0x2102
Flash memory
show version
When resetting a Cisco 1841 router, the default password recovery and administration key is "confreg 0x2142." This allows you to reset the router with a new configuration.
you can use 2100 when you have a corrupt nvram and your router refuses to boot up
The "default gateway" is your router.
The reset button in a router let you remove all the configuration you do and gives you the default configuration from factory.
ROM
Which default EIGRP configuration must be modified to allow an EIGRP router to advertise subnets that are configured with VLSM
NVRAM, TFTP,Console
When a router boots up, it follows a default order to search for startup configuration information. First, it checks the non-volatile memory (NVRAM) for the startup configuration file, typically named "startup-config." If it doesn't find a valid configuration there, it may look for a configuration file in a TFTP server, and if that fails, the router will proceed with its default settings, often leading to a mode where no configurations are applied.
Reload the device.
show version