Configuring a large number of Modbus devices can be arduous. Unlike Ethernet switches, where routing is accomplished automatically through an ARP table, the routing mechanism for Modbus gateways with multi-serial ports is much more complicated.
The main purpose of a routing table is to indicate which Modbus device (slave ID) is connected to which serial port on a gateway. Once a gateway receives a Modbus request for a specific Modbus device, it can dispatch this request via the referring
routing table to the serial port that connects to the target Modbus device. The routing table needs to be maintained for troubleshooting and maintenance; however, creating and managing a routing table is laborious.