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This appendix describes the factory default settings of the virtual configuration register, and procedures for changing those settings.
This appendix has the following sections:
The router has a 16-bit virtual configuration register in NVRAM. You can use the virtual configuration register to perform the following tasks:
Table C-1 describes each of the virtual configuration register bits.
| Bit Number | Hexadecimal | Meaning |
|---|---|---|
00-03 | 0x0000-0x000F | Boot field. (See Table C-2.) |
06 | 0x0040 | Causes the system software to ignore the contents of NVRAM. |
07 | 0x0080 | OEM bit enabled. |
08 | 0x0100 | Break disabled. |
09 | 0x0200 | Causes the system to use the secondary bootstrap. |
10 | 0x0400 | IP broadcast with all zeros. |
5, 11, 12 | 0x0020, 0x0800, 0x1000 | Console line speed. |
13 | 0x2000 | Boots default ROM software if the network boot fails. |
14 | 0x4000 | IP broadcasts do not have net numbers. |
15 | 0x8000 | Enables diagnostic messages and ignores the contents of NVRAM. |
You might want to modify the value in the virtual configuration register in order to perform the following tasks:
You can change the virtual configuration register from either the ROM monitor or the operating system software. To change the configuration register from the ROM monitor, see the "Configuration Register" section. To change the configuration register from the system software, do the following:
Step 1 Connect a terminal using an RJ-45 rollover cable and an RJ-45-to-DB-25 or RJ-45-to-DB-9 adapter (labeled TERMINAL). (See Figure C-1 through Figure C-3.)
For information about cable pinouts, see the online document Cisco Modular Access Router Cable Specifications. This document is on the Documentation CD-ROM that accompanied your router package, and on Cisco Connection Online.
Step 2 Configure your terminal or terminal emulation software for 9600 baud (default), 8 data bits, no parity, and 2 stop bits.
Step 3 Power ON the router.
Step 4 When asked if you would like to enter the initial dialog, answer no:
Would you like to enter the initial dialog? [yes]: no
You are now in the normal operating mode of the router.
Step 5 After a few seconds, you see the user EXEC prompt (Router>). Enter the enable command and your password to enter privileged mode:
Router> enable Password: <password> Router#
Step 6 At the privileged-mode prompt (Router#), enter the configure terminal command:
Router# configure terminal Enter configuration commands, one per line. Edit with DELETE, CTRL/W, and CTRL/U; end with CTRL/Z
Step 7 Enter the config-register value command, where value is a hexadecimal number preceded by 0x (see Table C-2), to set the contents of the configuration register:
Router# config-register 0xvalue
Router# configure terminalRouter(config)# line console 0Router(config-line)# speed 9600
Step 8 Press Ctrl-z to exit configuration mode.
Step 9 Copy the new console speed to NVRAM:
Router> copy run start
The new settings are saved to NVRAM, but they are not effective until the router restarts; for example, when you switch the power off and on or when you enter a reload command from the console.
Step 10 Enter the show version command to display the configuration register value currently in effect and the value that will be used at the next reload. The value is shown on the last line of the display:
Configuration register is 0x142 (will be 0x142 at next reload)
Step 11 Reboot the router. The new value is effective after the router reboots.
The lowest four bits of the virtual configuration register (bits 3, 2, 1, and 0) form the boot field. (See Table C-2.)
| Boot Field | Meaning |
|---|---|
00 | Stays at the ROM monitor on a reload or power cycle |
01 | Boots the first image in Flash memory as a system image |
02-F | Enables default booting from Flash memory Enables boot system commands that override default booting from Flash memory |
The boot field specifies a number in binary form. If you set the boot field value to 0, you must have console port access to boot the operating system manually. Refer to the boot command in the "Command Descriptions" section.
If you set the boot field to a value of 2 to F, and there is a valid boot system command stored 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 there are no boot commands in the configuration file, the router attempts to boot the first file in Flash memory.
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#
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 router into the bootstrap monitor, halting normal operation. Break can always be sent in the first 60 seconds while the router is rebooting, regardless of the configuration settings.
Bit 9 controls the system boot. Clearing bit 9 (the factory default) causes the system to boot from Flash memory. Clearing bit 9 causes the system to use the secondary bootstrap (netbooting). This is typically not used.
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 broadcast address. Table C-3 shows the combined effect of bits 10 and 14.
| Bit 10 | Bit 14 | Address (<net> <host>) |
|---|---|---|
Off | Off | <ones> <ones> |
On | Off | <zeros> <zeros> |
On | On | <net> <zeros> |
Off | On | <net> <ones> |
Bit 13 determines the router's response to a bootload failure. Setting bit 13 causes the router to load operating software from ROM after six unsuccessful attempts to load a boot file. Clearing bit 13 causes the router to continue indefinitely to attempt loading a boot file. By factory default, bit 13 is set to 0.
Bits 5, 11, and 12 of the configuration register determine the baud rate of the console terminal. Table C-4 shows the bit settings for the eight available rates. (The default baud rate is 9600 bps.)
| Baud | Bit 5 | Bit 12 | Bit 11 |
|---|---|---|---|
115200 | 1 | 1 | 1 |
57600 | 1 | 1 | 0 |
38400 | 1 | 0 | 1 |
19200 | 1 | 0 | 0 |
9600 | 0 | 0 | 0 |
4800 | 0 | 0 | 1 |
2400 | 0 | 1 | 1 |
1200 | 0 | 1 | 0 |
To enable booting from Flash memory, set bits 3, 2, 1, and 0 to a value between 2 to 15. To specify a filename to boot, enter the system software configuration command boot system flash [device:] [partition:] [filename] in the configuration file.
By specifying the device and partition in the command, you can configure the router to boot from the PCMCIA cards. If you only specify the filename, the router will be configured to boot from Flash memory.
To enter configuration mode while in the system software image, enter the configure command at the enable prompt as in the following example:
Router# configure Configuring from terminal, memory, or network [terminal]? terminal 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 this example, you do not need to enter the boot system flash command unless there is more than one image in Flash memory.
Posted: Wed Sep 1 08:13:23 PDT 1999
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