Router load and run the POST (Located in ROM), testing the hardware component, including memory and interfaces, then the bootstrap program is loaded and executed. The bootstrap program finds and loads an IOS image: the possible location of IOS images include Flash, TFTP server, or mini-IOS in ROM. Once IOS is loaded, IOS attempt to find and load the configuration file, which is normally stored in NVRAM, if the IOS can not find the configuration file, it starts up the system configuration dialog, after the configuration is loaded you are present wit the CLI interface

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The bootstrap program goes through the following steps when trying to locate the IOS and load the IOS image:
1) Examine the configuration register value.  This value is set for four hexadecimal digits. If the last digit is between 0x2 to 0xf, then the router proceeds to the next step.

2)Examine the configuration file in NVRAM for boot system commands, which tells the bootstrap program to where to find the IOS.

3)If no boot system commands are found in the NVRAM, use the first valid IOS image found in the flash

4) If there are no valid IOS images in a Flash, generate a TFTP local broadcast to locate TFTP server

5)If no TFTP server is found, load the mini-IOS in ROM (Rxboot mode)

6) If there is a 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 images or loads ROMMON and goes in to the ROMmonitor mode

Speed:-
Ethernet: – 10Mbps
Fast Ethernet: – 100Mbps
Gigabit Ethernet: – 1Gbps
10gigabit Ethernet: -10Gbps
Serial interface: -1.544Mbps
Console port: – 9.6kbps (9600bits per second

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