In this post we will understand the Router Boot Sequence !!!!!!!
So let start !!!!!!!!!!!!
Once the router boots up it under goes through various steps which are known as
Once the Router boots up it will first perform POST i.e Power On Self Test .
POST is a test where the Router verifies its Hardware components functionality . Its check whether all the hardware components are present and operational .
POST is saved and run from ROM.
Bootstrap is a program which executes programs.
It is stored in ROM of the Router.
It basically read the config-register , locate IOS and load the IOS .
If there is no valid IOS image file in flash , the bootstrap program will try to find the IOS image in TFTP server (which would need to be defined).
If there no TFTP server defined or there is no IOS image present in TFTP server then the router will load an "mini" IOS from ROM and the Router will enter in the ROM MONITOR MODE a.k.a ROMMON Mode
The ROMMON mode will provide with a interface wherein we would be able to execute basic commands .
The IOS will load the Start-up Configuration file from NVRAM into RAM which is know as Running Configuration file .
Whatever configuration changes are performed in Running Configuration (save in RAM) and to copy the same network admin needs to copy running configuration into startup configuration
#copy run start or simply #wr
If the IOS didnt find any configuration file in NVRAM it will enter in setup mode and prompt configuration input
So let start !!!!!!!!!!!!
Once the router boots up it under goes through various steps which are known as
"Router Boot Sequence"
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| ROUTER BOOT SEQUENCE |
1) POST - POWER ON SELF TEST
Once the Router boots up it will first perform POST i.e Power On Self Test .
POST is a test where the Router verifies its Hardware components functionality . Its check whether all the hardware components are present and operational .
POST is saved and run from ROM.
2) BOOTSTRAP PROGRAM
Bootstrap is a program which executes programs.
It is stored in ROM of the Router.
It basically read the config-register , locate IOS and load the IOS .
3) LOAD IOS
If the bootstrap program finds the config-register value as 0x2102 which is the default value then the bootstrap will locate IOS location as Flash of the Router and will load the IOS from the flash of the Router .If there is no valid IOS image file in flash , the bootstrap program will try to find the IOS image in TFTP server (which would need to be defined).
If there no TFTP server defined or there is no IOS image present in TFTP server then the router will load an "mini" IOS from ROM and the Router will enter in the ROM MONITOR MODE a.k.a ROMMON Mode
The ROMMON mode will provide with a interface wherein we would be able to execute basic commands .
4) LOCATE START UP FILE FROM NVRAM
The IOS will look for the an configuration file in NVRAM which is known as Start-up ConfigurationThe IOS will load the Start-up Configuration file from NVRAM into RAM which is know as Running Configuration file .
Whatever configuration changes are performed in Running Configuration (save in RAM) and to copy the same network admin needs to copy running configuration into startup configuration
#copy run start or simply #wr
If the IOS didnt find any configuration file in NVRAM it will enter in setup mode and prompt configuration input
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