string strHostName = "";
strHostName = System.Net.Dns.GetHostName();
IPHostEntry ipEntry = System.Net.Dns.GetHostEntry(strHostName);
IPAddress[] addr = ipEntry.AddressList;
string ip= addr[addr.Length - 1].ToString();
If you want to Retrive True IP Address then
string IPAddress = Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
if (IPAddress == null) //may be the HTTP_X_FORWARDED_FOR is null
{
IPAddress = Request.ServerVariables["REMOTE_ADDR"];//we can use REMOTE_ADDR
}