Understanding Bpdu Filtering - Cisco Nexus 3000 series Configuration Manual

Configuring STP Extensions
interface signals an invalid configuration, such as the connection of an unauthorized host or switch. BPDU
Guard, when enabled globally, shuts down all spanning tree edge ports when they receive a BPDU.
BPDU Guard provides a secure response to invalid configurations, because you must manually put the LAN
interface back in service after an invalid configuration.
Note When enabled globally, BPDU Guard applies to all operational spanning tree edge interfaces.

Understanding BPDU Filtering

You can use BPDU Filtering to prevent the switch from sending or even receiving BPDUs on specified ports.
When configured globally, BPDU Filtering applies to all operational spanning tree edge ports. You should
connect edge ports only to hosts, which typically drop BPDUs. If an operational spanning tree edge port
receives a BPDU, it immediately returns to a normal spanning tree port type and moves through the regular
transitions. In that case, BPDU Filtering is disabled on this port, and spanning tree resumes sending BPDUs
on this port.
In addition, you can configure BPDU Filtering by the individual interface. When you explicitly configure
BPDU Filtering on a port, that port does not send any BPDUs and drops all BPDUs that it receives. You can
effectively override the global BPDU Filtering setting on individual ports by configuring the specific interface.
This BPDU Filtering command on the interface applies to the entire interface, whether the interface is trunking
or not.
Use care when configuring BPDU Filtering per interface. If you explicitly configuring BPDU Filtering
Caution
on a port that is not connected to a host, it can result in bridging loops because the port will ignore any
BPDU that it receives and go to forwarding.
If the port configuration is not set to default BPDU Filtering, then the edge configuration will not affect BPDU
Filtering. The following table lists all the BPDU Filtering combinations.
Table 11: BPDU Filtering Configurations
BPDU Filtering Per Port
Configuration
Default
Default
Default
Disable
BPDU Filtering Global
Configuration
Enable
Enable
Disable
Enabled/Disabled
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1)
Information About STP Extensions
STP Edge Port BPDU Filtering State
Configuration
Enable EnableThe port transmits
at least 10 BPDUs. If this
port receives any BPDUs,
the port returns to the
spanning tree normal port
state and BPDU Filtering
is disabled.
Disable Disable
Enabled/Disabled Disable
Enabled/Disabled Disable
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