Multicast PIM dense mode

Protocol Independent Multicast (PIM) is a multicast routing protocol that operates in several modes. In dense mode, multicast traffic is forwarded on all router interfaces until a downstream router sends a request to stop forwarding.

In other words, multicast traffic is flooded by the multicast routers everywhere until it is pruned.

Links:

https://networklessons.com/multicast/multicast-pim-dense-mode