Cisco Systems 7500 Series manual Configuring the Software Configuration Register

Chapter 4 Performing a Basic Configuration of the System

Configuring the Software Configuration Register

Configuring the Software Configuration Register

Note Appendix A, “Configuration Register Information” also provides configuration register information.

Cisco 7500 series routers use a 16-bit software configuration register, which allows you to set specific system parameters. Settings for the software configuration register are written into NVRAM.

Following are some reasons for changing the software configuration register settings:

•To select a boot source and default boot filename

•To enable or disable the Break function

•To control broadcast addresses

•To set the console terminal baud rate

•To load operating software from Flash memory

•To enable booting from a Trivial File Transfer Protocol (TFTP) server

•To recover a lost password

•To allow you to manually boot the system using the boot command at the bootstrap program prompt

•To force the router to boot automatically from the system bootstrap software (boot image) or from its default system image in onboard Flash memory, and read any boot system commands that are stored in the configuration file in NVRAM

Table 4-1lists the meaning of each of the software configuration memory bits, and Table 4-2defines the boot field.

Caution To avoid confusion and possibly halting the router, remember that valid configuration register settings might be combinations of settings and not just the individual settings listed in Table 4-1. For example, the factory default value of 0x0101 is a combination of settings.

Table 4-1	Software Configuration Register Bit Meanings
Bit Number1		Hexadecimal	Meaning
00 to 03		0x0000 to 0x000F	Boot field
06		0x0040	Causes system software to ignore NVRAM contents
07		0x0080	OEM2 bit enabled
08		0x0100	Break function disabled
09		0x0200	Use secondary bootstrap
10		0x0400	Internet Protocol (IP) broadcast with all zeros
11 to 12		0x0800 to 0x1000	Console line speed (default is 9600 baud)
13		0x2000	Boot default Flash software if network boot fails
14		0x4000	IP broadcasts do not have network numbers
15		0x8000	Enable diagnostic messages and ignore NVRAM contents

1.The factory default value for the configuration register is 0x0101.

This value is a combination of the following: bit 8 = 0x0100 and bits 00 through 03 = 0x0001.

Cisco 7500 Series Installation and Configuration Guide

4-4 OL-5008-03 B0