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Why does our Windows service app's TCP connection keep failing with an "Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host." error?


I have a WCF based windows service that reads from an external device (scale) via a TCP connection.
A connection is made to the device when the service initially starts up.
This is the code we use to initiate the connection to the device:
scaleData.Client = New TcpClient(ipAddress, (portNumber))
scaleData.Stream = scaleData.Client.GetStream()

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The service is hosted as a Windows service (as opposed to through IIS).

We have two applications that pull data from the WCF service,
an asp.net application and a winforms application.

The request returns data from the stream to the caller/client.
                    Dim bytes As Int32 = scaleData.Stream.Read(data, 0, data.Length)
                    responseData = Text.Encoding.ASCII.GetString(data, 0, bytes)c
 Catch ex As IOException
                    exceptionMsg = String.Format("IOEXCEPTION!!! :: {0}", ex.Message)
End Try

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Both the (winforms) test application, web application and windows service all reside on the same Windows 7 machine.

For the most part, this configuration works fine. But occasionally it fails.(we can't quite determine the pattern to it or specifics to it's occurrence) with the following message:
Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host

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Upon failure, we now added retry logic to try to reestablish the TCP connection and read from the stream,
but that doesn't seem to fix the issue. I've also got logging enabled which captures the exceptions to a log file. All the log shows is the above mentioned message.

Does anyone have any suggestions as to what is going on here?
Is this a Firewall/Port/virus scanner issue?

How do we best proceed?

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2 Solutions
Dan McFaddenSystems EngineerCommented:
Since you're using Win7 to host the service (as opposed to a server OS), I am curious to how many tcp connections you are opening to the endpoint.  Win7 has a connection limit of 20.  If you were to try to establish a 21st connection, the service host would deny the connection.

As a suggestion, I would try to track the number of connections to the service endpoint to see if you occasionally exceed 20.  A quick way to watch active connections (in and out) is to download TCPView from Sysinternals.  It will display open udp/tcp connection details including origin, destination and a few other interesting tid-bits of info.

Another thought, are you establishing the connection via IP address to port 80/tcp (based on reference to IIS), if you have a proxy on your network that manages connections, it could also be a source of connection problems.

Dan McFaddenSystems EngineerCommented:
Carl TawnSystems and Integration DeveloperCommented:
Well, the error indicates that it is the remote device that is dropping the connection.  Perhaps it is disconnecting after a period of inactivity on the connection.

You starting point should probably be the supplier/documentation for the device you're connecting to.
jxbmaSoftware ConsultantAuthor Commented:
Ultimately, since we are trying to read to the device on demand, I reestablish the TCP connection on every request.
This seems to work for now (until I see another better solution).

Thanks for the responses,
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