What is the first step to enable MPLS on an IOS-based device?

A.
Enable MPLS at a global level.

B.
Enable tag-switching at the global level.

C.
Enable MPLS switching on the affected interfaces.

D.
Enable Cisco Express Forwarding (CEF) at the global and affected interfaces.

Explanation:

To enable MPLS, you must first enable CEF switching. Depending on the Cisco IOS software version, you may need to establish the range for the label pool. Reference: Cisco Press "Implementing Cisco MPLS" p.3-17