Creating virtual network configurations

Hyper-V makes it possible to extend nearly any existing physical network configuration into its virtual space or create a completely separated and isolated network within the Hyper-V environment.
The basic default configuration of a Hyper-V VM connects its network adapter to an external virtual switch, thus attaching the guest OS on the VM to the outside network. The VM can then take advantage of services running on the outside network and send traffic through routers to other networks, including the Internet.
This type of arrangement can enable administrators to consolidate many physical servers into VMs on a single Hyper-V server, providing them all with access to the entire network.

There is no distinction here between the physical network and the virtual one in the Hyper-V space.

Extending a production network into virtual space
Keep in mind that a Hyper-V server can have multiple physical network adapters installed in it, which might be connected to different networks to separate traffic or they might be connected to the same network to increase available bandwidth. You might also have adapters dedicated to SAN connections for shared storage and server clustering.
Microsoft recommends the use of at least two physical network adapters in a Hyper-V server, with one adapter servicing the parent partition and the other connected to the child partitions. When you have more than two physical adapters in the server, you can create separate external virtual network switches for the physical adapters and connect each one to a separate VM.

Creating an isolated network
For testing and evaluation purposes or for classroom situations, administrators might want to create isolated network environments. By creating internal or private virtual switches, you can create a network that exists only within the Hyper-V space, with or without the parent partition included.

An isolated network such as this has limitations, however. If you want to install the guest OSs by using Windows Deployment Services or configure the VMs by using DHCP, you must install and configure those services on your private network. The guest OSs also do not have access to the Internet, which prevents them from downloading OS updates. In this case, you must deploy appropriate substitutes on the private network.

One way to provide your systems with updates is to install two network adapters on each of your VMs, connecting one to a private switch and one to an external switch. This enables the VMs to access the Internet and the private network.

Another method for creating an isolated network is to use VLANs. This is particularly helpful if you have VMs on different Hyper-V servers that you want to add to the isolated network. By connecting the network adapters to an external switch and configuring t em with the same VLAN identifier, you can create a network within a network, which isolates  the VLAN from other computers. You can, for example, deploy a DHCP server on your VLAN without it interfering with the other DHCP servers in your production environment.