"if you insert the Sup8 in slot 4 with the Sup7 in slot3 in active state the Sup8 will be likely stopped in ROMMON being a different sup model."
It's been a long, long time since I dealt with a 4500 dual sup setup.
Again, I'm just wondering, if inserting the sup8 might result in the same results, and options, as if you inserted a sup7 but with a different IOS version.
I vaguely remember, when upgrading IOS on a dual sup, when you restarted one of the sups (the standby?) (using slot power options?), a like sup that was in hot standby would not rejoin as a hot standby.
Then, when the updated sup with the updated IOS seem to be fully powered, then you would do a forced switchover, which took much longer than a hot standby flip over. When it became active on the newer IOS, you could then power cycle the prior sup and it would then become the new hot standby, running the same IOS.
Again, long time ago, so I may not have much of that right. I do remember the 4500s being less complex for doing some upgrades than some changes on the 6500s as the former's line cards weren't as smart as the latter's.
I also vaguely recall, 4500 ISSU, tried to make dual sup IOS upgrades faster/better/easier and/or, especially reduce/eliminate downtime, although the early releases of ISSU, didn't always work correctly, and that's about the time I last had fist hand experience. If ISSU is still supported, I would expect it to work pretty well at this point, but have no idea whether it could be used for changing sup versions (not IOS versions).
I believe I did some sup upgrades, from supV, or less, to sup7s, possibly some to sup6 or sup8 upgrades too. But as @Flavio Miranda already mentioned, actual chassis being used was important, and the earlier supV or less, usually also required a chassis upgrade. Unsure I ever did a sup6, or later, to a newer sup upgrade.
Again, an interesting question, but these different sups have other differences, they might make them totally incompatible in the same chassis. I.e. not only might inserting a sup8 into an active sup7 chassis, have the sup8 stop in ROMMON, as Giuseppe thinks may happen, it might throw a major card fault and deactivate the slot. I doubt any permanent damage might be done, but might not be any benefit, trying to insert a sup8 into a chassis with an active sup7.
Some of the sup8 documentation might, somewhere, describe what might, or might not, be done when moving between sup versions on a chassis capable for both.
Oh, if you had a maintenance contract, a perfect question for TAC.
