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DNS NsLookup using Visual Basic .NET

Network Component provides an easy-to-use development interface to a variety of IP protocols. By using Network Component, you can very easily create or enhance applications with network features.

Network Component features the following: DNS, FTP, HTTP, HTTPs, ICMP Ping, IP-to-Country, MSN, NTP, RSH, SCP, SFTP, SNMP v1/v2c (Get, GetNext, Set), SNMP Traps, SNMP MIB, SSH, TCP, Telnet, TFTP, UDP, Telnet, Wake-On-LAN and more.

Network Component can be well integrated into any development platform that supports ActiveX objects.

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.

Step 1: Download and install the Network Component

Download Network Component 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 2008') 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 Network Component Library and create the objects

Now that a new project has been created, you must add a reference to the Network Component in the project to be able to use the the Network Component 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 'Network Component 4.4 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 Network Component namespace:

Imports AxNetwork

Step 4: Create the object

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

Public m_objDnsServer As DnsServer
m_objDnsServer = New DnsServer()

Appendix: Full source code

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

Imports System.IO
Imports AxNetwork

Module DnsProgram

  Sub Main()
    Dim objDnsServer As AxNetwork.DnsServer = New AxNetwork.DnsServer
    Dim objDnsRecord As AxNetwork.DnsRecord
    Dim objConstants As AxNetwork.NwConstants = New AxNetwork.NwConstants
    Dim strDnsServer As String = ""
    Dim strHost As String = ""
    Dim strQueryResult As String = ""

    ' A license key is required to unlock this component after the trial period has expired.
    ' Call 'Activate' with a valid license key as its first parameter. Second parameter determines whether to save the license key permanently 
    ' to the registry (True, so you need to call Activate only once), or not to store the key permanently (False, so you need to call Activate
    ' every time the component is created). For details, see manual, chapter "Product Activation".
    '
    ' objDnsServer.Activate("XXXXX-XXXXX-XXXXX", False)
    '

    ' Display component information
    Console.WriteLine("ActiveXperts Network Component {0}{1}Build: {2}{3}Module: {4}{5}License Status: {6}{7}License Key: {8}{9}", objDnsServer.Version, Environment.NewLine, objDnsServer.Build, Environment.NewLine, objDnsServer.Module, Environment.NewLine, objDnsServer.LicenseStatus, Environment.NewLine, objDnsServer.LicenseKey, Environment.NewLine)

    ' Set Logfile (optional, for debugging purposes)
    objDnsServer.LogFile = Path.GetTempPath() + "Dns.log"
    Console.WriteLine("Log file used: {0}{1}", objDnsServer.LogFile, Environment.NewLine)

    strDnsServer = ReadInput("Enter DNS server: ")
    strHost = ReadInput("Enter domain or host: ")
    objDnsServer.Server = strDnsServer
    objDnsServer.Lookup(strHost, objConstants.nwDNS_TYPE_ANY)
    Console.WriteLine("Lookup, result: " & objDnsServer.LastError.ToString() & " (" & objDnsServer.GetErrorDescription(objDnsServer.LastError) & ")")
    If (objDnsServer.LastError = 0) Then
        If (objDnsServer.IsAuthoritative) Then
            Console.WriteLine("Server is an authority for this domain")
        Else
            Console.WriteLine("Server is not an authority for this domain")
        End If
    End If
    Console.WriteLine("")

    If (objDnsServer.LastError = 0) Then
        objDnsRecord = objDnsServer.GetFirstRecord()
        While (objDnsServer.LastError = 0)

            If (objDnsRecord.Type = objConstants.nwDNS_TYPE_A) Then
                strQueryResult = strQueryResult & vbCrLf & "Type: A"
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Name: " & objDnsRecord.Name
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Address: " & objDnsRecord.Address
            End If

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

            If (objDnsRecord.Type = objConstants.nwDNS_TYPE_CNAME) Then
                strQueryResult = strQueryResult & vbCrLf & "Type: CNAME"
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Name: " & objDnsRecord.Name
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Alias: " & objDnsRecord.Address
            End If

            If (objDnsRecord.Type = objConstants.nwDNS_TYPE_NS) Then
                strQueryResult = strQueryResult & vbCrLf & "Type: NS"
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Name: " & objDnsRecord.Name
                strQueryResult = strQueryResult & vbCrLf & vbTab & "NameServer: " & objDnsRecord.NameServer
            End If

            If (objDnsRecord.Type = objConstants.nwDNS_TYPE_MX) Then
                strQueryResult = strQueryResult & vbCrLf & "Type: MX"
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Name: " & objDnsRecord.Name
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Preference: " & objDnsRecord.Preference
                strQueryResult = strQueryResult & vbCrLf & vbTab & "MailExchange: " & objDnsRecord.MailExchange
            End If

            If (objDnsRecord.Type = objConstants.nwDNS_TYPE_PTR) Then
                strQueryResult = strQueryResult & vbCrLf & "Type: PTR"
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Name: " & objDnsRecord.Name
                strQueryResult = strQueryResult & vbCrLf & vbTab & "Address: " & objDnsRecord.Address
            End If

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

            objDnsRecord = objDnsServer.GetNextRecord()
        End While
    End If

    Console.WriteLine(strQueryResult)

    Console.WriteLine("Ready.")
    System.Threading.Thread.Sleep(5000) ' Sleep for 5 seconds before exit
  End Sub

  Private Function ReadInput(ByRef strTitle As String) As String
    Dim strInput As String = ""

    Console.WriteLine(strTitle)
    While strInput = ""
        Console.Write("  > ")
        strInput = Console.ReadLine()
    End While
    ReadInput = strInput
  End Function

End Module

You can download the complete samples here. There are many other working Network Component scripts on our site and shipped with the product.

NOTE: Demo Projects are created with Microsoft Visual Studio 2008

The Network Component project ships with a set of Microsoft Visual Studio .NET samples, including samples for Microsoft Visual C# .NET. The projects are created with Microsoft Visual Studio 2008.

Users with a later version of Microsoft Visual Studio can open such a project. The Visual Studio Conversion Wizard will guide you through the process of converting the project to the version used.

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