VMM Bare Metal Builds and why you should use a Native vLAN

VMM Bare Metal Builds are an amazing way to ensure that your Hyper-V servers start out consistent. It’s a bit magical but part of that process just works better when you use a native VLAN. But why is that the case?

First let’s look at the VMM Bare Metal Build process.

  1. The VMM Server connects to the hardware management interface and instructs the server to reset. This is immediate and if you specified the wrong hardware management address, well congratulation you just rebooted a server.
  2. The new server being rebuilt goes through it’s boot process. Hopefully you have it configured to PXE boot. This will get a DHCP address and then request a PXE server to respond
  3. The WDS server receives the PXE boot request and checks with the VMM server to see whether this request is authorised. If it is then it responds to the request and send the WinPE image
  4. The new server loads the WinPE operating system and connects to the network. This network connection is a brand new network connection and is in no way connected to the PXE boot. You’ve just booted into an OS after all
  5. The new server runs the VMM scripts to discover the hardware inventory and then send this to the VMM server
  6. Once the admin inputs the required information (New server name and possibly network information) the new server begins the build process by cleaning the specified disk and downloading the VHDX image.
  7. The new server then reboots. This time the server is not authorised to PXE boot so proceeds to boot off the new VHDX boot image.
  8. The new server then customises the sysprepped operating system including any static IP address you provided and performs any additional customisation required by the VMM build process (ie. Adding the Hyper-V and MPIO role and installing the VMM agent).
  9. You should now be left with a server on the network using the configured network settings.

There are a few things to note here. Each time that the server uses either PXE or boots into WinPE it’s reliant on finding a DHCP server. If you’re using port-channel network connections, and very few people are not now, then how is this request going to work? It needs to know what vLAN to tag the request with.

Now you can configure most servers in the BIOS to PXE boot with vLAN tagging and that’s great. Now you have your WinPE image. How does WinPE know about the port-channel. This will be dependent on the NIC driver for your server. Is it even possible to modify it so that, when the driver is loaded, it automatically uses vLAN tagging with the correct vLAN ID. It’s possible but something else that needs to be managed. If VMM updates the WinPE image then you need to reconfigure it again.

Next when you boot off the VHDX this also needs be configured with the correct vLAN ID. Now I have to admit I have never got to this stage since the NIC driver in WinPE has always been a blocker for me but is VMM able to set the correct VLAN ID? You absolutely need to tell VMM what network switch to use and what logical network but does this mean that it will set the VLAN ID correctly. If it doesn’t then this is again another blocker.

So as you can see it may be possible to use vLAN tagging throughout the VMM Bare Metal Build process but sometimes you need to look at whether it’s worth the additional overhead. From managing the server BIOS, to the WinPE drivers and configuration, and the OS customisation. There’s a lot going on with this process and everything needs to work perfectly to result in a fully built server. Is it worth the additional overhead just to avoid setting a network as the native vLAN.

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