How do PIM sparse mode and PIM dense mode differ?
PIM sparse mode uses explicit Join messages to build multicast distribution-tree branches only where receivers have requested traffic. PIM dense mode instead uses a push model that initially floods multicast traffic throughout the network and then prunes branches with no receivers. The reversed description is incorrect because flooding is the defining initial behavior of dense mode, not sparse mode. Dense mode can ultimately retain a source-based distribution tree after pruning, but it begins with flood-and-prune behavior.
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