The increasing demand of internet services is pushing cloud services providers to increase the capacity of their data centers (DC) and create DC federations, where two or more cloud providers interconnect their infrastructures. As a result of the huge capacity required for the inter-DC network, the flexgrid optical technology can be used. In such scenario, applications can run in DCs placed in geographically distant locations, and hence, multicast-based communication services among their components are required. In this paper, we study two different approaches to provide multicast services in multilayer scenarios assuming that the optical network is based on the flexgrid technology: 1) establishing a point-to-multipoint optical connection (light-tree) for each multicast request, and 2) using a multipurpose virtual network topology (VNT) to serve both unicast and multicast connectivity requests. When that VNT is not able to serve an incoming request as a result of lack of capacity, it is reconfigured to add more resources. A control plane architecture based on the applications-based network operations (ABNO) one, currently being standardized by the IETF, is presented; workflows are proposed and PCEP extensions are studied for the considered approaches. The experimental validation is carried-out on a testbed setup connecting Telefonica, CNIT, and UPC premises.