I'm not sure I understood your observation - probably I am missing something quite basic.
I have a RasPi with Home Assistant installed (controller), with IP address 192.168.1.97, and I have connected to this RasPi an Arduino with the radio module - this is my serial controller.
I would like to use also an ethernet gateway (in home assistant you can have more than one fateway), to receive signals of sensors in some remote rooms, and therefore I am using a W5100, NRF24L01, and an arduino (nano). I am asking through the code that this should have the IP address 192.168.1.66.
What is wrong with this setup?