IP Multicast allows one-to-many and many-to-many communication through multicast addressing and routing protocols. It identifies multicast groups with class D IP addresses and uses IGMP for hosts to join and leave groups, while multicast routing protocols like PIM-SM and PIM-DM establish distribution trees. PIM-SM uses a shared tree by default rooted at a rendezvous point, while PIM-DM uses source-based trees and assumes dense receiver distribution initially pruned by leaves.