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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 15 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
Caution
Configure Port Fast only on STP ports that connect to end stations; otherwise, an accidental topology
loop could cause a data packet loop and disrupt switch and network operation.
You also can use the spanning-tree bpduguard enable interface configuration command to enable
BPDU guard on any STP port without also enabling the Port Fast feature. When the interface receives a
BPDU, it is put in the error-disabled state.
You can enable the BPDU guard feature if your switch is running PVST+, rapid PVST+, or MSTP.
Beginning in privileged EXEC mode, follow these steps to globally enable the BPDU guard feature. This
procedure is optional.
To disable BPDU guard, use the no spanning-tree portfast bpduguard default global configuration
command.
You can override the setting of the no spanning-tree portfast bpduguard default global configuration
command by using the spanning-tree bpduguard enable interface configuration command on an STP
port.
Enabling BPDU Filtering
When you globally enable BPDU filtering on Port Fast-enabled STP ports, it prevents interfaces that are
in a Port Fast-operational state from sending or receiving BPDUs. The interfaces still send a few BPDUs
at link-up before the switch begins to filter outbound BPDUs. You should globally enable BPDU filtering
on a switch so that hosts connected to these interfaces do not receive BPDUs. If a BPDU is received on
a Port Fast-enabled STP port, the interface loses its Port Fast-operational status, and BPDU filtering is
disabled.
Caution
Configure Port Fast only on STP ports that connect to end stations; otherwise, an accidental topology
loop could cause a data packet loop and disrupt switch and network operation.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
spanning-tree portfast bpduguard default
Globally enable BPDU guard. (By default, BPDU guard is
disabled.)
Note
Globally enabling BPDU guard enables it only on STP
ports; the command has no effect on ports that are not
running STP.
Step 3
interface interface-id
Specify the interface connected to an end station, and enter
interface configuration mode.
Step 4
spanning-tree portfast
Enable the Port Fast feature.
Step 5
end
Return to privileged EXEC mode.
Step 6
show running-config
Verify your entries.
Step 7
copy running-config startup-config
(Optional) Save your entries in the configuration file.
