I read that when a multicast aware router without receivers received a multicast message, the router will send an upstream prune message. I don't understand what is the purpose of the prune message. I read it in DVMRP - RPF:Pruning

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Dec 15 '19 at 3:26

It is quite simple - if router has no receivers for such multicast traffic, it has to say upstream to stop send this traffic to it, because nobody behind router wants this traffic. It keeps network resourses. Just imagine if it is TV traffic, and upstream send to us 100 chanells, but our users want only 30 from this bunch. Why we need other 70? It can be gigabits.

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  • But what if the middle router that has no receivers connects 2 routers with receivers? let's say the middle router acts as a bridge between the two. – Naruto Uzumaki May 28 '19 at 20:08
  • so middle router should use multicast routing with others and it knows everything about any downstream subscriptions. Actually, this reason why multicast routing exists - handle such design. – Konstantin Goncharenko May 29 '19 at 20:13

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