Dell SmartFabric OS10 User Guide Release 10.5.3

Multiple Spanning-Tree

MSTP is one of the variations of the rapid spanning-tree protocol that mitigates some of the challenges of Rapid-PVST. Rapid-PVST allows a spanning-tree instance for each VLAN. This 1:1 approach is not suitable if you have multiple VLANs — each spanning-tree instance costs bandwidth and processing resources. You can configure Multiple Spanning-Tree Instances (MSTIs) and map multiple VLANs to one spanning-tree instance to reduce the total number of instances..

When you enable MST, all ports in Layer 2 (L2) mode participate in all instances of MST. OS10 only supports one MST region.

You can achieve load balancing using the MST protocol (MSTP). For example, as shown in the following figure, when you map three VLANs to two multiple spanning-tree instances (MSTIs), VLAN 100 traffic takes a different path than VLAN 200 and 300 traffic.

Configuring MST is a four-step process:

1. Enable MST, if the current running spanning-tree protocol (STP) version is not MST.
2. (Optional) Map the VLAN to different instances in such a way that the traffic is load balanced well and the link utilization is efficient.
3. Ensure the same region name is configured in all the bridges running MST.
4. (Optional) Configure the revision number. The revision number is the same on all the bridges.