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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 16 Configuring Optional Spanning-Tree Features
Configuring Optional Spanning-Tree Features
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.
You can also use the spanning-tree bpdufilter enable interface configuration command to enable
BPDU filtering on any STP port without also enabling the Port Fast feature. This command prevents the
STP port from sending or receiving BPDUs.
Caution Enabling BPDU filtering on an STP port 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.
Step 3
interface interface-id Specify the interface connected to an end station, and enter
interface configuration mode.
If the interface is a UNI, before you enable Port Fast, you must
change the port type to NNI or ENI to enable STP:
• Enter the port-type nni interface configuration command to
change the port to an NNI with STP enabled by default.
• Or enter the port-type eni and spanning-tree interface
configuration commands to configure the port as an ENI STP
port.
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.
Command Purpose
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