Question regarding Multicasting

Oct 08, 2006 6 Replies

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dilan.weerasinghe 19 years ago

Quick question about multicasting, that I hope someone can help me with...unfortunately, I've never had any real life experience with it, so am having a bit of difficulty visualising it.

Say I have a multicast group set up for 224.2.155.145. The source is Host A, and the receivers are Hosts B, C, and D.

Does Host A send out three packets to the multicast IP address, knowing in advance that 3 hosts are subsribed to it, or does it only send out one packet that is somehow shared by the 3 hosts?

Thanks in advance.

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Guan Foo Wah 19 years ago

Hi,

Host A will send out only one packet and will be received by host B,C, and D. As such, it saves bandwith.

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dilan.weerasinghe 19 years ago

Thanks mate.

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Everyman 19 years ago

And what important this one IP mcst packet is "cloned" in proper nodes in internetwork. The routers in the internetwork run multicast routing protocols, such us PIM, thanks to that they know where are the recievers for each mcst group.

Wlodek.

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dilan.weerasinghe 19 years ago

proper nodes in

Thanks Wlodek...where exactly are the packets cloned?

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Paul Matthews 19 years ago

In the routers and switches!

Basically the point of multicastis to reduce traffic

Source |

Assuming all clients want to Rx the group, R1 will forward each packet to S1. S1 will duplicate it to Clients 1&2 R2 will forward t0 S2 which will forward to C3 R3 will duplicate to S3 and R4. R4 will forward to S4, to C4 S3 will duplicate to C5&6.

That's 6 clients all get a copy of the packet from just one sent by the source.

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dilan.weerasinghe 19 years ago

Thanks for the excellent explanation, Paul.

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