Thank you all for your responses. Thye have been very useful.
I’ve been able to do it using a real machine. It was indeed a Virtualbox problem.

@george1421 Thank you very much for your response.
1 How can I check if it tries to downlad that file?
2 I will do that later, right now I don’t have access but later in the day I will
3 Didn’t specify… I’m using dnsmasq 2.79 (the same as if installed via apt) compiled with the modifications shown in the post
4 rEFInd is installed in the host machine, not on the server.

Hi!

I’m trying to set up a FOG server for a class project. I’m doing it in VirtualBox but the goal is to implement it in a real classroom.
So far everything is going well but I’m having trouble trying to recreate the real setup that is already on the computers in the class.
The computers have 2 HDD. 1 with Windows 10 and Ubuntu and the other with Windows 10. They use rEFInd as a boot manager.
I have a VM already with this HDD and OS setup and EFI enabled and it works fine.
The problem is when I change the boot order to only enable the network boot. It goes directly into the rEFInd menu.

I’m using virtual box. The VMs have a bridged network adapter, DHCP is provided by my home router and I have a dnsmasq (compiled with EFI support) proxyDHCP as shown here: https://wiki.fogproject.org/wiki/index.php?title=ProxyDHCP_with_dnsmasq.
The FOG server is running Ubuntu 18 LTS.

I’ve also tried disabling the dnsmasq service and seting DHCP options 66 and 67 in my router. Same results.

Any idea about how can i do it?

Thanks.