Enabling Portfast; Prevent Network Disruptions With Bpdu Guard - Dell S4820T Configuration Manual

Enabling PortFast

The PortFast feature enables interfaces to begin forwarding traffic approximately 30 seconds sooner.
Interfaces forward frames by default until they receive a BPDU that indicates that they should behave
otherwise; they do not go through the Learning and Listening states. The bpduguard shutdown-on-
violation option causes the interface hardware to be shut down when it receives a BPDU. When you
only implement bpduguard, although the interface is placed in an Error Disabled state when receiving
the BPDU, the physical interface remains up and spanning-tree drops packets in the hardware after a
BPDU violation. BPDUs are dropped in the software after receiving the BPDU violation.
CAUTION: Enable PortFast only on links connecting to an end station. PortFast can cause loops if
it is enabled on an interface connected to a network.
To enable PortFast on an interface, use the following command.
• Enable PortFast on an interface.
INTERFACE mode
spanning-tree stp-id portfast [bpduguard | [shutdown-on-violation]]
Example of Verifying PortFast is Enabled on an Interface
To verify that PortFast is enabled on a port, use the show spanning-tree command from EXEC
Privilege mode or the show config command from INTERFACE mode. Dell Networking recommends
using the show config command.
Dell#(conf-if-te-1/1)#show conf
!
interface TenGigabitEthernet 1/1
no ip address
switchport
spanning-tree 0 portfast
no shutdown
Dell#(conf-if-te-1/1)#

Prevent Network Disruptions with BPDU Guard

Configure the Portfast (and Edgeport, in the case of RSTP, PVST+, and MSTP) feature 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 affect the STP topology. The BPDU Guard feature blocks an edgeport after
receiving a BPDU to prevent network disruptions, and Dell Networking OS displays the following
message.
3w3d0h: %RPM0-P:RP2 %SPANMGR-5-BPDU_GUARD_RX_ERROR: Received Spanning Tree BPDU
on
BPDU guard port. Disable TenGigabitEthernet 3/4.
Enable BPDU Guard using the bpduguard option when enabling PortFast or EdgePort. The bpduguard
shutdown-on-violation option causes the interface hardware to be shut down 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.
990
Spanning Tree Protocol (STP)