Enabling Portfast - Cisco Catalyst 4500 Series Configuration Manual

Chapter 23 Configuring Optional STP Features
unit (BPDU), spanning tree does not place the port into the blocking state. Spanning tree sets the port's
operating state to non-port fast even if the configured state remains port fast and starts participating in
the topology change.
Note Because the purpose of PortFast is to minimize the time that access ports must wait for spanning tree to
converge, it is most effective when used on access ports. If you enable PortFast on a port connecting to
another switch, you risk creating a spanning tree loop.

Enabling PortFast

Use PortFast only when connecting a single end station to a Layer 2 access port. Otherwise, you might
Caution
create a network loop.
To enable PortFast on a Layer 2 access port to force it to enter the forwarding state immediately, perform
this task:
Command
Step 1
Switch(config)# interface {{fastethernet |
gigabitethernet | tengigabitethernet} slot/port}
| {port-channel port_channel_number}
Step 2
Switch(config-if)# [no] spanning-tree portfast
Step 3
Switch(config-if)# end
Step 4
Switch# show running interface {{fastethernet |
gigabitethernet | tengigabitethernet} slot/port}
| {port-channel port_channel_number}
This example shows how to enable PortFast on Fast Ethernet interface 5/8:
Switch(config)# interface fastethernet 5/8
Switch(config-if)# spanning-tree portfast
Switch(config-if)# end
Switch#
This example shows how to verify the configuration:
Switch# show running-config interface fastethernet 5/8
Building configuration...
Current configuration:
!
interface FastEthernet5/8
no ip address
switchport
switchport access vlan 200
switchport mode access
spanning-tree portfast
end
Switch#
OL-25340-01
Purpose
Specifies an interface to configure.
Enables PortFast on a Layer 2 access port connected to a
single workstation or server.
Use the no keyword to disable PortFast.
Exits configuration mode.
Verifies the configuration.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Enabling PortFast
23-7