Alot of people does not know that there are no Virtual Machine additions any more in Hyper-V this are now called Integration services and you can install them on this OS-es. So if you use for example Ubuntu on Hyper-V you need to remove Network card that it added to Virtual machine by default and then Add Hardware and add Legacy Network Adapter (it behaves the same way as bridged adapter in Virtual PC and Virtual server) – as it is used for machines that do not have Integration services installed.
You need to intall Integration services on all MS Windows server 2008 machines to get best performance!
If you you need network connectivity imediatly after installation you can first use Legacy network adapter and after Integration services intallation you can replace it with Network adapter that was configurated during creation of Virtual Machine.
Integration services will also solve your unknown devices in device manager.
You install Integration services by clicking on Action / Insert Integration Services Setup Disk when you are logged on your virtual machine.
Luka Manojlovic 
Hello Luka,
Did you have some experience in migrating/installing linux VM under hyper-v 2012, with network performance problem? I have nagios on ubuntu 12.04.4. It works great on Windows server 2008, but after migrating, or installing on Windows server 2012 with hyper-v 2012, we are getting slow network response after rebbot and in some periods of time…
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