Diff b/w boot system and boot bootldr command

[manju.cisco]

Hi All,

I have not got clear picture of the commands "boot system" and "boot bootldr".

Thought i tried reading the explanation in cisco ref document for multiple times i didnt get what it exactly means

Can someone please help me to understand what those 2 commands.

On one of our 6509-E switch, we have below two statements configured

!

boot system bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

boot bootldr bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

!

And on another 6509-E switch, we have just "boot system" command configured and not "boot bootldr"

!

boot system bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

!

Still even on multiple planned reboots both switches come online without any issues

Thanks,

Manju

[Somasundaram Jayaraman]

Hi,

Boot system file is the exact IOS you are trying to load with.

In simple terms, the bootldr file is the helper file to load the IOS.

The BOOTLDR environment variable specifies the  Flash file system and filename that contains the boot loader image  required to load system software.

The variable defines the primary Cisco  IOS image that will load the final image from another source.

we need to set the BOOTLDR environment variable to specify  the Flash device and filename of the boot loader image.

For Old version of IOS, there is a requirement of boot loader image to boot up the IOS image.

But for the latest version of IOS, no need for boot loader image.

Hope this helps

Cheers

Somu

Rate helpful posts.

[manju.cisco]

Hi Somu,

Thanks for reply, but i am sorry still i am unable to understand.......i dont know why i am not able to visualize the difference

The BOOTLDR environment variable specifies the  Flash file system and filename that contains the boot loader image  required to load system software. 
The variable defines the primary Cisco  IOS image that will load the final image from another source.
we need to set the BOOTLDR environment variable to specify  the Flash device and filename of the boot loader image. 

As you said "The variable defines the primary Cisco  IOS image that will load the final image from another source."

Here you means to say the switch will initially load with x image and then as per bootldr command it load image y ?

Please explain me how the switch interprets the below boot configuration when the switch starts to boot up.

case 1) Note that bootsystem and bootldr both are set to same image...

!

boot system bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

boot bootldr bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

!

case 2)

!

boot system bootflash:cat4500e-ipbasek9-mz.122-53.SG3.bin

boot bootldr   !

!

[manju.cisco]

help again please

[ajaju]

To add to Somasundaram's reply, here is what happens when the router boots up:

1. The router initially boots into ROMMON (this is your bootstrap code, which you can see in the show version command).

2. Then the router loads into the bootloader code (this is the bootloadr code, which you see in show version). This bootloader code is just an intermediate step between the ROMMON mode and the IOS mode.

3. The router then boots into the IOS mode from the bootloadr mode.

So if you do not mention the bootloadr specifically by giving the "boot bootloadr" command, the router will assume the bootloadr to be in bootflash of the device and try to boot it from there. If you mention the "boot bootloadr flash:...." command, then the router will look for the bootloadr in the flash (instead of the bootflash). Thats the only difference.

However, in both cases, if you have a valid IOS to boot into, then the router will come up without a problem, irrespective of the fact whether bootloadr image is in bootflash or flash.

Hope this helps in answering your query.

[sbhadrav@cisco.com]

Boot system is used to specify the system image that loads at startup i.e the full IOS image that system will load.

boot bootldr command is used to specified a boot loader image which is an image with only booting featues and few limited commands, this image is like a safe mode for the system where we fall back on if system is unable to boot from main image.

bootstrap is the minimum software that is required to recongnize and run the hardware. It comes both in software and hardwares with the software.Like in cat 4K on Sup's is a special hardware with an image on it.