The startup sequence based on a Cisco router is as follows:
Step 1: The router performs a Power On Self Test (POST) to discover and verify the hardware.
Step 2: The router loads and runs bootstrap code from ROM.
Step 3: The router provides the IOS or other software and charging.
Step 4: The router is the configuration file and loads it into running configuration.
All routers attempt all four steps every time the router is powered on or reloaded. POST codes and functionscan not be changed by your router. The position of the bootstrap code to load the IOS and configuration file can be edited by the administrator, but it is almost always the default location for the bootstrap code (ROM) and the initial configuration (NVRAM). Thus the position of duties or other software, is the only part that usually changes. Three types of operating systems can be loaded into the router:
• The complete IOS image, which generallyLocation of flash memory, but can also find a TFTP server. This is the normal, full-function IOS used in production;
• A limited IOS feature that is in ROM, and provides basic IP connectivity, if the flash memory is faulty and you need IP connectivity, a new IOS in flash memory to be copied. This limited IOS feature is called RXBOOT mode.
• It is another operating system IOS, which is also stored in ROM. This operating system, called ROM Monitor (ROMMON) mode is used forDebugging low level and password recovery. If you do not recover your password, rarely using the ROMMON mode.
The register configuration of the router says if a full-featured IOS ROMMON mode, RXBOOT to use. The registry is a 16-bit recording software in the router, and its value is the command configregister global configuration. The boot camp is the name of low-bit 4 of the Registry. This field can be a 4-bit --Value, represented as a single hexadecimal digit. If the boot sector is hex 0 ROMMON is loaded. If the boot sector is 1 hex, so RXBOOT is used. For everything else, you load a full-featured IOS.