Modbus TCP/IP & Ethernet/IP


Thread Starter


Hello Friend,
I am in the design stage of a system where there are many devices (PLCs, HMIs, SCADA...) communicating over Ethernet network.
Some of these devices are communicating by modbus TCP/IP protocol while others by Ethernet/IP protocol.

Is it possible to implement Modbus TCP/IP & Ethernet/IP protocol communicating through one single unmanaged ethernet switch!
where both protocols are different? Should I separate them?

Both Modbus TCP/IP and EtherNet/IP will co-exist on the same network, if you need Modbus TCP/IP and EtherNet/IP to talk to each other try a protocol converter from FieldServer.


Jerry Miille

Sure you can do it. They are just packets of data so they will get thru the switch just fine. You probably should take a close look at the amount of traffic on the network and how that might affect your overall performance. If you have data that needs to move between Ethernet/IP and Modbus/TCP devices you will need some sort of a bridge device that supports both protocols. There are several available.

Jerry Miille
713-472-6272 (work)
713-472-0318 (fax)

James Ingraham

Yes, but... (It always seems to be that way, doesn't it?)

EtherNet/IP, in its original form, used broadcast UDP messages for I/O data. The problem with this is that every device on the network sees all of those packets. This can cause some devices to be overwhelmed. There are several things that can mitigate this issue.

1) If you're talking about a few devices (let's pick 3) then you're probably okay.

2) Most managed switches have a feature called "IGMP snooping" that will route broadcast messages only to those devices that want them. The EtherNet/IP implementation guide from Rockwell strongly suggests the use of switches with IGMP snooping.

3) Modern implementations of EtherNet/IP support unicast messages. This is an option during configuration. To my knowledge, only Rockwell products support this at the moment.

Remember that we are only talking about I/O traffic here (and produced-consumed tags between Logix PLCs.) If you're only doing MSG instructions and HMIs you have no issue.

There is never a need to separate the Modbus/TCP and EtherNet/IP traffic, other than the flooding caused by EtherNet/IP broadcasts.

-James Ingraham
Sage Automation, Inc.

Schneider Italy

> To my knowledge, only Rockwell products support this at the moment.

As Schneider Electric is one of the big member of ODVA, all Modicon Ethernet/ip modules support that.