© Copyright Lenovo 2016 Chapter 11: Spanning Tree Protocols 189Global STP ControlBy default, the Spanning Tree feature is globally enabled on the switch, and is setfor PVRST mode. Spanning Tree (and thus any currently configured STP mode)can be globally disabled using the following command:Spanning Tree can be re‐enabled by specifying the STP mode:where the command options represent the following modes: rstp: RSTP mode pvrst: PVRST mode mst: MSTP modePVRST ModeNote: Per‐VLAN Rapid Spanning Tree (PVRST) is enabled by default on theG8264.Using STP, network devices detect and eliminate logical loops in a bridged orswitched network. When multiple paths exist, Spanning Tree configures thenetwork so that a switch uses only the most efficient path. If that path fails,Spanning Tree automatically sets up another active path on the network to sustainnetwork operations.ENOS PVRST mode is based on IEEE 802.1w RSTP. Like RSTP, PVRST modeprovides rapid Spanning Tree convergence. However, PVRST mode is enhancedfor multiple instances of Spanning Tree. In PVRST mode, each VLAN may beautomatically or manually assigned to one of 255 available STGs. Each STG acts asan independent, simultaneous instance of STP. PVRST uses IEEE 802.1Q tagging todifferentiate STP BPDUs and is compatible with Cisco R‐PVST/R‐PVST+ modes.The relationship between ports, LAGs, VLANs, and Spanning Trees is shown inTable 17.RS G8264(config)# spanning tree mode disableRS G8264(config)# spanning tree mode {pvrst|rstp|mst}Table 17. Ports, LAGs, and VLANsSwitch Element Belongs ToPort LAG or one or more VLANsLAG One or more VLANsVLAN (non‐default) PVRST: One VLAN per STG RSTP: All VLANs are in STG 1 MSTP: Multiple VLANs per STG
