Doing Telnet from one System to another System via another system

As I mentioned, you "break into" a protected network. And the goal of the firewalls is to hinder access from outside to inside. And as you stated, you want to "break into" your own system. If this is true, you have the means to:

A) either change firewall settings, to let MineOne (but only that machine) get trough it, and reach DestOne directly,

B) or to install a proxy (as Dave explained). Proxying is dangerous! Why? Because it is blind if you don't implement access control, letting somebody use the proxy, you open your whole protected area. So be careful to use proper access control.

C) or even better, to install a monitoring system on SourceOne to monitor DestOne, and you could expose the monitor or service via the firewall

D) remotely execute code on SourceOne from MineOne. Have you tried psexec[^]? What you can do in psexec, you can do also in c#[^]. So if you have a user with proper rights on SourceOne, you can remotely execute something like tcping[^] for example.

There is an other scenario I can imagine: SourceOne is a gateway between two physically separated networks. If this is the case, option A is not usable.

Just a note telnet, is dangerous, since it is not encrypted. I you can, switch to ssh.

I decided to make an exe file that should be present in SourceOne Computer (somewhere in HDD), I set the environment variable for its path.

This exe file will accept the 2 parameter and will test the connectivity from SourceOne system itself and return the response back.

Now I have to catch that response and show it back to my main exe (application) which is running in MineOne computer system. In this way I can fix it.

I tried in my local system, but going to try as per the real scenario... Hope this should work.

Code Here

Imports System.Net.TcpClient
 Sub Main()
        Dim cmdLineparams As String() = Environment.GetCommandLineArgs()

        If cmdLineparams.Length > 2 Then

            Dim IP= cmdLineparams(1)
            Dim port = cmdLineparams(2)

            ' Check Input Parameter for null/empty/white-space characters  
            If String.IsNullOrEmpty(IP) Then
               ' MsgBox("Parameter 1 Invalid", MsgBoxResult.Ok)


            ElseIf String.IsNullOrEmpty(Port) Then
               ' MsgBox("Parameter 2 Invalid", MsgBoxResult.Ok)
            Else
                Dim checkConn As New TcpClient
                Try
                    checkConn.Connect(IP, Port)
                    return true
                Catch ex As Exception
                    Return false
                End Try
            End If

        Else
'            MsgBox("Two parameters are required", MsgBoxResult.Ok)
        End If
    End Sub