PIM Sparse

Based on RFC4601 - Protocol Independent Multicast Sparse Mode (PIM-SM)

• Explicit joins everywhere. No flooding.
• LHR, sends a PIM-Join towards the RP, building a (*,G).
• Phased *
  1. The RPT tree
  • Receivers sending their (*,G) messages towards the RP.
  • FHR encapsulates the multicast traffic directly towards the RP.
  • PIM-Register
  • RP de-encapsulates the traffic, sending it down the RPT.
  • 2. Register Stop
    • The RP sends a (S,G) towards the source.
    • When multicast packets start showing up, without encapsulation, the RP sends a Register-Stop.
  • 3. SPT tree
    • LHR requests a (S,G) entry towards it’s upstream, until it’s joined to the (S,G) tree.
    • When the LHR starts getting two copies of the traffic, it sends a (S,G,rpt) prune message, towards the RP. (A prune specific to the RPT)
• If two LHRs exist, and duplicate traffic is detected a PIM elections happens.
  • These Asserts are every 3 minutes.
  • RPTbit, 0 is preferred and means “has (S,G) tree”
    • Metric Preference (Administrative Distance)
      • Metric
        • IP address of subnet interface.
• Specify the tunnel, for the pim-register messages on Cisco via ip pim register-source loopback 0
• The tunnel interface encapsulates the entire multicast packet, which adds 28 bytes of overhead. Packets close to the MTU will be silently dropped on IOS-XE.

a DR is elected by highest priority, or highest IP in the subnet.

• DR sends the PIM join upstream.

The RP always gets the stream, even if it has no receivers to forward it to.

Captures

PIM-SM-register-register-stop-prune.pcap