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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 16 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.
Optional spanning-tree configuration commands are not supported on UNIs or on ENIs on which STP
has not been enabled.
Enabling Port Fast
An STP port 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.
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 STP interface to configure, and enter interface configuration
mode.
If the interface is a UNI, before you enable Port Fast, you must change
the port type to NNI or ENI to enable STP:
• Enter the port-type nni interface configuration command to change
the port to an NNI with STP enabled by default.
• Or enter the port-type eni and spanning-tree interface
configuration commands to configure the port as an ENI STP port.
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 does 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 STP ports.
Step 4 end Return to privileged EXEC mode.