Multicast - PIM

Protocol Independent Multicast (PIM) is not a dynamic routing protocol in the traditional sense, like RIP, OSPF, or BGP, which are used for unicast routing. Instead, PIM is a multicast routing protocol designed to efficiently route multicast packets. Multicast routing enables a single packet to be delivered to multiple destinations, saving bandwidth and reducing network load when sending the same data to multiple recipients.

PIM operates independently of any specific unicast routing protocol, which is why it's called "Protocol Independent." It leverages the existing unicast routing table to perform multicast forwarding, without requiring any specific underlying unicast routing protocol.

PIM is primarily used in scenarios where multicast traffic needs to be distributed across networks, such as video conferencing, IPTV, and other applications requiring data to be sent to multiple recipients simultaneously. It operates in two main modes:

  1. PIM Sparse Mode (PIM-SM): Optimized for networks where receivers are few and far apart. It uses a "pull" model, where multicast traffic is only sent to routers that have active receivers downstream requesting the multicast stream.

  2. PIM Dense Mode (PIM-DM): Suited for networks with a dense concentration of receivers. It uses a "push" model, initially flooding multicast packets to all routers and then pruning back the ones that do not have interested receivers.

PIM does not exchange multicast routing tables or information directly with other routers, which is a typical behavior of dynamic routing protocols. Instead, it relies on the existing unicast routing infrastructure to make forwarding decisions for multicast traffic, making it a unique tool in network management for multicast distribution.