I want to put a firewall hardware product between a RTU and PLC to block some Modbus function codes (e.g. write coil, read coil). (This firewall product is able to do deep packet inspection on Modbus protocol.)
This firewall hardware has two ethernet (RJ45) ports, IN and OUT. But the Modbus uses serial buses (should be RS485) between RTU and PLC. Hence, to solve this issue, can I use two ethernet – RS485 converters to connect firewall hardware between RTU and PLC? Is there any possible issue?