Cisco Systems Cisco 12816 Manuale Utente

This section provides detail about of the low-order bits in the software 
configuration register and how they interact during the router boot process.

As described in the 

, the boot field setting determines the source of the Cisco IOS software 

image used to boot the router.

If you set the boot field value to 0 (0x0000), you must boot the operating 
system manually by entering the boot command at the ROM monitor prompt 
(

rommon>

).

If you set the boot field value to 0x2 through 0xF and a valid boot system 
command is stored in the 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.

In the following example, the software configuration register is set to boot the 
router from the flash memory SIMM on the RP, and to ignore the Break function 
at the next reboot of the system (see 

):

Milo# configure terminal

Enter configuration commands, one per line. End with CTRL-Z.

Milo(config)# config-register 0x0102

Milo(config)# boot system flash filename

Milo# 

With the configuration register set to 0x0102, the system computes a default boot 
filename. In forming this filename, the system starts with cisco and appends the 
octal equivalent of the boot field number, a hyphen, and the processor type (grp 
or prp). 

 lists the range of possible computed default filenames for booting the 

system over the network. Note, however, that a valid boot system configuration 
command stored in the NVRAM configuration file overrides any computed 
default filename for booting over the network.