RxBoot mode
RXBoot mode is another configuration mode that has a limited version of the Cisco IOS which allows you to configure the router when a valid IOS image cannot be found on a TFTP server or in flash memory
The commands that are accepted are a subset of those in normal User Exec and Privileged Exec mode
You know you are in RxBoot mode because the prompt will be the name of the router followed by the word boot in parentheses, for example, router(boot)#.