private string GetClientIP()
  {
   string result = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
   if (null == result || result == String.Empty)
   {
    result = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
   }

   if (null == result || result == String.Empty)
   {
    result = HttpContext.Current.Request.UserHostAddress;
   }
   return result;
  }

DllImport("Iphlpapi.dll")]
  private static extern int SendARP(Int32 dest,Int32 host,ref Int64 mac,ref Int32 length);
  [DllImport("Ws2_32.dll")]
  private static extern Int32 inet_addr(string ip);

  private void Page_Load(object sender, System.EventArgs e)
  {
   // 在此处放置用户代码以初始化页面
   try
   {
    string userip=Request.UserHostAddress;
    string strClientIP = Request.UserHostAddress.ToString().Trim();
    Int32 ldest = inet_addr(strClientIP); //目的地的ip
    Int32 lhost = inet_addr("");   //本地服务器的ip
    Int64 macinfo = new Int64();
    Int32 len = 6;
    int res = SendARP(ldest,0, ref macinfo, ref len);
    string mac_src=macinfo.ToString("X");
    if(mac_src == "0")
    {
     if(userip=="127.0.0.1")
      Response.Write ("正在访问Localhost!");
     else
      Response.Write ("欢迎来自IP为" + userip + "的朋友！" + "
");
     return;
    }

    while(mac_src.Length<12)
    {
     mac_src = mac_src.Insert(0,"0");
    }

    string mac_dest="";

    for(int i=0;i<11;i++)
    {
     if (0 == (i % 2))
     {
      if ( i == 10 )
      {
       mac_dest = mac_dest.Insert(0,mac_src.Substring(i,2));
      }
      else
      {
       mac_dest ="-" + mac_dest.Insert(0,mac_src.Substring(i,2));
      }
     }
    }
 
//方法二
using System.Text.RegularExpressions;
using System.Diagnostics;
public class test
{
        public test
        {}
        public static string GetCustomerMac(string IP) //para IP is the client's IP
        {
               string dirResults="";
               ProcessStartInfo psi  = new ProcessStartInfo();
               Process proc = new Process();
               psi.FileName = "nbtstat";
               psi.RedirectStandardInput = false;
               psi.RedirectStandardOutput = true;
               psi.Arguments = "-A " + IP;
               psi.UseShellExecute = false;
               proc = Process.Start(psi);
               dirResults = proc.StandardOutput.ReadToEnd();
               proc.WaitForExit();
               dirResults=dirResults.Replace("\r","").Replace("\n","").Replace("\t","");

              Regex reg=new Regex("Mac[ ]{0,}Address[ ]{0,}=[ ]{0,}(?((.)*?)) __MAC",RegexOptions.IgnoreCase|RegexOptions.Compiled);
               Match mc=reg.Match(dirResults+"__MAC");

           if(mc.Success)
            {
                return mc.Groups["key"].Value;
           }
            else
           {
                reg=new Regex("Host not found",RegexOptions.IgnoreCase|RegexOptions.Compiled);
                mc=reg.Match(dirResults);
            if(mc.Success)
            {
                 return "Host not found!";
            }
            else
            {
                 return "";
            }
       }
  }
}

这种方法有些地方得好好摸索，不然看不懂的

//

获取服务器的IP地址方法以DNS法较为简单实用，如下：
  using System.Net;
 
 private void ButtonIP_Click(object sender, System.EventArgs e)
  { 
     System.Net.IPAddress[] addressList = Dns.GetHostByName(Dns.GetHostName()).AddressList;
     if ( addressList.Length>1)
     {   TextLIP.Text = addressList[0].ToString();
          TextSIP.Text = addressList[1].ToString();
     }
     else
     {
          TextLIP.Text = addressList[0].ToString();
          TextSIP.Text = "没有可用的连接";
     }
  }

   using System.Management;
 
   string stringMAC = "";
   string stringIP = "";
   ManagementClass MC = new ManagementClass "Win32_NetworkAdapterConfiguration");
   ManagementObjectCollection MOC= MC.GetInstances();
  
   foreach(ManagementObject MO in MOC)
   {
    if ((bool)MO["IPEnabled"] == true)
    {
     stringMAC += MO["MACAddress"].ToString();
     TextMAC.Text = stringMAC.ToString();
     string[] IPAddresses = (string[]) MO["IPAddress"];
     if(IPAddresses.Length > 0)
     stringIP = IPAddresses[0];
     TextIP.Text = stringIP.ToString();
    }
   } 

using System.Net;
 
TextIP.Text=Page.Request.UserHostAddress;