VB6 - Port Tester

The normal way to find your real external IP address is to use your browser to go to a site such as "WhatsMyIP". I needed to do this programatically without the burden of using HTML. What I came up with is a way to verify a forwarding port within a NAT router, while at the same time discovering your public IP address.

Port forwarding can be somewhat onerous for the casual user, and verifying that it is successful is part of the task. To accomplish this, we run a proxy type server on the other side of the NAT router. You send the port number that you want tested to that outside server, and the outside server tries to establish a TCP connection with your router on that port. If the router is properly configured, it will forward that request to your computer and the router's public IP address that was used to make the initial connection with the server will be sent to you.

Port forwarding usually requires that you use fixed IP addressing on your computer rather than DHCP, although it is sometimes possible to configure a NAT router to assign a fixed IP address using DHCP.

Even with the router properly configured, you can still have problems with your firewall. If you are running the Microsoft Firewall, it will prompt you to allow the outside connection.

Last but not least, most ISPs will block some problematic ports such as port 21(FTP), 25(SMTP), 80(WWW), 110(POP3), 6667(IRCD), 135-139(DCOM/NETBIOS), 443(SSL), 445(MS-DS), and 1433-1434(MS-SQL) on residential connections, and there is nothing you can do about it except use a different port or get a business connection.

If there is sufficient interest, I can later supply a service version of the server software.

Note: Both programs use SimpleSock, which requires operating systems that actively support both IPv4 & IPv6. This more or less restricts them to Windows Vista or better.

J.A. Coutts

What about https://www.ipify.org/ who offer an API?

Code:

---

Option Explicit

Private Sub Main()
    With New WinHttp.WinHttpRequest
        .Open "GET", "https://api.ipify.org"
        .Send
        If .Status = 200 Then
            MsgBox .ResponseText
        Else
            MsgBox .StatusText
        End If
    End With
End Sub

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Seems to work fine. Probably plenty of others out there too, it was just the first hit on a search.

Quote:

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Originally Posted by dilettante

What about https://www.ipify.org/ who offer an API?

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As the name suggests, it was primarily put together as a NAT port forwarding tester. The Public IP was an after thought that took about 2 lines of code. I realize that online port scanners could do the testing, but I needed to do this in code and I wanted to keep it small. It would have been nice to use the UPnP code that you posted, but that didn't work out.

As an aside, I found this bit of code to get the external IP, but it looks like it is for some other kind of Basic and I could not get it to work.

Code:

---

Imports NATUPNPLib
Public Class RouterInfo
Dim cRouter As NATUPNPLib.UPnPNAT

Public Sub New()
    cRouter = New NATUPNPLib.UPnPNAT
End Sub

Public Function GetExternalIP() As String
    Dim lMapper = cRouter.StaticPortMappingCollection
    Dim lMappedPort As NATUPNPLib.IStaticPortMapping
    Dim lExtIP As String
    If Not lMapper Is Nothing Then
          For Each lMappedPort In lMapper
              lExtIP = lMappedPort.ExternalIPAddress().ToString
              Exit For
          Next
          GetExternalIP = lExtIP
    Else
          GetExternalIP = "<Unable to resolve external IP>"
    End If
End Function

---

J.A. Coutts

Figured it out!

Code:

---

Dim cRouter As NATUPNPLib.UPnPNAT
    Set cRouter = New NATUPNPLib.UPnPNAT
    'Check to make sure NAT UPnP is active
    If cRouter.StaticPortMappingCollection Is Nothing Then
        Debug.Print "UPnP not Found!"
        exit sub
    End If
    'Find number of mappings
    Debug.Print "Mappings = " & cRouter.StaticPortMappingCollection.Count
    'Return properties IP of this router.
    Debug.Print "Description: " & cRouter.StaticPortMappingCollection(8765, "TCP").Description
    Debug.Print "Enabled: " & cRouter.StaticPortMappingCollection(8765, "TCP").Enabled
    Debug.Print "ExternalIPAddress: " & cRouter.StaticPortMappingCollection(8765, "TCP").ExternalIPAddress
    Debug.Print "ExternalPort: " & cRouter.StaticPortMappingCollection(8765, "TCP").ExternalPort
    Debug.Print "InternalClient: " & cRouter.StaticPortMappingCollection(8765, "TCP").InternalClient
    Debug.Print "InternalPort: " & cRouter.StaticPortMappingCollection(8765, "TCP").InternalPort
    Debug.Print "Protocol: " & cRouter.StaticPortMappingCollection(8765, "TCP").Protocol

---

Mappings = 0
Description: Demo Port Mapping
Enabled: True
ExternalIPAddress: 206.116.170.228
ExternalPort: 8765
InternalClient: 192.168.1.4
InternalPort: 8765
Protocol: TCP

This particular router (ActionTec T2200H) does not return the Count, nor will it allow port mappings to be removed. Now if I could only figure out how to assign "cRouter.StaticPortMappingCollection" to a variable.

J.A. Coutts

Quote:

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Originally Posted by couttsj

Now if I could only figure out how to assign "cRouter.StaticPortMappingCollection" to a variable.

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Not sure why you'd need to, but since this works fine:

Code:

---

    Dim UPnPNAT As NATUPNPLib.UPnPNAT
    Dim StaticPortMapping As NATUPNPLib.IStaticPortMapping
   
    Set UPnPNAT = New NATUPNPLib.UPnPNAT
    On Error Resume Next
    Set StaticPortMapping = _
        UPnPNAT.StaticPortMappingCollection.Add(lngExtPort, _
                                                "UDP", _
                                                lngIntPort, _
                                                Winsock.LocalIP, _
                                                True, _
                                                "Demo Port Mapping")
    If Err Then
        MsgBox "Add failed, error " & Msg(Err.Number)
    Else
        On Error GoTo 0
        MsgBox "Add succeeded, ExternalIPAddress = " _
            & StaticPortMapping.ExternalIPAddress
    End If

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Maybe:

Code:

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    Dim UPnPNAT As NATUPNPLib.UPnPNAT
    Dim StaticPortMappingCollection As NATUPNPLib.IStaticPortMappingCollection

    Set UPnPNAT = New NATUPNPLib.UPnPNAT
    Set StaticPortMappingCollection = UPnPNAT.StaticPortMappingCollection

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