Dense and Sparse Routing Modes

To keep packet replication to a minimum, multicast routing protocols use the two primary modes shown in Table 109.

A common multicast guideline is not to run dense mode on a WAN under any circumstances.

Table 109: Primary Multicast Routing Modes

Dense mode	Network is flooded with traffic on all possible branches, then pruned back as branches explicitly (by message) or implicitly (time-out silence) eliminate themselves.	LANs—Networks in which all possible subnets are likely to have at least one receiver.
Sparse mode	Network establishes and sends packets only on branches that have at least one leaf indicating (by message) a need for the traffic.	WANs—Network in which very few of the possible receivers require packets from this source.