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Influencing PVST+ Root Selection
As shown in the previous PVST+ illustration, all VLANs use the same forwarding topology because R2 is
elected the root, and all TengigabitEthernet ports have the same cost.
The following per-VLAN spanning tree illustration changes the bridge priority of each bridge so that a
different forwarding topology is generated for each VLAN. This behavior demonstrates how you can use PVST
+ to achieve load balancing.
Figure 102. Load Balancing with PVST+
The bridge with the bridge value for bridge priority is elected root. Because all bridges use the default priority
(until configured otherwise), the lowest MAC address is used as a tie-breaker. To increase the likelihood that a
bridge is selected as the STP root, assign bridges a low non-default value for bridge priority.
To assign a bridge priority, use the following command.
•
Assign a bridge priority.
PROTOCOL PVST mode
Per-VLAN Spanning Tree Plus (PVST+)
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Troubleshooting
