Difference Between MSTP and RPVST Spanning Tree Protocols

Multiple Spanning Tree Protocol (MSTP) IEEE 802.1s – allows us to create multiple separate spanning-tree instances, and it enables us to map and allocate multiple VLANs to the instances.

Rapid Per VLAN Spanning Tree Plus (RPVST+) Protocol – Cisco-proprietary enhancement to the IEEE 802.1w RSTP. Similar to PVST+, it enables us to create a one spanning-tree instance per VLAN as well. Network convergence is also faster with RPVST+.

Our multiple spanning-tree modes, IEEE 802.1s MSTP, PVST+, and RPVST+, allow us to have various spanning-tree instances. These instances can take different paths through the network by having different root bridges, enabling load balancing to be possible. The traffic will be taking optimized paths for the same reason as well.

With the MSTP spanning-tree mode, we have one instance of spanning tree for each group of VLANs.

We can map the Sales and the Management departments to SW1 as their root bridge. For the Engineering and the Production departments, we can make SW2 their root bridge. Now, we have two instances of spanning tree running. For the first instance, the traffic for VLAN 10 and VLAN 30 will be forwarded to SW1, and the links to SW2 will be blocked. In the second instance, the traffic for VLAN 20 and VLAN 40 will be forwarded to SW2 and will be blocked on SW1.

PVST+ and RPVST+ Cisco spanning-tree modes are both Per VLAN spanning tree protocols. This means that every VLAN has a single instance of spanning tree.

For example, we want the traffic from the Sales and the Management departments to be forwarded to their root bridge at SW2 and blocked on SW1. Also, the traffic from the Engineering and the Production departments will be forwarded to their root bridge at SW1, and SW2 will be in a blocked state. There will be a total of four spanning-tree instances running, as we have four VLANs in the network.

Assuming that we have 100 VLANs in our network, we will also have 100 spanning-tree instances. It would be consuming more resources as compared to grouping them like in MSTP.

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