For our PLX3x gateways that feature 2 Ethernet-based protocols (such as EtherNet/IP, Modbus/TCP, Profinet, and SIE) we offer 2 variants: the PLX31 and the PLX32. They are essentially identical except for one critical distinction.
The PLX31 variant has a single Ethernet port, and so both protocols share this port and thus the same IP address.
The PLX32 variant has two Ethernet ports, one dedicated to each protocol. Each protocol thus has its own IP address, and most importantly, they absolutely must reside on different subnets. Placing both protocols in the same subnet is not supported.
Therefore, prior to making a decision on whether to buy a PLX31 or PLX32, it is very important to determine whether the protocols will reside on the same subnet or different subnets. If both protocols will be on the same subnet, choose the PLX31 variant. If both protocols will be on different subnets, choose the PLX32 instead.