A couple of times now, I’ve had trouble getting a Hyper-V 2008 R2 guest to PXE boot. Even if I move the network adapter to the top of the list, the boot process still skips straight back the network boot. So I was having a bit of a poke around in the VM settings, when I noticed and option to add either a ‘network adapter’ or a ‘legacy network adapter’.
So I deleted the existing ‘network adapter’ and created a new ‘legacy network adapter’.
Sure enough, my virtual machine successfully PXE booted right away.
Later, I created a new virtual machine and noticed the option to ‘install an operating system from a network-based installation server’. I selected this option, completed the wizard, opened the VM’s settings and wouldn’t you know it, the wizard had created a VM with a ‘legacy network adapter’ this time.