Reference Guide

Spanning Tree Protocol | 989
Verify that PortFast is enabled on a port using the show spanning-tree command from the EXEC privilege
mode or the
show config command from INTERFACE mode; Dell Force10 recommends using the show
config command, as shown in the following example.
FTOS#(conf-if-gi-1/1)#show conf
!
interface GigabitEthernet 1/1
no ip address
switchport
spanning-tree 0 portfast
no shutdown
FTOS#(conf-if-gi-1/1)#
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 BPDUs. If an edge port 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 edge port 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. Configure the
bpduguard shutdown-on-violation option to cause the interface hardware to shut down when it receives a
BPDU. Otherwise with only the option enabled, 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 55-3 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.
Caution: Do not enable Portfast BPDU guard and loop guard at the same time on a port. Enabling both features
may result in a port that remains in a blocking state and prevents traffic from flowing through it. For example, 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 a
loop-inconsistent blocking state and no traffic is forwarded on the port.
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.