try 
 {
    IPAddress hostIPAddress = IPAddress.Parse(IpAddressString);
    IPHostEntry hostInfo = Dns.GetHostByAddress(hostIPAddress);
    // Get the IP address list that resolves to the host names contained in 
    // the Alias property.
    IPAddress[] address = hostInfo.AddressList;
    // Get the alias names of the addresses in the IP address list.
    String[] alias = hostInfo.Aliases;

    Console.WriteLine("Host name : " + hostInfo.HostName);
    Console.WriteLine("\nAliases :");
    for(int index=0; index < alias.Length; index++) {
      Console.WriteLine(alias[index]);
    } 
    Console.WriteLine("\nIP address list : ");
    for(int index=0; index < address.Length; index++) {
       Console.WriteLine(address[index]);
    }
 }
 catch(SocketException e) 
 {
Console.WriteLine("SocketException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
 }
 catch(FormatException e)
 {
Console.WriteLine("FormatException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
 }
 catch(ArgumentNullException e)
 {
Console.WriteLine("ArgumentNullException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
 }
 catch(Exception e)
 {
     Console.WriteLine("Exception caught!!!");
     Console.WriteLine("Source : " + e.Source);
     Console.WriteLine("Message : " + e.Message);
 }

//引入命名空间
using System;
using System.Net;

class MainClass
{
   public static void Main(string[] argv)
   {
      IPAddress test = IPAddress.Parse("64.200.123.1");

      IPHostEntry iphe = Dns.GetHostByAddress(test);

      foreach(string alias in iphe.Aliases)
      {
         Console.WriteLine("Alias: {0}", alias);
      }
   }
}