Check if computer is CONNECTED to internet?

Question

Hello, I know there has been other questions like this, but none of the answers worked for me.

I would like to check whether the computer is connected to the internet or not. I've got this code, but the program crashes everytime that I disconnect from the internet. The code is in a timer that runs every second btw.

        If My.Computer.Network.Ping("www.google.com") Then
            Connection.Image = My.Resources.high_connection
        Else
            Connection.Image = My.Resources.no_connection
        End If

Thanks, Andreas

Answer 1

I know you don't and that's a problem with Windows.

With asychronous returns you do not have to poll. It is like a event.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 2

Hi Andreas,

Before you execute the ping, first ensure that there is an active network connection on the PC.  I'd also suggest pinging a root DNS server since google could decide to one day block ICMP traffic, or could even be down (as unlikely as that is).  The root DNS server will be cloned several times so the IP address should always respond.  I'd wrap the whole thing up in a little function and then call that in your code:

Public Function IsInternetAvailable() As Boolean
    'first make sure that a network is available on the PC
    If Not My.Computer.Network.IsAvailable Then Return False
    'now try to ping a root dns server
    Return My.Computer.Network.Ping("198.41.0.4")
End Function
 

And then use it like:

If IsInternetAvailable() Then
    Connection.Image = My.Resources.high_connection
Else
    Connection.Image = My.Resources.no_connection
End If
 

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 3

Thanks Reed, but it still crashes when I disconnect from the internet, I dont know if I'am doing anything wrong. It is this line btw. Return My.Computer.Network.Ping("198.41.0.4") Thanks, Andreas

Answer 4

You can also respond to the local connection state change without polling by handling an event:

Public Class Form1

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        AddHandler My.Computer.Network.NetworkAvailabilityChanged, AddressOf ConnectionStateChange
    End Sub

    Private Sub ConnectionStateChange(sender As Object, e As EventArgs)
        If IsInternetAvailable() Then
            Connection.Image = My.Resources.high_connection
        Else
            Connection.Image = My.Resources.no_connection
        End If
    End Sub

    Public Function IsInternetAvailable() As Boolean
        'first make sure that a network is available on the PC
        If Not My.Computer.Network.IsAvailable Then Return False
        'now try to ping a root dns server
        Return My.Computer.Network.Ping("198.41.0.4")
    End Function

End Class
 

Now, this would not cause the image to change if your router lost connection to the internet. You would still have to poll to determine connectivity all the way through to the internet. You could probably set your timer to 5 or 10 seconds though, as every second might be a bit excessive.

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 5

I guess you're catching it in the middle of a ping.  Increasing the timer interval would probably help, but I suppose you'll need to catch that possible exception.  Modify the function to be:

Public Function IsInternetAvailable() As Boolean
    'first make sure that a network is available on the PC
    If Not My.Computer.Network.IsAvailable Then Return False
    'now try to ping a root dns server
    Try
        Return My.Computer.Network.Ping("198.41.0.4")
    Catch ex As Exception
        Return False
    End Try
End Function
 

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 6

I can't put the 

    Private Sub ConnectionStateChange(sender As Object, e As EventArgs)
        If IsInternetAvailable() Then
            Connection.Image = My.Resources.high_connection
        Else
            Connection.Image = My.Resources.no_connection
        End If
    End Sub

in my timer, and if I disconnect from the internet it doesn't change image, but it doesn't crash :D

I use a timer for a clock (with seconds, so it updates every second), should I use 2 timers?

Thanks, Andreas

Answer 7

No, you could use both and reduce the timer frequency.  Use the event to immediately catch the local connection state change and use a longer running timer to check for loss of connection to the internet.

On further thought, you probably should not ping a root DNS server on a regular interval... I'm not sure what the exact rules are but you can't flood a DNS server with pings.  Its ok to use them to verify connectivity occasionaly, but not every second.  I'm sure google has similar rules as well.  No body wants a constant string of pings to their servers.  =P

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 8

When I was doing it in 2008, they didn't care.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 9

Hehe, but is there another way to check if the computer is connected to the internet? Because I can't get your code to work. :-)

Thanks, Andreas

Answer 10

What doesn't work?

