, see the "Setting the BOOT Variable"
section on page 21. For more information on the RSFC boot process, see the "RSFC Boot Process"
section on page 5.
4 Catalyst 5000 Series Route Switch Feature Card Installation and Configuration Note
System image—This software image is the main Cisco IOS software image with full
multiprotocol routing support.
For information on how the RSFC uses these software images at startup, see the "RSFC Boot
When the boot field is set to 0000 (0x0), the RSFC does not load a system image. Instead, the
RSFC enters the ROM monitor, where you can manually specify a system image to load.
When the boot field is set to 0001 (0x1), the RSFC attempts to load the first system image found
on the bootflash: device.
When the boot field is set to any value between 0010 (0x2) and 1111 (0xF) inclusive, the RSFC
attempts to load the first system image specified in the BOOT environment variable. (For more
information on the BOOT variable, see the "BOOT Environment Variable" section on page 4.)