Configuring the configuration register and the show version command

The configuration register is a 16-bit software register in a Cisco router that determines how the router boots, what Cisco IOS version it loads, and how it processes some configuration settings. The default value for the configuration register is 0x2102, which tells the router to load the IOS from flash memory, load the startup-config file, and to use console messages to show the boot sequence.

The show version command displays the current operating system version, hardware type, processor type, configuration register value, and other information about the router. Here is an example output of the show version command:

Router# show version

Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), Version 15.1(4)M, RELEASE SOFTWARE (fc1)

Technical Support: http://www.cisco.com/techsupport

Compiled Thu 01-Sep-11 03:17 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

Router uptime is 1 day, 22 hours, 5 minutes

System returned to ROM by power-on

System image file is “flash:c2800nm-advipservicesk9-mz.151-4.M.bin”

Cisco 2811 (revision 53.51) with 249856K/12288K bytes of memory.

Processor board ID FTX1045W9D6

2 FastEthernet interfaces

1 Gigabit Ethernet interface

2 Serial interfaces

1 terminal line

1 Virtual Private Network (VPN) Module

DRAM configuration is 64 bits wide with parity enabled.

239K bytes of non-volatile configuration memory.

62720K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102 As shown in the output above, the configuration register value is displayed at the bottom of the output. This value can be changed using the configuration register command in global configuration mode.