Public Class Form1

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        AddHandler My.Computer.Network.NetworkAvailabilityChanged, AddressOf ConnectionStateChange
    End Sub

    Private Sub ConnectionStateChange(sender As Object, e As EventArgs)
        If IsInternetAvailable() Then
            Connection.Image = My.Resources.high_connection
        Else
            Connection.Image = My.Resources.no_connection
        End If
    End Sub

    Private Sub Timer1_Tick(sender As System.Object, e As System.EventArgs) Handles Timer1.Tick
        If IsInternetAvailable() Then
            Connection.Image = My.Resources.high_connection
        Else
            Connection.Image = My.Resources.no_connection
        End If
    End Sub

    Public Function IsInternetAvailable() As Boolean
        'first make sure that a network is available on the PC
        If Not My.Computer.Network.IsAvailable Then Return False
        'now try to ping a root dns server
        Try
            Return My.Computer.Network.Ping("198.41.0.4")
        Catch ex As Exception
            Return False
        End Try
    End Function

End Class
 

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 11

Here:

    Public Function IsInternetAvailable() As Boolean
        'first make sure that a network is available on the PC
        If Not My.Computer.Network.IsAvailable Then Return False
        'now try to ping a root dns server
        Return My.Computer.Network.Ping("198.41.0.4")
    End Function

At: Return My.Computer.Network.Ping("198.41.0.4") when I disconnect from the internet

Will someone be annoyed if i ping to a "root dns server"? (No body wants a constant string of pings to their servers.  =P)

Answer 12

Hello Andreas98cool,

Hehe, but is there another way to check if the computer is connected to the internet? Because I can't get your code to work. :-)

Thanks, Andreas

try this sample it use api  , is c# , but easy convertable in VbNet , http://sdrv.ms/VfJUxP

Regards.

---

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Answer 13

Hello Andreas98cool,

Hehe, but is there another way to check if the computer is connected to the internet? Because I can't get your code to work. :-)

Thanks, Andreas

try this sample it use api  , is c# , but easy convertable in VbNet , http://sdrv.ms/VfJUxP

Regards.

---

• Carmelo La Monica
• Visual Basic Tips e Tricks Blog
• WordPress.com Blog
• Twitter
• Blogger
• CrystalwebDotNetGroup

How do I convert it into VB? I'am not really an expert :-)

Answer 14

You are supposed to replace that with the version that uses a Try-Catch block around the ping.

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 15

But your still polling.....

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 16

Hello Andreas98cool,

How do I convert it into VB? I'am not really an expert :-)

try this converter http://www.developerfusion.com/tools/convert/csharp-to-vb/

Regards.

---

• Carmelo La Monica
• Visual Basic Tips e Tricks Blog
• WordPress.com Blog
• Twitter
• Blogger
• CrystalwebDotNetGroup

Answer 17

You could use a try catch statement to keep your application from crashing.

Imports System.Net.NetworkInformation

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Timer1.Interval = 5000
        Timer2.Interval = 10
        Timer1.Start()
    End Sub

    Private Sub RichTextBox1_TextChanged(sender As Object, e As EventArgs) Handles RichTextBox1.TextChanged

    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        RichTextBox1.Text = ""
        Timer2.Start()
        Timer1.Stop()
    End Sub

    Private Sub Timer2_Tick(sender As Object, e As EventArgs) Handles Timer2.Tick
        For Each face As NetworkInterface In NetworkInterface.GetAllNetworkInterfaces()
            RichTextBox1.AppendText(face.Description & vbCrLf)
            RichTextBox1.AppendText(face.Name)
            RichTextBox1.AppendText(face.NetworkInterfaceType.ToString() & vbCrLf)
            RichTextBox1.AppendText(face.OperationalStatus.ToString() & vbCrLf)
            RichTextBox1.AppendText(face.Speed & vbCrLf & vbCrLf)
            Timer1.Start()
            Timer2.Stop()
        Next

        Dim UP As String = "UP"
        Dim index1 As Integer = 0
        While index1 <> -1
            index1 = RichTextBox1.Find(UP, index1, RichTextBoxFinds.WholeWord)
            If index1 <> -1 Then
                RichTextBox1.SelectionStart = index1
                RichTextBox1.SelectionLength = UP.Length
                RichTextBox1.SelectionColor = Color.Green
                index1 += UP.Length
            End If
        End While

        Dim DOWN As String = "DOWN"
        Dim index2 As Integer = 0
        While index2 <> -1
            index2 = RichTextBox1.Find(DOWN, index2, RichTextBoxFinds.WholeWord)
            If index2 <> -1 Then
                RichTextBox1.SelectionStart = index2
                RichTextBox1.SelectionLength = DOWN.Length
                RichTextBox1.SelectionColor = Color.Red
                index2 += DOWN.Length
            End If
        End While
        RichTextBox1.Select(0, 0)

        Try
            If My.Computer.Network.Ping("www.google.com") Then
                Me.Text = "Internet Good"
            Else
                Me.Text = "Internet Down"
            End If
        Catch ex As Exception
            Me.Text = (ex.Message)
        End Try


    End Sub
End Class

---

You've taught me everything I know but not everything you know.

Answer 18

You can also do outside VB a Ping by using the Dos box.

I think you should first investigate what Reed wrote that it is not the problem seems strange to me.

