Per-VLAN Spanning Tree (PVST) maintains a spanning tree instance for each VLAN configured in the network. It uses ISL Trunking and allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs. Since PVST treats each VLAN as a separate network, it has the ability to load balance traffic (at layer-2) by forwarding some VLANs on one trunk and other Vlans on another trunk without causing a Spanning Tree loop.
The benefits of PVST+:
Per VLAN Spanning Tree Plus (PVST+) provides the same functionality as PVST using 802.1Q trunking technology rather than ISL. PVST+ is an enhancement to the 802.1Q specification and is not supported on non-Cisco devices.
The benefits of MST:
- Combines the best of PVST(+) and 802.1Q.
- Load balancing can be achieved.
- The CPU is spared by only computing specific instances.
- Flexible mapping of VLANs into instances
Also, MST will provide all the functions provided by RSTP as 802.1s. MST is an amendment to 802.1Q. It extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. Additional functions includes rapid convergence and load balancing in a VLAN environment.
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