Reference Guide

Multiple Spanning Tree Protocol (MSTP) | 601
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Multiple Spanning Tree Protocol (MSTP)
Multiple Spanning Tree Protocol (MSTP) is supported on the S5000 switch.
This chapter contains the following sections:
• Protocol Overview
• Configuring Multiple Spanning Tree Protocol
• Enabling Multiple Spanning Tree Globally
• Adding and Removing Interfaces
• Creating Multiple Spanning Tree Instances
• Influencing MSTP Root Selection
• Interoperating with Non-FTOS Bridges
• Modifying Global Parameters
• Modifying Interface Parameters
• Configuring an EdgePort
• Flushing MAC Addresses after a Topology Change
• MSTP Sample Configurations
• Debugging and Verifying MSTP Configuration
Protocol Overview
Multiple Spanning Tree Protocol (MSTP)—specified in IEEE 802.1Q-2003—is an RSTP-based spanning
tree variation that improves on 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.
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 traffic takes a different path than VLAN 200 and 300 traffic. The behavior demonstrates how
you can use MSTP to achieve load balancing.