---

Success
Cor

Answer 19

I'm not an expert, so what would be the easiest way to do this? :-)

Answer 20

That's great EXCEPT that you have used polling.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 21

So there is no easy solution/code that I maybe can understand? :-)

Answer 22

So there is no easy solution/code that I maybe can understand? :-)

I'm afraid not.

But don't care these forums are not made for one person who ask a question, but to solve as a knowledge base.

Most persons will understand it after they have tried the given solutions and if not tell what is the result of their attempts, the latter you seems to avoid in all ways.

---

Success
Cor

Answer 23

Try this ... should works

This works without pinging and annoying any server

(Add a COM reference to "Network List Type Library"  (NETWORKLIST.DLL) )

    Private Function IsConnectedToInternet() As Boolean
        If System.Environment.OSVersion.Version.Major >= 6 Then
            'Vista and Up
            Dim Networks As New NETWORKLIST.NetworkListManager
            If Networks.IsConnectedToInternet Then
                Return True
            Else
                Return False
            End If
        Else
            'XP and less
            Dim flags As UInteger = 0
            If InternetGetConnectedState(flags, 0) Then
                Return True
            Else
                Return False
            End If
        End If
    End Function

    Private Declare Function InternetGetConnectedState Lib "wininet.dll" (ByVal Flag As UInteger, ByVal Reserved As UInteger) As Boolean

If you like, you can also do it like this .. It will save you from having a reference to the COM library

    Private Function IsConnectedToInternet() As Boolean
        If System.Environment.OSVersion.Version.Major >= 6 Then
            'Vista and Up
            'Dim Networks As New NETWORKLIST.NetworkListManager
            Dim Networks = Activator.CreateInstance(Type.GetTypeFromCLSID(New Guid("{DCB00C01-570F-4A9B-8D69-199FDBA5723B}")))
            If Networks.IsConnectedToInternet Then
                Return True
            Else
                Return False
            End If
        Else
            'XP and less
            Dim flags As UInteger = 0
            If InternetGetConnectedState(flags, 0) Then
                Return True
            Else
                Return False
            End If
        End If
    End Function

    Private Declare Function InternetGetConnectedState Lib "wininet.dll" (ByVal Flag As UInteger, ByVal Reserved As UInteger) As Boolean

Answer 24

"This works without pinging and annoying any server"

Yay Crazypennie! You eliminated polling!!!

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 25

"This works without pinging and annoying any server"

Yay Crazypennie! You eliminated polling!!!

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

You can't "eliminate polling"... the objective is to test for internet connectivity... this requires some kind of polling routine.  In this case the user still has to call IsConnectedToInternet() on some kind of interval.

Crazypennie appears to have found the underlying mechanizm used by Windows to test for internet connectivity, and thats great.... no need to reinvent the wheel.  However, there is still likely an ICMP packet or short TCP connection to some server in order to verify connectivity (perform a packet capture while this method is executing). 

While the documentation does not explicity define how the method works, it may be that it is just performing a root dns query (actually querying DNS versus pinging the server), similar to what I suggested initially.

http://answers.microsoft.com/en-us/windows/forum/windows_7-networking/how-does-win-7-determine-internet-access/e9bc340b-53b2-4378-afb1-a857bf6ba50d

---

Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 26

That should be changed to "You cant eliminate polling on windows." Asynchronous techniques are something most of windows programming is missing although one may ask how a passive presence is 'checked". Perhaps the question itself is not meaningful.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 27

An interresting fact is that the class DCB00C01-570F-4A9B-8D69-199FDBA5723B  has an event

      NetworkConnectivityChanged

This event will fire whenever the IPV4 or IPV6 internet connectivity changes.

The bad part, is that all that is exposed from the class is an interface ... And I cannot find out how to implement the event sink

Answer 28

Hooray!!!!!!

Polling stinks as a technique.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 29

Try this ... should works

This works without pinging and annoying any server

(Add a COM reference to "Network List Type Library"  (NETWORKLIST.DLL) )

    Private Function IsConnectedToInternet() As Boolean
        If System.Environment.OSVersion.Version.Major >= 6 Then
            'Vista and Up
            Dim Networks As New NETWORKLIST.NetworkListManager
            If Networks.IsConnectedToInternet Then
                Return True
            Else
                Return False
            End If
        Else
            'XP and less
            Dim flags As UInteger = 0
            If InternetGetConnectedState(flags, 0) Then
                Return True
            Else
                Return False
            End If
        End If
    End Function

    Private Declare Function InternetGetConnectedState Lib "wininet.dll" (ByVal Flag As UInteger, ByVal Reserved As UInteger) As Boolean

If you like, you can also do it like this .. It will save you from having a reference to the COM library

