What ios version cannot be upgraded to another one

[Leftz]

Hello,

It was often said that some ios version cannot be upgraded to another. Of course different hardware ios cannot be upgraded. if for the same hardware switch or router, any oldest version ios can be upgraded to latest one? If not, What reason we cannot upgrade it?  Thanks

[balaji.bandi]

it is all about the device model and version of code running.

[Leftz]

Thank you balaji for your reply. Can you explain a little bit more on this?

[balaji.bandi]

i mean to what is the Model of the switch, what IOS running it based on that we can suggest.

as i know you running Cat 9300 ( 16.12.X good, but cisco suggesting 17.3.3)

[Leo Laohoo]

What model of Cisco appliances are we dealing with here?

[Leftz]

Hi Leo, sorry my question is a little bit big. 

If we have switch 9300 with ios 16.-, can we upgrade ios 16.- to any 17.- in the same switch ? Thank you

[Leo Laohoo]

Sure, direct upgrade from 16.X.X to 17.X.X is very much possible.  There is no need to jump into an intermediate version.  Go straight to 17.X.X is fine. 

NOTE:  Upgrading from 16.X.X to 17.X.X is a major jump.  There will be a mandatory microcode/ROMMON/Bootstrap upgrade and this will be around 10 to 15 minutes longer.  

IMPORTANT:  Read the Release Notes carefully.  Pay close attention if SMU need to be installed on top of the 17.X.X firmware is required.

[Joseph W. Doherty]

"If not, What reason we cannot upgrade it?"

Generally (and this is very dependent on the hardware under consideration), there's some firmware upgrades that are installed with certain IOS versions which later IOS versions require and which assume are already installed.

I recall (?) seeing this (and having to deal with it) on some Nexus upgrades.  Release notes describe such requirements.

[Leftz]

Thank you Leo and Joseph for your nice explanation! Sorry many questions. For firmware/microcode/ROMMON/Bootstrap upgrades for these iso upgrade, there are a lot of release notes that we need to review. But, for example, there are many release notes from ios 16 to 17, which release note is talking about this issue? or which subject in the release note is talking about the issue? Can you send the link for it? 

[Leo Laohoo]

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@Leftz wrote:

For firmware/microcode/ROMMON/Bootstrap upgrades for these iso upgrade, there are a lot of release notes that we need to review.

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Always read the Release Notes.  Because if someone in my place of work f*cked up an IOS upgrade because they neglected to read the Release Notes (in the checklist) ... allow me to say "we will tear him/her a new one". 

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@Leftz wrote:

Can you send the link for it? 

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Google it:  9300 release notes

See where it takes you.

[Joseph W. Doherty]

Generally, you only need to review the release notes for the version you wish to upgrade to.  It should list all prerequisites.