Change Spanning-Tree Priority of a Switch
Changing the Cost of Spanning Tree on an Interface
Changing the State of Spanning Tree on an Interface
The command spanning-tree portfast will force a port to move directly to the Forwarding state, without having to transition through the Blocking, Listening, and Learning states.
This can save up to 50 seconds of wait time. This is an excellent command on access ports that will never be hooked up to another switch. Examples where this would be useful are on ports connected to computers or other end devices, such as printers, servers, and so on. You must exercise caution with this command, however, because if a switch port is plugged into another switch and the portfast command is enabled, then spanning tree will be defeated and a potential switching loop might be created.
Spanning Tree Portfast BPDU Guard Command
There is a feature that has been added to Catalyst IOS called Spanning Tree Portfast BPDU Guard. This feature has been created to maintain stability within the active STP topology. Devices that are attached to ports with Portfast enabled are not allowed to take part in the spanning-tree process. If a port that has Portfast enabled receives a BPDU packet, that port is disabled by the switch. This is done by transitioning the port into the errdisable state. An error message will be sent to the console. Ports disabled by STP BPDU Guard remain in the disabled state unless it is manually enabled with the no shut command or configured to re-enable itself automatically.