On a private network, the virtual machine can communicate with other virtual machines but not with the host or with external networks. On an internal (or host bound) network, virtual machines can communicate with each other and the host but cannot communicate with external networks because the network is not bound to a physical network adapter.
On an external network, which is bound to a physical network adapter, the host and its virtual machines can communicate with external computers. External networks can be bound to the host also by selecting the Host access option in the network configuration in the host properties (Networking tab). (In Windows PowerShell – VMM, this is the -BoundToVMHost parameter of the New-VirtualNetwork and Set-VirtualNetwork cmdlets.) If this property is selected, the virtual network has access to the host. If the property is not selected, virtual machines can communicate with external computers but not with the host.
Virtual Server provides a DHCP server for virtual networks; Hyper-V does not. If you want a DHCP server on a Hyper-V host, one option is to create a virtual machine with Windows Server configured to provide the DHCP service and then add the virtual machine to the virtual network.
When you use VMM to manage ESX Server hosts, you can create virtual networks (known in VirtualCenter as virtual switches) on the host and connect the virtual networks to virtual network adapters. However, you cannot create console ports in VMM.