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A Unity Momentum PLC using MBP_MSTR will not open a connection to a device if that device responds with a Window Size of 0.

Goals and Symptoms

This Resolution explains why a Unity Momentum PLC using MBP_MSTR will not open a connection to a PowerLink G3 Controller.  .

 
Facts and Changes
 
A 171CBU9809x Unity Momentum using an MBP_MSTR will not open a connection to a PowerLink G3 Controller if the PowerLink replies with a Window Size of 0 in its [SYN, ACK].  Whenever a [SYN, ACK] packet with a Win = 0 is received, the Unity Momentum will respond with a Reset [RST, ACK].  This behavior will continue as long as the Window Size remains 0. 
  
   192.168.1.10 = Unity Momentum

   192.168.1.120 = PowerLink G3
 

Causes and Fixes

The issue occurs in Unity Momentum firmware versions less than V1.3. 
 
The issue is resolved in versions 1.3 or higher for the 171CBU98090 and 171CBU98091.  The connection will now be established even if the Window Size is 0 in the SYN, ACK.
 
   192.168.1.12 = Unity Momentum
   192.168.1.120 = PowerLink G3



 
Additional Information

Products affected:
  171CBU98090
  171CPU98091


 
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