@Jamie-Read Some machines Firmware are better than others, some are worse than others.
Some machines will try for 5 or 8 seconds and then give up and boot to the next option in the boot priority.
Others will just sit there and stare at the wall for 15 minutes trying to network boot.
We have no control over how manufacturer firmware acts - but if you’re really skilled and super motivated - you can probably flash the ROMs for the NIC chipset to reduce the wait period.
OR…
You can run dual TFTP servers, or chain one “always on” and simple TFTP server to the primary FOG server. Others here in the forums have accomplished setups like this in the past to reduce their downtime and prevent precisely what you’re describing.
If you’re running dnsmasq ProxyDHCP - it’s possible to ping the FOG sever every minute via a script with Cron-Tab, and if a response isn’t recieved, to simply swap out ProxyDHCP’s configuration file with another one that points to a different FOG server, and then restart the service. This can also be done with Linux DHCP quite easily. However I’m afraid there are no easy ways (or perhaps any way) to manipulate Windows DHCP in such a manner… this is where you will find that Linux excels beyond what Windows is capable of.
Just let us know what you’re interested in and we will try to help - and also feel free to search the forums and other sites to try to figure it out yourself as well, you’ll learn more if you do it on your own.