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It depends on the network. If the network is 100-1000 nodes and you can guarantee that the switches and routers you use to build it (and upgrade in future) impl

by mritun 10y ago

It depends on the network. If the network is 100-1000 nodes and you can guarantee that the switches and routers you use to build it (and upgrade in future) implement it correctly and won't break/introduce bugs in future firmware release then yes. In the kind of environments I worked in, this was a non-starter. edit: also "limit multicast messages only to ports that have actually joined a group" part is usually implemented by bloom-filters that I talked about above. They work well as long as there are not many groups and not many members.

SEJeff 10y ago
Sure in network topologies that size, you often have tiered access, leaf, and spine switches (and you can even build nonblocking topologies if you do things rihgt). Usually doesn't mean always. Many (most?) higher end switches use custom ASICs for IGMP Snooping, which means they scale fine until the ASIC limit at which they don't handle any more. In my career, I've worked in single networks with a max of maybe 4000 server nodes in 1 broadcast domain or so. Not huge, but I've seen no issues with big multicast uses provided you're using the right network cards / HBA and the right network switches. I've seen people build FPGAs to split market data into 10k+ multicast channels and was asked for help making Linux join so many channels (it is a PITA). It was amusing when we had to call around to find switch vendors which even supported it at all, most of them told us we were crazy (this was maybe 9 years ago). Take the Cisco Nexus switch as an example, it supports 32,000 IGMP groups, certain Aristas support 64,000, etc, and that is just for ethernet switches. Lets not get into Infiniband or some of the exotic Cray/IBM interconnects. I would be curious in your experiences if you're able to share it, but do very much believe there are options other than software for implementing multicast filtering on switches. What type of environments that you worked in made IGMP Snooping a non-starter?

by mritun 10y ago

SEJeff 10y ago

Sure in network topologies that size, you often have tiered access, leaf, and spine switches (and you can even build nonblocking topologies if you do things rihgt). Usually doesn't mean always. Many (most?) higher end switches use custom ASICs for IGMP Snooping, which means they scale fine until the ASIC limit at which they don't handle any more. In my career, I've worked in single networks with a max of maybe 4000 server nodes in 1 broadcast domain or so. Not huge, but I've seen no issues with big multicast uses provided you're using the right network cards / HBA and the right network switches. I've seen people build FPGAs to split market data into 10k+ multicast channels and was asked for help making Linux join so many channels (it is a PITA). It was amusing when we had to call around to find switch vendors which even supported it at all, most of them told us we were crazy (this was maybe 9 years ago). Take the Cisco Nexus switch as an example, it supports 32,000 IGMP groups, certain Aristas support 64,000, etc, and that is just for ethernet switches. Lets not get into Infiniband or some of the exotic Cray/IBM interconnects. I would be curious in your experiences if you're able to share it, but do very much believe there are options other than software for implementing multicast filtering on switches. What type of environments that you worked in made IGMP Snooping a non-starter?