In a Cisco switch, what command enables an interface?

In a Cisco switch, the command that enables an interface is "no shutdown." This command is essential for activating a previously administratively down interface. By default, many interfaces on Cisco switches are in a down state for administrative reasons, and simply bringing the interface into operational status requires issuing this specific command within the interface configuration mode.

Using "no shutdown" effectively transitions the interface from being administratively down to up, allowing it to participate in data transmission. After this command is entered and executed, the switch will start to process traffic on that interface, provided that other configurations like IP addressing (for layer 3 interfaces) and VLAN assignments (for layer 2 interfaces) are also correctly set.

The other options listed do not correspond with the standard commands used in Cisco IOS for enabling interfaces. Therefore, they cannot fulfill the requirement of enabling an interface like "no shutdown" does.