What is a design aspect regarding multicast transport for MPLS Layer 3 VPNs using the Rosen Draft implementation?

LDP is the unicast label distribution protocol for MPLS forwarding and does not serve as the multicast control plane; PIM is used in the provider core to build MDT trees in the Rosen Draft.

In the Rosen Draft implementation, PE routers create Multicast Distribution Tree (MDT) tunnels that are GRE-encapsulated overlays across the MPLS core; customer VPN multicast traffic is encapsulated in GRE and carried over these MDT tunnels, with PIM running in the provider core to build and maintain the underlying multicast trees.

Rosen Draft uses GRE-based MDT tunnels for multicast transport, not native MPLS LSPs signaled by LDP or RSVP - those LSPs carry only unicast VPN traffic.

MDT SAFI in BGP is used for MDT address discovery and advertisement between PE routers, but PIM remains required in the core to build MDT trees and cannot be disabled in the Rosen Draft model.