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14-5
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 14 Configuring STP Features
Overview of PortFast
This example shows how to verify the previous configuration of port 4/4:
Switch# show spanning-tree interface fastethernet 4/4 detail
Port 196 (FastEthernet4/4) of VLAN0010 is forwarding
Port path cost 1000, Port priority 160, Port Identifier 160.196.
Designated root has priority 32768, address 00d0.00b8.140a
Designated bridge has priority 32768, address 00d0.00b8.140a
Designated port id is 160.196, designated path cost 0
Timers:message age 0, forward delay 0, hold 0
Number of transitions to forwarding state:1
The port is in the portfast mode by portfast trunk configuration
Link type is point-to-point by default
Bpdu filter is enabled
Loop guard is enabled by default on the port
BPDU:sent 0, received 0
To enable loop guard on an interface, perform this task:
This example shows how to enable loop guard on port 4/4:
Switch(config)# interface fastEthernet 4/4
Switch(config-if)# spanning-tree guard loop
Switch(config-if)# ^Z
This example shows how to verify the configuration impact on port 4/4:
Switch# show spanning-tree interface fastEthernet 4/4 detail
Port 196 (FastEthernet4/4) of VLAN0010 is forwarding
Port path cost 1000, Port priority 160, Port Identifier 160.196.
Designated root has priority 32768, address 00d0.00b8.140a
Designated bridge has priority 32768, address 00d0.00b8.140a
Designated port id is 160.196, designated path cost 0
Timers:message age 0, forward delay 0, hold 0
Number of transitions to forwarding state:1
The port is in the portfast mode by portfast trunk configuration
Link type is point-to-point by default
Bpdu filter is enabled
Loop guard is enabled on the port
BPDU:sent 0, received 0
Switch#
Overview of PortFast
Spanning Tree PortFast causes an interface configured as a Layer 2 access port to enter the forwarding
state immediately, bypassing the listening and learning states. You can use PortFast on Layer 2 access
ports connected to a single workstation or server to allow those devices to connect to the network
immediately, rather than waiting for spanning tree to converge. If the interface receives a bridge protocol
data unit (BPDU), which should not happen if the interface is connected to a single workstation or server,
spanning tree puts the port into the blocking state.
Command Purpose
Step 1
Switch(config)# interface {
type
slot/port
} |
{port-channel
port_channel_number
}
Selects an interface to configure.
Step 2
Switch(config-if)# spanning-tree guard loop
Configures loop guard.
Step 3
Switch(config)# end
Exits configuration mode.
Step 4
Switch# show spanning tree interface 4/4 detail
Verifies the configuration impact on that port.