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ActiveSocket Toolkit Add network capabilities to any Windows or .NET application

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DNS NsLookup using Visual Basic

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: 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.

Step 1: Download and install the ActiveSocket Toolkit

Download 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 project

Launch 'Microsoft Visual Basic' from the Start menu, and choose 'New' from the 'File Menu'. The 'New Project' dialog appears.
Select 'Standard Exe' and click 'OK':

Visual Basic

(Click on the picture to enlarge)

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

A new Project is created, with a blank form.

First, you must add a reference to ActiveSocket in the project to be able to use the object. To do so, choose 'References...' from the 'Project' menu. In the 'References' dialog that pops up, enable the 'ActiveSocket 3.1 Type Library' reference as shown in the following picture:

(Click on the picture to enlarge)

Click 'OK' to close the 'References...' dialog.

Then, select the Project form and choose 'View Code' from the context menu:

(Click on the picture to enlarge)

On top of your code, declare the following object:

Public objDnsServer As DnsServer

Step 4: Create the object

From the Code window, select 'Form'. The Private Sub 'Form_Load()' will be displayed now. In the 'Form Load' function, create the object in the following way: 

Set objDnsServer = CreateObject("ActiveXperts.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:

Public objDnsServer As DnsServer
Public objConstants As SocketConstants

Private Declare Function GetTempPath Lib "kernel32" Alias "GetTempPathA" (ByVal nBufferLength As Long, ByVal lpBuffer As String) As Long
Private Const MAX_PATH = 260

'///////////////////////////////////////////////////////////////////////

Private Sub CommandLookup_Click()
    Dim lType As Long
    Dim objDnsRecord As DnsRecord
        
    Select Case (ComboType.ListIndex)
        Case 0
            lType = objConstants.asDNS_TYPE_A
        Case 1
            lType = objConstants.asDNS_TYPE_NS
        Case 2
            lType = objConstants.asDNS_TYPE_CNAME
        Case 3
            lType = objConstants.asDNS_TYPE_SOA
        Case 4
            lType = objConstants.asDNS_TYPE_PTR
        Case 5
            lType = objConstants.asDNS_TYPE_MX
        Case 6
            lType = objConstants.asDNS_TYPE_AAAA
        Case 7
            lType = objConstants.asDNS_TYPE_ANY
    End Select
        
    objDnsServer.Server = TextServer.Text
    objDnsServer.LogFile = TextLogFile.Text
    
    objDnsServer.Lookup TextHost.Text, lType
   
    ListResult.Clear
        
    If (GetResult() = 0) Then
        
        Set objDnsRecord = objDnsServer.GetFirstRecord
        On Error Resume Next
            
        While (objDnsServer.LastError = 0)
        
           Select Case objDnsRecord.Type
              Case objConstants.asDNS_TYPE_A
                ListResult.AddItem ("Type: A")
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "IPv4 Address: " & objDnsRecord.Address
              Case objConstants.asDNS_TYPE_AAAA
                ListResult.AddItem "Type: AAAA"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "IPv6 Address: " & objDnsRecord.Address
              Case objConstants.asDNS_TYPE_CNAME
                ListResult.AddItem "Type: CNAME"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "Alias: " & objDnsRecord.Address
              Case objConstants.asDNS_TYPE_MX
                ListResult.AddItem "Type: MX"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "Preference: " & objDnsRecord.Preference
                ListResult.AddItem vbTab & "Mail Exchange: " & objDnsRecord.MailExchange
              Case objConstants.asDNS_TYPE_NS
                ListResult.AddItem "Type: NS"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "Name Server: " & objDnsRecord.NameServer
              Case objConstants.asDNS_TYPE_PTR
                ListResult.AddItem "Type: PTR"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "Host: " & objDnsRecord.Address
              Case objConstants.asDNS_TYPE_SOA
                ListResult.AddItem "Type: SOA"
                ListResult.AddItem vbTab & "Name: " & objDnsRecord.Name
                ListResult.AddItem vbTab & "Name Server: " & objDnsRecord.NameServer
                ListResult.AddItem vbTab & "MailBox: " & objDnsRecord.MailBox
                ListResult.AddItem vbTab & "Serial: " & objDnsRecord.SerialNumber
                ListResult.AddItem vbTab & "Refresh: " & objDnsRecord.RefreshInterval
                ListResult.AddItem vbTab & "Retry Interval: " & objDnsRecord.RetryInterval
                ListResult.AddItem vbTab & "Expiration Limit: " & objDnsRecord.ExpirationLimit
                ListResult.AddItem vbTab & "Minimum TTL: " & objDnsRecord.MinimumTTL
            End Select
        Set objDnsRecord = objDnsServer.GetNextRecord
        On Error Resume Next
        Wend
    End If
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub CommandView_Click()
    If FileExists(TextLogFile.Text) = True Then
        Shell "notepad " + TextLogFile.Text, vbNormalFocus
    End If
End Sub

'///////////////////////////////////////////////////////////////////////

Public Function FileExists(sFileName As String) As Boolean
  FileExists = CBool(Len(Dir$(sFileName))) And CBool(Len(sFileName))
End Function

'///////////////////////////////////////////////////////////////////////

Private Sub Form_Load()
    Set objDnsServer = CreateObject("ActiveXperts.DnsServer")
    Set objConstants = CreateObject("ActiveXperts.ASConstants")
    
    SetDefaultLogFile
    
    ComboType.AddItem ("A Record")
    ComboType.AddItem ("NS Record")
    ComboType.AddItem ("CNAME Record")
    ComboType.AddItem ("SOA Record")
    ComboType.AddItem ("PTR Record")
    ComboType.AddItem ("MX Record")
    ComboType.AddItem ("AAAA Record")
    ComboType.AddItem ("ANY Record")
    
    ComboType.ListIndex = 7
End Sub

'///////////////////////////////////////////////////////////////////////

Private Function GetResult() As Long
    Dim lResult As Long

    lResult = objDnsServer.LastError
    TextResult.Text = lResult & " : " & objDnsServer.GetErrorDescription(lResult)
   
    GetResult = lResult
End Function

'///////////////////////////////////////////////////////////////////////

Private Function SetDefaultLogFile()

Dim Buffer As String
Buffer = Space(MAX_PATH)

If GetTempPath(MAX_PATH, Buffer) <> 0 Then
    TextLogFile.Text = Left$(Buffer, InStr(Buffer, vbNullChar) - 1) & "DnsLog.txt"
Else
    TextLogFile.Text = "C:\DnsLog.txt"
End If
End Function

'///////////////////////////////////////////////////////////////////////

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