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3-27
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 3 Configuring the Switch for the First Time
Modifying the Supervisor Engine Startup Configuration
Modifying the Boot Field and Using the boot Command
The configuration register boot field determines whether the switch loads an operating system image
and, if so, where it obtains this system image. The following sections describe how to use and set the
configuration register boot field and the procedures you must perform to modify the configuration
register boot field. In ROMMON, to modify the configuration register and change boot settings, use the
the confreg command.
Bits 0 through 3 of the software configuration register contain the boot field.
Note The factory default configuration register setting for systems and spares is 0x2101. However, the
recommended value is 0x0102.
Table 3-3 Software Configuration Register Bits
Bit Number
1
1. The factory default value for the configuration register is 0x2101. This value is a combination of the following: binary bit 13,
bit 8 = 0x0100 and binary bits 00 through 03 = 0x0001. See Table 3-4.
Hexadecimal Meaning
00 to 03 0x0000 to 0x000F Boot field (see Table 3-4)
04 0x0010 Unused
05 0x0020 Bit two of console line speed
06 0x0040 Causes system software to ignore NVRAM contents
07 0x0080 OEM
2
bit enabled
2. OEM = original equipment manufacturer.
08 0x0100 Unused
09 0x0200 Unused
10 0x0400 IP broadcast with all zeros
11 to 12 0x0800 to 0x1000 Bits one and zero of Console line speed (default is 9600 baud)
13 0x2000 Loads ROM monitor after netboot fails
14 0x4000 IP broadcasts do not have network numbers
Table 3-4 Explanation of Boot Field (Configuration Register Bits 00 to 03)
Boot Field Meaning
00 Stays at the system bootstrap prompt (does not autoboot).
01 Boots the first file in onboard flash memory.
02 to 0F Autoboots using image(s) specified by the BOOT environment variable. If more than one
image is specified, the switch attempts to boot the first image specified in the BOOT
variable. As long as the switch can successfully boot from this image, the same image is
used on a reboot. If the switch fails to boot from the image specified in the BOOT variable,
the switch tries to boot from the next image listed in the BOOT variable. If the end of the
BOOT variable is reached without the switch booting successfully, the switch attempts the
boot from the beginning of the BOOT variable. The autoboot continues until the switch
successfully boots from one of the images specified in the BOOT variable.