I imagine you want to test the approach is software before implementing it in an FPGA.
You can then construct Ethernet frames to be as simple as you like [3].
This question seems like what you might be trying to do [4].
[1] https://stackoverflow.com/questions/12229155/how-do-i-send-a...
[2] https://stackoverflow.com/questions/57133295/how-can-i-liste...
[3] https://en.wikipedia.org/wiki/Ethernet_frame
[4] https://stackoverflow.com/questions/815758/simple-serial-poi...