# Siemens S7 1200 (Negoiate PDU Request/Disconnect Issue) **URL:** \ **Category:** Ignition\ **Tags:** ignition81\ **Created:** [December 8, 2025, 3:46pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683 "2025-12-08T15:46:31Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Noah\_Casey](https://avatars.discourse-cdn.com/v4/letter/n/e480ec/32.png) [@Noah\_Casey](https://forum.inductiveautomation.com/u/Noah_Casey)\ **Post date:** [December 8, 2025, 3:46pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683/1 "2025-12-08T15:46:31Z")
Hi All, I am posting this to see if anyone else has issues with Siemens S7-1200 not connecting/connection breaking randomly. Background information: This server has been running for ~2+ years with no issues for this specific OPCUA connection I have 23 other Siemen S7 1200’s running which are connecting and working. This issue happened randomly no changes have been made to the PLC/Networking/Firewall at least this is what I was told… PLC: Siemens S7-1200, CPU 1214 DC/DC/DC Ignition Version: 8.1.33 Log Errors: ```python NegotiatePDURequest 08Dec2025 14:47:22 NegotiatePDURequest failed. FailureType: DISCONNECTED java.lang.Exception: RequestCycle stopped. at com.inductiveautomation.xopc.driver.api.BasicRequestCycle$AddToQueue.run(BasicRequestCycle.java:120) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.base/java.util.concurrent.FutureTask.run(Unknown Source) at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source) S71200Driver 08Dec2025 14:47:22 Socket connection closed; DriverState was Connecting. java.net.SocketException: Connection reset at java.base/sun.nio.ch.NioSocketImpl.implRead(Unknown Source) at java.base/sun.nio.ch.NioSocketImpl.read(Unknown Source) at java.base/sun.nio.ch.NioSocketImpl$1.read(Unknown Source) at java.base/java.net.Socket$SocketInputStream.read(Unknown Source) at java.base/java.io.InputStream.read(Unknown Source) at com.inductiveautomation.iosession.socket.AsyncSocketIOSession.run(AsyncSocketIOSession.java:71) at java.base/java.lang.Thread.run(Unknown Source) ``` ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/6/e60e6c63fdf6049c92638a2dbe3f02b0072f9a29.png) I’m able to ping the PLC from the server the Ignition gateway is running on. We have checked the switch and everything seems to be fine. Inside of the OPC UA device connection the status shows Disconnected. I have tried deleting then connecting and reestablishing this makes the error occur again. Any insight would be greatly appreciated, I am assuming it is a PLC issue. I don’t have experience troubleshooting or using PLCs directly, only connecting them to Ignition. If anyone has had this issue before and knows a fix please let me know. ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [December 8, 2025, 3:55pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683/2 "2025-12-08T15:55:23Z")
> [@Noah\_Casey](#): > > `Connection reset` This, in my experience, always comes from the PLC, or from an overloaded firewall along the path. I don't do Siemens much myself, but there are many reports here of connection limits in the PLC being a sporadic problem. Especially if systems outside Ignition have been added that talk directly to the same PLC. ---
**Author:** ![Cody\_Morgan](https://avatars.discourse-cdn.com/v4/letter/c/db5fbb/32.png) [@Cody\_Morgan](https://forum.inductiveautomation.com/u/Cody_Morgan)\ **Post date:** [December 8, 2025, 3:57pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683/3 "2025-12-08T15:57:03Z")
I was just about to give a similar answer. This looks like the PLC is closing the connection. Siemens PLCs have a limit to how many connections they can have. You should check the PLC diagnostics to see if there are too many active connections. ---
**Author:** ![Noah\_Casey](https://avatars.discourse-cdn.com/v4/letter/n/e480ec/32.png) [@Noah\_Casey](https://forum.inductiveautomation.com/u/Noah_Casey)\ **Post date:** [December 8, 2025, 3:59pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683/4 "2025-12-08T15:59:02Z")
@pturmel and @Cody_Morgan thanks for the quick replies, I’ll go ahead and start diagnosing on the PLC side. ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [December 8, 2025, 4:11pm UTC](https://forum.inductiveautomation.com/t/siemens-s7-1200-negoiate-pdu-request-disconnect-issue/112683/5 "2025-12-08T16:11:35Z")
One cause might be the PLC is out of allocated S7 PG/PC/OP connections (whatever type Ignition uses I can't remember).