When used in a PVST+ network, loop guard is performed per-port or per-port channelat a VLAN level. If no BPDUs are received on a VLAN interface, the port or port-channeltransitions to a Loop-Inconsistent (blocking) state only for this VLAN.Enabling Portfast BPDU guard and loop guard at the same time on a port results in aport that remains in a Blocking state and prevents traffic from flowing through it. Forexample, when Portfast BPDU guard and loop guard are both configured:• If a BPDU is received from a remote device, BPDU guard places the port in an Err-Disabled Blocking state and no traffic is forwarded on the port.• If no BPDU is received from a remote device, loop guard places the port in aLoop-Inconsistent Blocking state and no traffic is forwarded on the port.On PE ports and on VP-LAGs (LAGs formed with PE ports)• Spanning-tree with bpdu guard shutdown-on-violation is enabled bydefault• No spanning tree command is valid. This command is not visible and issuing thiscommand on VP-LAG ports results in a failure.-Example Dell(conf-if-te-1/1)#spanning-tree pvst vlan 3 cost 18000Dell(conf-if-te-1/1)#endDell(conf-if-te-1/1)#show config!interface TenGigabitEthernet 1/1no ip addressswitchportspanning-tree pvst vlan 3 cost 18000no shutdownDell(conf-if-te-1/1)#endRelatedCommandsshow spanning-tree pvst — views the PVST+ configuration.spanning-tree pvst err-disablePlace ports in an Err-Disabled state if they receive a PVST+ BPDU when they are members an untagged VLAN.C9000 SeriesSyntax spanning-tree pvst err-disable cause invalid-pvst-bpduDefaults Enabled; ports are placed in the Err-Disabled state if they receive a PVST+ BPDU whenthey are members of an untagged VLAN.Command Modes INTERFACEPer-VLAN Spanning Tree Plus (PVST+) 1649
