Working with Spanning Tree Protocol for Cisco Networking

By Edward Tetz

Part of Cisco Networking All-in-One For Dummies Cheat Sheet

Spanning Tree Protocol (STP) enables you to create redundant loops on your Cisco network for fault tolerance, and prevents inadvertent loops that may be created on your network from bringing the network to its knees.

The following code will enable the Cisco proprietary Rapid Per VLAN Spanning Tree Protocol (PVST) over the open standard of Multiple Spanning Tree Protocol (MSTP). In addition to configuring STP on the switch, you will also configure port 2 on the switch for portfast, which allows the port to immediately transition to forwarding mode.

Switch1> enable
Switch1# configure terminal 
Switch1(config)#spanning-tree mode rapid-pvst
Switch1(config)#interface FastEthernet 0/2
Switch1(config-if)#spanning-tree portfast
%Warning: portfast should only be enabled on ports connected to a single
 host. Connecting hubs, concentrators, switches, bridges, etc... to this
 interface when portfast is enabled, can cause temporary bridging loops.
 Use with CAUTION
%Portfast will be configured in 10 interfaces due to the range command
 but will only have effect when the interfaces are in a non-trunking mode.