We have just bought 3 new 3550 24 fx smi switches and one 3550 12 Gbic Switch. All the 24 fx smi switches are connected to the 12 GBIC switch.
Also, Two of the 24 fx Switches are connected to each other on the fast Ethernet ports 22/23.
We are using MSTP protocol. The 12G Switch is the root bridge.
For some strange reason, the MSTP protocol decides that one of the Gbic ports that connect the 12G switch is in blocking state. Meaning, best root path for one of the interconnected switches is through the 24 fx connected to it.
I tried lowering the priority and the cost of the ports 22/23 but the mystery remains.
I will be grateful if you could help me in this manner.
For your connivance, I have attached detailed connection diagram to this conversation.