Cisco Catalyst 4500 Series - About Portfast BPDU Filtering

23-9
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
OL-25340-01
Chapter 23 Configuring Optional STP Features
About PortFast BPDU Filtering
About 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 ignores any BPDU it receives and goes 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 23-15), PortFast enables or
disables PortFast BPDU filtering.
If the port configuration is not set to default, then the PortFast configuration does not affect PortFast
BPDU filtering. Table 23-1 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
Table 23-1 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.