OK So my latest hang-up here is with xSTP BIDs. I understand the purpose of ext sys-id and MAC Address Reduction (thanks to other posts). While I understand that one can use the same or different MACs for different spanning-tree BIDs using the aforementioned features, I'm not exactly grasping the impact of using trying to use the same BID with multiple VLANS and/or xSTP instances. As I've examined it, the initial MAC commonly used in the BID appears to be the BIA of the system board, not any particular virtual or physical interface. Is there some sort of table/database that restricts us from using the same BID for multiple instances? Is the xSTP instance defined in part or full by the BID? I suppose if I understood the impact of NOT using multiple BIDs then things would make sense. Thanks in advance.
PS- Still haven't gotten through MSTP, so if the answer's there then I apologize in advance.