Enabling PortFastThe PortFast feature enables interfaces to begin forwarding traffic approximately 30 seconds sooner.Interfaces forward frames by default until they receive a BPDU that indicates that they should behave otherwise; they do not go throughthe Learning and Listening states. The bpduguard shutdown-on-violation option causes the interface hardware to be shut downwhen it receives a BPDU. When you only implement bpduguard, although the interface is placed in an Error Disabled state when receivingthe BPDU, the physical interface remains up and spanning-tree drops packets in the hardware after a BPDU violation. BPDUs are droppedin the software after receiving the BPDU violation.CAUTION: Enable PortFast only on links connecting to an end station. PortFast can cause loops if it is enabled on an interfaceconnected to a network.To enable PortFast on an interface, use the following command.• Enable PortFast on an interface.INTERFACE modespanning-tree stp-id portfast [bpduguard | [shutdown-on-violation]]Example of Verifying PortFast is Enabled on an InterfaceTo verify that PortFast is enabled on a port, use the show spanning-tree command from EXEC Privilege mode or the show configcommand from INTERFACE mode. Dell Networking recommends using the show config command.Dell#(conf-if-te-1/1/1/1)#show conf!interface TenGigabitEthernet 1/1/1/1no ip addressswitchportspanning-tree 0 portfastno shutdownDell#(conf-if-te-1/1/1/1)#Prevent Network Disruptions with BPDU GuardConfigure the Portfast (and Edgeport, in the case of RSTP, PVST+, and MSTP) feature on ports that connect to end stations. End stationsdo not generate BPDUs, so ports configured with Portfast/ Edgport (edgeports) do not expect to receive BDPUs.If an edgeport does receive a BPDU, it likely means that it is connected to another part of the network, which can negatively affect theSTP topology. The BPDU Guard feature blocks an edgeport after receiving a BPDU to prevent network disruptions, and Dell NetworkingOS displays the following message.3w3d0h: %RPM0-P:RP2 %SPANMGR-5-BPDU_GUARD_RX_ERROR: Received Spanning Tree BPDU onBPDU guard port. Disable TenGigabitEthernet 1/1/4/1.Enable BPDU Guard using the bpduguard option when enabling PortFast or EdgePort. The bpduguard shutdown-on-violationoption causes the interface hardware to be shut down when it receives a BPDU. Otherwise, although the interface is placed in an ErrorDisabled state when receiving the BPDU, the physical interface remains up and spanning-tree will only drop packets after a BPDU violation.The following example shows a scenario in which an edgeport might unintentionally receive a BPDU. The port on the Dell Networkingsystem is configured with Portfast. If the switch is connected to the hub, the BPDUs that the switch generates might trigger anundesirable topology change. If you enable BPDU Guard, when the edge port receives the BPDU, the BPDU is dropped, the port is blocked,and a console message is generated.NOTE: Unless you enable the shutdown-on-violation option, spanning-tree only drops packets after a BPDU violation; thephysical interface remains up.Dell Networking OS Behavior: Regarding bpduguard shutdown-on-violation behavior:• If the interface to be shut down is a port channel, all the member ports are disabled in the hardware.Spanning Tree Protocol (STP) 871
