Network Virtualization

Network virtualization is a part of IT virtualization.

Virtual networks
As a concept, virtual network should be considered as a switch, but in opposite to a physical device it is a virtual switch.

All virtual machines within one network are connected to one switch. Each virtual switch is logically isolated from the rest of virtual switches. If there is a need for nodes connected to one virtual switch to connect to nodes connected to another virtual switch, a virtual router, VPN server, virtual firewall or similar device should be set up, just like for physical network.

It is very handy to create different virtual switches if there is a need for network isolation similar to isolation that exists in a physical network, where different segments are separated with a firewall or another access control device.

Virtual network types
There are three types of virtual networks, which can be connected with Hyper-V:

  1. Private Virtual Network
  2. Internal Virtual Network
  3. External Virtual Network

Private Virtual Network

Private Virtual Network is a part of network virtualization. It is a virtual switch, which connects virtual machines only. Guest OS’s connected to one segment of virtual network can interact with each other, but cannot interact with Host operating system, and similarly host operating system cannot interact with virtual machines on the private virtual network.

Private virtual networks are extremely handy if you are aimed at complete isolation from the rest of virtual networks, but sometimes this approach can introduce problems if you need to copy files to virtual machines since virtual machines cannot connect to underlying (host) OS. In this case another virtual machine should be set up, which will take the role of a router or a firewall. Then, one virtual network adapter should be connected to the private virtual network, while the other should be connected to the physical network (via an external virtual network).

Internal Network virtualization

Internal Virtual Network is similar to private virtual network in a part that it is not bound to any physical NIC. Internal virtual network is also an isolated virtual switch like in private virtual network, but in case of internal virtual network Host OS has access to guest virtual machines via virtual switch of internal virtual network.
However, these virtual switches lack DHCP function (which VMware Workstation offers in some cases). Therefore, if there is a need of interacting with virtual machines connected to internal virtual network’s switch, you will have to allocate IP address for a virtual NIC of Host OS connected to internal virtual network such that address is also valid for the virtual network to be interacted with.

External Network virtualization

External Virtual Network differs from other types of virtual networks, since this type is bound to physical network adapters. You can have one external virtual network per each physical NIC installed to your Hyper-V server. External virtual network’s switch will be treated in a way as if it was a physical network adapter of the server. That’s why if you look through configuration of the previous NIC, you will probably think that it has no IP addresses configured. Instead, virtual NIC is added in Network Connections window and this virtual network adapter is connected to external virtual network’s switch. Besides, IP addresses allocated to this virtual NIC provide for its interaction with physical network.