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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 14 Configuring STP Features
Overview of PortFast BPDU Filtering
Overview of PortFast BPDU Filtering
Cisco IOS Release 12.2(25)EW and later support PortFast BPDU filtering, which allows the
administrator to prevent the system from sending or even receiving BPDUs on specified ports.
When configured globally, PortFast BPDU filtering applies to all operational PortFast ports. Ports in an
operational PortFast state are supposed to be connected to hosts that typically drop BPDUs. If an
operational PortFast port receives a BPDU, it immediately loses its operational PortFast status. In that
case, PortFast BPDU filtering is disabled on this port and STP resumes sending BPDUs on this port.
PortFast BPDU filtering can also be configured on a per-port basis. When PortFast BPDU filtering is
explicitly configured on a port, it does not send any BPDUs and drops all BPDUs it receives.
Caution Explicitly configuring PortFast BPDU filtering on a port that is not connected to a host can result in
bridging loops, because the port will ignore any BPDU it receives and go to the forwarding state.
When you enable PortFast BPDU filtering globally and set the port configuration as the default for
PortFast BPDU filtering (see the “Enabling BackboneFast” section on page 14-15), PortFast enables or
disables PortFast BPDU filtering.
If the port configuration is not set to default, then the PortFast configuration will not affect PortFast
BPDU filtering. Table 14-1 lists all the possible PortFast BPDU filtering combinations. PortFast BPDU
filtering allows access ports to move directly to the forwarding state as soon as the end hosts are
connected.
Enabling PortFast BPDU Filtering
To enable PortFast BPDU filtering globally, perform this task:
This example shows how to enable PortFast BPDU filtering on a port:
Switch(config)# spanning-tree portfast bpdufilter default
Switch(config)# Ctrl-Z
Table 14-1 PortFast BPDU Filtering Port Configurations
Per-Port Configuration Global Configuration PortFast State PortFast BPDU Filtering State
Default Enable Enable Enable
1
1. The port transmits at least 10 BPDUs. If this port receives any BPDUs, then PortFast and PortFast BPDU filtering are disabled.
Default Enable Disable Disable
Default Disable Not applicable Disable
Disable Not applicable Not applicable Disable
Enable Not applicable Not applicable Enable
Command Purpose
Step 1
Switch(config)# spanning-tree portfast bpdufilter default
Enables BPDU filtering globally on the
switch.
Step 2
Switch# show spanning-tree summary totals
Verifies the BPDU configuration.
