Category: Networking

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”

Building a SharePoint 2007/2010 development environment – Part VI: Issues and Results

In the first five parts of this series I covered the project objectives and the system design, then turned my attention to the Hyper-V host image build, automated deployment and the guest virtual machine build. In this post I review some of the questions and issues we’ve encountered after a few months of working this way and some overall reflections on the approach. Continue reading “Building a SharePoint 2007/2010 development environment — Part VI: Issues and Results”

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)”

Disabling IPv6 on Server Core and Hyper-V Server

Note: this original KB article from which this guidance was taken has now been removed. Please see the comments below for more information.

I recently posted about the Conflicting Microsoft guidance on IPv6. While you can remove IPv6 from a NIC on a full installation of Windows Server 2008 by un-ticking the IPv6 box in the NIC properties (satisfying the Hyper-V performance guidance), you may have noticed that there’s no obvious way to disable IPv6 in server core or Hyper-V Server. If you looked in to it in a bit more detail you may have noticed a registry “fix” for this. Personally I’m always a bit skeptical of registry fixes until I see Microsoft recommending them, but now Tonyso has posted a link to a Microsoft KB article that endorses this approach (when necessary):

To completely disable IPv6 on a Windows Server 2008-based computer yourself, follow these steps:

  1. Open Registry Editor.
  2. Locate the following registry subkey:
    HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpip6Parameters
  3. In the details pane, click New, and then click DWORD (32-bit) Value.
  4. Type DisabledComponents, and then press ENTER.
  5. Double-click DisabledComponents, and then type 0xffffffff in Hexadecimal or 4294967295 in Decimal.Note The 0xffffffff value or the 4294967295 value disables all IPv6 components except for the IPv6 loopback interface.

A reboot is required before the change will take effect.

Conflicting guidance on IPv6

I recently noticed that Cable Guy is saying “don’t disable IPv6“. While I broadly agree with the approach and the reasons he suggests not to, I’ve not yet seen any down-side to disabling it, and I know we aren’t using the IPv6 technologies that Cable Guy mentions. But why did I turn it off? SharePoint’s Hyper-V performance and capacity guidance suggests that performance is improved by disabling it.

“Use IPv4 as the network protocol for Hyper-V guests. During the tests, better performance was observed when IPv4 was used exclusively. IPv6 was disabled on each network card for both the Hyper-V host and its guest VMs.”

In this case, I’m going with the SharePoint guys, especially when there’s a quantified test versus a theory, especially when it simplifies troubleshooting and not everyone is IPv6-fluent yet.

Windows Deployment Services trumps Internet Connection Sharing

I imagine the responses to this post’s title will fall in to one of three categories:

  • What’s Windows Deployment Services?
  • What’s Internet Connection Sharing?
  • Why on earth would you use both in one machine?

To answer the last question I need to unveil a bit about the network approach that we’ve adopted for the Hyper-V on Windows Server 2008 R2 laptop build that I mentioned in my last post. Continue reading “Windows Deployment Services trumps Internet Connection Sharing”

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”

Hyper-V Manager over VPN may fail if the server is VMM-managed

About a year ago John Howard published guidance on how to get Hyper-V Manager to connect to Hyper-V servers over VPN. His network monitoring and suggestion to change the VPN connection IP settings so that the VPN adapter registers the machine’s new address in DHCP/DNS went a long way towards fixing the issue  for me – however, we recently uncovered a couple of caveats as detailed in the comments on his original post. Continue reading “Hyper-V Manager over VPN may fail if the server is VMM-managed”