A P2MP LSP is a unidirectional label switched path (LSP) which inserts packets at the root (ingress LER) and forwards the exact same replication of the packet to one or more leaf nodes (egress LER). The packet can be replicated at the root of P2MP LSP tree and, or at a transit LSR which acts as a branch node for the P2MP LSP tree.
Note that the data link layer code-point, for example Ethertype when Ethernet is the network port, continues to use the unicast codepoint defined in RFC 3032, MPLS Label Stack Encoding, and which is used on P2P LSP. This change is specified in draft-ietf-mpls-multicast-encaps, MPLS Multicast Encapsulations.
When a router sends a packet over a P2MP LSP which egresses on an Ethernet-based network interface, the Ethernet frame uses a MAC unicast destination address when sending the packet over the primary P2MP LSP instance or over a P2P bypass LSP). Note that a MAC multicast destination address is also allowed in the draft-ietf-mpls-multicast-encaps. Therefore, at the ingress network interface on an Ethernet port, the router can accept both types of Ethernet destination addresses.