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The following information is found in this appendix:
•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
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.
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.
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, cisco2-7201). 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.
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 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. Bit 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.
|
|
|
---|---|---|
Off |
Off |
<ones><ones> |
Off |
On |
<zeros><zeros> |
On |
On |
<net><zeros> |
On |
Off |
<net><ones> |
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.)
|
|
|
---|---|---|
9600 |
0 |
0 |
4800 |
0 |
1 |
2400 |
1 |
1 |
1200 |
1 |
0 |
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.
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 7201 router.
Router# show version
Cisco IOS Software, 7200 Software (C7200P-ADVENTERPRISEK9-M), Version 12.4(biffDEV.061001), INTERIM SOFTWARE Copyright (c) 1986-2006 by Cisco Systems, Inc.
Compiled Sun 01-Oct-06 23:42 by biff
ROM: System Bootstrap, Version 12.4(4r)XD5, RELEASE SOFTWARE (fc1)
BOOTLDR: Cisco IOS Software, 7200 Software (C7200P-KBOOT-M), Version 12.4(TAZ3DEV.060927), INTERIM SOFTWARE
c7201alpha1 uptime is 5 days, 18 hours, 32 minutes System returned to ROM by power-on System image file is "disk0:c7200p-adventerprisek9-mz.2006-10-01.biffdev"
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Cisco 7201 (c7201) processor (revision A) with 917504K/65536K bytes of memory.
Processor board ID 2222222222222
MPC7448 CPU at 1666Mhz, Implementation 0, Rev 2.2
1 slot midplane, Version 2.255
Last reset from power-on
1 FastEthernet interface
4 Gigabit Ethernet interfaces
2045K bytes of NVRAM.
62443K bytes of USB Flash usbflash0 (Read/Write)
250880K bytes of ATA PCMCIA card at slot 0 (Sector size 512 bytes).
65536K bytes of Flash internal SIMM (Sector size 512K).
Configuration register is 0x2
If the bootstrap prompt is ">", 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]
The configuration register can be set in the configuration mode with the config-register 0x value command. See the following sample output:
Router# configure terminal
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
If the prompt is ">", the o/r0x 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-c7201
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 >