Acquire tag value via MODBUS, which LAN Port to use?


I have a Flexy205 connected, via Ethernet/IP, to three machines with Rockwell PLC and from which I collect data through specific Flexy tags.
The customer asks me to be able to collect this data through his LAN where a M.E.S. (Manifacturing Execution System) application is connected.

Since the three LAN ports of the Flexy205 are already used to connect to the three machines and the WAN port is connected to the customer network for Internet access, what must the customer do to be able to access the data?

Does he have to install an ethernet switch on one of the 3 LAN ports and then connect a machine and its MES application from this?
Can he uses the WAN port to access the data, as it is already connected to the customer’s LAN network?



You can use any of the 3 LAN ports on the Flexy205. If you require more than 3 LAN ports, you can put a switch to the port, and they will still communication with the Flexy.

As for the WAN port, the LAN and WAN networks are on separate networks. By default, he will not be able to access the PLC through the WAN Port.

However you can Use NAT translation with the Flexy to allow the WAN network to be able to access the LAN side.

Hi Kevin,

thanks for your kind and quick reply.

Great to know, this is the solution I’ve proposed to the customer!

The access to PLC is reserved only for us for remote support, the customer needs just to poll Flexy tag value via Modbus using his application, because the Flexy is already connected to the customer LAN via the WAN port so Flexy can access to internet, he asked me if the additional switch is required or if he can read the Modbus Registers also via the WAN port also because the Flexy via the WAN port (using DHCP) is already on the local LAN, instead if they have to use one of the Flexy LAN port, the have to put their application on the machine LAN.

From what I’ve seen, I need only to activate the Modbus flag for each tag I need to serve to the costumer application, naming the Modbus Register, isn’t it?


The WAN port on the Flexy is not tied to the LAN side. The WAN port is only used to get internet to enable the VPN tunnel. The WAN side will not be able to access the MODBUS registers on the Flexy, without the use of NAT1:1.

If the WAN network needs this data, they will need to NAT1:1 to the Flexy only. See the guide attached.

NAT 1to1 without vpn.docx (685.6 KB)

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Thanks Kevin.

Could you kindly check the attachment, because I can’t download it.


My apologies.

You can find that document on the following post:

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