When you install Windows Server 2012 RTM to a server with X520 series NIC cards you’ll notice that there is a native driver available and the performance of that driver is fantastic. It’s really impressive to see.

That’s great news but I’ve noticed an issue in RTM that I already dealt with in the release candidate.

The moment you install Hyper- V some of the X520 NIC ports can start flapping (connected/disconnected).  You’ll see the sequence below endlessly on one port, sometimes more.

As you can imagine this ruins the party in Hyper-V networking an bit too much for comfort But it can be fixed. The root cause for this I do not know but it is driver related. The same thing happened in the release candidate. But now things are easier to fix. Navigate to the Intel Site to download their freshly released driver for the X520 series on Windows Server 2012 and install it (you don’t need to install the extra software with Advanced Network Services => native Windows NIC teaming has arrived). After that the flapping will be gone.

Hope this helps some folks out!