Cisco 2950 Software Configuration Guide - Page 357
Enabling BPDU Filtering
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Chapter 16 Configuring Optional Spanning-Tree Features Configuring Optional Spanning-Tree Features You can also use the spanning-tree bpduguard enable interface configuration command to enable BPDU guard on any port without also enabling the Port Fast feature. When the port receives a BPDU, it is put in the error-disabled state. You can enable the BPDU guard feature if your switch is running PVST+, rapid PVST+, or MSTP. Beginning in privileged EXEC mode, follow these steps to globally enable the BPDU guard feature. This procedure is optional. Step 1 Step 2 Command configure terminal spanning-tree portfast bpduguard default Step 3 interface interface-id Step 4 Step 5 Step 6 Step 7 spanning-tree portfast end show running-config copy running-config startup-config Purpose Enter global configuration mode. Globally enable BPDU guard. By default, BPDU guard is disabled. Specify the interface connected to an end station, and enter interface configuration mode. Enable the Port Fast feature. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. To disable BPDU guard, use the no spanning-tree portfast bpduguard default global configuration command. You can override the setting of the no spanning-tree portfast bpduguard default global configuration command by using the spanning-tree bpduguard enable interface configuration command. Enabling BPDU Filtering When you globally enable BPDU filtering on Port Fast-enabled ports, it prevents ports that are in a Port Fast-operational state from sending or receiving BPDUs. The ports 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 port, the port loses its Port Fast-operational status, and BPDU filtering is disabled. Caution Configure Port Fast only on ports that connect to end stations; otherwise, an accidental topology loop could cause a data packet loop and disrupt switch and network operation. You can also use the spanning-tree bpdufilter enable interface configuration command to enable BPDU filtering on any port without also enabling the Port Fast feature. This command prevents the port 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 if your switch is running PVST+, rapid PVST+, or MSTP. 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 16-15
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