You can send raw packets with something like this [1] [2].

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...