Cisco 7600 Series Router Installation Guide
Configuration Register Information
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Configuration Register Information

Table Of Contents

Configuration Register Information

Configuration Bit Meanings

Bits 0-3

Bit 6

Bit 7

Bit 8

Bit 10 and Bit 14

Bit 11 and Bit 12

Bit 13

Bit 15

Displaying the Configuration Register While Running Cisco IOS

Displaying the Configuration Register While Running ROM Monitor

Setting the Configuration Register While Running Cisco IOS

Setting the Configuration Register While Running ROM Monitor


Configuration Register Information


The following information is found in this appendix:

Configuration Bit Meanings

Displaying the Configuration Register While Running Cisco IOS

Displaying the Configuration Register While Running ROM Monitor

Setting the Configuration Register While Running Cisco IOS

Setting the Configuration Register While Running ROM Monitor

Configuration Bit Meanings

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

Table C-1 lists the meaning of each of the configuration memory bits. Following the table is a more in-depth description of each setting.

Table C-1 Configuration Register Bit Settings 

Bit No.
Hex
Meaning

00-03

0x0000-0x000F

Boot field

06

0x0040

Causes the system software to ignore nonvolatile random-access memory (NVRAM) contents

07

0x0080

OEM (original equipment manufacturer) bit enabled

08

0x0100

Break disabled

10

0x0400

IP broadcast with all zeros

11-12

0x800-0x1000

Console line speed

13

0x2000

Boots default ROM software if initial boot fails

14

0x4000

IP broadcasts do not have network numbers

15

0x8000

Enables diagnostic messages and ignores NVRAM contents


Bits 0-3

The lowest four bits of the processor configuration register (bits 3, 2, 1, and 0) form the boot field. Table C-2 provides information about the bits settings.

Table C-2 Bits 0-3 Settings

Boot Field
Meaning

0

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

1

Boots the boot helper image as a system image

2

Full boot process, which loads the Cisco IOS image into Flash memory

2-F

Specifies a default filename for booting over the network from a TFTP server


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 C-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.

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, cisco2-7301). 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. Table C-3 lists the default boot filenames or actions.


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


Table C-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

Flash software

0

0

1

0

cisco3-< image-name1>

0

0

1

1

cisco4-<image-name2>

0

1

0

0

cisco5-<image-name3>

0

1

0

1

cisco6-<image-name4>

0

1

1

0

cisco7-<image-name5>

0

1

1

1

cisco10-<image-name6>

1

0

0

0

cisco11-<image-name7>

1

0

0

1

cisco12-<image-name8>

1

0

1

0

cisco13-<image-name9>

1

0

1

1

cisco14-<image-name10>

1

1

0

0

cisco15-<image-name11>

1

1

0

1

cisco16-<image-name12>

1

1

1

0

cisco17-<image-name13>

1

1

1

1


Bit 6

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

Bit 7

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

Bit 8

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 and Bit 14

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. Table C-4 shows the combined effect of bit 10 and bit 14.

Table C-4 Bit 10 and Bit 14 Settings

Bit 14
Bit 10
IP Address (<net> <host>)

Off

Off

<ones><ones>

Off

On

<zeros><zeros>

On

On

<net><zeros>

On

Off

<net><ones>


Bit 11 and Bit 12

Bit 11 and Bit 12 in the configuration register determine the baud rate of the console terminal. Table C-5 shows the bit settings for the four available baud rates. (The factory set default baud rate is 9600.)

Table C-5 Bit 11 and Bit 12 Settings

Baud
Bit 12
Bit 11

9600

0

0

4800

0

1

2400

1

1

1200

1

0


Bit 13

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

Bit 15 enables diagnostic messages and ignores NVRAM contents.

Displaying the Configuration Register While Running Cisco IOS

The configuration register can be viewed by using the show version or show hardware command.

The following is sample output of the show version command from a Cisco 7301 router.

