A definition of different PIM modes

There are three different PIM (Protocol Independent Multicast) modes.

  • dense mode – havving multiple clients, which are tightly spaced together, it’s implicit for all devices in the PIM domain that they are joined to the multicast domain, if they don’t want to receive the multicast stream, they have to send a „prune“ message. It’s called the „flood and prune“ behavior
  • sparse mode – devices have to send a join message, without they will not receive the multicast stream. It’s designed for networks which have clients that are few and far between. It’s called an „explicit join“ mechanism. It depends on a central RP (rendezvous point“, which is organizing forwarding in the multicast domain
  • sparse-dense mode – is a combination of both. if there is an RP configured it will use sparse mode. But if the RP fails or is not reachable any more, the router will fall back to dense mode. If you want to prohibit this, there is an „no ip pim dense fallback“

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