Adding Cisco Switches to the stack with different IOS versions

I am reading conflicting things.  The whitepapers for the 3750's seem to say that as long as the IOS's are in the same group firmware wise, the stack will auto upgrade the IOS for you.  Sounds great in theory.  But others are saying you have to make sure everything is exactly the same before hand.  Here is what I have now.  I have a stack of two and have two more seperate ones to bring into the stack.  I am a big fan of letting the devices do what they were designed to do for me.  No need to fight what people a lot smarter than me worked hard to make happen so I didn't have to get my less-experienced hands into the mess.  Any comments on if I will be ok or not?  Will these IOS versions work and upgrade themselves or am I in big trouble if I try to join them the way they are? Any help would be great.  Thanks

WS-C3750 Stack  (stack of two)    12.2(35)SE5 - IP-BASE  (current version) (these are two 48 port POE)
WS-C3750G-24T  (two to add)       12.2(53)SE2 - IP-BASE  (current version) (these are two 24 port)
KingPezAsked:
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FideliusConnect With a Mentor Commented:
Hello,

As Cisco recommends, all stack members should (not must) have same software version:
"The Cisco IOS software version on all stack members, including the stack master, should be the same. This helps ensure full compatibility in the stack protocol version among the stack members."
Also:
"Switches with different Cisco IOS software versions likely have different stack protocol versions. Switches with different major stack protocol version numbers are incompatible and cannot exist in the same switch stack."

You can check the stack protocol version with privileged EXEC command:
show platform stack-manager all

My advice is to downgrade new switches before adding them into stack. It is the easiest way to avoid any trouble.

Kind regards!
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luc_royConnect With a Mentor System AdminCommented:
The switch IOS's do not have to be the same.  I am not sure what features you are trying to use but 12.2(35) is a good solid IOS and it supports most of the features you will want.  They will not have any conflicts with each other.

VLANS?
Trunks?
QOS?
Voice?

These are all good in your older IOS.
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
This question has been classified as abandoned and is being closed as part of the Cleanup Program.  See my comment at the end of the question for more details.
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