Symptom
Under the following conditions, STP topology can converge without blocking where necessary leading to a bridging loop:
1. Spanning-tree mode MST containing multiple MST regions.
2. FabricPath leaf switches are in one MST region.
3. CE Switches are in a different MST region (than the FabricPath switches)
4. No FabricPath VLANs mapped to MST instance 0
Conditions
The following conditions are necessary for this issue to be seen.
1. Spanning-tree mode MST containing multiple MST regions.
2. FabricPath leaf switches are in one MST region.
3. CE Switches are in a different MST region (than the FabricPath switches)
4. No FabricPath VLANs mapped to MST instance 0
Workaround
This scenario can be avoided by one of the following:
1. Configure MST such that there is only one MST region.
OR
2. Map at least one FabricPath VLAN to MST instance 0.
Further Problem Description
