Dell Force10 Z9000 Configuration Manual

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Dell Force10 Z9000 Configuration Manual Manual pdf 591 page image

Multiple Spanning Tree Protocol (MSTP) | 59127Multiple Spanning Tree Protocol (MSTP)Multiple Spanning Tree Protocol (MSTP) is supported on platforms: e c s zProtocol OverviewMultiple Spanning Tree Protocol (MSTP)—specified in IEEE 802.1Q-2003—is an RSTP-based spanningtree variation that improves on PVST+. MSTP allows multiple spanning tree instances and allows you tomap 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 ifyou 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 howyou can use MSTP to achieve load balancing.Figure 27-1. MSTP with Three VLANs Mapped to Two Spanning Tree InstancesR1 R2R31/213/113/211/312/112/31MSTI 1 rootMSTI 1: VLAN 100MSTI 2: VLAN 200, VLAN 300MSTI 2: VLAN 200, VLAN 300MSTI 2 rootForwardingBlocking