Dell Force10 S4810P - Preventing Network Disruptions with BPDU Guard

Spanning Tree Protocol (STP) | 1011
To enable PortFast on an interface:
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 Figure 49-3.
Figure 49-3. PortFast Enabled on Interface
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 49-4 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.
Task Command Syntax Command Mode
Enable PortFast on an interface.
spanning-tree stp-id portfast [bpduguard |
[shutdown-on-violation]]
INTERFACE
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.
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)#
Indicates that the interface is in PortFast mode