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This appendix describes the router virtual configuration register, the factory default settings, and the procedures for changing those settings.
The router has a 16-bit virtual register, which is written into the nonvolatile memory (NVRAM). Use the processor configuration register information contained in this appendix to do the following:
Table B-1 lists the meaning of each of the virtual configuration memory bits, and Table B-2 defines the boot field names.
| Bit No. | Hex | Meaning |
|---|---|---|
| 00-03 | 0x0000-0x000F | Boot field (see Table B-2) |
| 06 | 0x0040 | Causes system software to ignore nonvolatile memory contents |
| 07 | 0x0080 | OEM bit enabled |
| 08 | 0x0100 | Break disabled |
| 10 | 0x0400 | IP broadcast with all zeros |
| 11-12 | 0x0800-0x1000 | Console line speed |
| 13 | 0x2000 | Boot default ROM software if network boot fails |
| 14 | 0x4000 | IP broadcasts do not have net numbers |
| 15 | 0x8000 | Enable diagnostic messages and ignore NVM contents |
| Boot Field | Meaning |
|---|---|
| 00 | Stays at the system bootstrap prompt |
| 01 | Boots system image on EPROM |
| 02-F | Specifies a default netboot filename
Enables boot system commands that override default netboot filename1 |
Some common reasons to modify the value of the virtual configuration register follow:
To change the configuration register while running the system software, follow these steps:
Step 1 Enter the enable command and your password to enter the privileged level, as follows:
enable
Step 2 At the privileged level system prompt (router #), enter the command configure terminal. You will be prompted as shown in the following example:
configure term
Step 3 To set the contents of the configuration register, enter the config-register value configuration command where value is a hexadecimal number preceded by 0x
(See Table B-3
), as in the following:
config-register 0xvalue
(The virtual configuration register is stored in nonvolatile memory.)
Step 4 Exit the configuration mode by entering Ctrl-Z. The new value settings will be saved to memory; however, the new settings do not take effect until the system software is reloaded by rebooting the router.
Step 5 To display the configuration register value currently in effect and the value that will be used at the next reload, enter the show version EXEC command, and the value will be displayed on the last line of the screen display as in the example following:
Step 6 Reboot the router. The new value takes effect. Configuration register changes take effect only when the server restarts: such as when you switch the power off and on or when you issue a reload command from the console.
The lowest four bits of the processor configuration register (bits 3, 2, 1, and 0) form the boot field. (See Table B-2.) The boot field specifies a number in binary. If you set the boot field value to 0, you must boot the operating system manually 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]--Netboots using TFTP b flash [filename]--Boots the file (filename) from Flash memoryFor more information about the b [tftp] flash filename command, see the Router Products Configuration and Reference publication.
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, then the router boots the system software as directed by that value. (See Table B-3 .) 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.
In the following example, the virtual configuration register is set to boot the router automatically from Flash memory and to ignore Break at the next reboot of the router:
router# configure terminal
Enter configuration commands, one per line.
Edit with DELETE, CTRL/W, and CTRL/U; end with CTRL/Z
config-register 0x102
Ctrl-Z
router#
The server creates a default boot 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 processor-type name. Table B-3 lists the default boot filenames or actions for the processor.
| Action/File Name | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
|---|---|---|---|---|
| bootstrap mode | 0 | 0 | 0 | 0 |
| ROM software | 0 | 0 | 0 | 1 |
| cisco2-igs | 0 | 0 | 1 | 0 |
| cisco3-igs | 0 | 0 | 1 | 1 |
| cisco4-igs | 0 | 1 | 0 | 0 |
| cisco5-igs | 0 | 1 | 0 | 1 |
| cisco6-igs | 0 | 1 | 1 | 0 |
| cisco7-igs | 0 | 1 | 1 | 1 |
| cisco10-igs | 1 | 0 | 0 | 0 |
| cisco11-igs | 1 | 0 | 0 | 1 |
| cisco12-igs | 1 | 0 | 1 | 0 |
| cisco13-igs | 1 | 0 | 1 | 1 |
| cisco14-igs | 1 | 1 | 0 | 0 |
| cisco15-igs | 1 | 1 | 0 | 1 |
| cisco16-igs | 1 | 1 | 1 | 0 |
| cisco17-igs | 1 | 1 | 1 | 1 |
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
60 seconds while the system reboots, regardless of the configuration settings.
Bit 10 controls the host portion of the Internet 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. Bit 10 interacts with bit 14, which controls the network and subnet portions of the broadcast address.
Table B-4 shows the combined effect of bits 10 and 14.
| Bit 14 | Bit 10 | Address (<net> <host>) |
|---|---|---|
| off | off | <ones> <ones> |
| off | on | <zeros> <zeros> |
| on | on | <net> <zeros> |
| on | off | <net> <ones> |
Bit 13 determines the server response to a bootload failure. Setting bit 13 causes the server to load operating software from ROM after five unsuccessful attempts to load a boot file from the network. Clearing bit 13 causes the server to continue attempting to load a boot file from the network indefinitely. By factory default, bit 13 is cleared to 0.
Bits 11 and 12 in the configuration register determine the baud rate of the console terminal.
Table B-5
shows the bit settings for the four available baud rates. (The factory-set default baud rate is 9600.)
| Baud | Bit 12 | Bit 11 |
|---|---|---|
| 9600 | 0 | 0 |
| 4800 | 0 | 1 |
| 1200 | 1 | 0 |
| 2400 | 1 | 1 |
To enable booting from Flash, set bits 3, 2, 1, and 0 to a value between 2 and 15 in conjunction with the system software configuration command boot system flash filename.
To enter the configuration mode, while in the system software image, enter the configure command at the enable prompt as in the example following:
Gateway# configure
Configuring from terminal, memory, or network [terminal]? term
Enter configuration commands, one per line.
Edit with DELETE, CTRL/W, and CTRL/U; end with CTRL/Z
boot system flash filename
To disable break and enable the boot system flash command, enter the config-register command with a value as in the example following:
config-reg 0x102
CTRL/Z
Gateway#
If you set the configuration register value to 0x102, as in the example, it is not necessary to enter the boot system flash command unless there is more than one image in Flash.
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