Multicast bidirectional PIM advantages

Bidirectional PIM is more efficient for situations where you have many multicast sources and receivers, whereas PIM sparse mode is more efficient for few sources and many receivers.

PIM Sparse mode characteristics:

  • the RP builds both (*,G) and (S,G) entries
  • an SPT is built towards each and every source
  • traffic only flows down the shared tree
  • PIM register/register-stop mechanisms are used to register sources to the RP

Bidirectional PIM characteristics:

  • (S,G) entries are not built and the (*,G) entry is allowed for the shared tree
  • an SPT is never built towards the sources
  • traffic can move both up and down the shared tree
  • no PIM register/ register-stop mechanisms are used to register sources to the RP, as each source can start and stop whenever it likes (there is no way for the RP to tell a source to stop sending multicast traffic)