4-14 PIM ConfigurationWhen configuring PIM, go to these sections for information you are interested in:z PIM Overviewz Configuring PIM-DMz Configuring PIM-SMz Configuring Common PIM Parametersz Displaying and Maintaining PIMz PIM Configuration Examplesz Troubleshooting PIMIn this manual, the term “router” refers to a router in the generic sense or a Layer 3 Ethernet switchrunning an IP multicast protocol.PIM OverviewProtocol Independent Multicast (PIM) provides IP multicast forwarding by leveraging static routes orunicast routing tables generated by any unicast routing protocol, such as Routing Information Protocol(RIP), open shortest path first (OSPF), Intermediate System to Intermediate System (IS-IS), or BorderGateway Protocol (BGP). Independent of the unicast routing protocols running on the device, multicastrouting can be implemented as long as the corresponding multicast routing entries are created throughunicast routes. PIM uses the Reverse Path Forwarding (RPF) mechanism to implement multicastforwarding. When a multicast packet arrives on an interface of the device, it is subject to an RPF check.If the RPF check succeeds, the device creates the corresponding routing entry and forwards the packet;if the RPF check fails, the device discards the packet.Based on the forwarding mechanism, PIM falls into two modes:z Protocol Independent Multicast–Dense Mode (PIM-DM), andz Protocol Independent Multicast–Sparse Mode (PIM-SM).To facilitate description, a network comprising PIM-capable routers is referred to as a “PIM domain” inthis document.
