I want to establish a Profinet network in my production plant to connect multiple devices, including a PLC, HMI, and multiple Profinet-based Weight Transmitters. I understand that for communication, all devices need to be on the same subnet. However, due to the considerable distance between them, direct connections or connecting through a single network switch is not practical.

My plan is to connect each device to the nearest Ethernet port provided by the IT department for workstation intranet connections in the plant. These ports automatically assign IP addresses to connected computers that may or may not be in the same subnet. For instance, computers on the 3rd floor have IP addresses in the subnet 172.16.103.x, while those on the ground floor use 172.16.102.x. Even though they are on different subnets, computers on different floors can communicate with each other, likely due to routing configurations set up by IT to enable plant-wide communication. I said "likely" because I am not sure.

Now, if I connect a weight transmitter to a port on the 3rd floor, will my PLC on the first floor be able to communicate with it? I'm skeptical because the 3rd floor and the first floor are on different subnets. However, considering that computers on different floors can communicate, possibly due to routing configurations, I'm hopeful. But will this still hold true in my case when the IP addresses are assigned manually to each device?

Furthermore, I'm uncertain about the physical connection between the 3rd and 1st floors. Are their networks physically connected? My understanding of network infrastructure is limited, so I need to clarify these points before proceeding with the project and purchasing equipment.

And If this won't work what are the alternatives? 

Hello aamirawan91

If the partners are in  different subnets then you have to use a more open subnetmask (but bigger networks produce bigger access and more collitions and reduce also speed sometimes). Or you use  routers/gateways for accessing other subnets or vlans.

which protocol do you usw? do you use Profinet realtime protocols or only tcpip based communication? (its because for some special communication you need SCALANCE Switches or components)

Or if you have S71500 PLCs with more than one Enthernet ports (some bigger PLCs have) then you could use also the IP forwarding functionality

Bye Murof

Murof

Hello aamirawan91

If the partners are in  different subnets then you have to use a more open subnetmask (but bigger networks produce bigger access and more collitions and reduce also speed sometimes). Or you use  routers/gateways for accessing other subnets or vlans.

which protocol do you usw? do you use Profinet realtime protocols or only tcpip based communication? (its because for some special communication you need SCALANCE Switches or components)

Or if you have S71500 PLCs with more than one Enthernet ports (some bigger PLCs have) then you could use also the IP forwarding functionality

Bye Murof

 "Or you use  routers/gateways for accessing other subnets" 

Just went through a siemens document "Entry ID:109479139" about cross-subnet profinet communication and it says that profinet real-time communication across different subnets is not possible. Then how would routing work? 

"which protocol do you usw? do you use Profinet realtime protocols or only tcpip based communication?"

I seriously don't know :( I am just planning to connect a weight transmitter from a non-seimens brand and it has profinet connectivity and can easily be integrated to the siemens tia portal profinet system using a GSDML file. I am not sure what protocol exactly this would be. 

"Or if you have S71500 PLCs with more than one Enthernet ports (some bigger PLCs have) then you could use also the IP forwarding functionality"

I actually have an S7-1200 for this project. It has two ethernet ports but i don't think 1200s have this ip forwarding functionality.

So what option am i left with now?