Users Guide
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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 94. MSTP with Three VLANs Mapped to TWO Spanning Tree Instances
Congure Multiple Spanning Tree Protocol
Conguring multiple spanning tree is a four-step process.
1. Congure interfaces for Layer 2.
2. Place the interfaces in VLANs.
3. Enable the multiple spanning tree protocol.
4. Create multiple spanning tree instances and map VLANs to them.
Multiple Spanning Tree Protocol (MSTP)
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