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I'm having trouble understanding how multicast addresses work.

First off, is it true that if I have N clients or peers working on separate networks, they all subscribe to the same multicast group, and this group allows any source to send messages, these peers/hosts can all communicate to each other through this group? (sounds like black magic!)

Second, I've heard hints that the IANA controls/regulates the multicast addresses. So do you have to request / ask IANA for a specific multicast address for your project / company? How does this work? Am I mistaken? Can you clarify multicast networking for me?

Thanks much!

Josh G
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  • This sounds like something for serverfault.com instead – Oskar Kjellin Apr 08 '11 at 20:55
  • @Oskar: Maybe partially, except for the fact that I want to implement this in a program, so there's a direct programming application. I may just post there as well. – Josh G Apr 09 '11 at 02:41

1 Answers1

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Firstly, multicast only works if the routers in the network support it. The IGMP protocol is used for this purpose: http://en.wikipedia.org/wiki/Internet_Group_Management_Protocol. Assuming you have N clients on separate networks connected by multicast capable routers, then they could send messages to a multicast address and other peers that have subscribed to that multicast address will then receive those messages. You can read up further on multicast on Wikipedia.

I think you're confusing IEEE with IANA, the Internet Assigned Numbers Authority (IANA). Have a look at http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xml for multicast address assignments.

Ralf
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  • You are right about IEEE and IANA. I couldn't remember the exact name / organization. Updated. I'll check out the rest of this later. – Josh G Apr 08 '11 at 20:53