Hyper-V Virtual Netwotk

In Hyper-V 2008 R2 you have three types of virtual networks i.e. External , Internal and Private.

Private- a virtual network between VM-to-VM

Internal- a virtual network between VM-to- Host. Here the virtual network act like as a loopback adapter.

External- a virtual network between VM-to-External or physical access to the network card.

Cheers:)