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Configuration Registers

The global configuration command - config-register is used to modify the behavior of the router. Weather or not it boots from saved configuration. Weather or not it boots from the flash or the boot-proms.

The boot field is bits 0-3 (4 bits) in the configuration register

Monitor Command Function
o Displays the virtual configuration register, currently in effect, with a description of the bits
o/r Resets the virtual configuration register to the defaults as follows:
9600 baud console UART speed
break/abort has no effect
ignore the system configuration NVRAM
boot from ROM
o/r 0xvalue Sets the virtual configuration register to the (hex) value, value
Enter the i command after entering the o/r command to automatically reboot the router.

Virtual Configuration Register Bit Meanings

Bit No.(1) Hexadecimal Meaning
00 to 03 0x0000 to 0x000F Boot field
06 0x0040 Causes system software to ignore NVRAM contents
07 0x0080 OEM bit enabled
08 0x0100 Break disabled
10 0x0400X IP broadcast with all zeros
11 to 12 0x0800 to 0x1000 Console line speed
13 0x2000 Boot default ROM software if network boot fails
14 0x4000 IP broadcasts do not have net numbers
15 0x8000 Enable diagnostic messages and ignore NVRAM contents

(1)The factory default value for the configuration register is 0x2102.
This value is a combination of the following:
bit 13 = 0x2000
bit 8 = 0x0100
bits 00 through 03 = 0x0002.

Explanation of Boot Field (Configuration Register Bits 00 to 03)

Boot Field Meaning
0x0X Stays at the system bootstrap prompt
0x1 Boots system image in system ROM
0x2 to 0xF Specifies a default netboot filename Enables boot system commands that override default netboot filename

System Console Terminal Baud Rate Settings

Baud Bit 12 Bit 11
9600 0 0
4800 0 1
1200 1 0
2400 1 1

Here is a Configuration Register Calculator for your use. Quite handy!