Sparse-mode PIM
Efficient for networks where multicast is not widely deployed, or where there is intermittent multicast traffic, or over WAN links
Explicit join required
- everybody joins to a common Rendez-vous Point (RP); this can be learned automatically (Auto-RP) or statically
- if a message is lost, only the router trying to join the RP is affected
- warning: choose carefully the location of the RP (can become a bottleneck)
Builds shared trees, changeable to source-rooted trees; the RPF check is done:
- on the rendez-vous point for shared-trees
- on the source for source-trees