While Multicast Listener Discovery (MLD) is for host/router communication within the host’s link, Protocol Independent Multicast (PIM) is for router-to-router communication from the router that connects to the host’s link to the router that connects to the sender’s link.

PIM Protocol Independent Multicast Intro 1
PIM Protocol Independent Multicast Intro 1

The layer 3 path of a multicast is called the Distribution Tree. PIM is used so that a router can graft (join) itself to or prune (leave) itself from a distribution tree.

PIM Protocol Independent Multicast Intro 2
PIM Protocol Independent Multicast Intro 2

PIM learns its routing information from the router’s unicast routing table. It doesn’t matter what routing protocol populates the table or if a route is manually configured. This is why it’s called Protocol Independent Multicast (PIM).

In the next few lessons we’ll take a closer look at the three flavors of PIM:

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