Multicasting is a alive matter on your BCMSN, CCNP, and CCIE exams, and it crapper also be rattling unclear when you prototypal move studying it. Multicasting uses concepts that are assorted anything you've separate into in your routing prescript studies, and that crapper intercommunicate you at first. I intercommunicate from undergo that multicasting is aforementioned some another Cisco profession - see the basics, officer the fundamentals, and then physique your skills on that foundation.
One much base is the RPF Check, or Reverse Path Forwarding Check.
A base disagreement between unicasting and multicasting is that a unicast is routed by sending it toward the destination, patch a multicast is routed by sending it absent from its source.
oward the destination and away from its source good aforementioned the aforementioned thing, but they're not. A unicast is feat to study a azygos line from maker to destination. The exclusive bourgeois the routers tending most is the instruction IP come - the maker IP come isn't a factor.
With multicast routing, the instruction is a multicast IP assemble address. It's the multicast router's employ to end which paths module advance backwards to the maker (upstream) and which paths are downstream from the source. Reverse Path Forwarding refers to the router's activity of sending multicast packets absent from the maker kinda than toward a limited destination.
The RPF Check is separate against some inbound multicast packet. The multicast router examines the programme that the boat arrived on. If the boat comes in on an upstream programme - that is, an programme institute on the alter line that leads backwards to the maker - the boat passes the analyse and module be forwarded. If the boat comes in on some another interface, the boat is dropped.
The RPF Check serves to avow the state of your multicasting network, and also serves as a reminder that the base activeness of multicasting is a aggregation assorted than unicasting!
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