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Configuring Optional Spanning-Tree
Features
Prerequisites for the Optional Spanning-Tree Features
You can configure all of these features when your switch is running the per-VLAN spanning-tree plus (PVST+). You can
configure only the noted features when your switch is running the Multiple Spanning Tree Protocol (MSTP) or the rapid
per-VLAN spanning-tree plus (rapid-PVST+) protocol.
Restrictions for the Optional Spanning-Tree Features
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+.
Information About Configuring the Optional Spanning-Tree
Features
PortFast
PortFast immediately brings an interface configured as an access or trunk port to the forwarding state from a blocking
state, bypassing the listening and learning states. You can use PortFast on interfaces connected to a single workstation
or server, as shown in Figure 44 on page 354, to allow those devices to immediately connect to the network, rather than
waiting for the spanning tree to converge.
Interfaces connected to a single workstation or server should not receive bridge protocol data units (BPDUs). An interface
with PortFast enabled goes through the normal cycle of spanning-tree status changes when the switch is restarted.
Note: Because the purpose of PortFast is to minimize the time interfaces must wait for spanning-tree to converge, it is
effective only when used on interfaces connected to end stations. If you enable PortFast on an interface connecting to
another switch, you risk creating a spanning-tree loop.
You can enable this feature by using the spanning-tree portfast interface configuration or the spanning-tree portfast
default global configuration command.
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