You could always use SolarWinds Free TFTP Server on two separate servers (assuming you have them) or two regular old computers would even work.
Just configure both and copy your FOG server’s /tftpboot into both TFTP server’s root folder for their TFTP directories.
Of course this isn’t completely fail-safe…but this may do the trick:
Hostname: TFTP-Server01 (10.0.0.5)
Hostname: TFTP-Server02 (10.0.0.6)
Set option 66 to point at TFTP-Server01.
Add static DNS entries:
As you can see, TFTP-Server01 has two entries, the second being TFTP-Server02’s IP.
This works in a Windows environment as long as the second IP for the specific host is numerically higher (e.g. 10.0.0.6/10.0.0.7/10.0.0.8/etc.)
The only way hosts would be stuck waiting for their PXE bootfile is if both TFTP servers went down…you could even add a third server (TFTP-Server03 (10.0.0.7)) and just add another entry for TFTP-Server01 (10.0.0.7).
This is how I have FOG setup in one of my environments. This way I can freely reboot my FOG server and only need to worry about it being up when I want to image.