    Private Function IsConnectedToInternet() As Boolean
        If System.Environment.OSVersion.Version.Major >= 6 Then
            'Vista and Up
            'Dim Networks As New NETWORKLIST.NetworkListManager
            Dim Networks = Activator.CreateInstance(Type.GetTypeFromCLSID(New Guid("{DCB00C01-570F-4A9B-8D69-199FDBA5723B}")))
            If Networks.IsConnectedToInternet Then
                Return True
            Else
                Return False
            End If
        Else
            'XP and less
            Dim flags As UInteger = 0
            If InternetGetConnectedState(flags, 0) Then
                Return True
            Else
                Return False
            End If
        End If
    End Function

    Private Declare Function InternetGetConnectedState Lib "wininet.dll" (ByVal Flag As UInteger, ByVal Reserved As UInteger) As Boolean

It appears to work without polling anything. I used Microsoft Network Monitor 3.4 with it and WireShark current rev free Network Monitor with the following code and I didn't see any polling occuring (note that I couldn't find NETWORK.Dll to reference so I had to reference add reference, COM, Network List Manager 1.0 Type Library which only allow 1/2 of your code to work. InternetGetConnectedState was unreferenced). However Microsoft Network Monitor 3.4 with the code running kept knocking out my internet connection while wireshark caused no problems. Never had a problem with Microsoft Network Monitor 3.4 before.

Anyhow the code I used follows along with two images, top image is MS Net Mon which brought down my network. Bottom image is Wireshark which no problems with network occured. No polling is seen at all in the Network Monitors. Also note that in the top image the connection between my P/C and wireless modem is up because I'm connected to the wireless modem but the wireless connection status shows the internet being down (bottom right corner of the image).

Public Class Form1

    'Add reference, COM, Network List Manager 1.0 Type Library

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Timer1.Interval = 10000
        Timer1.Start()
    End Sub

    Private Function IsConnectedToInternet() As Boolean
        If System.Environment.OSVersion.Version.Major >= 6 Then
            'Vista and Up
            Dim Networks As New NETWORKLIST.NetworkListManager
            If Networks.IsConnectedToInternet Then
                Return True
            Else
                Return False
            End If
        Else
            MessageBox.Show("Your OS is incompatable")
        End If
    End Function

    Private Sub RichTextBox1_TextChanged(sender As Object, e As EventArgs) Handles RichTextBox1.TextChanged

    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        Me.Text = CStr(IsConnectedToInternet())
    End Sub
End Class

---

You've taught me everything I know but not everything you know.

Answer 30

Monkeyboy,

   Network List Manager 1.0 Type Library   ---    NETWORKLIST.DLL  ---   the class DCB00C01-570F-4A9B-8D69-199FDBA5723B 

All those are the same thing, just different way to access it.

-------------------------------------------------------

The second part of the code is using wininet.dll.

those libraries mainly targetting XP and before ... However they works on Vista.

On Window7 some get you to a dead lock

-------------------------------------------------------

Answer 31

I'm not really sure why you need to know this. It's possible to have an Internet connection, but there is no way to know whether a particular host is available until a specific request is initiated (which is how browser software handles this issue). In other words, you have to code for a request failure (Try...Catch) regardless of whether a connection exists.

---

Paul ~~~~ Microsoft MVP (Visual Basic)

Answer 32

Paul it just seems to the unaquainted that they should have it.

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 33

MonkeyBoy,

Where did the network Monitor come from?

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 34

I'm not really sure why you need to know this. It's possible to have an Internet connection, but there is no way to know whether a particular host is available until a specific request is initiated (which is how browser software handles this issue). In other words, you have to code for a request failure (Try...Catch) regardless of whether a connection exists.

---

Paul ~~~~ Microsoft MVP (Visual Basic)

I do agree whit what you are saying here, All this is interresting as general knowledge, but it would be rarely usefull.

However, I can see some use for that, ... An application may choose not to propose to the user to check for upgrade if internet is not there .. or thing like that.

It is sure not usefull to the user since he already have an icon in the task bar telling him if internet is available.

 ... Another usage of this would be to recreate this icon in the case of an application that use a custom desktop without explorer ... like a kiosk app.

Answer 35

Renee

Wireshark is free from http://www.wireshark.org/

Microsoft Network Monitor is free from http://www.microsoft.com/en-us/download/details.aspx?id=4865

I recommend Wiresharks, it's much better.

Regards

---

You've taught me everything I know but not everything you know.

Answer 36

Thank you So much, Monkeyboy!!! The network monitor Fatals out upon installation But Wireshark does fine!!!

Renee

---

"MODERN PROGRAMMING is deficient in elementary ways BECAUSE of problems INTRODUCED by MODERN PROGRAMMING." Me

Answer 37

You're welcome! :)

---

You've taught me everything I know but not everything you know.