Cisco Systems 3750E Manual De Usuario
20-13
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 20 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
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.
Note
You can use the spanning-tree portfast default global configuration command to globally enable the
Port Fast feature on all nontrunking ports.
Port Fast feature on all nontrunking ports.
To disable the Port Fast feature, use the spanning-tree portfast disable interface configuration
command.
command.
Enabling BPDU Guard
When you globally enable BPDU guard on ports that are Port Fast-enabled (the ports are in a Port
Fast-operational state), spanning tree shuts down Port Fast-enabled ports that receive BPDUs.
Fast-operational state), spanning tree shuts down Port Fast-enabled ports that receive BPDUs.
In a valid configuration, Port Fast-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 feature puts the port in the error-disabled state. When this happens, the switch shuts
down the entire port on which the violation occurred.
Fast-enabled port means an invalid configuration, such as the connection of an unauthorized device, and
the BPDU guard feature puts the port in the error-disabled state. When this happens, the switch shuts
down the entire port on which the violation occurred.
To prevent the port from shutting down, you can use the errdisable detect cause bpduguard shutdown
vlan global configuration command to shut down just the offending VLAN on the port where the
violation occurred.
vlan global configuration command to shut down just the offending VLAN on the port where the
violation occurred.
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.
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.
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.
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.
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
portfast
Verify your entries.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.