WDS respective PXE boot and VMware

If you try to PXE boot a VMware guest system that e.g. uses WDS / Windows Deployment Services or similar, you might encounter that the boot.wim etc. download unbelievable slow. This can take several hours. This has especially to do with booting via the VMware EFI environment. VMware BIOS does not cause this issue. You could switch a EFI system to BIOS to capture/deploy the image – but this is not really a solution rather then bypassing it.

The solution for this is pretty simple, while the download is transferred through a TFTP, VMware has an issue with the blocksize and this gets a bit messed up due to the variable blocksize between the VM guest system and your PXE server.

Set the Maximum Block Size to 1456 – what is the exact value VMware needs to work properly. Disable further the Variable Window Extension and try to PXE boot again – you will see it will load in about a minute now – depending on your WinPE image size and your issues are in the past.

In detail:

  1. open your Windows Deployment Services
  2. right click on the server and select Properties
  3. navigate to the register card TFTP
  4. set the Maximum Block Size to 1456
  5. uncheck the Enable Variable Window Extension checkbox