MAC duplication issues with captured VMs and WDS

I’ve previously reported problems with MAC duplication on Hyper-V host external network connections on Windows Server 2008 R2, which I’ve never fully resolved, although we have been successfully working around the issue as detailed in the first link above.

A couple of weeks ago I was working simultaneously on my Windows Server 2008 R2 laptop with Hyper-V (the same laptop build that’s been previously mentioned) and a Windows 7 x64 build that I was using for testing, when I noticed severe but intermittent network problems on both machines. After a fair amount of head scratching, I noticed that the two laptops had duplicated MAC addresses. Blatantly that shouldn’t happen, as the whole point of a MAC address is to provide uniqueness. The most perplexing issue was that the addresses conflicted across two different operating systems. However, it happened. Both wired adapters on the two machines had the MAC address 00-21-9B-DC-8E-0B. I uninstalled the wired adapter on the Windows 7 machine and scanned for new hardware. When the device reinstalled the problem went away. Continue reading “MAC duplication issues with captured VMs and WDS”

More on routine loss of external network connectivity on Hyper-V hosts (not guests)

Further to my post from a few months ago on the this topic (dating back to the RC build), I’ve seen this same problem a few more times on the RTM build of Windows Server 2008 R2. My suggested approach still fixes the problem and it doesn’t recur, but I’ve still not been able to pin down a cause and I can find no documentation on host machine MAC assignments anywhere. Continue reading “More on routine loss of external network connectivity on Hyper-V hosts (not guests)”

Routine loss of connectivity on a Hyper-V host’s external connection

We’ve recently been piloting a laptop developer build on Windows Server 2008 R2 Release Candidate (Build 7100) with the Hyper-V role. One of the first receipients of this build complained of connectivity problems in Office Communicator once every minute or two. For as-yet undiagnosed reasons we have lengthy sign-in times for Communicator, so this loss of connectivity rendered it completely unusable. This same problem was visible in Outlook, although less disruptive since we use Cached Exchange Mode. Both Exchange and the OCS server are hosted but we also noticed the problem with interrupted file transfers so it clearly wasn’t just an internet connectivity issue. It looked like something to do with the NIC, the cable or a network device.

The network trouble was accompanied by a series of System log event errors from MVSMP:

Port ‘SWITCHPORT-SM-F277C685-E5F8-490D-8CD1-913B854FABD2-0-1′ was prevented from using MAC address ’00-15-C5-7E-EB-39’ because it is pinned to port ‘SWITCHPORT-SM-F277C6’. Continue reading “Routine loss of connectivity on a Hyper-V host’s external connection”