سلام منconf reg رو بر اساس این مطلب عرض کردم: The bootstrap program goes through the following steps when trying to locate and load the IOS image:
1. Examine the configuration register value. This value is a set of four hexadecimal digits. The last digit affects the bootup process. If the last digit is between 0x2 and 0xF, then the router proceeds to the next step. Otherwise, the router uses the values to determine how it should proceed next.
2. Examine the configuration file in NVRAM for boot system commands, which tell the bootstrap program where to find the IOS.
3. If no boot system commands are found in the configuration file in NVRAM, use the first valid IOS image found in flash.
4. If there are no valid IOS images in flash, generate a TFTP local broadcast to locate a TFTP server (this is called a netboot and is not recommended because it is very slow and not very reliable for large IOS images).
5. If no TFTP server is found, load the Mini-IOS in ROM (RXBOOT mode).
6. If there is Mini-IOS in ROM, then the Mini-IOS is loaded and you are taken into RXBOOT mode; otherwise, the router either retries finding the IOS image or loads ROMMON and goes into ROM Monitor mode.