To simplify the unwieldy state of computer naming, the Domain Name System (DNS) was created. It allows the master host database to be split up and distributed among multiple systems on the Internet. DNS uses a hierarchical database approach, creating levels of information that can be split and stored on various systems throughout the Internet.

DNS Structure

Using DNS

The last way to determine system IP information is to utilize the C# DNS (Domain Name System) classes. DNS can be used to obtain Internet hostnames and IP Addresses. The C# System.Net namespace contains the DNS class, which comprises several methods that allow you to obtain DNS information about hosts. The GetHostName() method retrieves the hostname of the local system. The GetHostByName() method attempts to find the IP address of a hostname.

DNS Configuration

When your C# application is running on a customer's system, you have no guarantee that there are any DNS servers configured. You can find out what (if any) DNS servers are configured by using the .NET Registry class methods to examine the DNS Registry values.

Fortunately, all Windows platforms store the DNS server information in the same place:

Registry Data Values for DNS Servers

The value of most interest here is NameServer . This should contain a single string value representing all the configured DNS servers, separated by spaces. The primary DNS server will be listed first, followed by the alternate servers.

Example: Demonstrate DNS and its Configuration in Registry

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Net;

using Microsoft.Win32;

namespace _CSharpApplication

{

  public partial class Form6 : Form

    {

    public Form6()

        {

     InitializeComponent();

        }

    private void button1_Click( object sender, EventArgs e)

        { //Demonstrate DNS..

            string _hostName = Dns .GetHostName();

            lstDNS.Items.Add( "Local hostname :: " + _hostName);

            IPHostEntry _ipHostEntry = Dns .GetHostByName(_hostName);

            foreach ( IPAddress _address in _ipHostEntry.AddressList)

            {

                lstDNS.Items.Add( "IP Address ::" + _address.ToString());

            }

        }

    private void button2_Click( object sender, EventArgs e)

        { //DNS Configuration in Registry

            RegistryKey start = Registry .LocalMachine;

            string DNSservers = @"SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" ;

            RegistryKey DNSserverKey = start.OpenSubKey(DNSservers);

      if (DNSserverKey == null )

            {

                lstDNSConfiguration.Items.Add( "Unable to open DNS servers key" );

        return ;

            }

            string serverlist = ( string )DNSserverKey.GetValue( "NameServer" );

            lstDNSConfiguration.Items.Add( "DNS Servers: " + serverlist);

            DNSserverKey.Close();

            start.Close();

            char [] token = new char [1];

            token[0] = ' ' ;

            string [] servers = serverlist.Split(token);

      foreach ( string server in servers)

            {

                lstDNSConfiguration.Items.Add( "DNS server: " + server);

            }

        }

    }

}

Output:

Click on both the buttons will display the respective outputs in the list box specified below