Company ABC is using an Ethernet virtual circuit as its provider's DCI solution. A goal is to reduce the time to detect the link failure. Which protocol accomplishes this goal?

A link aggregation group (LAG/LACP) bundles physical links for redundancy and load balancing, but it does not speed up failure detection on a single Ethernet virtual circuit.

Ethernet OAM (IEEE 802.3ah / ITU-T Y.1731) uses Continuity Check Messages (CCMs) sent at configurable sub-second intervals to detect loss of connectivity on an Ethernet segment. In a DCI context using an Ethernet virtual circuit, CFM endpoints can detect a link failure in milliseconds, meeting the goal of reducing failure-detection time. This operates directly at Layer 2, independent of any IP routing protocol.

UDLD is a Cisco proprietary protocol that detects unidirectional link conditions on directly connected Cisco devices and is not designed for end-to-end failure detection across a provider DCI Ethernet circuit.

Spanning Tree Bridge Assurance detects a non-forwarding STP peer on a point-to-point link but is a loop-prevention mechanism and does not address failure detection on a provider-managed Ethernet virtual circuit.