Resolution
The spanning-tree portfast disable command explicitly disables PortFast for the given port. The configuration line appears in the running-configuration because this is not a default option.
The no spanning-tree portfast command implicitly enables PortFast if these conditions are met:
- The global configuration contains the spanning-tree portfast default command.
- The port is not a trunk port.
If PortFast is not configured globally, the no spanning-tree portfast command is equivalent to the spanning-tree portfast disable command.
For more information, refer to the spanning-tree portfast (interface configuration mode) section of Catalyst 6500 Series Cisco IOS Command Reference, 12.1 E.