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3-176
Configuring Multiple Spanning Trees
MSTP generates a unique spanning tree for each instance. This provides
multiple pathways across the network, thereby balancing the traffic load,
preventing wide-scale disruption when a bridge node in a single instance
fails, and allowing for faster convergence of a new topology for the failed
instance.
By default all VLANs are assigned to the Internal Spanning Tree (MST
Instance 0) that connects all bridges and LANs within the MST region.
This switch supports up to 65 instances. You should try to group VLANs
which cover the same general area of your network. However, remember
that you must configure all bridges within the same MSTI Region (page
3-166) with the same set of instances, and the same instance (on each
bridge) with the same set of VLANs. Also, note that RSTP treats each
MSTI region as a single node, connecting all regions to the Common
Spanning Tree.
To use multiple spanning trees:
1. Set the spanning tree type to MSTP (STA Configuration, page 3-163).
2. Enter the spanning tree priority for the selected MST instance (MSTP
VLAN Configuration).
3. Add the VLANs that will share this MSTI (MSTP VLAN
Configuration).
Note: All VLANs are automatically added to the IST (Instance 0).
To ensure that the MSTI maintains connectivity across the network, you
must configure a related set of bridges with the same MSTI settings.