6500 sup 720 boot images and statements question

[Aaron Greene]

As long as I have been doing this stuff, I have never had a clear understanding of all of the 6500 boot images and statements.  The more I read online, the more I get confused.  Can someone please answer the following questions for me?

1.  What is the boot image "boot-mz" for?  Where should it be placed (i.e. bootflash)?  what command do I need to issue in order to use the boot image I want?

2.  What is the IOS rommon image for?  I thought the rommon image was the boot image but apparently these are two different images.  Where should it be placed (i.e. bootflash, sup-bootflash, etc).  What command do I use to ensure that I am using this IOS rommon image?

3.  What is the difference between the following IOS commands:

boot system disk0:<filename>

boot system flash disk0:<filename>

ALSO

boot system sup-bootflash:<filename>

boot system flash sup-bootflash:<filename>

4.  Should I use two boot statements for my IOS image, the first one pointing to the sup-bootflash and the second pointing to the disk0:?  (Just in case someone ever removed the flash card)?

Thanks!

[Marvin Rhoads]

There are a couple guides explaining the memory types and locations on the Supervisor. Please see here and here.

1. Boot image software is "more than ROMMON, less than full IOS". I've never used it personally but it's explained in some more detail here.

2. Typically you only need to deal with ROMMON when things are broken (e.g, your IOS boot image is missing) and you need to recover from console. ROMMON is a stripped down image with very limited functionality to allow you to get going with a proper fulll-feature IOS image. It's very rare that you would have any casue to upgrade the ROMMON image. Please see here and here for details.

3. I believe the correct syntax is "boot system flash :"

4. That's certainly an option. I tend to prefer not to use externally accessible flash cards as the long term location in part becasue of this reason.

[Aaron Greene]

I still don't understand what the boot image and the associated "boot bootldr" command do. Why would I ever want or need it?  If I can just boot a 6500 by configuring boot system flash, what is the purpose of having this boot image and the boot bootldr command?  I have read the Cisco documentation and a bunch of stuff on the forums but nothing tells me what its significance is.

[Marvin Rhoads]

From the link in my answer #1 above:

"Boot image—A subset of the Cisco IOS software. This image is used to perform network booting or to load Cisco IOS images onto the router. This image is also used if the router cannot find a valid system image. Depending on your platform, this image may be called xboot image, rxboot image, bootstrap image, or boot loader/helper image.

On some platforms, the boot image is contained in ROM. In others, the boot image can be stored in Flash memory. On these platforms, you can specify which image should be used as the boot image using the boot bootldr command."

Bottom line - It is not strictly necessary for most use cases. If you're not booting from the network or want to use it as (another) backup image, don't worry about it.