cat6500 failover different IOS

[Kn1ghtR1d3rOfD00m]

Hi, I probably exagerating, but I just want to confirm

we have 2 6500 boxes (one SUP each) not in VSS just independent boxes with firewall service modules on each box

we have only updagraded the secondary box and we verified asa failover is in place,however, we did not upgrade the primary box due to the lack of time of the window, we will proceed in another rescheduled window, 

however, what will happen in case of a failure either at the harwarre level or fwsm, will it work automatic failover? just because they have different IOS versions?

they dont share control plane info suchs as the VPCs in nexus, and we are not running any VSS but just want to confirm if the primary box fails (with the old IOS version for now), will the secondary box with newer IOS version will take place normally with no problem assuming all config is the same?

or is there any consideration I can take ?

[Leo Laohoo · Accepted solution]

Depends on how many boot variable statements are present.
If the boot variable statement specifies the new IOS will be used, old IOS will be used in case the new IOS fails to load, then this is possible (highly recommended).

[Kn1ghtR1d3rOfD00m]

Thanks for your clarification,