Virtual networks allow you to create networks to which only specified virtual machines can connect. They can also be used to allow virtual machines to attach directly to the physical network through the host computer's network adapter. You can have any number of virtual networks defined within Virtual Server. Each virtual machine can use up to four network adapters, each of which can have different configurations.
When using virtual networks that are not connected to a physical network adapter, you can create environments where virtual machines can talk only to other virtual machines. This is valuable when creating test environments such as when testing ISA Server configurations.
When a virtual network adapter is connected to a physical network through a network adapter in the host server, the virtual machine has complete access to the physical network. This allows for virtual machines to function on the network just as any other machine. For example, you could easily create a caching-only ISA server as a virtual machine and attach that virtual machine to the physical network.