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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 15 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
You can also use the spanning-tree bpduguard enable interface configuration command to enable
BPDU guard on any port without also enabling the Port Fast feature. When the port 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.
Enabling BPDU Filtering
When you globally enable BPDU filtering on Port Fast-enabled ports, it prevents ports that are in a Port
Fast-operational state from sending or receiving BPDUs. The ports 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 ports do not receive BPDUs. If a BPDU is received on a Port
Fast-enabled port, the port loses its Port Fast-operational status, and BPDU filtering is disabled.
Caution Configure Port Fast only on ports that connect to end stations; otherwise, an accidental topology loop
could cause a data packet loop and disrupt switch and network operation.
You can also use the spanning-tree bpdufilter enable interface configuration command to enable
BPDU filtering on any port without also enabling the Port Fast feature. This command prevents the port
from sending or receiving BPDUs.
Caution Enabling BPDU filtering on an interface is the same as disabling spanning tree on it and can result in
spanning-tree loops.
You can enable the BPDU filtering feature if your switch is running PVST+, rapid PVST+, or MSTP.
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.
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.
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