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 enviornment 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).