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I am trying to use IGMP for my NAVbus it as several systems connected to it. I am sending out a package every 1/100sec. Originally I was going to use UDP but would like to use multicast. But this network is not connected to a router to perform the IGMP tasks. since I am using a homogenous network (only ubuntu), with just a cisco 2924xlen for my switch. So this boils down to is there a way that I can use my NAVserver box as the IGMP server as well? Thanks

Burgi
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Phoenixcomm
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2 Answers2

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IGMP is not multicast replacement for UDP. Rather, as its name says ("Group Management Protocol"), it's the multicast control protocol, used to manage group membership for UDP (and other datagram protocols).

In order to receive multicast packets meant for a specific group (be they UDP or something else), you would first send an IGMP "join group" request. The switches along the path will note that your port wants to subscribe to that group.

(To send multicast packets, that is not required – you can just send regular UDP datagrams to the group's IP address.)

Multicast doesn't strictly require a router to work – on a small network such as yours, most of it will be handled by switches (which use IGMP to remember which switch ports have subscribed to which multicast groups).

Search your documentation for "IGMP snooping" and "IGMP querier" features.

u1686_grawity
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  • Better explanation of IGMP then what I provided, that is awesome. – Frostalf Aug 10 '16 at 14:23
  • @grawity ... **Yes. thank you.** I do really understand what IGMP is and the role of the router in a multicast network. Is there any software that will let my Linux box become the IGMP host (the router, that isn't there)? – Phoenixcomm Aug 12 '16 at 02:14
  • @Phoenixcomm: Um, in that case, what specifically do you expect the Linux box to do? Become an IGMP querier? Something else? "the IGMP host" is much too vague. – u1686_grawity Aug 12 '16 at 07:00
  • @grawity yes I believe that's it. thank you. because normally the router would tell the switch by using IGMP + PIM-SPARSE, and I do not see the need for any router on this network. but I will need that sort of functionality as all the clients must have the same data at the same time. But if one system dies i need it to be pruned. as It will no longer respond to status pull requests. – Phoenixcomm Aug 12 '16 at 20:35
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Just to let you know, UDP can use multicast. And IGMP uses bare IP Packets meaning, you don't need a router for it to work. Any type of network given it uses the IP Protocol should work.

Frostalf
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