Understanding Bpdu Guard; Understanding Bpdu Filtering; Understanding Etherchannel Guard - Cisco ME 3400 Software Configuration Manual

Chapter 16 Configuring Optional Spanning-Tree Features

Understanding BPDU Guard

The BPDU guard 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 enable BPDU guard on Port Fast-enabled STP ports by using the spanning-tree
portfast bpduguard default global configuration command. Spanning tree shuts down STP ports that
are in a Port Fast-operational state if any BPDU is received on those ports. In a valid configuration, Port
Fast-enabled STP ports do not receive BPDUs. Receiving a BPDU on a Port Fast-enabled port signals
an invalid configuration, such as the connection of an unauthorized device, and the BPDU guard feature
puts the interface in the error-disabled state.
At the interface level, you enable BPDU guard on any STP port by using the spanning-tree bpduguard
enable interface configuration command without also enabling the Port Fast feature. When the STP port
receives a BPDU, it is put in the error-disabled state.
The BPDU guard feature provides a secure response to invalid configurations because you must
manually put the interface back in service. Use the BPDU guard feature in a service-provider network
to prevent an access port from participating in the spanning tree.
You can enable the BPDU guard feature for the entire switch or for an interface.

Understanding 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 Port Fast-enabled STP ports by using the
spanning-tree portfast bpdufilter default global configuration command. This command 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 ports 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.
At the interface level, you can enable BPDU filtering on any STP port by using the spanning-tree
bpdufilter enable interface configuration command without also enabling the Port Fast feature. This
command prevents the interface from sending or receiving BPDUs.
Enabling BPDU filtering on an STP port is the same as disabling spanning tree on it and can result in
Caution
spanning-tree loops.
You can enable the BPDU filtering feature for the entire switch or for an STP port.

Understanding EtherChannel Guard

You can use EtherChannel guard to detect an EtherChannel misconfiguration between the switch and a
connected device. A misconfiguration can occur if the switch STP ports are configured in an
EtherChannel, but the interfaces on the other device are not. A misconfiguration can also occur if the
channel parameters are not the same at both ends of the EtherChannel. For EtherChannel configuration
guidelines, see the
OL-9639-07
"EtherChannel Configuration Guidelines" section on page
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Understanding Optional Spanning-Tree Features
34-10.
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