A company would like to distribute a virtual machine (VM) hosting cluster between three data centers with the capability to move VMs between sites. The connectivity between data centers is IP only and

VPLS requires an MPLS-enabled core network to operate, making it incompatible with an IP-only WAN without adding MPLS infrastructure.

L2TPv3 can tunnel Layer 2 over IP but is a point-to-point technology that lacks the MAC-routing intelligence and native multi-site scalability required for VM mobility across three data centers.

OTV is specifically designed for data center interconnect (DCI) over any IP transport, including an existing WAN, using IS-IS as a MAC-routing control plane to encapsulate Ethernet frames in IP. It supports VM mobility across multiple sites without requiring MPLS infrastructure, and actively prevents spanning tree loops and broadcast domain extension from crossing site boundaries. These properties make it the ideal fit for a three-site VM cluster over an IP-only WAN.

AToM (Any Transport over MPLS) requires MPLS as its underlying transport mechanism, which directly contradicts the IP-only WAN constraint.