Cisco Internetwork Operating System Software 
IOS (tm) 7301 Software (C7301-JS-M), Experimental Version 12.2(20020904:004736) [biff 107]
Copyright (c) 1986-2002 by cisco Systems, Inc.
Compiled Mon 09-Sep-02 18:02 by biff
Image text-base:0x600088F8, data-base:0x61A94000
 
   
ROM:System Bootstrap, Version 12.2(20020730:200705) [biff-TAZ2_QA_RELEASE_16B 101], 
DEVELOPMENT SOFTWARE
BOOTLDR:7301 Software (C7301-BOOT-M), Experimental Version 12.2(20020813:014224) 
[biff-TAZ2_QA_RELEASE_17B 101]
 
   
7301p2b uptime is 0 minutes
System returned to ROM by reload at 00:01:51 UTC Sat Jan 1 2000
System image file is "tftp://10.1.8.11/tazii/images/c7301-js-mz"
 
   
cisco 7301 (NPE-G1) processor (revision A) with 491520K/32768K bytes of memory.
Processor board ID 0
BCM1250 CPU at 700Mhz, Implementation 1, Rev 0.2, 512KB L2 Cache
1 slot midplane, Version 2.0
 
   
Last reset from power-on
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
3 Gigabit Ethernet/IEEE 802.3 interface(s)
509K bytes of non-volatile configuration memory.
          
62976K bytes of ATA PCMCIA card at slot 0 (Sector size 512 bytes).
32768K bytes of Flash internal SIMM (Sector size 256K).
Configuration register is 0x102
 
   

Displaying the Configuration Register While Running ROM Monitor

If the bootstrap prompt ">", the o command displays the virtual configuration register currently in effect. It includes a description of the bits. See the following sample output:

>o
Configuration register + 02x100 at last boot
Bit#	       Configuration register option settings:
15         Diagnostic mode disabled
14         IP broadcasts do not have network numbers
13         Boot default ROM software if network boot fails
12-11      Console speed is 9600 baud
10         IP broadcasts with ones
09         Do not use secondary bootstrap
08         Break disabled
07         OEM disabled
06         Ignore configuration disabled
05         Fast boot disabled
04         Fan boot disabled
03-00      Boot to ROM monitor
 
   

If the prompt is "rommon1", the confreg command displays the virtual configuration register currently in effect. It includes a description of the bits. See the following sample output:

rommon 1 > confreg
 
   
Configuration Summary
enabled are:
load rom after netboot fails
console baud: 9600
boot: the ROM Monitor
 
   
Do you wish to change the configuration? y/n  [n]

Setting the Configuration Register While Running Cisco IOS

The configuration register can be set in the configuration mode with the config-register 0x<value> command. See the following sample output:

Router# config t
Enter configuration commands, one per line. End with CNTRL/Z.
Router(config)#config-register 0x2142
Router(config)#end
Router#
%SYS-5-CONFIG_I: Configured from console by console
 
   

Setting the Configuration Register While Running ROM Monitor

If the prompt is ">", the or0x<value> command sets the configuration register. See the following sample output:

>o/r 0x2102
>
 
   

If the prompt is "rommon1", the confreg command sets the configuration register. It prompts the user about each bit. See the following sample output:

rommon 1 > confreg
 
   
Confiuration Summary
enabled are:
load rom after netboot fails
console baud: 9600
boot: the ROM Monitor
 
   
do you wish to change the configuration y/n    [n]:  y
enable  "diagnostic mode"? y/n   [n]:   n
enable   "use net in IP bcast address"? y/n  [n]:   n
disable  "use rom after netboot fails"? y/n  [n]:  n
enable   "use all zero broadcast"? y/n  [n]:  n
enable   "break/abort has effect"? y/n  [n]:  n
enable   "ignore system config info"? y/n   [n]:  n
change console baud rate? y/n  [n]:  n
change the boot characteristics? y/n   [n]:y
enter to boot:
0 = ROM Monitor
1 = the boot helper image
2 - 15 = boot system
[0]: 2
 
   
Configuration Summary:
enabled are:
load rom after netboot fails
console baud: 9600
boot: image sepcified by the boot system commands or default to: cisco2-c7301
 
   
do you wish to change the configuration? y/n   [n]   n
 
   
You must reset or power cycle for new config to take effect
rommon 2 >