Virtual Switches and Networks

When many VMs live on one physical server, they still need to talk to each other and the outside world. A virtual switch (vSwitch) is software inside the hypervisor that does the job of a physical switch, but for virtual machines.

It forwards Ethernet frames between VMs and out through the host physical network cards, so the network now reaches inside the server itself.

Each VM is given one or more virtual NICs (virtual network interface cards). To the guest OS, a vNIC looks exactly like a real Ethernet adapter with its own MAC address (Media Access Control hardware address).

The vNIC connects to a port on the virtual switch. From there the hypervisor decides whether traffic stays inside the host or exits onto the physical LAN.