Reference Guide

Spanning Tree Protocol | 693
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 38-8 shows a scenario in which an edgeport might unintentionally receive a BPDU. The port on the
Dell Networking 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.
FTOS(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
FTOS(conf-if-gi-0/7)#do show ip int br gi 0/7
Interface IP-Address OK Method Status Protocol
GigabitEthernet 0/7 unassigned YES Manual up up