The most popular and widely deployed multicast protocol is PIM, which is known as Protocol Independent Multicast (PIM). Unlike other multicast routing protocols such as Distance Vector Multicast Routing Protocol (DVRMP) or Multicast Open Shortest Path First (MOSPF), PIM does not maintain a separate multicast routing table, but relies on the existing IGP table when performing its Reverse Path Forwarding (RPF) check.
PIM can be configured as Dense Mode, Sparse Mode and Spare-Dense mode (Hybrid Mode).
PIM Dense Mode (PIM-DM)
PIM-DM uses a flood like broadcast and prune mechanism. When a source sends to an IP multicast group address, each router that receives the packet will create a (S, G) forwarding state entry. The receiving router will initially forward the multicast packet to output interfaces that meet the following requirements:
• Reverse Path Forwarding (RPF) check.
• Internet Group Membership Protocol (IGMP) receivers