4-4
Cisco 7500 Series Installation and Configuration Guide
OL-5008-03 B0
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 4-1
lists the meaning of each of the software configuration memory bits, and
Table 4-2
defines
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 Number
1
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.
Hexadecimal
Meaning
00 to 03
0x0000 to 0x000F
Boot field
06
0x0040
Causes system software to ignore NVRAM contents
07
0x0080
OEM
2
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
