As mentioned in earlier sections, the virtual switch, or vSwitch, forms the core of all the Microsoft® Hyper-V® Server 2008 virtual networks.
NOTE: The virtual switch never appears as an entity or icon in the Microsoft® Windows Server® 2008 parent partitions, including the Network Connection window. It is a logical representation.
Four virtual network options are available in Hyper-V. Each of these options offer different advantages and disadvantages, and some are only appropriate for special cases. The virtual network options are:
Private virtual network
Internal virtual network
External virtual network
Dedicated virtual network
NOTE: The dedicated virtual network implementation allows virtual machine (VM) traffic to be dedicated to a specific physical network port instead of being shared between VMs and the parent partition. The dedicated virtual network is the preferred implementation for most deployments of Hyper-V.
Private Virtual Network
In Hyper-V, you can use the private virtual network to allow network communications between VMs on a host. Private virtual network is the first of the three virtual switch configuration modes that you can configure from the Hyper-V GUI.
When you select and configure the private virtual network:
A virtual switch is created and made available for VMs. See the vSwitch #1 in Figure 4-1.
Advantages
The private virtual network offers complete isolation from the parent partition and the external network.
NOTE: The private virtual network is not recommended for environments utilizing Failover Clustering because the private network is localized to each host.
Figure 4-1 shows the logical representation of the private network configuration. It additionally shows VMs connected to the virtual switch.
Figure 4-1. Private Virtual Network Diagram
Internal Virtual Network
In Hyper-V, you can use the internal virtual network to allow network communication between VMs on a host, and also between VMs and the parent partition.
When you select and configure the internal virtual network:
A virtual switch is created and made available for the VMs. See the
vSwitch #1 in Figure 4-2.
A new virtual network adapter is created and connected to the parent
partition.
Advantages
The internal virtual network enables isolation of VMs from the external network.
NOTE: The internal virtual network is not recommended for environments utilizing failover clustering because the internal network is localized to each host.
Figure 4-2 shows the logical representation of the internal virtual network configuration. It additionally shows two VMs and the parent partition connected to the virtual switch.
Figure 4-2. Internal Virtual Network Diagram
External Virtual Network
In Hyper-V, you can use the external virtual network to allow network communication between VMs, the parent partition, and the external network.
When you select and configure the external virtual network:
A virtual switch is created and connected to the VMs. See the vSwitch #1
in Figure 4-3.
A new virtual network adapter is created and connected to the parent
partition.
The parent partition virtual network adapter is connected to the virtual
switch.
The virtual switch is connected to the physical network adapter that you
enabled for external network access.
Disadvantages
The second adapter in the parent partition can cause host connectivity issues. These issues include multiple DNS entries, delayed or incomplete NetBIOS resolution, and routing confusion.
The multiple parent partition network adapter causes delayed NetBIOS resolution or incomplete network browsing. Multiple browsing lists are associated with each network adapter.
Figure 4-3 shows the logical representation of the external virtual network configuration. This diagram shows two VMs, the parent partition, and one physical network adapter connected to the virtual switch.
Figure 4-3. External Virtual Network Diagram
Dedicated Virtual Network
The dedicated virtual network is a modified form of the external virtual network offered by Hyper-V. This virtual network allows VMs to communicate with other VMs on the same system and to VMs on other systems. The VMs can also access the external network.The VMs have access to the parent partition through the external network if the parent partition virtual network adapter is connected to the virtual switch.
NOTE: The VMs on a dedicated virtual network do NOT have direct access to the parent partition as with the external virtual network configuration. Removing this direct path eliminates many of the drawbacks of the external virtual network.
Unlike the other three virtual network types, you cannot directly configure the dedicated virtual networks with the Hyper-V Virtual Network Manager. You can create the dedicated virtual network by first creating an external virtual network and then modifying the virtual network adapter that you added to the parent partition.
Advantages
The physical network adapter is dedicated for VM traffic, so there is no sharing with the parent partition
Disadvantages
The disabled network adapter appears in the Network Connections window of the parent partition. You must not modify the network adapter settings or enable the network adapter.
NOTE: The Microsoft® Windows Management Instrumentation (WMI) can be used to implement a dedicated virtual network without causing an additional virtual network adapter to appear in the parent partition. For more information, see the Hyper-V WMI programming reference listed in Appendix B.
Figure 4-4 shows the logical representation of the dedicated virtual network configuration. It shows two VMs, the parent partition, and one physical network adapter connected to the virtual switch.
