Protocol-Independent Multicast

Protocol-Independent Multicast (PIM) is a family of multicast routing protocols for Internet Protocol (IP) networks that provide one-to-many and many-to-many distribution of data over a LAN, WAN or the Internet.

[1]: 56–57 There are four variants of PIM: PIM-SM is commonly used in IPTV systems for routing multicast streams between VLANs, subnets or local area networks.

The basic assumption behind dense mode is that the multicast packet stream has receivers at most locations.

Dense Mode uses a fairly simple approach to handle IP multicast routing.

Upon receiving a Prune message, the router will modify its state so that it will not forward those packets out that interface.

[6] In older Cisco IOS releases, PIM-DM would re-flood all the multicast traffic every 3 minutes.

When a data packet is received on a non-RPF interface, a mechanism is required to prevent loops.

Non-Forwarder routers then send a Prune on their RPF interface if they don't need the multicast stream.

Suppose a router has Pruned, and some time later a receiver requests the multicast stream with an IGMP message.