DNS NsLookup using Visual Basic .NET

The Domain Name System (DNS) is the method by which Internet addresses in mnemonic form - such as www.activexperts.com - are converted into the equivalent numeric IP address such as 212.97.55.136. To the user and application process this translation is a service provided either by the local host or from a remote host via the Internet. The DNS server (or resolver) may communicate with other Internet DNS servers if it cannot translate the address itself.
DNS names are constructed hierarchically. The highest level of the hierarchy is the last component or label of the DNS address. Labels can be up to 63 characters long and are not case sensitive. A maximum length of 255 characters is allowed. Labels must start with a letter and can only consist of letters, digits and hyphens.

Nslookup is a popular program for UNIX, LINUX and Windows to query Internet domain name servers. It allows the user to query name servers for information about various hosts and domains or to print a list of hosts in a domain.

ActiveSocket provides an easy-to-use development/scripting interface to use the same operations as NsLookup, through the DnsServer class. By using ActiveSocket, you can very easily create or enhance Windows applications/scripts with DNS lookup features.

ActiveSocket features the following: ICMP, HTTP and HTTPs (supporting for proxy servers, secure web sites), FTP, DNS, Telnet, NTP time protocol, RSH remote shell script interface, SNMP (Simple Network Management Protcol), SNMP Traps, Sockets, WOL (Wake-On-LAN), and more.

Step 1: Download and install the ActiveSocket Toolkit

Download the the ActiveSocket Toolkit from the ActiveXperts Download Site and start the installation. The installation guides you through the installation process.

Step 2: Create a new Visual Basic .NET Project

Launch Microsoft Visual Studio (for instance 'Microsoft Visual Studio 2005') from the Start menu. Choose 'New' from the 'File' menu and click on 'Project'. In the 'New Project' dialog, select a Visual Studio template (for instance: 'Console Application'). Select a name for the application (for instance: 'DemoApp') and a name for the solution (for instance: 'DemoSolution'). Also, select the directory where you want to store the project (for instance: 'C:\MyProjects):

(Click on the picture to enlarge)

Step 3: Refer to the ActiveSocket Library and create the objects

Now that a new project has been created, you must add a reference to the ActiveSocket Toolkit in the project to be able to use the the ActiveSocket object. To do so, choose 'Add Reference...' from the 'Project' menu. In the 'Add Reference' dialog that pops up, select the 'COM' tab and select the 'ActiveSocket 3.1 Type Library' as shown in the following picture:

(Click on the picture to enlarge)

Click 'OK' to close the 'Add Reference' dialog.

On top of your code, type the following line to use the ActiveSocket namespace:

   Imports ASOCKETLib

In your Main function, declare and create the following object:

   Public m_objDnsServer As DnsServer

   m_objDnsServer = New DnsServer()

Step 5: Query an hostname

When the required DNS object is created, you can implement the code to query a hostname on a DNS server:

Imports ASOCKETLib

Public Class DnsForm
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "
#End Region

    Private objDnsServer As IDnsServer
    Private objConstants As ISocketConstants

    Private Sub DnsForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        objDnsServer = New DnsServer
        objConstants = New SocketConstants

        objDnsServer.Clear()

        comboType.Items.Add("A Record")
        comboType.Items.Add("NS Record")
        comboType.Items.Add("CNAME Record")
        comboType.Items.Add("SOA Record")
        comboType.Items.Add("PTR Record")
        comboType.Items.Add("MX Record")
        comboType.Items.Add("AAAA Record")
        comboType.Items.Add("ANY Record")

        comboType.SelectedIndex = 7

        textLogFile.Text = System.IO.Path.GetTempPath() + "DnsLog.txt"
    End Sub

    Private Sub buttonView_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles buttonView.Click
        If (System.IO.File.Exists(textLogFile.Text.ToString())) Then
            System.Diagnostics.Process.Start(textLogFile.Text)
        End If
    End Sub

