The Purpose of the Configuration Register

The configuration register can be used to change router behavior in several ways, such as:

how the router boots (into ROMmon, NetBoot)

options while booting (ignore configuration, disable boot messages)

console speed (baud rate for a terminal emulation session)

The configuration register can be set from configuration mode using the config-register command. From ROMmon, use the confreg command. Issue the show version command to view the current setting of the configuration register:

Router#show version
Cisco Internetwork Operating System Software
IOS ™ 2500 Software (C2500-JS-L), Version 12.1(5), RELEASE SOFTWARE (fc1)
Copyright © 1986-2000 by cisco Systems, Inc.
Compiled Wed 25-Oct-00 05:18 by cmong
Image text-base: 0x03071DB0, data-base: 0x00001000
ROM: System Bootstrap, Version 5.2(8a), RELEASE SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-RXBOOT), Version 10.2(8a), RELEASE SOFTWARE (fc1)
Router uptime is 7 minutes
System returned to ROM by reload
System image file is “flash:c2500-js-l_121-5.bin”
cisco 2500 (68030) processor (revision D) with 16384K/2048K bytes of memory.
Processor board ID 03867477, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
SuperLAT software (copyright 1990 by Meridian Technology Corp).
TN3270 Emulation software.
1 Token Ring/IEEE 802.5 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102

The factory-default setting for the configuration register is 0x2102. This indicates that the router should attempt to load a Cisco IOS® software image from Flash memory and load the startup configuration with a console speed of 9600 baud.