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Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 20 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Optional Spanning-Tree Configuration Guidelines
You can configure PortFast, BPDU guard, BPDU filtering, EtherChannel guard, root guard, or loop
guard if your switch is running PVST+, rapid PVST+, or MSTP.
You can configure the UplinkFast or the BackboneFast feature for rapid PVST+ or for the MSTP, but the
feature remains disabled (inactive) until you change the spanning-tree mode to PVST+.
Enabling Port Fast
An interface with the Port Fast feature enabled is moved directly to the spanning-tree forwarding state
without waiting for the standard forward-time delay.
Caution
Use Port Fast
only
when connecting a single end station to an access or trunk port. Enabling this feature
on an interface connected to a switch or hub could prevent spanning tree from detecting and disabling
loops in your network, which could cause broadcast storms and address-learning problems.
If you enable the voice VLAN feature, the Port Fast feature is automatically enabled. When you disable
voice VLAN, the Port Fast feature is not automatically disabled. For more information, see
Chapter 17,
“Configuring Voice VLAN.”
You can enable this feature if your switch is running PVST+, rapid PVST+, or MSTP.
Beginning in privileged EXEC mode, follow these steps to enable Port Fast. This procedure is optional.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface
interface-id
Specify an interface to configure, and enter interface
configuration mode.
Step 3
spanning-tree portfast
[
trunk
]
Enable Port Fast on an access port connected to a single
workstation or server. By specifying the
trunk
keyword, you can
enable Port Fast on a trunk port.
Note
To enable Port Fast on trunk ports, you must use the
spanning-tree portfast
trunk
interface configuration
command. The
spanning-tree portfast
command will
not work on trunk ports.
Caution
Make sure that there are no loops in the network
between the trunk port and the workstation or server
before you enable Port Fast on a trunk port.
By default, Port Fast is disabled on all interfaces.
Step 4
end
Return to privileged EXEC mode.
Step 5
show spanning-tree interface
interface-id
portfast
Verify your entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
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