In Dense mode the packets flooded to entire network and then branches where there are no receivers are eliminated.
In Sparse mode packets branches distribution growth as new nodes join the multicast group.
- sparse mode usually scale better in terms of routing state:
- only routers on the path from source and members need to keep state
- dense mode protocol require state in all routers in the network - sparse mode protocols are more efficient:
- explicit join messages means multicast traffic flows across links that have been explicitly added to the tree - sparse mode disadvantages:
- the RP can be a single point of failure - the RP can be a hot spot for multicast traffic
- the traffic may flow non-optimal paths (from source to RP and back members)
- the first solved using the bootstrap router protocol
Sparse mode :
In sparse mode, a router assumes that other routers do not want to forward multicast packets for a group, unless there is an explicit request for the traffic. When hosts join a multicast group, the directly connected routers send PIM Join messages toward the RP. The RP keeps track of multicast groups. Hosts that send multicast packets are registered with the RP by the first hop router of that host. The RP then sends Join messages toward the source. At this point, packets are forwarded on a shared distribution tree. If the multicast traffic from a specific source is sufficient, the first hop router of the host may send Join messages toward the source to build a source-based distribution tree.
sparse mode
Dense Mode:
In dense mode, a router assumes that all other routers want to forward multicast packets for a group. If a router receives a multicast packet and has no directly connected members or PIM neighbors present, a prune message is sent back to the source. Subsequent multicast packets are not flooded to this router on this pruned branch. PIM builds source-based multicast distribution trees.
dense mode
Sparse-dense:
In this case, the interface is treated as dense mode if the group is in dense mode; the interface is treated in sparse mode if the group is in sparse mode. You must have an RP if the interface is in sparse-dense mode and you want to treat the group as a sparse group.
If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the groups for which the router is a member.
Another benefit of sparse-dense mode is that Auto-RP information can be distributed in a dense mode; yet, multicast groups for user groups can be used in a sparse mode manner. Therefore there is no need to configure a default RP at the leaf routers.
spaese-dense
