Unable to read data from the transport connection : An existing connection was forcibly closed by the remote host

c# .net ioexception
Alex picture Alex · Mar 24, 2011 · Viewed 393.1k times · Source

I have a server app and sometimes, when the client tries to connect, I get the following error:

enter image description here

NOTE: the "couldn't get stream from client or login failed" is a text that's added by me in catch statement

and the line at which it stops ( sThread : line 96 ) is : 

tcpClient = (TcpClient)client;
clientStream = tcpClient.GetStream();
sr = new StreamReader(clientStream);
sw = new StreamWriter(clientStream);

// line 96:                 
a = sr.ReadLine();

What may be causing this problem? Note that it doesn't happen all the time

Answer

Hans Vonn picture Hans Vonn · Mar 10, 2017

I received this error when calling a web-service. The issue was also related to transport level security. I could call the web-service through a website project, but when reusing the same code in a test project I would get a WebException that contained this message. Adding the following line before making the call resolved the issue:

System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

Edit

System.Net.ServicePointManager.SecurityProtocol - This property selects the version of the Secure Sockets Layer (SSL) or Transport Layer Security (TLS) protocol to use for new connections that use the Secure Hypertext Transfer Protocol (HTTPS) scheme only; existing connections are not changed.

I believe the SecurityProtocol configuration is important during the TLS handshake when selecting the protocol version.

TLS handshake - This protocol is used to exchange all the information required by both sides for the exchange of the actual application data by TLS.

ClientHello - A client sends a ClientHello message specifying the highest TLS protocol version it supports ...

ServerHello - The server responds with a ServerHello message, containing the chosen protocol version ... The chosen protocol version should be the highest that both the client and server support. For example, if the client supports TLS version 1.1 and the server supports version 1.2, version 1.1 should be selected; version 1.2 should not be selected.

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