WinCC Unified and PLC weird communication issue

[aamirawan91]

I have created a project in TIA Portal v16 Upd6 with S7-1200 (6ES7214-1AG40-0XB0) and WinCC Unified (PC station). The communication between the runtime and the PLC was perfect, and all the IO fields, buttons, and everything else were working smoothly when the PC was directly connected to the PLC with an Ethernet cable.

The PLC needs to be installed in a location which is at a considerable distance from the PC. I installed the PLC there and connected it to the nearest Ethernet port in the plant, then connected my PC to its closest Ethernet port. Both of these ports are in the same network/subnet. I manually assigned a static IP to the PC, which was configured in the project. I can ping the PLC from the PC, but in the browser, the runtime doesn't seem to be connected to the PLC, and the IO fields etc. are showing an exclamation mark as if there is no connectivity to the PLC.

Now, the interesting part: I brought the PLC back to the PC and connected it directly again; it starts working. Then I connected it back to the same Ethernet port where it was not working, but now it works. It keeps working until the PC restarts or its IP address is changed. If I want them to communicate again, I have to do this weird trick again: connect them directly, and it works; connect them back via network, and it will keep working. Please note that both of these Ethernet ports are in the same subnet. No routing is done or required. PG/PC interface is also set correctly to TCPIP.

Why is this happening, and how can I make it work without having to connect them directly the first time before connecting them indirectly in the network?

 

[aamirawan91]

Update: Found the problem. The PG/PC interface was set to "TCPIP.Auto.1". I changed it to "TCPIP.1" and it works fine.

 

[mk42]

For either your info, or the info of people who come later, TCPIP.Auto assigns itself an IP address automatically in the subnet of the device it's trying to communicate to. Very helpful when you're walking up to a bunch of random PLCs and plugging in (might not have to change your IP for each); but it prevents you from doing Routing/NAT and gives IT departments headaches.

 

[JesperMP]

Yes. Avoid '.auto'.

For either your info, or the info of people who come later, TCPIP.Auto assigns itself an IP address automatically in the subnet of the device it's trying to communicate to. [..] but it prevents you from doing Routing/NAT and gives IT departments headaches.

I think something more is happening when you select the .auto option.
Just like aamirawan91 says, ports are in the same subnet, routing is not needed. Have experienced the same. Usually it is colleagues that start with TIA for the first time, they chose the .auto option, because why not, and then they cant come online.

 

[mk42]

There could be more magic than I mentioned above, that's just the part I know about