PIM encapsulation and de-encapsulation interfaces

This feature supports the internal PIM encapsulation and de-encapsulation interfaces used for PIM Register processing. The encapsulation interface is used by a designated router or first-hop router to encapsulate multicast packets in unicast PIM Register messages and send them toward the rendezvous point (RP). The de-encapsulation interface is used by the RP to decapsulate received PIM Register messages, recover the original multicast packets, and forward them through the multicast distribution tree.