Cisco Router Configuration Handbook, Second Edition

Appendix E. Configuration Register Settings

This appendix contains an overview of the virtual configuration register used by the router during initialization. The configuration register controls many of the boot parameters, as well as the console speed. Each router has a configuration register; however, they differ slightly based on the system architecture. For example, the Cisco 2600 series configuration registers vary slightly from the 2500 series by allowing a previously unused bit (bit 5) to define more console port speeds.

Virtual Configuration Register

When a router boots, the virtual configuration register is checked to determine many boot parameters, including what mode to enter upon booting, where to get the software image, and how ...