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Kepware Knowledge Base: Solution

Unable to Connect to Devices when Using a Windows Server 2012 or 2016 Machine

Last Update: 1/16/2019
A server project running on any operating system besides Windows Server 2012 or Windows Server 2016 can connect to and receive data from a device. When the same project is used on a Windows Server 2012 or 2016 machine, it fails to connect to the device.
Possible Cause:
With the introduction of Windows Server 2012, Microsoft enabled the Explicit Congestion Notification (ECN) on all network adapters by default. ECN adds information to the packet header that allows properly-equipped network gear to reduce network traffic speed when needed. Although this feature is available on older server operating systems, it was not enabled by default until Windows Server 2012 (and is still on Windows Server 2016). When ECN is enabled, some older devices will drop or reject the packets because of the manipulated header.
  1. While logged in as an administrator, open a DOS command prompt
  2. Type "netsh int tcp set global ecncapability=disabled" and press Enter.