title: Why does this connection sometimes closes (RESET) Flags: 0x014 (RST, ACK) TCP
body: <p>We have an issue on the acceptance environment during a handshake process. External service tries to send some data and during handshake sometimes we reset the connection after timeout around 2 minutes. In the picture below you can see communication between two services our server IP ends with 11 and external service IP ends with 5.
  <a href="https://i.stack.imgur.com/3yObI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3yObI.png" alt="RST, ACK" /></a></p>
  <p>The strange thing is that is more than 50% it's working and when it's happened (they will try to send us data every hour and we reject each of them). In between, if we send data to them the next try from them will be successful (picture below). In this case, they use the server IP ends with .6.
  <a href="https://i.stack.imgur.com/wrrry.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wrrry.png" alt="success" /></a></p>
  <p>Does someone have a clue what can be a problem here? We have tried to find something in our logs but nothing wasn't logged. Some help regarding additional logging will be appreciated (we tried with <a href="https://docs.microsoft.com/en-us/dotnet/framework/network-programming/how-to-configure-network-tracing" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/framework/network-programming/how-to-configure-network-tracing</a> and <a href="https://docs.microsoft.com/en-us/dotnet/framework/wcf/diagnostics/tracing/configuring-tracing?redirectedfrom=MSDN" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/dotnet/framework/wcf/diagnostics/tracing/configuring-tracing?redirectedfrom=MSDN</a>). Our backed in written in C# WCF. The additional fact, when we try to send data to them we never have an issue, it's always working.</p>