Way back in Chapter 6, we took an introductory look at how a Cisco router boots by default, according to factory-configured settings. However, you will also need to know how to alter settings such that a router can boot into different environments, if necessary. For example, if a router password is lost or misplaced and you can’t log into the router, you will need to alter the boot process such that settings stored in the startup configuration file are ignored. Doing so requires that you change the configuration register settings on your router. This presents a problem – if you can’t log on to the router, how you change its configuration? The answer involves understanding a little bit more about two different operating environments – ROM Monitor and RxBoot (Boot Image) mode.