Open vSwitch is a powerful network abstraction. The following figure shows how OVS interacts with the VMs, Hypervisor, and the Physical Switch. Every VM has a vNIC associated with it. Every vNIC is connected through a VIF (also called a virtual interface) with the Virtual Switch:
OVS uses tunnelling mechanisms such as GRE, VXLAN, or STT to create virtual overlays instead of using physical networking topologies and Ethernet components. The following figure shows how OVS can be configured for the containers to communicate between multiple hosts using GRE tunnels: