Administrator Guide

Enabling PortFast
The PortFast feature enables interfaces to begin forwarding trac 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.
PDU Filtering enabled on an interface stops sending and receiving BPDUs on the port fast enabled ports. When you enable BPDU
guard and BPDU lter on the port, then BPDU lter takes the highest precedence. By default BPDU ltering on an interface is
disabled.
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] | bpdufilter]
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
Congure 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 congured 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 aect
the STP topology. The BPDU Guard feature blocks an edgeport after receiving a BPDU to prevent network disruptions, and the
system displays the following message.
3w3d0h: %RPM0-P:RP2 %SPANMGR-5-BPDU_GUARD_RX_ERROR: Received Spanning Tree BPDU on
BPDU guard port. Disable GigabitEthernet 3/41.
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.
The following example shows a scenario in which an edgeport might unintentionally receive a BPDU. The port on the Dell Networking
system is congured with Portfast. If the switch is connected to the hub, the BPDUs that the switch generates might trigger an
undesirable topology change. If you enable BPDU Guard, when the edge port receives the BPDU, the BPDU is dropped, the port is
blocked, and a console message is generated.
NOTE: Unless you enable the shutdown-on-violation option, spanning-tree only drops packets after a BPDU
violation; the physical interface remains up.
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Spanning Tree Protocol (STP)