About Portfast Bpdu Filtering - Cisco Catalyst 4500 Series Configuration Manual

Chapter 23 Configuring Optional STP Features

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.
Explicitly configuring PortFast BPDU filtering on a port that is not connected to a host can result in
Caution
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
disables PortFast BPDU filtering.
If the port configuration is not set to default, then the PortFast configuration does not affect PortFast
BPDU filtering.
filtering allows access ports to move directly to the forwarding state as soon as the end hosts are
connected.
Table 23-1
Per-Port Configuration
Default
Default
Default
Disable
Enable
1. The port transmits at least 10 BPDUs. If this port receives any BPDUs, then PortFast and PortFast BPDU filtering are
Enabling PortFast BPDU Filtering
To enable PortFast BPDU filtering globally, perform this task:
Command
Step 1
Switch(config)# spanning-tree portfast bpdufilter default
Step 2
Switch# show spanning-tree summary totals
This example shows how to enable PortFast BPDU filtering on a port:
Switch(config)# spanning-tree portfast bpdufilter default
OL-25340-01
Table 23-1 lists all the possible PortFast BPDU filtering combinations. PortFast BPDU
PortFast BPDU Filtering Port Configurations
Global Configuration
Enable
Enable
Disable
Not applicable
Not applicable
disabled.
"Enabling BackboneFast" section on page
PortFast State
Enable
Disable
Not applicable
Not applicable
Not applicable
Purpose
Enables BPDU filtering globally on the
switch.
Verifies the BPDU configuration.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
About PortFast BPDU Filtering
23-15), PortFast enables or
PortFast BPDU Filtering State
1
Enable
Disable
Disable
Disable
Enable
23-9