Which command is used to enable a switch interface for routing?

The command to enable a switch interface for routing is “ip routing.” This command is used in Cisco devices to enable the routing functionality on a Layer 3 switch. When you enter this command in global configuration mode, it allows the switch to perform routing functions, as opposed to just switching functions.

In a typical configuration, especially on Layer 2 switches, the devices primarily handle the data link layer tasks. However, by enabling IP routing, the switch is now capable of making forwarding decisions based on Layer 3 IP addresses, allowing it to route traffic between different VLANs or subnets.

The other options do not have the correct syntax or purpose for enabling routing on a switch. For instance, “ip route” is used to create static routes, while “enable routing” and “routing enable” are not valid commands in Cisco IOS for enabling routing. Thus, "ip routing" is the precise command needed to activate routing on the switch.