Cisco DistributedDirector 4700-M Install and Config Guide
Virtual Configuration Register
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Virtual Configuration Register

Table Of Contents

Virtual Configuration Register

Virtual Configuration Register Settings

Changing Configuration Register Settings

Configuring the Boot Field

Enabling Booting from Flash Memory


Virtual Configuration Register


This appendix describes the DistributedDirector 4700-M virtual configuration register, the factory-default settings, and the procedures for changing those settings.

Virtual Configuration Register Settings

The Director has a 16-bit virtual register, which is written into the nonvolatile random access memory (NVRAM). Use the processor configuration register information contained in this appendix to do the following:

Set and display the configuration register value

Force the system into the bootstrap program

Select a boot source and default boot filename

Enable or disable the Break function

Control broadcast addresses

Set the console terminal baud rate

Load operating software from ROM

Enable booting from a Trivial File Transfer Protocol (TFTP) server

lists the meaning of each of the virtual configuration memory bits.

Table D-1 Virtual Configuration Bit Meanings

Bit No.
Hex
Meaning

00-03

0x0000-0x000F

Boot field (see )

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

Boots default ROM software if network boot fails

14

0x4000

IP broadcasts do not have net numbers

15

0x8000

Enables diagnostic messages and ignores NVRAM contents


Changing Configuration Register Settings

Some common reasons to modify the value of the virtual configuration register follow:

Recover a lost password

Change the console baud rate

Enable or disable the Break function

Manually boot the operating system using the b command at the ROM monitor prompt

Force the Director to boot automatically its system image in Flash memory, or boot as per any boot system commands that are stored in its configuration file in NVRAM


Note   If the Director finds no boot system commands, it uses the configuration register value to form a filename from which to boot a default system image stored on a network server. (See .)


Take the following steps to change the configuration register while running the Cisco IOS software:


Step 1 Enter the enable command and your password to enter the privileged level, as follows:

DD> enable
Password: 
DD#

Step 2 At the privileged-level system prompt (DD#), enter the command configure terminal. You will be prompted as shown in the following example:

DD# configure terminal
Enter configuration commands, one per line.
Edit with DELETE, CTRL/W, and CTRL/U; end with CTRL/Z 

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 ), as in the following:

config-register 0xvalue

(The virtual configuration register is stored in nonvolatile memory.)

Step 4 Press Ctrl-Z to exit the configuration mode. 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 Director.

Step 5 Enter the show version EXEC command to display the configuration register value currently in effect and the value that will be used at the next reload. The value will be displayed on the last line of the screen display as in the following example:

Configuration register is 0x142 (will be 0x102 at next reload)

Step 6 Reboot the Director. The new value takes effect. Configuration register changes take effect only when the server restarts, for example, when you turn the power OFF and ON or when you issue a reload command from the console.

Configuring the Boot Field

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

Table D-2 Explanation of Boot Field (Configuration Register Bits 00-03)

Boot Field
Meaning

00

Stays at the system bootstrap prompt (ROM monitor) on a reload or power cycle

01

Boots the boot helper image as a system image

02-F

Specifies a default netboot filename

Enables default booting from system Flash memory

Enables boot system commands that override the default netboot filename1

1 Values of the boot field are 2-15 in the form cisco<n>-processor_name, where 2 ð n ð 15.


The boot field specifies a number in binary. If you set the boot field value to 0, you must have console port access to boot the operating system manually. 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]—Boots over the network using TFTP

b flash [filename]—Boots the file filename from Flash memory

For more information about the b [tftp] flash filename command, see the appropriate Cisco IOS software publications.

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 Director boots the system software as directed by that value. (See .) If you set the boot field to any other bit pattern, the Director uses the resulting number to form a default boot filename for booting from a network (TFTP) server.

If there are no boot commands in the configuration file, the Director attempts to boot the first file in system Flash memory. If no file is found in system Flash memory, the Director attempts to netboot a default file whose name is derived from the value of the boot field (for example, cisco2-4500). If the attempt to boot from a network (TFTP) server fails, the boot helper image in boot Flash will boot up.

If boot commands are in the configuration file, the Director 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 Director will retry the netboot commands up to six times unless the boot default ROM software "if netboot fails" bit (bit 13 of the virtual configuration register) is set. If bit 13 is set, the system boots the boot helper image found in boot Flash memory without any retries.

In the following example, the virtual configuration register is set to boot the Director automatically from Flash memory and to ignore Break at the next reboot of the Director:

DD# 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
DD# 

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. lists the default boot filenames or actions for the processor.


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


Table D-3 Default Boot Filenames

Action/File Name
Bit 3
Bit 2
Bit 1
Bit 0

bootstrap mode

0

0

0

0

ROM software

0

0

0

1

cisco2-4000
or cisco2-4500

0

0

1

0

cisco3-4000
or cisco3-4500

0

0

1

1

cisco4-4000
or cisco4-4500

0

1

0

0

cisco5-4000
or cisco5-4500

0

1

0

1

cisco6-4000
or cisco6-4500

0

1

1

0

cisco7-4000
or cisco7-4500

0

1

1

1

cisco10-4000
or cisco10-4500

1

0

0

0

cisco11-4000
or cisco11-4500

1

0

0

1

cisco12-4000
or cisco12-4500

1

0

1

0

cisco13-4000
or cisco13-4500

1

0

1

1

cisco14-4000
or cisco14-4500

1

1

0

0

cisco15-4000
or cisco15-4500

1

1

0

1

cisco16-4000
or cisco16-4500

1

1

1

0

cisco17-4000
or cisco17-4500

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. shows the combined effect of bits 10 and 14.

Table D-4 Configuration Register Settings for Broadcast Address Destination

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 indefinitely to attempt loading a boot file from the network. 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. shows the bit settings for the four available baud rates. (The factory-default baud rate is 9600.)

Table D-5 System Console Terminal Baud Rate Settings

Baud
Bit 12
Bit 11

9600

0

0

4800

0

1

1200

1

0

2400

1

1


Enabling Booting from Flash Memory

To enable booting from Flash memory, set bits 3, 2, 1, and 0 to a value between 2 through 15. To specify a filename to boot, enter the system software configuration boot system flash filename command in the configuration file.

To enter the configuration mode while in the system software image, enter the configure command at the enable prompt as follows:

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 follows:

config-reg 0x102
CTRL/Z

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 memory.