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Cisco IE 2000 Switch Software Configuration Guide
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Chapter 22 Configuring Optional Spanning-Tree Features
Information About Configuring the Optional Spanning-Tree Features
BPDU Filtering
The BPDU filtering feature can be globally enabled on the switch or can be enabled per interface, but
the feature operates with some differences.
At the global level, you can enable BPDU filtering on PortFast-enabled interfaces by using the
spanning-tree portfast bpdufilter default global configuration command. This command prevents
interfaces that are in a PortFast-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 PortFast-enabled interface, the interface loses its PortFast-operational status,
and BPDU filtering is disabled.
At the interface level, you can enable BPDU filtering on any interface by using the spanning-tree
bpdufilter enable interface configuration command without also enabling the PortFast feature. This
command prevents the interface from sending or receiving 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 can enable the BPDU filtering feature for the entire switch or for an interface.
UplinkFast
Switches in hierarchical networks can be grouped into backbone switch es, distribution switches, and
access switches. Figure 22-2 shows a complex network where distribution switches and access switches
each have at least one redundant link that spanning tree blocks to prevent loops.
Figure 22-2 Switches in a Hierarchical Network
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Active link
Blocked link
Root bridge
Backbone switches
Distribution switches
Access switches