The Hyper-V virtual switch provides a number of features you can use to isolate traffic. Before diving into specific features, we'll discuss its basic switching capability. The virtual switch parses the Ethernet header, just like a typical physical switch. It knows only to deliver frames to the MAC address that they are bound for. This means that one virtual machine isn't going to be able to snoop traffic meant for another port without compromising the Hyper-V configuration.
There are a number of other techniques that Hyper-V's switch uses to enable isolation.
Most virtual switches will use an external virtual switch. This bonds to a physical network adapter or a team of adapters, and allows direct communication with systems that are external to the guest and its host. Most of this chapter will deal with this type.