Dell Force10 S55T S55 Configuration Guide FTOS 8.3.5.3 - Page 711

Preventing Network Disruptions with BPDU Guard The Portfast (and Edgeport, in the case of RSTP, PVST+, and MSTP) feature should be configured on ports that connect to end stations. End stations do 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 effect the STP topology. The BPDU Guard feature blocks an edgeport upon receiving a BPDU to prevent network disruptions, and FTOS displays Message 1. Enable BPDU Guard using the option bpduguard when enabling PortFast or EdgePort. The bpduguard shutdown-on-violation option causes the interface hardware to be shutdown when it receives a BPDU. Otherwise, although the interface is placed in an Error Disabled state when receiving the BPDU, the physical interface remains up and spanning-tree will only drop packets after a BPDU violation. Figure 39-8 shows a scenario in which an edgeport might unintentionally receive a BPDU. The port on the Dell Force10 system is configured with Portfast. If the switch is connected to the hub, the BPDUs that the switch generates might trigger an undesirable topology change. If BPDU Guard is enabled, when the edge port receives the BPDU, the BPDU will be dropped, the port will be blocked, and a console message will be generated. Message 1 BPDU Guard Error 3w3d0h: %RPM0-P:RP2 %SPANMGR-5-BPDU_GUARD_RX_ERROR: Received Spanning Tree BPDU on BPDU guard port. Disable GigabitEthernet 3/41. Note: Note that unless the shutdown-on-violation option is enabled, spanning-tree only drops packets after a BPDU violation; the physical interface remains up, as shown below. Force10(conf-if-gi-0/7)#do show spanning-tree rstp brief Executing IEEE compatible Spanning Tree Protocol Root ID Priority 32768, Address 0001.e805.fb07 Root Bridge hello time 2, max age 20, forward delay 15 Bridge ID Priority 32768, Address 0001.e85d.0e90 Configured hello time 2, max age 20, forward delay 15 Interface Designated Name PortID Prio Cost Sts Cost Bridge ID PortID Gi 0/6 128.263 128 20000 FWD 20000 32768 0001.e805.fb07 128.653 Gi 0/7 128.264 128 20000 EDS 20000 32768 0001.e85d.0e90 128.264 Interface Name Role PortID Prio Cost Sts Cost Link-type Edge Gi 0/6 Root 128.263 128 20000 FWD 20000 P2P No Gi 0/7 ErrDis 128.264 128 20000 EDS 20000 P2P No Force10(conf-if-gi-0/7)#do show ip int br gi 0/7 Interface IP-Address OK Method Status GigabitEthernet 0/7 unassigned YES Manual up Protocol up Spanning Tree Protocol | 711