When configuring Portfast on a switch port, which command is correct?

The correct command to configure PortFast on a switch port is simply spanning-tree portfast. When you use this command, it enables PortFast on the specific interface you are configuring.

PortFast is a feature used in spanning tree protocol (STP) configurations that allows a port to transition directly to the forwarding state, bypassing the usual listening and learning states that occur in STP. This is especially useful for ports connected to end devices, like computers or printers, where you want to minimize the time it takes for the devices to connect to the network and start communicating.

Using spanning-tree portfast is concise and aligns with Cisco's command syntax for enabling this feature, making it the correct choice. The other options either include incorrect syntax or unnecessary words that do not match the standard command structure found in Cisco documentation. For instance, adding "enable" directly after "spanning-tree" is redundant, and "portfast enable" lacks the necessary "spanning-tree" prefix, which renders those commands ineffective for configuring PortFast on an interface.