We have some ~10-20 year old PLC's that seem to have trouble communicating with a new switch upgrade. We change from the Avaya 4550 to the Avaya 4850, but we have been seeing some weird symptoms. Some of these PLC's will stop communicating at random times, until rebooted. I'm trying to get operations to reseat the ethernet connection to see if that can bring communications back.
After issues in production we reverted back to the old 4550's and see the issue go away. The devices don't disappear.
We aren't utilizing a majority of the security features on either of the switches, just RSTP on the edge ports. The old and new switches are configured basically the same.
My only thought is that this is a problem with auto-negotiation, So i turned it off and manually configured the port speeds, but the issue still remained. Most of the PLC's run at 10 half duplex, with some at 100 full. I've done a bunch of packet captures, and all I can see is that the devices stop responding.
Anyone have thoughts on this?
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