So this is a bit of a rant post, just so you are aware, although it does have kind of a happy ending(ish).
For people that still believe in email lists these days there has been a huge debate about using WDS and DHCP options to control which boot file gets sent to which client. I started investigating why DHCP options for PXE booting where not recommended by Microsoft, hey they even go as far to say that its "Not Supported" to use WDS DHCP options in the following White Paper: http://www.microsoft.com/en-us/download/details.aspx?id=44598
But I like challenges and took them up on this one. Why did it not work to the point where it couldn't be a supported option? Okay, I'm sticking my neck out here, far out… but I think it’s a bug in the EFI boot loader. I suspect that this is why Microsoft doesn't/Can't “support” using DHCP options, its not working as it should. And since there's not a lot of people in the world that can read native C (which the loader is made of) they have just dismissed it and said “not supported”.
If I set Option 60 in my DHCP scope when DHCP and PXE server are on different servers the MS EFI loader starts working, i.e. it talks to the right host. Opposite of BIOS behavior… hmmm…
I bet it’s a TRUE/FALSE statement or possibly AND/OR evaluation that fails. I haven confirmed with a debugger but I am pretty sure. I can boot any EFI loader from WDS using a wide range of hardware, without Option 60. As soon as I try with the WDSMGFW.EFI, it loads and then hits a brick, trying to contact my DHCP server instead. If I set Option 60 it goes directly to the PXE server. Opposite land of BIOS…Strange huh?
Well it's one thing crying and whingeing about bugs and supported/not supported behavior but we thought that we'd have a go at fixing it (we're nice like that). And whaddya know? We did :-)