Cisco 2950 Software Configuration Guide - Page 356
Enabling BPDU Guard
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Configuring Optional Spanning-Tree Features Chapter 16 Configuring Optional Spanning-Tree Features Beginning in privileged EXEC mode, follow these steps to enable Port Fast. This procedure is optional. Step 1 Step 2 Command configure terminal interface interface-id Step 3 spanning-tree portfast [trunk] Purpose Enter global configuration mode. Specify an interface to configure, and enter interface configuration mode. Enable Port Fast on an access port connected to a single workstation or server. By specifying the trunk keyword, you can enable Port Fast on a trunk port. Note To enable Port Fast on trunk ports, you must use the spanning-tree portfast trunk interface configuration command. The spanning-tree portfast command will not work on trunk ports. Step 4 Step 5 Step 6 end show spanning-tree interface interface-id portfast copy running-config startup-config Caution Make sure that there are no loops in the network between the trunk port and the workstation or server before you enable Port Fast on a trunk port. By default, Port Fast is disabled on all ports. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. Note You can use the spanning-tree portfast default global configuration command to globally enable the Port Fast feature on all nontrunking ports. To disable the Port Fast feature, use the spanning-tree portfast disable interface configuration command. Enabling BPDU Guard When you globally enable BPDU guard on ports that are Port Fast-enabled (the ports are in a Port Fast-operational state), spanning tree shuts down Port Fast-enabled ports that receive BPDUs. In a valid configuration, Port Fast-enabled 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 port in the error-disabled state. The BPDU guard feature provides a secure response to invalid configurations because you must manually put the port back in service. Use the BPDU guard feature in a service-provider network to prevent an access port from participating in the spanning tree. 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. 16-14 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 78-11380-10
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