An private update has been released for users experiencing the following issues:

You cannot connect to a virtual machine when the Windows Server 2008 Hyper-V VMMS certificate has expired

Cannot connect to the virtual machine because the authentication certificate is expired or invalid. Would you like to try connecting again?

'VMName' failed to initialize.
Could not initialize machine remoting system. Error: ‘Unspecified error’ (0x80004005).
Could not find a usable certificate. Error: ‘Unspecified error’ (0x80004005).

And then today I noticed this posted on Ben Armstrong's blog:

Management Operating System

This is a new term that we are introducing in Windows Server 2008 R2.  We have been struggling without a good term here – as with Virtual PC / Virtual Server we had a nice set of terms where we could talk about the physical computer / virtual machine and the host operating system / guest operating system.  However this became muddier with Hyper-V – because we no longer really have a host operating system, and all operating systems run on top of the hypervisor.  Most people have been just using the term “Parent” or “Parent partition” to refer to what we used to call the host operating system – but this is not really architecturally correct.  Unfortunately the architecturally correct terms are – frankly – hideous; they are the “parent partition guest operating system” and the “child partition guest operating system”.  Yuck.  So after a lot of thought we decided to call the “parent partition guest operating system” the “Management operating system” as this is the operating system you use to manage your virtual machines, and “guest operating system” will be reserved to mean the operating system running inside virtual machines.

I came across this problem the other day, where I wanted to determine if a Virtual Machine was running on Hyper-V or Virtual Server 2005 host system.

WMI exposes the Win32_ComputerSystem class which contains information about the Manufacturer and Model of a particular system (this is very hand if you want to check type of system before installing an application, e.g. Virtual Machine Additions). The unfortunate news is that Win32_ComputerSystem returns the following on both Hyper-V and Virtual Server hosts:

So how to determine what it is I am looking at? Well there is another WMI class, Win32_BIOS, which can help. Here you can see a difference in the Version between products.

Hyper-V

Virtual Server 2005 SP1

So far this seems to work for me; I am interested if anyone has alternate suggestions on how to solve my little problem, especially if there are cases where this will break (for example limiting the CPU functionality to run NT 4.0?)

Last week I was configuring a lab server with Hyper-V RC0 when I came across this error after creating a Virtual Switch with VLAN ID enabled:

Switch set up failed, name='3742d220-e73d-4ae5-bf0c-429ca168dc41', external port='d02dcb9e-76d4-496a-9c17-ea808e5ce125', internal port='375e5f91-b1fb-415d-8717-cd3ea36c9753', NIC='{165929BF-5BA2-4887-BC54-1D52C1A6BE61}', internal name='07b53c30-5d56-4a2d-a542-146773d39299', internal friendly name='Virtual Network Connection (VLAN Trunk)', error=2147749896, mof code=0.

Located in the Hyper-V application log this error resulted in a failed switch configuration and without a supported way to remove Virtual Switches (doesn’t seem right does it?) prevents you from creating any other network using that interface.

Turns out that this error occurs if you are creating a new network (with VLAN ID enabled) on a physical interface that doesn’t have a default VLAN ID specified, see example image below.

Hyper-V Networking
Hyper-V provides many networking improvements and the Virtual PC Guy’s has put together a great blog post explaining the changes, worth while reading for those making the move from Virtual Server.
Understanding Networking with Hyper-V