Protocol Independent Multicast - Sparse Mode (PIM-SM) overview

PIM relies on the unicast routing tables to identify the path back to a multicast source (reverse path forwarding (RPF)). The unicast routing protocols create the unicast routing tables. With this information, PIM sets up the distribution tree for the multicast traffic.

PIM-Sparse Mode (PIM-SM) can be configured on physical ports, VLAN interfaces, LAG interfaces, and loopback interfaces. All such configurations work in the mentioned interfaces context.

IGMP/MLD provides the multicast traffic link between a host and a multicast router running PIM-SM. Both PIM-SM and IGMP/MLD must be enabled on VLANs whose member ports have directly connected hosts with a valid need to join multicast groups.

PIM-SM uses the pull mode for multicast forwarding, and it is suitable for large and medium-sized networks with sparsely and widely distributed multicast group members.

PIM-SM assumes that most hosts do not want to receive multicast traffic. It uses a nonflooding multicast model to direct traffic from the source to the interface when there are multicast receivers in the group. As a result, this model sends traffic only to the routers that specifically request it.