Reference Guide

Spanning Tree Protocol (STP) | 897
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 shutdown when it receives a BPDU. When only
bpduguard is
implemented, although the interface is placed in an Error Disabled state when receiving the BPDU, the
physical interface remains up and spanning-tree will drop
packets in the hardware after a BPDU violation.
BPDUs are dropped in the software after receiving the BPDU violation.
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 Networking recommends using the show
config
command, as shown in Figure 50-7.
Figure 50-7. 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 Dell
Networking OS 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.
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.
Task Command Syntax Command Mode
Enable PortFast on an interface.
spanning-tree stp-id portfast [bpduguard |
[shutdown-on-violation]]
INTERFACE
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)#
Indicates that the interface is in PortFast mode