Tuesday, February 24, 2009

New Hyper-V Dedicated Network is Coming

Windows Server 2008 R2 will offer Hyper-V V2, the second version of Microsoft's hypervisor virtualization solution.

Among the new features, Hyper-V V2 will feature a new "Dedicated" virtual network type. This will be in addition to the External, Internal, and Private networks currently available in Windows Server 2008.

As background, when you create a new virtual network in Windows Server 2008 Hyper-V converts the physical network adapter to a Microsoft Virtual Switch. It also creates a new virtual network adapter attached to the new virtual switch.

In the example above, we see a Hyper-V host with four physical NICs. The first NIC is dedicated to the host, as per best practice, and is attached to the corporate LAN. The other three NICs have been configured as External virtual networks using the Hyper-V Virtual Network Manager.

You will note that there are three disabled virtual NICs at the bottom of the image for the host to use. These virtual NICs were automatically created by Hyper-V when you configure the External virtual network, and are normally enabled by default. I've renamed each NIC and virtual switch on my host server for clarity.

If you're following the best practice of using a dedicated NIC for the Hyper-V host, as above, there normally would be no reason to use these virtual NICs. If you leave them enabled, it can cause a number of problems for the Hyper-V host:

  • The virtual NICs will attempt to get DHCP addresses. If no DHCP server is available, it will get the automatic private IP address (169.254.x.x).
  • The network binding order may be out of order, causing network inefficiencies.
  • The Windows Firewall will apply vastly different settings (I'll blog more on this later).
  • Trying to sort out an IPCONFIG /ALL is a mess

The current recommended way of dealing with this in the Windows Server 2008 version of Hyper-V is to remove all the connections for the new virtual NIC (IPv6, IPv4, etc.) and then disable the virtual NIC. Finally, you should check the network bindings to ensure that the host's NIC is at the top, followed by the virtual switches, and then the disabled NICs.

In Windows Server 2008 R2, Microsoft introduces the Dedicated virtual network type. When you create a Dedicated virtual network, Hyper-V does not automatically create a corresponding virtual NIC. It simply converts the selected physical NIC to a Microsoft Virtual Switch for the VM(s) to use. No need to disable anything or change network binding orders. Very cool!

Note that you will be unable to create a Dedicated virtual network on a single NIC Hyper-V host. If you did, the host would be unable to connect to the corporate LAN since there would be no NIC (physical or virtual) for it to use.

This new network will be a welcome addition to Hyper-V!


2:18 PM