Pim Dense

Based on RFC 3973 Protocol Independent Multicast Dense Mode (PIM-DM)

• Push Model

  • Good for when every subnet probably wants this traffic

• No PIM DR

  • All FHR forward multicast traffic
    • Multicast traffic is flooded out every interface that isn’t the RPF.

• Eventually builds a SPT after prunes

• IGMP joins turn into graft messages

• Prunes last 3 minutes

  • Flood and Prune
  • Routers with no Receivers or duplicate S,G traffic prune.
  • 224.0.0.13 to find neighbors
  • Receivers prune back
  • Router attached to LAN listens for multicast control plane.
    • Receives source traffic
      • Insert (*,G) and (S,G) into mrib
      • Incoming traffic is attached to IIL
      • OIL is all other interfaces
      • Flood to OIL
      • PIM dense always uses SPT.

• Prune occurs

  • Traffic flows stop, but (S,G) remains in table
  • Multicast fails RPF
  • No downstream neighbor or reciever
  • Downstream sent prune
  • LAN Prune override exception

• After pruning

  • Flood again, prune back, flood again, prune back