Logix 5550 to Server Communications

Dear Sirs,
I have five Logix 5550 PLC's in use. Also five console computers, three workstation computers, and two servers. (The PLC's are 1756L1M3 series A.)

At the moment everything communicates with everything else. We tried to change the IP addresses so that IT can secure the network, and it looks like the Primary Server and the PLC's lost communications.

When the system was originally set up some 17 years ago everything was on the same subnet . . . Then 'they' moved the Servers into a separate subnet. The PLC's and workstations are addressed around 192.168.11.50 and the server is 192.168.10.44

First question. When I set up two PC's with different subnets (10 versus 11) I can not ping between them. (Both are connected to the same switch. When they are in the same subnet I can ping between them.) What is the black magic that enables the Servers and workstations and PLC's to ping across different subnets?

The Servers and the consoles are Windows 2000, and the workstations are Windows 7. The Servers used to use RSLinx to communicate with the PLC's. (At least RSLinx Service was, and still is, in use. License installed.) They virtualized the Servers - no more physical Server computer for me to yell at or push the power button on. I did not actually do the work - but I have been told that 'they' had to install 'Factory Talk' to get the virtual server to communicate with the PLC's.

What can I look at on the Server to see if Factory Talk is enabling communications between the PLC and the Server?

When we changed all the IP addresses, we were able to get the consoles and workstations communicating with the Server. It looks like we did not get the Server to communicate with the PLC's. Any ideas on what we might have missed? (We could ping the PLC's from the Server.)

Poet.

Mad_Poet said:

What is the black magic that enables the Servers and workstations and PLC's to ping across different subnets?

Click to expand...

https://learningnetwork.cisco.com/thread/28157

The above thread will go into detail on how you can ping across different subnets.

http://www.plctalk.net/qanda/archive/index.php/t-79162.html
This thread may also help you out.

Regards,

This probably isn't an appropriate setting for a broad introduction to IP subnetting; there are thousands of textbooks and tutorials for that.

But it's worth discussing that the most common reason for this kind of issue is the Default Gateway setting on the 1756-ENET or 1756-ENBT modules.

When TCP/IP devices are on the same subnet, it doesn't matter what the Default Gateway setting is. The Ethernet switches just get the data from one port to another using their "Level 2" switching function.

But when the devices are on different subnets, all the traffic has to go through a device that's functioning as a "gateway". Usually this is a router, and I'll bet that MadPoet's IT department installed one between the network that handles the servers and workstations and the network that handles the PLCs.

The 1756-ENET or 1756-ENBT modules are probably still configured for no Default Gateway, or for something like 192.168.10.1 that isn't correct for the system.

Don't rely solely on PING for network troubleshooting. For ControlLogix, at least type the IP address of the 1756-ENxT module into a Web browser to be sure that you're actually looking at a ControlLogix Ethernet module.

This is a great opportunity to engage with your IT and networking group so that they understand your needs and you understand their work.

The Ethernet module does have the default gateway set. When I tried changing things over, I changed that as well as the modules IP address . (From the 11 subnet to a 13 subnet.)
Poet.

Ken > Don't rely solely on PING for network troubleshooting. For ControlLogix, at least type the IP address of the 1756-ENxT module into a Web browser to be sure that you're actually looking at a ControlLogix Ethernet module.

Dear Ken,
I will definitely have to try that.
Poet.

Okay, so what device is a the IP address that is configured for the Default Gateway on the 1756-ENET/ENBT ?

This might also be related to the browsing method of the RSLinx drivers; the "EtherNet/IP" driver will usually not browse across a router, while the "Ethernet Devices" driver knows the IP address of the ControlLogix and has no problem with browsing.

Another very good diagnostic tool is "TCPing", freeware from Eli Fulkerson. TCP Port 44818 is used by ControlLogix on Ethernet.

Ken > Okay, so what device is a the IP address that is configured for the Default Gateway on the 1756-ENET/ENBT ?

Dear Ken,
The Guru says the device is a router - probably built into the smart switch.
My Ethernet module is a 1756-ENET/B (or equivalent). I tried accessing it by typing the IP address into a web browser . . and got a '501 not implemented' error. The Guru thinks that device is so old it can't make a web page . . .

I can ping the Gateway, it does respond. When I tried to access it by way of its IP address in a web browser it denied me any access.

(I appreciate all the help and suggestions I can get. Thanks.)
Poet.

The 1756-ENET definitely has an embedded Web page, but you're probably using a modern Web browser that uses HTTP 1.1, and the module is too old to understand its request. You can turn off HTTP 1.1 in some Web browsers.

My troubleshooting steps would be:

1. PING, then ARP -A.

This will give you the MAC Address of the device that's responding to your PING. The MAC Address is listed on the sticker on the side of the 1756-ENET module.

2. TCPing utility, using Port 80 (to verify Web browser) and Port 44818 (to verify EtherNet/IP).

3. RSLinx with the Ethernet Devices driver. If your version supports it, add ":EIP" to the end of the IP address to skip the PLC/SLC old protocol support probe that uses TCP Port 2222.

Since you describe the work being done on the servers as a security measure, there's probably something that's been done in the name of security that is interfering with the ability of the servers to communicate with the controllers.

Persist, and keep bringing your IT guys into it. You'll find the problem.

Dear Ken,
Many thanks. More things I can try.

I also just stumbled across some old notes . . .
In the PLC program there is an I/O configuration area and there is a PLC IP address in there. While I did change the IP address inside the ENET module . . . I did NOT change it in the configuration.

Do I need to change the address in both places? (The ENET module and the program configuration.)

Poet.

Great question !

The 1756-ENxT modules all hold their configuration in their own nonvolatile memory. You can pick one up and move it to a chassis all by itself and it will still power up with the IP address that was saved into it.

This is unlike the PLC-5E and SLC-5/05 and MicroLogix 1100/1400. In those devices, the IP address is part of the PLC program. If you download a new program with a new IP address, the controller's IP address changes.

In general the place in the RSLogix 5000 program where you enter the IP address of your local Ethernet module is just so the program can tell if all your I/O devices on the network are on the same subnet. If you change it in RSLogix 5000, I don't think it actually tries to change it in the module (but I haven't checked in years, since that's not how it's supposed to work).

90% of the time, I change the IP address of a ControlLogix family Ethernet module using a right-click in RSLinx Classic. 10% of the time I'm getting new ones out of the box and using BOOTP/DHCP.

Dear Ken,
I tried changing the Ethernet address of the module with RSLinx, and then downloaded the PLC program and checked the I/O configuration. The address did not change in the configuration.

I'm guessing now, but could it be that I changed the address of the module, allowing it to ping. I changed the Server address (in the controller tags) so the PLC could send stuff to the Server . . . but I did not change the address in the I/O configuration. Could it be that the Server tried sending stuff to the PLC, but because the configuration had a different address it ignored the instructions from the Server? (As in these instructions can't be for me because that is not my address.)

Anyway, I'm hoping that all this becomes academic in short order. The Guru decided today that it would be a lot easier to move seven other computers off 'my subnet' and into someplace else rather than trying to change eight computers and five PLC's to a different subnet.

The Servers are also supposed to be changing their IP addresses - but we've been down this road before. All I had to do for them was change the addresses inside the PLC controller tags. (One place for each Server.) Worked good last time.

Thanks,
Poet.

Dear Ken,
That was just too cool.
My console computers have internet explorer version 6 on them . . . and they would not access the PLC E-net module.

I have an old laptop, Windows 2000, with internet explorer 5 on it. So I set the IP, unplugged the console computer and plugged in the laptop. Pinged the PLC and then used I.E. 5 and the PLC E-Net Module came right up. Gave me the configuration data and the module layout in the PLC. Just too cool.

Thanks,
Poet.