White Papers
Multiple Spanning Tree Protocol (MSTP)
MSTP — specied in IEEE 802.1Q-2003 — is a rapid spanning tree protocol (RSTP)-based spanning tree variation that improves on per-
VLAN spanning tree plus (PVST+). MSTP allows multiple spanning tree instances and allows you to map many VLANs to one spanning tree
instance to reduce the total number of required instances.
Protocol Overview
In contrast, PVST+ allows a spanning tree instance for each VLAN. This 1:1 approach is not suitable if you have many VLANs, because each
spanning tree instance costs bandwidth and processing resources.
In the following illustration, three VLANs are mapped to two multiple spanning tree instances (MSTI). VLAN 100 trac takes a dierent
path than VLAN 200 and 300 trac. The behavior demonstrates how you can use MSTP to achieve load balancing.
Figure 93. MSTP with Three VLANs Mapped to TWO Spanning Tree Instances
Topics:
• Congure Multiple Spanning Tree Protocol
• Enable Multiple Spanning Tree Globally
• Adding and Removing Interfaces
• Creating Multiple Spanning Tree Instances
• Inuencing MSTP Root Selection
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