Virtual Configuration Register

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, refer to the section "Configuration Register" in the appendix "ROM Monitor." 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. (See Figure E-1.) The provided adapter is labeled Terminal. For information about cable pinouts, see the "Cable Specifications" appendix.

Figure E-1 : Connecting the Console

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 term command:

Router# configure term

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 E-2), to set the contents of the configuration register:

Router# config-register 0xvalue

Step 8 Press Ctrl-Z to exit configuration mode.

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 9 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 10 Reboot the router. The new value is effective after the router reboots.

Configuring the Boot Field

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

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

Boot Field	Meaning
00	Stays at the 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 Flash memory Enables boot system commands that override the default netboot filename1

¹ Values of the boot field are 2 to 15 in the form cisco<n>-model_number, where 2 >= n " 15.

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 section "Command Descriptions" in the appendix "ROM Monitor."

If you set the boot field value to a value of 2 to 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 E-3.) If there are no boot commands in the configuration file, the router attempts to boot the first file in Flash memory.

If there are boot commands 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.

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 router creates a default boot filename as part of the automatic configuration processes. To form the boot filename, the router starts with cisco and links the octal equivalent of the boot field number, a dash, and the model number. Table E-3 lists the default boot filenames or actions for the processor.

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

config-reg 0x102
Ctrl-Z