Creating a forwarded port within an SSH tunnel

Question

I'm attempting to use SSH.NET to create a tunnel from localhost:3306 to port 3306 on a remote machine:

  PrivateKeyFile file = new PrivateKeyFile(@" .. path to private key .. ");
  using (var client = new SshClient(" .. remote server .. ", "ubuntu", file))
  {

      client.Connect();
      var port = new ForwardedPortLocal(3306, "localhost", 3306);
      client.AddForwardedPort(port);
      port.Start();

            // breakpoint set within the code here

      client.Disconnect();
  }

When the breakpoint is hit, client.IsConnected is returning true, but telnet localhost 3306 is not connecting. If I create the connection using Putty instead, and set up the same tunnel there, it succeeds. What have I missed?

Answer 1

By changing the parameters of ForwardedPortLocal to:

    var port = new ForwardedPortLocal("localhost", 3306, "localhost", 3306);

(to make it explicit which interface I was binding to), and adding the following code in just before port.Start();:

    port.RequestReceived += delegate(object sender, PortForwardEventArgs e)
    {
        Console.WriteLine(e.OriginatorHost + ":" + e.OriginatorPort);
    };

I noticed the following being output:

    ::1:60309

The e.OriginatorHost part of this was ::1, which is the IPv6 equivalent of localhost; however, the destination server was using IPv4. Changing the parameters to:

    var port = new ForwardedPortLocal("127.0.0.1", 3306, "localhost", 3306);

forced the tunnel to run over IPv4 instead, and my code then worked exactly as I'd expected it to.

Answer 2

After hitting the same problem and analyzing it, and considering I came to the conclusion that it is a bug (though it might be considered arguable, clearly the behavior surprises users of SSH.NET API).

So I reported it on Unexpected behavior (a.k.a. bug) on local tunnel · Issue #117 · sshnet/SSH.NET · GitHub.

Until it is fixed, the workaround in c# - Creating a forwarded port within an SSH tunnel - Stack Overflow works.