    Private Function GetResult()
        GetResult = objDnsServer.LastError

        If (objDnsServer.LastError = 22355) Then
            textResult.Text = "0 : Success"
        Else
            textResult.Text = objDnsServer.LastError & " : " & objDnsServer.GetErrorDescription(objDnsServer.LastError)
        End If
    End Function

    Private Sub buttonLookup_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles buttonLookup.Click
        Dim nType As Integer = objConstants.asDNS_TYPE_ANY

        Select Case (comboType.SelectedIndex)
            Case 0
                nType = objConstants.asDNS_TYPE_ANY
            Case 1
                nType = objConstants.asDNS_TYPE_NS
            Case 2
                nType = objConstants.asDNS_TYPE_CNAME
            Case 3
                nType = objConstants.asDNS_TYPE_SOA
            Case 4
                nType = objConstants.asDNS_TYPE_PTR
            Case 5
                nType = objConstants.asDNS_TYPE_MX
            Case 6
                nType = objConstants.asDNS_TYPE_AAAA
            Case 7
                nType = objConstants.asDNS_TYPE_ANY
        End Select

        objDnsServer.LogFile = textLogFile.Text
        objDnsServer.Server = textServer.Text

        objDnsServer.Lookup(textHost.Text, nType)

        textQueryResults.Text = ""

        If (GetResult() = 0) Then

            Dim objDnsRecord As DnsRecord

            objDnsRecord = objDnsServer.GetFirstRecord()

            While (GetResult() = 0)

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_A) Then
                    textQueryResults.AppendText(vbCrLf & "Type: A")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Address: " & objDnsRecord.Address)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_AAAA) Then
                    textQueryResults.AppendText(vbCrLf & "Type: AAAA")
                    textQueryResults.AppendText(vbCrLf & vbTab & "tName: " + objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Address: " + objDnsRecord.Address)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_CNAME) Then
                    textQueryResults.AppendText(vbCrLf & "Type: CNAME")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Alias: " & objDnsRecord.Address)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_NS) Then
                    textQueryResults.AppendText(vbCrLf & "Type: NS")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "NameServer: " & objDnsRecord.NameServer)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_MX) Then
                    textQueryResults.AppendText(vbCrLf & "Type: MX")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Preference: " & objDnsRecord.Preference)
                    textQueryResults.AppendText(vbCrLf & vbTab & "MailExchange: " & objDnsRecord.MailExchange)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_PTR) Then
                    textQueryResults.AppendText(vbCrLf & "Type: PTR")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Address: " & objDnsRecord.Address)
                End If

                If (objDnsRecord.Type = objConstants.asDNS_TYPE_SOA) Then
                    textQueryResults.AppendText(vbCrLf & "Type: SOA")
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name: " & objDnsRecord.Name)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Name Server: " & objDnsRecord.NameServer)
                    textQueryResults.AppendText(vbCrLf & vbTab & "MailBox: " & objDnsRecord.MailBox)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Serial: " & objDnsRecord.SerialNumber)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Refresh: " & objDnsRecord.RefreshInterval)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Retry Interval: " & objDnsRecord.RetryInterval)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Expiration Limit: " & objDnsRecord.ExpirationLimit)
                    textQueryResults.AppendText(vbCrLf & vbTab & "Minimum TTL: " & objDnsRecord.MinimumTTL)
                End If

                objDnsRecord = objDnsServer.GetNextRecord()
            End While
        End If
    End Sub
End Class

You can download the complete sample from our ftp site ftp.activexperts-labs.com/samples/asocket.
There are many other working ActiveSocket scripts on our site and shipped with the product.

The ActiveSocket tool is a Network Communications ActiveX software component (SDK). This control supports SNMP, SMTP, POP3, Telnet, TCP, NTP, RSH, HTTP, HTTPs, FTP, DNS, ICMP and more, and can be used by any Windows development platform, including Visual Basic .NET, Visual CSharp .NET, ASP .NET (VB,CS), ASP, Visual Basic, Visual Studio/Visual C++, Delphi, PHP, ColdFusion, HTML, VBScript and any other ActiveX/COM compliant platform. The ActiveSocket Toolkit is an ActiveXperts Software B.V. Product.