How to get domain name from Given IP in C#?

Question

I want to get domain name from a given IP. E.g If I give IP as "172.24.17.85" I should get only domain name like my domain name is sonata.net.

Any code snippet for this in C#?

Answer 1

Have you tried Dns.GetHostEntry?

Example:

using System;
using System.Net;

class Test
{
    static void Main(string[] args)
    {
        IPAddress addr = IPAddress.Parse("69.59.196.211");
        IPHostEntry entry = Dns.GetHostEntry(addr);
        Console.WriteLine(entry.HostName); // Prints "stackoverflow.com"
    }
}

Note that this didn't work for the example you gave... if a reverse DNS lookup doesn't work, I'm not sure what you can do.

Answer 2

Console.WriteLine("DomainName: {0}", Dns.GetHostEntry("1.1.1.1").HostName);

Answer 3

I really doubt if this is going to be possible. There could be n number of domains pointing to a single IP. You can do some research on Reverse DNS lookup.

Answer 4

Here is a complete program based on @Jon Skeets answer, but with input/output file.

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text.RegularExpressions;

namespace IP_reverse_checker
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // based on source: https://stackoverflow.com/a/44040867/6584859
            // based on source: https://stackoverflow.com/a/3252871

            Regex ip = new Regex(@"\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b");

            Console.WriteLine(">>> IP reverse checker <<<");
            Console.WriteLine();
            Console.WriteLine("Please enter the complete path to the text file containing the list of IP addresses:");
            string fileNameInput = @"" + Console.ReadLine();

            // Lets remove leading/trailing double quotes, if present:
            char[] trimChars = { '"' };
            string cleanFileNameInput = fileNameInput.Trim(trimChars);

            int numberFileLines = 0;
            string[] inputLines = new string[] { };

            try
            {
                inputLines = File.ReadAllLines(cleanFileNameInput);
                numberFileLines = inputLines.Length;
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error reading the file!  error: " + ex.Message);
                Console.WriteLine();
                Console.WriteLine("Press ENTER to exit the program.");
                Console.ReadLine();
                Environment.Exit(0);
            }

            List<string> outputLines = new List<string>();

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("The file contains " + numberFileLines + " lines. I start processing...");
            Console.WriteLine();

            int counter = 0;

            foreach (string line in inputLines)
            {
                counter++;

                try
                {
                    MatchCollection result = ip.Matches(line);

                    if (result[0].Success)
                    {
                        string hostName = "";
                        IPAddress addr = IPAddress.Parse(line);

                        try
                        {
                            IPHostEntry entry = Dns.GetHostEntry(addr);
                            hostName = entry.HostName;
                        }
                        catch (Exception)
                        {
                            hostName = ">> No Reverse-DNS entry found!";
                        }

                        if (hostName != "")
                        {
                            outputLines.Add(line + " | " + hostName);
                            Console.WriteLine("line " + counter + " of " + numberFileLines + ": " + line + " | " + hostName);
                        }
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error processing line " + counter + "  -  error: " + ex.Message);
                }
            }

            if (outputLines.Count > 0)
            {
                Console.WriteLine();
                Console.WriteLine();
                Console.WriteLine("Done! " + outputLines.Count + " IP adresses were processed.");
                Console.WriteLine();
                Console.WriteLine("Please enter the complete path to the text file where the list with IP addresses AND hostnames should be stored:");

                string fileNameOutput = @"" + Console.ReadLine();
                string cleanFileNameOutput = fileNameOutput.Trim(trimChars);

                try
                {
                    File.AppendAllLines(cleanFileNameOutput, outputLines);
                }
                catch (Exception ex)
                {
                    Console.WriteLine("Error writing the file!  error: " + ex.Message);
                }

                Console.WriteLine();
                Console.WriteLine("Done! Output file was written. Please press ENTER to exit the program.");
                Console.ReadLine();
            }
        }
    }
}

The input file should be in a format like this example:

10.0.10.126
10.0.10.17
10.0.20.120
10.0.20.126
10.0.20.127
10.0.20.138
10.0.20.139

The output file will look like this example:

10.0.10.126 | Thinkpad23.dnssuffix
10.0.10.17 | desktop63.dnssuffix
10.0.20.120 | Thinkpad16.dnssuffix
10.0.20.126 | Thinkpad08.dnssuffix
10.0.20.127 | desktop19.dnssuffix
10.0.20.138 | Thinkpad04.dnssuffix
10.0.20.139 | Thinkpad09.dnssuffix