Ingress of traffic to the virtual machines when they fail across data centers is extremely important to consider, because without a solution in place, traffic destined for virtual machines on Site A can be returned through Site B. This is often referred to as asymmetric routing.

Route ingress optimization can be achieved in a number of ways and can be dependent on the physical networking capabilities. One solution is to leverage route injection through APIs during an event, such as a long-distance vSphere vMotion migration. See Ingress Optimisation with NSX for vSphere.