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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 10 Configuring STP
Understanding Advanced STP Features
Figure 10-4 Port Fast-Enabled Ports
Understanding BPDU Guard
When the BPDU guard feature is enabled on the switch, STP shuts down Port Fast-enabled interfaces
that receive BPDUs rather than putting them into the blocking state. In a valid configuration, Port
Fast-enabled interfaces do not receive BPDUs. Receipt of a BPDU by a Port Fast-enabled interface
means an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard
feature places the interface into the ErrDisable state. The BPDU guard feature provides a secure
response to invalid configurations because you must manually put the interface back in service. For more
information, see the
“Configuring BPDU Guard” section on page 10-33
.
Note
When enabled on the switch, STP applies the BPDU guard feature to all Port Fast-enabled interfaces.
Catalyst 6000
series switch
Catalyst 3550
switch
Catalyst 3550
switch
Workstations
Workstations
Server
Port
Fast-enabled port
Port
Fast-enabled
ports
Catalyst 3550
switch
43265