The lowest four bits of the processor configuration register (bits 3, 2, 1, and 0) form the boot field.

The boot field specifies a number in binary. If you set the boot field value to 0, you must have a console port access to boot the operating system manually. Boot the operating system by entering the b command at the bootstrap prompt as follows:

> b [tftp] flash filename

Definitions of the various command options follow:

b—Boots the default system software from ROM

b flash—Boots the first file in Flash memory

b filename [host]—Boots over the network using TFTP

b flash filename—Boots the file (filename) from Flash memory

If you set the boot field value to a value of 2 through F, and there is a valid system boot command stored in the configuration file, the router boots the system software as directed by that value. (See Table 2) If you set the boot field to any other bit pattern, the router uses the resulting number to form a default boot filename for netbooting.

If there are no boot commands in the configuration file, the router attempts to boot the first file in system Flash memory. If no file is found in system Flash memory, the router attempts to netboot a default file with a name derived from the value of the boot field (for example, cisco2-7200). If the netboot attempt fails, the boot helper image in boot flash memory will boot up.

If boot commands are in the configuration file, the router software processes each boot command in sequence until the process is successful or the end of the list is reached. If the end of the list is reached without a file being successfully booted, the router will retry the netboot commands up to six times if bit 13 of the configuration register is set, otherwise it will load the operating system software available in ROMmon. If bit 13 is not set, the router will continue to netboot images indefinitely. The default setting for bit 13 is 0. If bit 13 is set, the system boots the boot helper image found in boot flash memory without any retries.

The server creates a default filename as part of the automatic configuration processes. To form the boot filename, the server starts with Cisco and links the octal equivalent of the boot field number, a dash, and the image name.

Note	A boot system configuration command in the router configuration in NVRAM overrides the default netboot filename.

Bit 6 causes the system software to ignore nonvolatile random-access memory (NVRAM) contents.

Bit 7 enables the OEM bit. It disables the bootstrap messages at startup.

Bit 8 controls the console Break key. Setting bit 8 (the factory default) causes the processor to ignore the console Break key. Clearing bit 8 causes the processor to interpret Break as a command to force the system into the bootstrap monitor, halting normal operation. A Break can be sent in the first sixty seconds while the system reboots, regardless of the configuration settings.

Bit 10 controls the host portion of the Internet IP broadcast address. Setting bit 10 causes the processor to use all zeros; clearing bit 10 (the factory default) causes the processor to use all ones. B it 10 interacts with bit 14, which controls the network and subnet portions of the IP broadcast address. The table below shows the combined effect of bit 10 and bit 14:

Note	The console line rate on Cisco universal broadband routers is fixed at 9600 and cannot be changed. For more information about configuring baud rates, see Appendix B: Cisco CMTS Router ROM Monitor Commands in the Cisco IOS CMTS Cable Command Reference .

Bit 11 and Bit 12 in the configuration register determine the baud rate of the console terminal. The table below shows the bit settings for the four available baud rates (the factory set default baud rate is 9600):

Note	The console line rate on Cisco universal broadband routers is fixed at 9600 and cannot be changed. For more information about configuring baud rates, see Appendix B: Cisco CMTS Router ROM Monitor Commands in the Cisco IOS CMTS Cable Command Reference .

Bit 13 determines the server response to a bootload failure. If boot commands are in the configuration file, the router software processes each boot command in sequence until the process is successful or the end of the list is reached. If the end of the list is reached without a file being successfully booted, the router will retry the netboot commands up to six times if bit 13 of the configuration register is set, otherwise it will load the operating system software available in ROMmon. If bit 13 is not set, the router will continue to netboot images indefinitely. The default setting for bit 13 is 0. If bit 13 is set, the system boots the boot helper image found in boot flash memory without any retries.

Bit 15 enables diagnostic messages and ignores NVRAM contents.