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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter19 Configuring Optional Spanning-Tree Features
Understanding Optional Spanning-Tree Features
Understanding Port Fast
Port Fast immediately brings an interface configured as an access or trunk port to the forwarding state
from a blocking state, bypassing the listening and learning st ates . You can use Port Fast on inte rface s
connected to a single workstation or server, as shown in Figure19-1, to allow those devices to
immediately connect to the network, rather than waiting for the spanning tree to converge.
Interfaces connected to a blade server should not receive bridge protocol data units (BPDUs). An
interface with Port Fast enabled goes through the normal cycle of sp anning- tree statu s change s when the
switch is restarted.
Note Because the purpose of Port Fast 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 Port Fast
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.
Figure 19-1 Port Fast-Enabled Interfaces
Understanding BPDU Guard
The BPDU guard feature can be globally enabled on the switch or can be enabled per port, bu t the feature
operates with some differences.
At the global level, you enable BPDU guard on Port Fast-enabled ports by using the spanning-tree
portfast bpduguard default global configuration command. Spanning tree shuts down ports that are in
a Port Fast-operational state if any BPDU is received on them. In a v alid config uration, Port F ast-enabled
ports do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled port means an invalid
configuration, such as the connection of an unauthorized device, and the BPDU guard featur e puts the
port in the error-disabled state. When this happens, the switch shuts down the e ntire p ort on which the
violation occurred.
To prevent the port from sh utting do wn, you can us e the errdisable det ect cause bpduguard shutdown
vlan global configuration command to shut down just the offending VLAN on the port where the
violation occurred.
Blade Servers
B
lade Servers
Port
Fast-enabled
ports
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Blade Switch