Reference Guide

Modifying Interface STP Parameters
You can set the port cost and port priority values of interfaces in Layer 2 mode.
● Port cost — a value that is based on the interface type. The greater the port cost, the less likely the port is selected to be
a forwarding port.
● Port priority — influences the likelihood that a port is selected to be a forwarding port in case that several ports have the
same port cost.
The default values are listed in Modifying Global Parameters.
To change the port cost or priority of an interface, use the following commands.
● Change the port cost of an interface.
INTERFACE mode
spanning-tree 0 cost cost
The range is from 0 to 65535.
The default values are listed in Modifying Global Parameters.
● Change the port priority of an interface.
INTERFACE mode
spanning-tree 0 priority priority-value
The range is from 0 to 15.
The default is 8.
To view the current values for interface parameters, use the show spanning-tree 0 command from EXEC privilege mode.
Refer to the second example in Enabling Spanning Tree Protocol Globally.
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]]
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)#
Spanning Tree Protocol (STP)
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