Is it possible to connect a WS-C3750G-12S-S (Fiber) with a WS-3750G-24TS (Copper) via the StackWise cable ?
The purpose is to connect the end devices of the "copper" switch with the fiber backbone of the "fiber" switch.
That is exactly what the stack cable is for , this makes it a stack and you use a single ip address to manage the stack .
Yes, you can certainly connect 2 two switches via stackwise connectors.The Catalyst 3750-12S switch supports desktop and aggregator Switch Database Management (SDM) templates. All other Catalyst 3750 switches support only the desktop SDM templates. So you have to run desktop SDM on both the switches to connect them. Make sure that you have the IOS software version running on both the switches.
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HTH, Please rate if it does.