TGW Multicast scalability

Question

A customer has asked the following question:

> "What is the scalability of Transit Gateway based multicast?  For example, when 10 VMs are created within a single Placement Group Cluster, can we have 5 multicast sessions, each transmitting at 12Gbps?"

I'm assuming that the EC2 acting as the multicast source would be limited to the normal 5Gbps bandwidth for single-flow traffic, which would be the limiting factor here, but wanted to check that multicast traffic wasn't treated differently in some way and hence subject to different limits. I'm also assuming that the multicast group address wouldn't be counted as being within the cluster placement group and so wouldn't get the 10Gbps limit instead.

Could someone more knowledgeable validate my assumptions please!

Thanks!

Accepted Answer

Multicast is implemented by TGW, which means that all packets are first forwarded to the TGW service and then copied and forwarded out from there on a unicast basis. Therefore, this is not a multicast service that should be thought of as a very high bandwidth or very low latency service. It's not slow but it has some overhead. The customer should test to see if it meets the customer's throughput and latency requirement, but it will not be nearly as fast as direct communication within a cluster placement group.

TGW Multicast scalability

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