Does mutlicast needs broadcast ?

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Jul 17th, 2007
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To be able to send multicast packets, do we need to enable broadcast, for example, in a frame relay hub and spoke configuration ?

If I type 'frame-relay map ip ....' without the 'broadcast' at the end, I won't be able to send multicast ?



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Richard Burts Tue, 07/17/2007 - 03:14
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You are correct. In Frame Relay where you are manually configuring the map you need to include the broadcast parameter if you want to forward multicast packets.

It may seem odd the require configuration of "broadcast" when what you want is "multicast" but it is the same underlying process for both and that is why it has a single name. With broadcast or multicast on a LAN segment the router sends a single frame and multiple receivers can receive and process the frame. But with Frame Relay it is not possible to send a single frame and have multiple receivers. The router must make a copy of the frame for each PVC over which it will be transmitted. So to get the router to make copies of multicast frames to send over various PVCs you must configure the broadcast parameter.




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