Performing Other Configuration Tasks
Cisco 12008 Gigabit Switch Router Installation and Configuration Guide
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Boot Field Settings and the Use of the Boot Command

The four low-order bits of the software configuration register (bits 3, 2, 1, and 0) form a
boot field that defines the source of a Cisco IOS software image for booting the router.
You can set or change the contents of the boot field by issuing the config-register command
at the global configuration mode prompt [Router(config)#].
Note The factory default setting for the software configuration register (and RP spares) is
0x0102.
When the boot field is set to either 0 or 1 (0-0-0-0 or 0-0-0-1), the s ystem ig nor es an y bo ot
instructions in the system configuration file and one of the following occurs, depending on
the boot field setting:
•When the boot field is set to 0, you must boot the system manually by issuing the boot
command at the ROM monitor prompt (rommon>). You can issue the boot command
with or without arguments.
If you issue the boot command without an argument (that is, without specifying a file
or any other boot instructions), the system automatically boots using the default image
in the Flash memory SIMM on the RP.
If you issue the boot command with arguments (that is, by instructing the system to boot
from a specific source), the following options are available to you:
—You can instruct the system to boot from a specific Flash SIMM image (by issuing
the boot system flash filename command), or you can instruct the system to boot
from a specific image stored on a PCMCIA Flash memory card (by issuing the boot
<slot #:> <imagename> command).
—You can instruct the system to boot from a network TFTP s erver either by sending
broadcast TFTP requests (by issuing a boot system filename command), or by
sending a direct request to a specific network TFTP server (by issuing a boot
system filename ip-address command).