Multicast Label Distribution Protocol (MLDP)-supported multicast VPN (MVPN) allows VPN multicast streams to be aggregated over a VPN-specific tree. No customer state is created in the MLDP core;, there is only state for default and data multicast distribution trees (MDTs). In certain scenarios, the state created for VPN streams is limited and does not appear to be a risk or limiting factor. In these scenarios, MLDP can build in-band MDTs that are transit Label Switched Paths (LSPs).
Trees used in a VPN space are MDTs. Trees used in the global table are transit point-to-multipoint (P2MP) or multipoint-to-multipoint (MP2MP) LSPs. In both cases, a single multicast stream (VPN or not) is associated with a single LSP in the MPLS core. The stream information is encoded in the Forwarding Equivalence Class (FEC) of the LSP. This is in-band signaling.
MLDP in-band signaling uses access control lists (ACLs) with the range of the multicast (S, G) to be transported by the MLDP LSP. Each multicast channel (S, G) maps, one-to-one, to each tree in the in-band tree. The (S,G) join is registered in the Multicast Routing Information Base (MRIB), which is a client of MLDP. Each MLDP LSP is identified by the FEC of [(S,G) + RD], where RD is the Route Distinquisher (RD) obtained from BGP. This differs from MLDP-based MVPN, where the identity is in a FEC of [MDT #, VPN ID, Tree #]).
The ingress Provider Edge (PE) device uses the FEC to decode the stream information and associate the multicast stream with the LSP (in the FEC). This service model is only applicable for transporting Protocol Independent Multicast (PIM) source-specific multicast (SSM) traffic. There is no need to run PIM over the LSP because the stream signaling is done in-band.
The MLDP In-Band Signaling/Transit Mode feature is supported on IPv4 and IPv6 networks. MLDP in-band signaling and MLDP-based MVPN cannot be supported in the same VRF.