Spanning Tree Protocol | 1057To enable PortFast on an interface:Verify that PortFast is enabled on a port using the show spanning-tree command from the EXEC privilegemode or the show config command from INTERFACE mode; Dell Force10 recommends using the showconfig command, as shown in Figure 52-7.Figure 52-7. PortFast Enabled on InterfacePreventing Network Disruptions with BPDU GuardThe Portfast (and Edgeport, in the case of RSTP, PVST+, and MSTP) feature should be configured onports that connect to end stations. End stations do not generate BPDUs, so ports configured with Portfast/Edgport (edgeports) do not expect to receive BPDUs. If an edge port does receive a BPDU, it likely meansthat it is connected to another part of the network, which can negatively effect the STP topology.The BPDU Guard feature blocks an edge port upon receiving a BPDU to prevent network disruptions, andFTOS displays Message 1.Enable BPDU Guard using the option bpduguard when enabling PortFast or EdgePort. Configure thebpduguard shutdown-on-violation option to cause the interface hardware to shut down when it receives aBPDU. Otherwise with only the option enabled, although the interface is placed in an Error Disabled statewhen receiving the BPDU, the physical interface remains up and spanning-tree will only drop packetsafter a BPDU violation.Task Command Syntax Command ModeEnable PortFast on an interface. spanning-tree stp-id portfast[bpduguard [shutdown-on-violation]]INTERFACECaution: Do not enable Portfast BPDU guard and loop guard at the same time on a port. Enabling both featuresmay result in a port that remains in a blocking state and prevents traffic from flowing through it. For example, whenPortfast 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-disabledblocking 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.FTOS#(conf-if-gi-1/1)#show conf!interface GigabitEthernet 1/1no ip addressswitchportspanning-tree 0 portfastno shutdownFTOS#(conf-if-gi-1/1)#Indicates that the interface is in PortFast mode
