Profinet Network Setup across Different Subnets in a Plant

[aamirawan91]

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?

 

[JesperMP]

In Profinet, the IO Controller assigns the IP addresses to the IO Devices. You cannot let a 3rd party assign the IP addresses, i.e. the DHCP server of the office network.
Theoretically, you could coorporate with IT that they reserve IP addresses for you to use, but even then I would not mix the Profinet with the office network. Even if it is possible to mix, the IT department have totally different priorities to production. F.ex. IT will start server maintenance or network changes when the office workers have gone home. But at that time the production is still running.
If you have a large distributed plant, then you should design a corresponding Profinet network to match. Profinet cable is not expensive.

 

[aamirawan91]

In Profinet, the IO Controller assigns the IP addresses to the IO Devices. You cannot let a 3rd party assign the IP addresses, i.e. the DHCP server of the office network.
Theoretically, you could coorporate with IT that they reserve IP addresses for you to use, but even then I would not mix the Profinet with the office network. Even if it is possible to mix, the IT department have totally different priorities to production. F.ex. IT will start server maintenance or network changes when the office workers have gone home. But at that time the production is still running.
If you have a large distributed plant, then you should design a corresponding Profinet network to match. Profinet cable is not expensive.

Btw this weight transmitter is actually a non-seimens product but have the profinet connectivity to integrate it to the siemens profinet network using a GSDML file in TIA Portal. Just a piece of information.
Alright, So if they reserve ip addresses for my transmitters but I am connecting them to the ports on the 3rd floor will be PLC be able to find and connect to them? Though IP addresses will be assigned by the PLC but they are still in the different networks physically. Aren't they?

 

[JesperMP]

It might be possible to mix Profinet with the office network, maybe not; even if it is possible I would not do it.
Profinet cable is not expensive.

If the Profinet IO Controller is connected to the IO Device via regular Ethernet switches, then it can see the IO Device. It does not matter that it has to go through multiple switches to find the IO Device.
But office networks may be complex and IT may have split it into multiple networks, connected together via routers. IT may have rules and limitations that may block a Profinet Device to be integrated into the same network system.
Troubleshooting Profinet that is mixed with office network will be difficult.

 

[aamirawan91]

It might be possible to mix Profinet with the office network, maybe not; even if it is possible I would not do it.
Profinet cable is not expensive.

If the Profinet IO Controller is connected to the IO Device via regular Ethernet switches, then it can see the IO Device. It does not matter that it has to go through multiple switches to find the IO Device.
But office networks may be complex and IT may have split it into multiple networks, connected together via routers. IT may have rules and limitations that may block a Profinet Device to be integrated into the same network system.
Troubleshooting Profinet that is mixed with office network will be difficult.

Alright. Are you saying "Profinet cable is not expensive" to tell me that I should just directly connect the IO device to my PLC instead of the IT ports? Well, Yeah that's possible and would rule out every network uncertainty but laying profient cables that long might not be feasible. I think the maximum distance is 100 meters for a profinet cable. Yes i could use switches but that would add extra cost and my manager wants me to use the nearest ethernet ports to connect the transmitters to the PLC through company's network. Anyway, I think i should just tell him that it's best we use switches and just directly connect the transmitters to the PLC. Can we go over 100 meters if we are using switches in between the PLC and IO device (transmitters)?

 

[JesperMP]

Yes you can extend Ethernet with switches.

 

[aamirawan91]

Yes you can extend Ethernet with switches.

Thanks mate

 

[joseph_e2]

I'm not necessarily endorsing this method for your system, but...
At my last place, we had a large physical IT network. Each port on each switch was assigned individually to a particular VLAN with routing set up so that traffic on each VLAN was segregated from the others. We had some machines on a "machine" VLAN and it worked...BUT...we only used it for programming/monitoring, not for IO. All machine IO was always on a physically isolated local network on a completely different and non-routable subnet than the VLANs.

It's possible that IT can set up a VLAN for your Profinet devices that would properly separate traffic so it all works.
It's also possible (likely...) that something will go wrong at the worst possible time. As Jesper noted, you'll be far better served by an isolated physical network that's independent of the office IT system and not managed by them at all. It may be a little more expensive up front but will serve you better in the long run.

 

[Lare]

Profinet IO is time critical and needs profinet capable switches (It means use Siemens Profinet switches unamanged or managed and you won't have problems).
(Or at least managed switches which have Profinet functionality mentioned on manual

Part of Profinet IO traffic is transferred on above normal ethernet TCP packets and normal ethernet (managed) switches won't pass this Profinet IO data trought and firewall on switch destroys it. This leads to communication breaks or profinet IO won't work at all.

