Hello,

I'm doing some traffic measurement on VM instances created in OpenStack Juno. I'm using a standard OpenStack configuration with 3 interfaces: Management, Data and External networks.

The Data (em1) and External (em3) interface have bandwidth of 10Gbps and 1Gbps. So intra-network VMs located in 2 different Compute nodes should have much higher data transfer throughput if they use em1 instead of em3. In other words, connecting to private tenant network IP address (east-west traffic) should be much faster than floating IP.

Weird thing is that, while throughput measured with data transfer using Floating IP (via em3) is about 550-800 Mbps (say, 60-80% of the achievable throughput), the throughput measured via Tenant network (em1) is only ~400Mbps (out of 10Gbps that the host compute node is able to reach).

Anybody could guess what configuration could make it wrong? I personally don't think that OpenStack limits the data tenant interface while maximises external network interface.

Thank you!