Protocol Independent Multicast (PIM)
Protocol Independent Multicast (PIM) is a multicast routing protocol and is currently the only multicast routing protocol fully supported by Cisco IOS devices.
PIM depends 100% on the information in the unicast routing table but it doesn’t matter which unicast routing protocol you use to fill it. Other multicast routing protocols like DVMRP and MOSPF don’t use the unicast routing table but build their own tables.
PIM supports three different modes: