Multiple PC connectivity to ControlLogix

Hi folks, I'm new to this forum, learning my way around. Please bear with me.

At my company, a contractor is wrapping up a project where multiple PLC's are getting condensed into a single CPU (with redundancy), upgraded from PLC5 on Data Highway +, to ControlLogix on Ethernet IP.

They gave us multiple laptops each with an activation for Studio 5000 Logix designer.

Most of the time, we are able to have more than one laptop connected concurrently, for monitoring, making online edits, etc.

But sometimes the network doesn't allow it. This problem is characterized by seeing a link in RSLinx to each of the dozen's of nodes on the network (remote i/o racks, barcode scanners, etc.) but getting a red X on the node containing the CPU. We can't go online, nor can we ping the IP address. Unplugging the other PLC's will allow the one that was blocked access.

Has anyone seen this happen before? All the managed network switches are locked down by our IT department, but they are not seeing anything in the configuration that would cause this issue.

Any suggestions would be greatly appreciated.

There's a limit to the number of connections a CompactLogix (or any other PLC) will accept. However, the latest models should have a fairly large number.

How are you accessing the PLC? Are you going through a switch? Is it managed? My guess is that something between the PLC and the laptops is causing the bottleneck.

Also, I'd try disconnecting the PLC from other devices and seeing if that eliminates the problem. It's possible (depending on the setup) that it prioritizes other hardware (high-speed modules, safety, motion, etc.).

I don't have access to the full network topology, but yes, from any point of access, the path goes through 1 or 2 managed switches. I just find it odd that I can link up with any device on the network except the CPU.

What is the part number of the Ethernet module you are connecting to?

They have a built in web page that provide good utilization statistics. That is the first place I'd start.

If they are Stratix type switches and not setup properly, they will shutdown all ports for a while if an "unauthorized" device is plugged into them. I would make sure the port you are using is set for "PC For Automation". That will prevent it from shutting down. Also any IO devices in a port should be set for "Automation Device", that insures the IO wont drop out. Switch to switch ports should be set as "Trunk" or "Switch For Automation"