A VPN (Virtual Private Network) extends a private network across a public network, and enables users to send and receive data across shared or public networks similar to being directly connected to a private network. This provides a few benefits to applications running across the VPN. These benefits include:
- Management of the private network
Virtual Private Networks allow employees to securely access a corporate Intranet while located outside the office. VPNs are used to securely connect geographically separated offices of an organization, thus creating a cohesive network. On the other side, Internet users could secure their wireless transactions with a VPN. In doing so, geo-restrictions and censorship are circumvented.
The .NET Framework includes the System.Net.NetworkInformation namespace, which provides access to network traffic data, network address information, and notification of address changes for the local computer. The System.Net.NetworkInformation namespace also contains classes that implement the Ping utility that can used to check whether a computer is reachable across a network.
The NetworkInterface class provides configuration and statistical information for a network interface. And, the getAllNetworkInterfaces method returns objects that describe the network interfaces on the local computer.
RasPhone and RasDial
RasPhone is a wrapper around the Win32 RasPhonebookDlg API, and is typically used when an interface may be allowed. RasDial is a wrapper around the Win32 RasDial API, and is typically used in situations where no user interface can be shown.
The aim of today's project is to show you different ways you can determine a VPN connection and some methods on how to disconnect and connect to a VPN. Start a new Visual Basic Windows Forms project and add two buttons onto the form.
Open the code window and add the necessary Namespace to your project:
Add the following sub procedure:
Private Sub CheckConnection() Dim niVPN As NetworkInterface() = _ NetworkInterface.GetAllNetworkInterfaces Dim blnExist As Boolean = _ niVPN.AsEnumerable().Any(Function(x) x.Name = "VPN Name") If blnExist Then MessageBox.Show("VPN Exists") Else MessageBox.Show("VPN Does Not Exist") End If End Sub
This is probably the easiest and most convenient way of determining whether or not you have a VPN connection. It makes use of the NetworkInterface class and uses LINQ to loop through all the known network interfaces. If a VPN connection exists, it returns true; else, false. Use this sub procedure when button 1 has been clicked:
Private Sub Button1_Click(sender As Object, e As EventArgs) _ Handles Button1.Click CheckConnection() End Sub
Add a new class to your project and name it anything simple, such as clsVPN. Add the following members to your clsVPN class:
Private strRASPhone As String = _ "C:\WINDOWS\system32\rasphone.exe" Private strVPNCon As String = "" Private strIPAddress As String = "" Private blnConnected As Boolean = False
Here, you get access to the RasPhone object, and enable your application to store the connection string and IP Address. Add the following Delegates and Events:
Public Delegate Sub delPing() Public Delegate Sub delConnect() Public Delegate Sub delIdle() Public Delegate Sub delDisconnect() Public Delegate Sub delStatus(blnConnected As Boolean) Public Event Ping As delPing Public Event Con As delConnect Public Event Discon As delDisconnect Public Event Idle As delIdle Public Event StatusChanged As delStatus Protected Sub OnStatusChanged(blnConnected As Boolean) RaiseEvent StatusChanged(blnConnected) End Sub Protected Sub OnDisconnect() RaiseEvent Discon() End Sub Protected Sub OnPing() RaiseEvent Ping() End Sub Protected Sub OnIdle() RaiseEvent Idle() End Sub Protected Sub OnConnect() RaiseEvent Con() End Sub
Add the following Properties to your class:
Public ReadOnly Property Connected() As Boolean Get Return blnConnected End Get End Property Public Property ConName() As String Get Return strVPNCon End Get Set(strValue As String) strVPNCon = strValue End Set End Property
The properties keep track of the Connection name and Connected state. Connect to the VPN:
Private Function Connect() As Boolean Dim blnSucceed As Boolean = False OnConnect() Process.Start(strRASPhone, Convert.ToString(" -d ") _ & strVPNCon) Application.DoEvents() System.Threading.Thread.Sleep(5000) Application.DoEvents() blnSucceed = True OnIdle() Return blnSucceed End Function
Test the Connection
Public Function Test() As Boolean Dim blnSucceed As Boolean = False OnPing() Dim p As New Ping() If p.Send(strIPAddress).Status = IPStatus.Success Then blnSucceed = True Else blnSucceed = False End If p = Nothing If blnSucceed <> blnConnected Then blnConnected = blnSucceed OnStatusChanged(blnConnected) End If OnIdle() Return blnSucceed End Function
Private Function Disconnect() As Boolean Dim blnSucceed As Boolean = False OnDisconnect() Process.Start(strRASPhone, Convert.ToString(" -h ") _ & strVPNCon) Application.DoEvents() System.Threading.Thread.Sleep(8000) Application.DoEvents() blnSucceed = True OnIdle() Return blnSucceed End Function
Add the following code to test the connection from your Form:
Private Sub Button2_Click(sender As Object, e As EventArgs) _ Handles Button2.Click Dim vp As New clsVPN vp.Test() If vp.Connected Then MessageBox.Show("Connected") Else MessageBox.Show("Not Connected") End If End Sub
The code for this article is available on GitHub.
The System.Net.NetworkInformation Namespace is very powerful. Detecting network connections and whether or not your are making use of a VPN can come in quite handy.