Problem while getting all IP's from local network C#

Question

I have tried a lot of solutions on internet for getting IP's from my local network and all of them have been failed to get all IP's. I also try to get IP's using ARP commands "arp /a" and "arp -a" but this command is also unable to do the job finally after searching for a while I found a software called "Advance IP Scanner" and when I run this software it gets all the IP's from local network and the most strange thing for me is that after running the Advance IP Scanner when I run the ARP command "arp /a" or "arp -a" it gets all the IP's from my local network.

This is what I have tried.

 public List<IPScanEntity> GetArpResult()
        {
            List<IPScanEntity> List = new List<IPScanEntity>();
            
            string baseIp = ConfigurationManager.AppSettings["baseIp"];

            //getting my own system IP
            List.Add(HostIPScanResult());
            for (int subnet = 1; subnet < 255; subnet++)
            {
                bool a = List.Any(x => x.Ip.Equals(baseIp+subnet.ToString()));

                if (a == true)
                {
                    continue;
                }

                try
                {
                    var p = Process.Start(new ProcessStartInfo("arp", "/a " + baseIp + subnet)
                    {
                        CreateNoWindow = true,
                        UseShellExecute = false,
                        RedirectStandardOutput = true
                    });

                    var output = p?.StandardOutput.ReadToEnd();
                    p?.Close();
                    var lines = output.Split('\n').Where(l => !string.IsNullOrWhiteSpace(l));
                    if (!lines.Contains("No ARP Entries Found.\r"))
                    {
                        var result =
                        (from line in lines
                         select Regex.Split(line, @"\s+")
                            .Where(i => !string.IsNullOrWhiteSpace(i)).ToList()
                            into items
                         where items.Count == 3                        
                         select new IPScanEntity
                         {
                             Ip = items[0],
                             MacAddress = items[1],
                         });
                        List.Add(result.FirstOrDefault());
                    }
                }
                catch (Exception ex)
                {
                    log.Error(ex.Message);                    
                }                
            }
         
            return List;
        }

Answer 1

The Problem with arp is it only lists IP-Addresses your system is aware of (it already communicated with).

If you really want to get all IPs you should loop a ping for your subnet. (see the link posted by Mikael for example)

Edit 1)

If the ICM Protocol is blocked by the machine (is enabled by default) and you know a port that is open you can use a tool like PPing to ping a specific tcp/udp port. Maybe theres some other tool I don't know about with an api or exitcode support, if not you can use this wrapper I wrote for pping:

public static bool PPing(string host, int port, PPingProtocolType type = PPingProtocolType.tcp)
{
  var cmdOutput = new StringBuilder();
  var cmdStartInfo = new ProcessStartInfo()
  {
    //Path to PPing.exe
    FileName = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "tools", "pping.exe"),
    Arguments = $"-r 1 -w 0{(type == PPingProtocolType.udp ? " -u " : " ")}{host} {port}",
    UseShellExecute = false,
    RedirectStandardOutput = true,
    CreateNoWindow = true,
  };

  using (Process proc = Process.Start(cmdStartInfo))
  {
    while (!proc.StandardOutput.EndOfStream)
    {
      cmdOutput.AppendLine(proc.StandardOutput.ReadLine());
    }
  }

  return cmdOutput.ToString().Contains("(1 OPEN, 0 CLOSED)");
}

public enum PPingProtocolType
{
  tcp = 0,
  udp = 1,
}