There is a lot of discussion around networking and network changes on a Windows Server 2008 server after the Hyper-V role is installed.
Part of this issue goes back to what happens (what is done) to your WS08 server when the Hyper-V role is installed.
As I had mentioned in a previous post when the Hyper-V role is installed the WS08 server is fundamentally changed. As an administrator you login to a console and you see WS08 - it looks like nothing changed, however it has.
Ben Armstrong has a quick posting here that gives some basics.
Lets take a more architectural look at the server and what has happened / is happening..
During the process of adding the Hyper-V role the WS08 installation was turned into a virtual machine itself and it is running on top of the hypervisor as the parent partition. Unlike other hypervisors where you see a Linux based console, in this case you see your WS08 server - a nice, friendly GUI interface that really does not look any different than it did before.
Now, what does this have to do with the networking? It has to do with modifications that were made to the network interfaces of the WS08 server when the Hyper-V role was installed.
Quite honestly, the modifications that are made are no different than what happens when modifying any other Windows server in a similar way.
Most likely, if you set a manual IP address (any manual settings) they were lost.
If you look at Network Connections in the WS08 server you notice new Virtual Network Adapters and your original network connections were changed.
Noting back, your WS08 server was turned into a VM (its hardware was changed) - the original network connection (which you can still see) was turned into a virtual switch (the WS08 server no longer owns that NIC).
Your WS08 server (WS08 parent partition - that is what it is now) was given new virtual network card(s). And as with adding any new NIC to any Windows server it gets the default settings (DHCP for example).
Now, there is also talk about performance (the parent partition performance is terrible, but a VM runs great - or the other way around).
Now we have to begin looking at the NIC driver and driver configuration.
First of all, good old TCP Offloading, long a performance issue in many Windows environments might need to be turned off. Mind you, this issue seems to be environment specific.
The other is the NIC driver itself. You are pretty safe using the included WS08 drivers.
Some troubleshooting questions:
Did you install a non-Windows delivered driver?
Did you install a teaming driver?
Did you configure teaming?
Was there management software installed with the teaming driver or was only the driver installed? (some experience has shown that the driver itself might be fine but the management software causes problems - as it is trying to monitor a NIC that the parent partition no longer owns)
My goal with this post was to help an administrator understand what is going on, and with that where to look to solve his/her problems.