Connecting to ModBus via Ethernet Card

Hello,

I have a computer with ModBus and an Arduino Mega with Modbus and an ethernet shield ENC28J60 attached.

I have 2 radios ( https://www.gegridsolutions.com/communications/catalog/inetii.htm ) the computer goes into the radio and the Arduino is connected to the other radio off-site.

I want to use ModBus to connect from the computer to the Arduino. I was told that I needed to use the EtherCard.h library and set an IP to the Arduino.

Does that make sense? I know the Subnet Mask, Gateway and IP from the receiving (Arduino Side). How do I set those so the Computer can query Modbus using its IPs?

EtherCard.h ( https://github.com/njh/EtherCard )