S7 - Ethernet communications problem between PC and PLC

[RMA]

I'm sitting here in an office at the customer's factory - all alone, everybody else is out on site - and I want to do some testing, but the Ethernet link to the PC, which was fine two weeks ago, doesn't work any more.

I'm using my own PC, which the customer IT guy set up so that I can run on their Intranet, to which the PLC is also connected. The funny thing is that I can ping the PLC OK, (possibly more to the point, when I switch the PLC off the ping fails), but even the backup copy of the program from Sep. 12th, when I know from my work log I was testing online, doesn't work anymore. The command to show all users turns up no other users.

The windows firewall is switched off, the PG/PC interface is set to TCP/IP(Auto) NVIDIA nForce Networking and I'm running out of ideas!

Since I'm not that well up on network stuff, here's the network setup:

The PLC IP address is 191.168.94.190 (and as I said, I can ping it)

On the development PC ipconfig returns the following:

IP address: 191.168.92.30
Subnet mask: 255.255.252.0
Standard gateway: 191.168.94.254

The one thing I can't be sure of is whether or not the IT guys have modified anything in my absence, so the first question is, does the above look like it ought to work?

Apart from that, any other ideas of where to look would be most welcome, otherwise I'm not going to get a lot more done this week!

[PeterW]

shouldn't the gateway be the same sub net as yourself, i.e. the 94 = 92. (Or your address 92=94)

[RMA]

That's basically what I was wondering as well, but since I certainly haven't modified anything (I don't even know how to!) I wasn't sure, so I was hoping some network guru could tell me for sure.

[PeterW]

The how to, is to right click on My Network Places and select properties, for me here I get about 4 choices and I would right click and select properties of Local Area Connection.

Scroll down and select Internet Protocol (TCP/IP) and properties on that enables you to change the address or gateway etc.

If you have administrative rights of course.

The fact you can ping the PLC is confusing.

[JesperMP]

Originally Posted by PeterW

The fact you can ping the PLC is confusing.

No, you can allways ping between devices if they are directly connected with each other.

[RMA]

I went into the Lan properties box, but initially couldn't find anywhere where I could modify the IP address, however, while I was in there anyway, I decided to run through the list of elements. The following were listed:

Client for MS Networks
File and Printer access for MS Networks (loosely translated from the German)
QoS Packet planner
Profinet IO RT-Protocol
Simatic Industrial Ethernet (ISO)
Internet protocol (TCP/IP)

All of them are checked but when I click on the top 5 I get the option to install and de-install them, but when I click on TCP/IP the de-install option is greyed out. Looking at it's properties, the button for automatically receiving an IP address was marked (the top button)! So where the data that IP-config presented is coming from, I've no idea!

[RMA]

Although I'm certain that the TCP/IP(Auto) PG/PC Setup was correct, I decided to change it to the non-Auto version just to see what happened. What happened - suddenly the communications are working again! Then I changed back to TCP/IP(Auto) and everthing carried on working fine!

Evidently something, somewhere, had got its knickers in a twist, but I haven't a clue what!

Frankly, right now I don't really care, I'm just pleased that after about 6 hours of wasted effort (I initially started on this yesterday) I can get back to some useful work!

Thanks for the help though, as is often the case, the effort of co-ordinating your thoughts to create an understandable post is often as useful as the answers.

Cheers

Roy

[PeterW]

From Start - Settings - Network Connections I get this folder.




On right clicking and selecting properties I get this pop-up.




Scrolling down to Internet protocol (TCP/IP), highlighting it and selectiung properties I get this





From here you canm change the IP address

[JesperMP]

In the TCP/IP(Auto) setup, there is an option to set additional IP addresses that must be used by STEP7.
Maybe this is where the 191.168.92.30 address came from.

[RMA]

Peter, that's exactly where I was, curiously enough, in your screen dump the uninstall button is also greyed out.

Even though everything is working fine now the button for "Obtain an IP address automatically" is still set and the parameter boxes underneath are empty. I would have expected them to have shown(greyed out) the settings which Step7 (or whoever) had set up.

I guess I'll have to settle for the fact that there are some things (many things?) I'll never understand, especially where Microsoft and Siemens are concerned!

Jesper, I had a look in the properties box for TCP/IP(Auto) and manged to increase my confusion one notch more! This is what's in there:

IP address Subnet mask Net address 1st IP address Last IP address
192.168.94.241 255.255.255.0 192.168.94.0 192.168.94.241 192.168.94.250

How do I persuade the editor to keep my spacing???