Profinet PLC communication (PLC <> Scada) is not as time critical as IO, so it can work trought normal ethernet switches. Still it is not recomended to use non profinet switches.

Unamanaged switches maybe work for both as there isn't firewalls on switches which would block any data.

 

[JesperMP]

Profinet IO is time critical and needs profinet capable switches (It means Siemens Profinet switches).

As long as it is not Profinet IRT, then switches that support QoS are sufficient.

 

[Lare]

As long as it is not Profinet IRT, then switches that support QoS are sufficient.

True. Siemens switches have settings enabled by default for profinet communications. For non Siemens switches you maybe need to adjust firewall settings or on worst case switches don't support Profinet IRT at all on site.
For CPU to PC communications haven't had any problems as it isn't IRT.

 

[aamirawan91]

True. Siemens switches have settings enabled by default for profinet communications. For non Siemens switches you maybe need to adjust firewall settings or on worst case switches don't support Profinet IRT at all on site.
For CPU to PC communications haven't had any problems as it isn't IRT.

Do I need to worry about it when using a normal non-siemens network switch to connect my PLC to the weight transmitter?

 

[Lare]

Do I need to worry about it when using a normal non-siemens network switch to connect my PLC to the weight transmitter?

I assume that weight transmitter data is IRT communication to PLC as it is Profinet IO so yes and switches should have Profinet functionality.
Transmitters datasheet should say which communication is used.
(It would be at least case if you would have Profinet IO cards there like ET200S or ET200SP series)

If you would have another PLC near weight transmitters and all transmitters connected to this "remote" plc then you could communicate it to another PLC or PC on non profinet network.
S7 communications outside of PLC isn't profinet IRT, but transmitters IO data to PLC can be problem.

 

[mk42]

Do I need to worry about it when using a normal non-siemens network switch to connect my PLC to the weight transmitter?

Plugging into the IT infrastructure and hoping for the best is a bad plan.

Any switch can do regular Profinet IO traffic, in theory. In practice, some switches block certain functions by default. Cisco switches, for example, block traffic that has a Priority assigned, but no VLAN, (which is how PN works) unless you enable some voip setting, and then it works fine. Some unmanaged switches block some of the diagnostics, which also causes issues. Many many industrial network brands sell switches that have been specifically tested for Profinet; office grade stuff will probably work but you might need to fight with tech support more to get it just right.

I would be very suprised if a weight transmitter was using IRT (typically reserved for drives and other high speed motion components), it is almost certainly regular profinet IO. Data sheet will confirm, though. IRT requires special switches or direct connections, as has been stated. Even from Siemens, very few switches support IRT; there's only a handful and they're 4 port only.

In order of preference:
Option 1) create a completely separate OT network infrastructure with switches distributed around the facility
Option 2) use fiber optic cable for the run back to the main PLC instead of copper cable (much longer lengths are allowed)
Option 3) negotiate with IT that you can do what you want, and pray that they are merciful. VLANs can make it happen, but you're still trusting that they do maintenance at appropriate times. As others have said, they won't.

 

[Lare]

Plugging into the IT infrastructure and hoping for the best is a bad plan.

Any switch can do regular Profinet IO traffic, in theory. In practice, some switches block certain functions by default. Cisco switches, for example, block traffic that has a Priority assigned, but no VLAN, (which is how PN works) unless you enable some voip setting, and then it works fine. Some unmanaged switches block some of the diagnostics, which also causes issues. Many many industrial network brands sell switches that have been specifically tested for Profinet; office grade stuff will probably work but you might need to fight with tech support more to get it just right.

I would be very suprised if a weight transmitter was using IRT (typically reserved for drives and other high speed motion components), it is almost certainly regular profinet IO. Data sheet will confirm, though. IRT requires special switches or direct connections, as has been stated. Even from Siemens, very few switches support IRT; there's only a handful and they're 4 port only.

In order of preference:
Option 1) create a completely separate OT network infrastructure with switches distributed around the facility
Option 2) use fiber optic cable for the run back to the main PLC instead of copper cable (much longer lengths are allowed)
Option 3) negotiate with IT that you can do what you want, and pray that they are merciful. VLANs can make it happen, but you're still trusting that they do maintenance at appropriate times. As others have said, they won't.

Have tested Siemens Remote IO for cisco non profinet switches years ago. Switch was configured to allow VoIP and all other settings which was mentioned for profinet. Remote IO was seen on PLC, but on non regular intervals IO dropped for few seconds on remote side. Still IO worked several hours and then suddently dropped.
CPU showed errors on communications and switch log files showed that firewall still blocked some profinet packets sometimes.
After all it was needed to reroute all Remote IO to direct cabling instead of non profinet switches between as we didn't have cisco profinet series switch.