This topic explains the spanning-tree modes and protocols supported by the switch, including PVST+, Rapid PVST+, and MSTP, and describes their key features and differences.
The switch supports these Spanning Tree modes and protocols: PVST+, Rapid PVST+, and MSTP.
PVST+: This Spanning Tree mode is based on the IEEE 802.1D standard and Cisco proprietary extensions. PVST+ runs on each VLAN on the switch up to the maximum supported. This architecture ensures that each VLAN has a loop-free path through the network. PVST+ provides layer 2 load balancing for the VLAN on which it runs. You can create different logical topologies by configuring VLANs on your network. This approach ensures that all links are utilized while preventing any single link from being oversubscribed. Each instance of PVST+ on a VLAN has a single root switch. This root switch propagates the Spanning Tree information associated with that VLAN to all other switches in the network. Because each switch has the same information about the network, this process ensures that the network topology is maintained.
Rapid PVST+: This Spanning Tree mode is the same as PVST+ except that it uses rapid convergence based on the IEEE 802.1w standard. Rapid PVST+ is the STP default mode. To provide rapid convergence, Rapid PVST+ immediately deletes dynamically learned MAC address entries on a per-port basis upon receiving a topology change. In contrast, PVST+ uses a short aging time for dynamically learned MAC address entries.Rapid PVST+ uses the same configuration as PVST+ (except where noted), and the Switch needs only minimal extra configuration. The benefit of Rapid PVST+ is that you can migrate a large PVST+ install base to Rapid PVST+ without having to learn the complexities of the Multiple Spanning Tree Protocol (MSTP) configuration and without having to reprovision your network. In Rapid PVST+ mode, each VLAN runs its own spanning-tree instance up to the maximum supported.
MSTP: This Spanning Tree mode is based on the IEEE 802.1s standard. You can map multiple VLANs to the same Spanning Tree instance, which reduces the number of Spanning Tree instances required to support a large number of VLANs. MSTP runs on top of RSTP (based on IEEE 802.1w), which provides for rapid convergence of the Spanning Tree by eliminating the forward delay and by quickly transitioning root ports and designated ports to the forwarding state. In a switch stack, the cross-stack rapid transition (CSRT) feature serves the same function as RSTP. You cannot run MSTP without RSTP or CSRT.