When configured with PVRDMA adapters, VMs with network-intensive applications can communicate over RDMA. When two VMs need to communicate across ESXi hosts and each host has an HCA installed, PVRDMA communication is enabled. If two VMs with PVRDMA adapters need to communicate on the same ESXi host, the HCA, if installed, is not used, and traffic is kept within the VMkernel itself. If a VM with RDMA enabled needs to communicate with a VM that does not support RDMA, the communication falls back to TCP/IP.