Overview
Protocol Independent Multicast (PIM) provides IP multicast forwarding by leveraging unicast static routes or unicast routing tables generated by any unicast routing protocol, such as RIP, OSPF, IS-IS, or BGP. PIM uses the underlying unicast routing to generate a multicast routing table without relying on any particular unicast routing protocol.
PIM uses the RPF mechanism to implement multicast forwarding. When a multicast packet arrives on an interface of the device, it undergoes an RPF check. If the RPF check succeeds, the device creates a multicast routing entry and forwards the packet. If the RPF check fails, the device discards the packet. For more information about RPF, see "Configuring multicast routing and forwarding."
Based on the implementation mechanism, PIM includes the following categories:
Protocol Independent Multicast–Dense Mode (PIM-DM)
Protocol Independent Multicast–Sparse Mode (PIM-SM)
Bidirectional Protocol Independent Multicast (BIDIR-PIM)
Protocol Independent Multicast Source-Specific Multicast (PIM-SSM)
In this document, a PIM domain refers to a network composed of PIM routers.