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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 13 Configuring Optional Spanning-Tree Features
Configur ing Optiona l Spanning-Tree Features
To disable BPD U guard, use the no spanning-tree portfast bpduguard default global configur ation
comm an d.
You can o verride the setting o f th e no spanning-tr ee portfast bpduguard default global configuration
comm and by u s ing the spanning- tree bpduguard enable interface con figuration co mman d.

Enabling BPDU Filtering

When you global ly e nab le BPDU filtering on Port Fast- enabled ports, it pr even ts p orts t hat ar e 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 on ly o n p orts t hat c onn ect to en d stations; othe rwis e, a n a cci dent al topolo gy l oop
could ca use a data pac ket loop an d disrupt swi tch and net work operat ion.
You ca n also use th e spanning-tree bpdufilter enable interface configuration command to enable
BPDU filtering on any port without also enabling the Port Fast feature. This command pre v ents the port
from se nding or rec eiving 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 ca n enab le the BPDU filtering feature if your swi tch is run ning PVST or MST P. Th e MSTP is
available o nl y if you have the E I i nstall ed on you r s witc h.
Beginning in privileged EXEC mode, follow these steps to globally enable the BPDU filtering feature:
Step 6 show running-config Verify yo ur ent ries.
Step 7 copy running-config startup-config (Optiona l) Save your entries in the co nfigurati on file.
Command Purpose
Command Purpose
Step 1 configure terminal Enter g lo bal c onfigurat ion m ode.
Step 2 spanning-tree portfast bpdufilter default Globally enable BPDU filtering.
By default, BPDU filtering is disabled.
Step 3 interface interface-id Enter interface configuration mode, and specify the interface
connec ted to an e nd sta tion .
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.