Protocol-Independent Multicast
PIM has two variants: Dense mode (DM) and sparse mode (SM)
- DM builds source-based trees in a data-driven (broadcast-and-prune), implicit join manner
- SM allows both source-based and shared trees. But the trees are built a priori and using explicit join.
Not dependent upon mechanisms provided by any particular unicast protocol. Can leverage upon RIP, OSPF, BGP-4 etc
PIM: broadcasts on all non-incoming interfaces until explicit prune messages are received