With PIM SDM configured on an interface, the operational mode for a given multicast group is determined by the presence or otherwise of a PIM Rendezvous Point (RP) for the group, designated as RP(G). Select operational mode as Sparse-Mode (SM) if an RP(G) is present for a given multicast group, otherwise select Dense-Mode (DM).
The presence or otherwise of RP(G) is determined at the start of traffic flow. Change of RP(G) when traffic is flowing may result in indeterminate behavior until traffic ceases to flow. RP(G) can be configured statically making use of route access-lists for given multicast groups or learned dynamically for example, via BSR. RP(G) can be modified via the configuration of PIM dense-groups, forcing designated groups to operate in dense mode and over-riding any RP(G). SDM operates correctly for SM and DM flows when PIM is configured appropriately and consistently at each router in a network (minimum of a single RP). Use existing show commands to elicit PIM operational state - statistics continue to be displayed as SM or DM for a given group.