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Spanning Tree Protocol | 1057
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 52-7.
Figure 52-7. 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 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.
Task Command Syntax Command Mode
Enable PortFast on an interface.
spanning-tree stp-id portfast
[
bpduguard [shutdown-on-violation]]
INTERFACE
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.
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