Network demand for controller nodes

Hello, Does anyone know if controller nodes are demanding on network needs? I have a situation where I don't have enough 10GB/s port in the switch. Would a cluster be network constrained if I have three controllers using 1GB/s connections and the execution and storage nodes are on 10GB/s connections? Does the VM traffic ever transverse the controller's network cards? In another word, is there a valid requirement for 10GB/s on openstack controllers? Regards, William