Datasheet

OL-17436-01

Additional Configuration and Maintenance Tasks

Boot Field Settings

Bits 00 to 03 of the software configuration register are referred to as the boot field, which defines a

source for booting the default Cisco IOS software image required to run the router. The value of the boot

field is specified as a binary number, as described in Table 19.

Note Cisco 12000 Series Internet Routers are typically delivered from the factory with a mini-Cisco IOS

software boot image in the boot flash and a flash card containing a suitable working Cisco IOS image.

If you need a Cisco IOS upgrade, download the appropriate Cisco IOS image from Cisco.com.

Configuring the Software Configuration Register

To configure the software configuration register, follow these steps:

Table 19 Definition of Bits in Boot Field of Software Configuration Register

Boot Field Meaning

00 On power up, the system remains at the ROM monitor prompt (

Rommon>), awaiting a user

command to boot the system manually.

01 On power up, the system automatically boots the first system image found in the onboard

Flash memory SIMM on the RP.

02 to 0F If a valid boot system command is stored in the NVRAM configuration file, the router

boots the Cisco IOS software image as directed by that value.

If no boot system command is present in the configuration file, the router forms a default

boot filename and attempts to acquire that file from a network TFTP server. To compute

the filename of this default image, the router starts with cisco and appends the octal

equivalent of the boot field value, a hyphen, and the processor type (grp or prp). Table 20

lists the range of possible computed default filenames for booting over the network.

The router would use one of these filenames to boot a default system image stored on a

network TFTP server. If the configuration file contains a valid boot system configuration

command, the system uses these instructions to boot the system, rather than using the

filename it computed from the software configuration register settings.

For this setting, it is assumed that the Ethernet port on the RP is configured and

operational.

Note If a bootable Cisco IOS software image exists in a Flash memory card inserted in

PCMCIA slot 0 or slot 1, the software configuration register boot field setting is

overridden, and the system boots from the Cisco IOS software image in the Flash

memory card, rather than from a network TFTP image.

Command Purpose

Step 1

Router> enable

Password: <password>

Enters privileged EXEC mode.

Step 2

Router# configure terminal

Enters global configuration mode.

Step 3

Router(config)# config-register 0xvalue

Sets the contents of the software configuration register, where

value is a 4-bit hexadecimal number as described in Table 18.